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Eugenio DRAGONI

Professore Ordinario
Dipartimento di Scienze e Metodi dell'Ingegneria


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Pubblicazioni

- Actuator with a non-contact position sensor [Brevetto]
Colli, Marcello; Dragoni, Eugenio; N., Bellato; A., Baldassari
abstract

An actuator having a fixed part, a movable part movable with respect to the fixed part in a travelling direction, and a non-contact position sensor connected to the movable part to read the position of the movable part. The position sensor has a reading device connected to the fixed part and having a ferromagnetic core; and a magnetic cursor, which is integrated in the movable part, is defined by a magnetized portion of the movable part, and is so magnetized as to locally saturate the ferromagnetic core at the magnetic cursor.


- Actuator with a non-contact position sensor [Brevetto]
Colli, Marcello; Dragoni, Eugenio; N., Bellato; A., Baldassari
abstract

An actuator having a fixed part, a movable part movable with respect to the fixed part in a travelling direction, and a non-contact position sensor connected to the movable part to read the position of the movable part. The position sensor has a reading device connected to the fixed part and having a ferromagnetic core; and a magnetic cursor, which is integrated in the movable part, is defined by a magnetized portion of the movable part, and is so magnetized as to locally saturate the ferromagnetic core at the magnetic cursor.


- Attuatore a memoria di forma ad alta efficienza [Brevetto]
Dragoni, Eugenio; SCIRE' MAMMANO, Giovanni
abstract

Il presente trovato si riferisce al campo degli attuatori di moto utilizzanti fili a memoria di forma di qualsiasi sezione.Gli attuatori di moto utilizzanti fili a memoria di forma oggetto del presente trovato prevedono di utilizzare un supporto idoneo a guidare il filo a memoria di forma. Il filo può essere sia esterno che interno al supporto. Lo scopo del supporto è quello di guidare il filo a memoria di forma e fargli seguire durante il movimento un determinato percorso in modo che la lunghezza di filo che costituisce l’attuatore sia massimizzata col minimo ingombro complessivo. Il filo è in contatto con il supporto e durante il movimento vi è uno strisciamento fra i due elementi. L’attrito di strisciamento tra elementi filo e supporto caratterizza le prestazioni in termini di forza e corsa dell’attuatore. Negli attuali attuatori che prevedono lo strisciamento fra filo a memoria di forma e supporto, la riduzione dell’attrito radente è ottenuta utilizzando tamburi in materiale antifrizione e/o rivestendo la superficie del supporto in contatto con il filo con un riporto di materiale antifrizione. Gli attuatori del presente trovato sono caratterizzati dal fatto che la riduzione dell’attrito radente tra supporto e filo è ottenuta facendo vibrare o il supporto o il filo o entrambi gli elementi. Questo principio può essere adottato sia in aggiunta che in alternativa all’utilizzo di materiali antifrizione per il supporto.Il presente trovato è in grado di incrementare notevolmente la lunghezza del filo a memoria di forma che costituisce l’attuatore permettendo di realizzare corse elevate, riducendo al tempo stesso l’ingombro del dispositivo e diminuendone la complessità. A parità di deformazione imposta al filo, la corsa erogata è infatti direttamente proporzionale alla lunghezza del filo stesso. In tutti i casi l’invenzione consiste nell’utilizzo di fili a memoria di forma striscianti su supporti di forma generica per la realizzazione di attuatori di moto lineari o rotativi, caratterizzati dal fatto che la minimizzazione dell’attrito radente fra filo e supporto è realizzata utilizzando vibrazione meccaniche appositamente applicate al supporto e/o al filo a memoria di forma.


- Choke device for an internal combustion engine intake system [Brevetto]
N., Bellato; S., Sirani; M., Colli; Dragoni, Eugenio
abstract

A choke device for an intake system of an internal combustion engine; the choke device has at least one choke body fitted movably inside an intake conduit, and an actuating device for moving the choke body to and from a work position in which the choke body reduces the cross section of the intake conduit; and the actuating device has a filiform actuating member made of a shapememory material that changes shape when subjected to physical external stress, and having a first portion embedded in the choke body, and a second portion located outside the choke body and secured mechanically to a fixed part.


- Combined actuator with rheological control brake [Brevetto]
Spaggiari, Andrea; Dragoni, Eugenio; N., Bellato; M., Pecora; F., Lancioni; S., Fornara; A., Baldassari
abstract

A combined actuator provided with: a mobile element; a driver for displacing the mobile element; and a rheological control brake, which is mechanically coupled to the mobile element to adjust the displacement of the mobile element; the rheological control brake has: two contiguous adjustment chambers; a rheological fluid contained in the two adjustment chambers; a sliding piston, which tightly separates the two adjustment chambers and is mechanicalli connected to the mobile element; at least one external connection pipe, which reciprocally connects the two adjustment chambers; and a driving device which is coupled to the external connection pipe so as to apply a variable electromagnetic field to the rheological fluid contained in the external connection pipe for varying the viscosity of the rheological fluid between a minimum value and a maximum value.


- Fuel pump operated by means of a shape memory material [Brevetto]
N., Bellato; Colli, Marcello; C., Pancotti; L., Toschi; Dragoni, Eugenio
abstract

A fuel pump for an internal combustion engine; the fuel pump is equipped with at least one pumping chamber with variable volume; with at least one inlet valve communicating with the pumping chamber; with at least one outlet valve communicating with the pumping chamber; with at least one flexible membrane that delimits the pumping chamber; and with an actuating device that acts on the flexible membrane to cyclically vary the volume of the pumping chamber; the actuating device presents at least one shape memory material thet modifies its geometry upon application of an external influence of a physical nature and is mechanically coupled with the flexible membrane, and a piloting device to cyclically apply an external influence of a physical nature to the shape memory material.


- Metodo e dispositivo per controllare la posizione della lancetta di un indicatore [Brevetto]
SCIRE' MAMMANO, Giovanni; Spinella, Igor; Dragoni, Eugenio; P., Cani
abstract

La presente invenzione è relativa a un metodo e a un dispositivo per controllare la posizione della lancetta di un indicatore, e a un indicatore comprendente tale dispositivo.In particolare, la presente invenzione trova vantaggiosa, ma non esclusiva applicazione negli indicatori che si trovano nei pannelli di controllo di veicoli o strumentazioni industriali e che impiegano uno o più fili di materiale e memoria di forma (Shape Memory Alloy - SMA) come attuatori per la movimentazione della lancetta dell'indicatore, cui la descrizione che segue farà esplicito riferimento senza per questo perdere in generalità.


- Molle elicoidali a memoria di forma a sezione cava [Brevetto]
Spinella, Igor; Dragoni, Eugenio
abstract

Il presente trovato si riferisce al campo delle molle elicoidali a memoria di forma.Le molle elicoidali a memoria di forma oggetto del presente trovato sono caratterizzate da un filo a sezione cava, in grado di incrementare l’efficienza delle molle stesse, in termini di energia elastica accumulabile per unità di peso, in termini di risparmio energetico per l’attivazione della molla ed in termini di risposta dinamica della stessa.Le molle elicoidali a memoria di forma a sezione piena attualmente utilizzate sono caratterizzate da un’efficienza minore rispetto all’invenzione oggetto del presente trovato.In tutti i casi l’invenzione si basa sull’utilizzo di molle elicoidali a memoria di forma caratterizzate da un filo a sezione cava.


2024 - Stress distributions around the interference fit between a round pin and a perforated finite plate [Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract


2023 - CONSULENZA TECNICA SU ANALISI STRUTTURALE E VERIFICA DI NUOVO MODELLO DI SERBATOIO IN POLIPROPILENE [Altro]
Dragoni, Eugenio; Castagnetti, Davide; Spaggiari, Andrea
abstract

Fornire consulenza tecnica per l’analisi strutturale agli elementi finiti di un serbatoio per accumulo di acqua ad una temperatura compresa tra 5 e 80°C ed una pressione massima di 3 bar, realizzato in polipropilene soffiato.


2023 - Heuristic structural optimization of two-dimensional filling materials with square-triangular supercells [Articolo su rivista]
Dragoni, Eugenio
abstract

Cellular filling materials are a commonplace in additively manufactured parts to lower the structural weight without detriment to the mechanical properties. This technical note undergoes the heuristic optimization of a 2D metamaterial with repetitive supercells derived from a square frame divided by median and diagonal lines into eight triangles. The inherent quadriaxiality of this layout is ideally suited to resist multiaxial stress fields, while enabling size refinement to match the local scale of the component. A step-by-step procedure is developed which optimizes the thickness of the beams along the principal axes of the cell (sidewise and diagonal) according to a fully stressed design concept. Preliminary Finite Element models, including either bar or beam elements, confirm the theoretical results for a case study. Extension of the optimal approach to 3D geometries is envisioned using a cubic cell which incorporates the present 2D grid on each face of the cube.


2022 - Fatigue Testing of Superelastic NiTi Wires Thermally Activated for Shape Memory Effect [Articolo su rivista]
Dragoni, E.; SCIRE' MAMMANO, Giovanni
abstract

A few years ago, a unique way to use shape memory alloys for actuation purposes was proposed, involving repeated heating of wires in the superelastic state. Named high-performance shape memory effect (HPSME), this behavior was supplemented with preliminary test data on the fatigue life of the wires cycled under constant-stress loading. The present paper investigates the HPSME of superelastic wires under thermomechanical cycling for an extended range of loading conditions: “constant stress with limited maximum strain,” “linear stress–strain variation with limited maximum strain,” and “constant strain.” The tests confirm that the HPSME generates higher stresses (around 1000 N/mm2 against the usual 200–250 N/mm2) at temperature well above the activation temperature of the classical SMAs. However, the net stroke of the wires rapidly decreases with the number of cycles and the fatigue life hardly achieves a few thousands of cycles, especially under constant-strain loading. Based on the experimental findings, the recourse to the HPSME is strongly advised for low cycle or one-shot devices but not particularly encouraged for applications involving sustained cycling.


2022 - From three-dimensional tessellations to lightweight filling materials for additively manufactured structures: Concept, simulation, and testing [Articolo su rivista]
Ciace, Valerio A.; Dragoni, Eugenio; Grasselli, Luigi
abstract

To improve the structural efficiency and reduce costs, most additively manufactured parts are printed as thin shells filled with a lightweight cellular material. The filling material reacts to secondary stresses and provides distributed support for the load-carrying outer shell. In a recent publication, the authors have proposed a two-step method to design lightweight filling metamaterials that are intrinsically strong and stiff. Conceptually, the space is first divided into repetitive volumes according to known three-dimensional tessellation schemes. The tessellation is then replaced by a kinematically rigid wireframe with beams along the edges and across the faces of the native volumes. Elaborating on that idea, the present paper pursues three objectives: (a) show the variety of material designs that derive from the tessellation-wireframe approach; (b) characterize the materials through finite element analyses on full-scale models and compare them with former predictions based on scaling and homogenization techniques; (c) validate the numerical results against experimental tests on a selection of prototype structures. Good correlation is revealed between theoretical predictions, computational models, and experimental data.


2022 - Predicting the Macroscopic Shear Strength of Tightened-Bonded Joints from the Intrinsic High-Pressure Properties of Anaerobic Adhesives [Articolo su rivista]
Castagnetti, Davide; Corigliano, Pasqualino; Barone, Calogero; Crupi, Vincenzo; Dragoni, Eugenio; Guglielmino, Eugenio
abstract

This scientific study aims to validate the applicability of a micromechanical model for predicting the static shear strength of hybrid interfaces that are pressure-reinforced and bonded with anaerobic adhesives. To identify the parameters for the micromechanical model, a systematic experimental test plan involving high-strength steel butt specimens bonded with anaerobic adhesive in a finite thickness was performed. The experimental investigation was based on torque tests, which provided the shear strength of two anaerobic adhesives subjected to different values of contact pressure, ranging from 0 up to 1000 MPa. Based on the intrinsic high-pressure properties of the finite-layer adhesives, the formerly developed micromechanical model of hybrid interfaces satisfactorily predicted the macroscopic strength of tightened-bonded joints taken from the literature.


2022 - PROGETTO E SVILUPPO DI MODELLI PREDITTIVI PER LA VALUTAZIONE E OTTIMIZZAZIONE DI FATTIBILITA’ E RESISTENZA DI COMPONENTI FILETTATI STAMPATI A FREDDO [Altro]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio
abstract


2022 - Rapid evaluation of notch stress intensity factors using the peak stress method with 3D tetrahedral finite element models: Comparison of commercial codes [Articolo su rivista]
Meneghetti, Giovanni; Campagnolo, Alberto; Visentin, Alberto; Avalle, Massimiliano; Benedetti, Matteo; Bighelli, Andrea; Castagnetti, Davide; Chiocca, Andrea; Collini, Luca; De Agostinis, Massimiliano; De Luca, Alessandro; Dragoni, Eugenio; Fini, Stefano; Fontanari, Vigilio; Frendo, Francesco; Greco, Alessandro; Marannano, Giuseppe; Moroni, Fabrizio; Pantano, Antonio; Pirondi, Alessandro; Rebora, Alessandro; Scattina, Alessandro; Sepe, Raffaele; Spaggiari, Andrea; Zuccarello, Bernardo
abstract

The peak stress method (PSM) allows a rapid application of the notch stress intensity factor (NSIF) approach to the fatigue life assessment of welded structures, by employing the linear elastic peak stresses evaluated by FE analyses with coarse meshes. Because of the widespread adoption of 3D modeling of large and complex structures in the industry, the PSM has recently been boosted by including four-node and ten-node tetrahedral elements of Ansys FE software, which allows to discretize complex geometries. In this paper, a Round Robin among eleven Italian Universities has been performed to calibrate the PSM with seven different commercial FE software packages. Several 3D mode I, II and III problems have been considered to investigate the influence of (i) FE code, (ii) element type, (iii) mesh pattern, and (iv) procedure to extrapolate stresses at FE nodes. The majority of the adopted FE software packages present similar values of the PSM parameters, the main source of discrepancy being the stress extrapolation method at FE nodes.


2022 - Synthesis and optimization of an eight-bar linkage mechanism for seat suspensions [Articolo su rivista]
Spaggiari, A.; Cocconcelli, M.; Castagnetti, D.; Dragoni, E.; Rubini, R.
abstract


2022 - Thermomechanical characterization of metal-polyurethane bonded joints: effect of manufacturing parameters and working temperature [Articolo su rivista]
Ragni, M.; Castagnetti, D.; Spaggiari, A.; Dragoni, E.; Milelli, M.; Girlando, S.; Borghi, P.
abstract

Metal-elastomer bonded joints are typical of different industrial applications, specifically pallet truck wheels, where the solid elastomeric layer is bonded to the metal body. This paper focuses on the effect of manufacturing parameters and working temperature, on the shear strength of a metal-elastomer bonded joint. Through a comprehensive experimental test plan, the paper investigates the effect of thermal conditioning of the adhesive, shot peening of the metal adherend, type of solvent-based adhesive, and working temperature of the joint. The test plan uses a TAST-like specimen with a sandwich configuration (metal-elastomer-metal), loaded in order to originate a nearly pure-shear stress state. The results show which parameters influence most the shear strength of the joint helping the designer in maximizing the load-carrying capacity of the joint.


2021 - Actuators [Capitolo/Saggio]
Dragoni, E.
abstract


2021 - ANALISI SPERIMENTALE DELLA PERDITA DEL PRECARICO IN UNIONI VITE-PERNO PER GRUPPO RULLI DI SISTEMI SOTTOCARRO [Altro]
Spaggiari, Andrea; Dragoni, Eugenio; Castagnetti, Davide
abstract

ANALISI SPERIMENTALE DELLA PERDITA DEL PRECARICO IN UNIONI VITE-PERNO PER GRUPPO RULLI DI SISTEMI SOTTOCARRO, grazie ad piano di esperimenti secondo metodo Design of Experiments, con unico metodo di serraggio coppia-angolo. Assistenza per strumentazione viti di misura con estensimetro centrale e successiva esecuzione degli esperimenti con serraggio viti e monitoraggio del precarico nel tempo. La analisi statistica dei risultati e loro interpretazione ingegneristica portano alla comprensione del problema e alla proposta di possibili soluzioni che aiutino nell'eliminazione della perdita di precarico.


2021 - Chapter 12 - Design and development of advanced SMA actuators [Capitolo/Saggio]
Dragoni, Eugenio; Spaggiari, Andrea
abstract

Applications of the superelastic effect of shape memory materials are well-established and understood in the manufacture of engineering devices with adaptive properties. Conversely, exploitation of the shape memory effect for building solid-state actuators is still characterized by a trial-and-error approach. Although the thermomechanical phenomena behind the behavior of shape memory alloys (SMAs) are theoretically well-known, there is an open challenge for engineering methods to help the designer capitalize on these alloys to develop smart devices. This chapter describes research aimed at identifying simple but effective design rules for SMA-based actuators and motors, linear and rotary. The presentation concentrates on the development of SMA devices, which try to overcome the stroke limitations of conventional actuators without compromising with the force generated. It will be shown that the class of passive mechanical springs can be fruitfully turned into intelligent high-performance devices upon replacement of the material with an SMA. Alternatively, widely available SMA wires can be used smartly in compact designs with unconventional architecture. The basic theoretical model behind the design of unconventional devices will be addressed, together with laboratory prototypes demonstrating the feasibility of all of the concepts explored.


2021 - Measuring the static shear strength of anaerobic adhesives in finite thickness under high pressure [Articolo su rivista]
Corigliano, P.; Ragni, M.; Castagnetti, D.; Crupi, V.; Dragoni, E.; Guglielmino, E.
abstract

Although anaerobic adhesives are extensively used in addition to mechanical tightening in flanged couplings, interference fits, and threaded connections, their constitutive behaviour still needs to be investigated. According to the micromechanical model proposed by Dragoni and Mauri [Proc. of the IMECHE Part L J. of Mat.: Des. and Appl. 2002; 216: 9–15], the shear strength of the anaerobic adhesives significantly improves with the contact pressure applied to the thin adhesive layer. In order to assess this hypothesis, this work investigates the shear strength of an anaerobic adhesive layer with finite thickness and surface area, subject to a nearly-uniform contact pressure, up to 1000 MPa. The tests involved a head to head bonded specimen, made of high strength steel adherends (39NiCrMo3), with a controlled roughness on the bonding surfaces. Both a weak and a strong anaerobic adhesive (Loctite 243 and Loctite 638) are investigated. A full-field technique, such as the Digital Image Correlation, was used in order to detect the 3D displacement and strain fields, and to evaluate the twist angle of the entire external surface, with particular attention to the interface area. The preliminary results prove the reliability of the test bench and confirms the piezo-resistive response of the anaerobic adhesive.


2021 - Mechanical design and modelling of lightweight additively manufactured lattice structures evolved from regular three-dimensional tessellations [Articolo su rivista]
Dragoni, E.; Ciace, V. A.
abstract

To lower costs and improve efficiency, most additively manufactured parts are printed as thin shells filled with a lightweight cellular material, which reacts to secondary stresses and provides distributed support to the load-carrying outer casing. This paper proposes a two-step method to design filling metamaterials that are intrinsically strong, stiff and lightweight. First, the space is divided into repetitive volumes according to available three-dimensional tessellation schemes. The tessellation is then transformed into a trabecular wireframe by converting each unit volume into a kinematically-rigid open cell with edge beams and bracings. Dimensional analysis allows the lattice structures to be characterized mechanically and elastically with a finite number of simple computational analyses. The paper shows that the properties of metamaterials with triangular, square and hexagonal prismatic cells compare favourably with state-of-the art porous materials like foams and honeycombs.


2021 - Validation and optimization of a compact push-pull rubber actuator energized by an outer coil of shape memory wire [Articolo su rivista]
Dragoni, E.; Mammano, G. S.
abstract

The authors have formerly published the analytical model and finite element validation of a push-pull actuator made by winding a thin shape memory wire on a solid rubber cylinder. The cylinder provides elastic backup for the wire upon cooling down and transforms its circumferential contraction into a magnified axial elongation upon heating up. Building on that study, this paper accomplishes three tasks: (1) build prototype actuators and perform simple tests to validate the theory; (2) develop simple procedures for the optimal design of the actuator starting from high-level engineering specifications; (3) envision how the present concept could be improved by replacing the rubber block with a compliant lattice-like or shell-like scaffold with designed properties to further enhance the axial stroke.


2020 - Design of shape memory alloy sandwich actuators: an analytical and numerical modelling approach [Articolo su rivista]
Mizzi, Luke; Spaggiari, Andrea; Dragoni, Eugenio
abstract

Shape memory alloy (SMA)-based actuator composites are characterised by a high force output which is activated by a temperature increase. In this work we exploit this property to design sandwich structures with SMA-matrix composite actuator skins capable of exhibiting a reversible, tailored flexural response. A theoretical model which predicts the resultant deflection and flexural moment produced as a result of selectively actuating one of the system skins was developed and confirmed using a multi-step Finite Element (FE) analysis which takes into account the fabrication pathway through which these systems may be manufactured. The model correlates the geometric parameters and material properties of the various components making up the system and provides a quantitative description of the role which each variable plays in determining the overall sandwich actuator performance. This is necessary for the future production and implementation of such systems in real-life applications.


2020 - Metodologie non distruttive per l’individuazione di difetti su sanitari in ceramica: indagine sperimentale. [Altro]
Castagnetti, Davide; Cocconcelli, Marco; Spaggiari, Andrea; Strozzi, Matteo; Dragoni, Eugenio; Rubini, Riccardo
abstract

Metodologie non distruttive per l’individuazione di difetti su sanitari in ceramica: pianificazione sperimentale, prove sperimentali, analisi dei risultati, proposta di parametri identificativi dei difetti.


2019 - A design oriented multiaxial stress-based criterion for the strength assessment of adhesive layers [Articolo su rivista]
Spaggiari, A.; Castagnetti, D.; Dragoni, E.
abstract

Adhesively bonded joints are becoming widespread in the composites industry and therefore there is a need for quantitative information on the mechanical strength of the material used. The great strength and stiffness of a composites structure may be strongly undermined by their weakest part, the bonded joint. Unfortunately, the testing of adhesives in bulk form may not be representative of their behaviour in a layered state, typically quite thin, because of differences in the polymerization process and lack of adhesive-adherend interfaces. The drawback of the test in thin layer is the stress concentration at the edges, typical in the single lap or t-peel joints, and also the chance of having the adhesive subjected both to a shear and predominant peel stress. This work deals with the characterization of adhesives in thin film under uniform distributions of multi-axial stresses, which is the typical application condition. The test exploits a tubular butt-bonded specimen, previously investigated by the authors, which guarantees a non-singular stress field over the adhesive layer both in shear and normal directions. According to the analytical prediction, in addition to the direct normal stress, both radial and circumferential secondary stresses arise in the adhesive, due to the constrained lateral contraction imposed by the adherends (Poisson's effect). The test campaign investigates two chemically different, commercial adhesives, an acrylic and an epoxy resin. By means of a biaxial testing machine, we applied to the specimens eight different combinations of normal and shear loads ranging from pure tensile to a shear-compressive stress state. As expected, both the pure shear stress and the compressive stresses lead to better performances of the adhesive layer with respect to tensile loading. The authors compare a variety of failure criteria from the literature and propose a simple multiaxial criterion to obtain a failure envelop of the experimental data. The applicability of the criterion is also assessed on experimental tests found in literature on different configurations and gives fairly good results. The outcome of study is a simple stress based, failure criterion, which can be used to predict the failure of several adhesive bonded joints, relying only on monoaxial experimental data.


2019 - CONSULENZA TECNICA SU ANALISI STRUTTURALE E PROGETTAZIONE RIDUTTORE DI VELOCITÀ MAZZONI [Altro]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio; Mizzi, Luke
abstract

Fornire consulenza tecnica per l’analisi strutturale di un riduttore di velocità per accoppiamento di motori endotermici a benzina e pompe acqua a pistoni assiali. Lo studio è finalizzato all’analisi di un riduttore commerciale di riferimento, al fine di valutarne le prestazioni, e allo studio della gamma di riduttori di comune uso presso Mazzoni. Sulla base dei primi due passi si andrà a studiare la fattibilità tecnica per la produzione, da parte del Committente, di una piattaforma di riduttori modulari, adatti alla gamma di prodotti d’interesse.


2019 - CONSULENZA TECNICA SU SISTEMA HEART DAMPER [Altro]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio; Mizzi, Luke
abstract

La collaborazione riguarda la consulenza tecnica per l’analisi della deformazione e la valutazione della resistenza di un heart damper in Nitinol per la terapia dell’insufficienza cardiaca tramite metodi numerici FEM


2019 - Design-oriented modelling of composite actuators with embedded shape memory alloy [Articolo su rivista]
Mizzi, Luke; Spaggiari, Andrea; Dragoni, Eugenio
abstract

Shape memory alloy (SMA) actuators have generated a great deal of interest in recent years due to their reusability and ability to exhibit a wide spectrum of actuation properties. In this work we present an analytical approach through which one may predict the actuation stroke as well as recovery potential of a two-component SMA-based composite actuator. The predictions of the analytical model were validated using Finite Element (FE) simulations on a composite SMA actuator designed in the form of an SMA strip embedded within an elastic matrix, where the shape memory effect of the SMA component was modelled using the numerical Souza-Auricchio model. The results obtained from the two approaches show extremely good agreement. The trends found upon altering various geometric and material parameters within the system provide a thorough understanding of how one can vary these parameters in order to obtain a tailored actuation and recovery response from the SMA-based actuator.


2019 - Development of a driveshaft torque transducer for low-cost structural health monitoring of off-highway vehicles [Articolo su rivista]
Golinelli, Nicola; Spaggiari, Alan; Castagnetti, Davide; Fornari, Lorenzo; Dragoni, Eugenio; Gualdi, G.; Brunazzi, A.
abstract

Mechatronic agricultural machines and equipment are continuously increasing their complexity and cost. In order to ensure their efficiency and reliability and preserve their value, it is important to actively monitor the working loads and register damaging and wear occurring on critical components. This approach needs the introduction of sensors on the machine, which allow continuous monitoring and evaluate the residual life of components. The work presents the development and testing of an innovative low-cost systems for monitoring and diagnostic of off-highway vehicles. The sensor measures the torque of a mechanical power transmissions, and it was designed especially for agricultural machinery. The torque transducer monitors the mechanical power flowing from the tractor into the gearbox and the agricultural implement and is fully integrated with the power take-off driveshaft, thus being generally applicable. The design and development of the transducer was performed following a quality function deployment approach. The system is less expensive considering the typical torque measuring system commercially available and, thanks to its wireless module and integrated power supply, it is reliable and generally applicable to many power take-off to implement combinations.


2019 - Mechanical design of flywheels for energy storage: A review with state-of-the-art developments [Articolo su rivista]
Dragoni, Eugenio
abstract

For years, engineers and designers have capitalized on electrochemical batteries for long-term energy storage, which can only last for a finite number of charge–discharge cycles. More recently, compressed hydrogen is being scrutinized as a large-scale storage medium but this poses the risk of spreading high-pressure vessels with inflammable content. Historically, flywheels have provided an effective way to smooth out speed fluctuations in irregular achines and mechanisms. With advancements in composite materials, magnetic bearings, and mechatronic drives, flywheels have become the subject of extensive research as power storage devices for mobile or fixed installations. Flywheel energy storage systems are considered to be an attractive alternative to electrochemical batteries due to higher stored energy density, higher life term, deterministic state of charge and ecological operation. The mechanical performance of a flywheel can be attributed to three factors: material strength, geometry, and rotational speed. Focusing on the simple relationship between these variables, this paper reviews the literature of flywheel technology and explores the merits of four simple but unconventional flywheel configurations that have not been examined so far. Two geometries assume the use of monolithic isotropic materials two solutions are based on the use of high-strength strips or tapes wound up to form a multilayered structure.


2019 - Metodologie non distruttive per l’individuazione di difetti su sanitari in ceramica [Altro]
Castagnetti, Davide; Cocconcelli, Marco; Spaggiari, Andrea; Dragoni, Eugenio; Rubini, Riccardo
abstract

Studio di metodologie per l’individuazione, a fine linea di produzione, di difetti (sfili, cricche) su sanitari in ceramica


2019 - Shape optimization of the fillet under a bolt’s head [Articolo su rivista]
Sorrentino, Andrea; Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio
abstract

The stress concentration in the fillet under a bolt’s head is a critical issue for the fatigue life of this component. Remembering the variable notch radius solution observed in many biological structures to lower stress concentrations due to normal loads, this work proposes, examines and optimizes a double circular arc fillet, not re-entering the head. The work implements an ad hoc shape optimization procedure that combines a genetic algorithm (the particle swarm optimization) and a parametric, axisymmetric finite-element model of the bolt: by focusing on an M12 bolt, the analysis focuses on two issues: first, the optimization of the radius of each arc in the fillet; second, the optimization of the bolt’s head height and head’s diameter in combination with the fillet radiuses. By comparing the proposed solution with the fillet geometries for the bolt’s heads from the literature, it appears a noticeable stress reduction, about 14% lower than the standard circular fillet, combined with an easy manufacturing.


2019 - Smart materials: Properties, design and mechatronic applications [Articolo su rivista]
Spaggiari, Andrea; Castagnetti, Davide; Golinelli, Nicola; Dragoni, Eugenio; SCIRE' MAMMANO, Giovanni
abstract

This paper describes the properties and the engineering applications of the smart materials, especially in the mechatronics field. Even though there are several smart materials which all are very interesting from the research perspective, we decide to focus the work on just three of them. The adopted criterion privileges the most promising technologies in terms of commercial applications available on the market, namely: magnetorheological fluids, shape memory alloys and piezoelectric materials. Many semi-active devices such as dampers or brakes or clutches, based on magnetorheological fluids are commercially available; in addition, we can trace several applications of piezo actuators and shape memory-based devices, especially in the field of micro actuations. The work describes the physics behind these three materials and it gives some basic equations to dimension a system based on one of these technologies. The work helps the designer in a first feasibility study for the applications of one of these smart materials inside an industrial context. Moreover, the paper shows a complete survey of the applications of magnetorheological fluids, piezoelectric devices and shape memory alloys that have hit the market, considering industrial, biomedical, civil and automotive field.


2019 - Tailoring the flexural response of sandwich structures with faces made from shape memory alloy composite actuators [Relazione in Atti di Convegno]
Mizzi, L.; Spaggiari, A.; Dragoni, E.
abstract


2018 - Adhesively bonded disk under compressive diametrical load [Articolo su rivista]
Radi, E.; Dragoni, E.; Spaggiari, A.
abstract

A closed-form full-field solution is presented for stresses and displacement in a circular disk containing a diametrical adhesive thin layer induced by two opposite compressive loads acting along an arbitrary di- ametrical direction. For the sake of simplicity, the adhesive layer is treated as a tangential displacement discontinuity between the two disk halves. The problem is split into symmetric and skew-symmetric loading conditions. No contribution is expected from the adhesive layer for the symmetric problem. For the skew-symmetric loading condition, a general integral solution in bipolar coordinates has been as- sumed for the Airy stress function in the form of a Fourier sine transform. The imposition of the boundary conditions then allows us to reduce the problem to a Fredholm integral equation of the first kind defined on the half-line or equivalently to a singular integro-differential equation defined on a bounded interval. A preliminary asymptotic analysis of the stress and displacement fields at the edges of the adhesive thin layer shows that the stress field is finite therein, but the rotation displays a logarithmic singularity. A numerical solution of the singular integro-differential equation is then provided by assuming a power se- ries expansion for the shear stress, whose coefficients are determined by using a collocation method. An approximate closed-form solution is also derived by exploiting a perturbation method that assumes the ratio between the shear modulus of the disk material and the shear stiffness of the adhesive thin layer as small parameter. The shear stress distribution along the thin layer turns out to be more and more uni- form as the adhesive shear stiffness decreases. In order to validate the analytical results, FE investigations and also experimental results obtained by using Digital Image Correlation (DIC) techniques are presented for varying loading orientation and material parameters.


2018 - Analytical Design of Superelastic Ring Springs for High Energy Dissipation [Relazione in Atti di Convegno]
Spaggiari, Andrea; Scire' Mammano, Giovanni; Dragoni, Eugenio
abstract

Classical ring springs are mechanical elements used in industrial applications and in transport for shock absorption and energy dissipation. They are constituted by a stack of internal and external metal rings (typically high strength steel), with tapered surfaces in contact with one another. Under the action of an axial load these surfaces slide, the rings are deformed circumferentially and energy is dissipated due to friction. The main advantages of these springs are the high specific energy stored and the large damping capacity due to sliding friction. Furthermore, the stiffness and damping are independent on the strain rate and the temperature, which limits or avoids the occurrence of any resonance problems. The superelastic materials, characterized by an almost flat stress plateau and large reversible deformation, can be used to replace traditional steels in ring springs giving a significant performance increase. Compared to the traditional version where energy is dissipated only due to friction, in superelastic ring springs there is an increase of the dissipated energy thanks to the internal hysteresis of the material. This paper studies analytically the ring springs in traditional material and in superelastic material, providing equations to dimension these mechanical elements, which enable the designer to customize this useful structural element.


2018 - Brazilian test for the characterization of adhesively bonded joints [Abstract in Atti di Convegno]
Radi, E.; Dragoni, E.; Spaggiari, A.
abstract

In the present work, we propose the use of the Brazilian test on a adhesively bonded disk for the characterization of adhesion properties of the adhesive. The main advantage of this test is that any combination of shear and normal loading can be achieved by appropriate choice of the bonding inclination angle with respect to the loading direction. A closed-form full-field solution is presented for stresses and displacement in a circular disk containing a diametrical adhesive thin layer induced by two opposite compressive loads acting along an arbitrary diametrical direction. For the sake of simplicity, the adhesive layer is treated as a tangential displacement discontinuity between the two disk halves. The problem is split into symmetric and skew symmetric loading conditions. No contribution is expected from the layer for the symmetric problem. For the skew-symmetric loading condition, a general integral solution in bipolar coordinates has been assumed for the Airy stress function in the form of a Fourier sine transform [1, 2]. The imposition of the boundary conditions then allows us to reduce the problem to a Fredholm integral equation of the first kind defined on the half-line or equivalently to a singular integro-differential equation defined on a bounded interval. A preliminary asymptotic analysis of the stress and displacement fields at the edges of the adhesive thin layer shows that the stress field is regular therein, but the rotation displays a logarithmic singularity [3]. A numerical solution of the singular integro-differential equation is then provided by assuming a power series expansion for the shear stress distribution, whose coefficients are found by means of a collocation method. An approximate closed-form solution is also derived by exploiting a perturbation method that assumes the ratio between the shear modulus of the disk material and the shear stiffness of the adhesive thin layer as small parameter [4]. The shear stress distribution along the thin layer turns out to be more and more uniform as the adhesive shear stiffness decreases. In order to validate the analytical results, FE investigations and also experimental results obtained by using Digital Image Correlation (DIC) techniques are presented for varying loading orientation and material parameters. The present investigation thus provides some fundamental understandings of the effects of adhesive compliance on the distribution of the shear stress along the adhesive bonding. The analytical solution presented here may be considered particularly valuable, since it allows for the validation of numerical methods as well as for a preliminary design of adhesively bonded connections employed in many structural engineering applications.


2018 - consulenza tecnica per l’analisi della deformazione e la valutazione della resistenza di un heart damper in Nitinol per la terapia dell’insufficienza cardiaca [Altro]
Spaggiari, Andrea; Dragoni, Eugenio; Castagnetti, Davide; Mizzi, Luke
abstract

– Analisi del materiale, del sistema di carichi e vincoli agenti sul sistema e della geometria attuale dell'heart damper – Analisi agli elementi finiti del sistema e previsione di tensioni e deformazioni – Analisi critica dei risultati e suggerimento delle possibili migliorie strutturali


2018 - Consulenza tecnica per lo sviluppo concettuale, la riprogettazione e il proporzionamento di massima di un sistema di blocco/sblocco automatico del gruppo scapolare del sedile COBO ICS – 16 [Altro]
Spaggiari, A.; Dragoni, E.
abstract

Consulenza tecnica per lo sviluppo concettuale, la riprogettazione e il proporzionamento di massima di un sistema di blocco/sblocco automatico del gruppo scapolare del sedile COBO ICS – 16


2018 - CONSULENZA TECNICA SU RESISTENZA STRUTTURALE DI VOLANTE C.O.B.O S.P.A [Altro]
Spaggiari, A.; Castagnetti, D.; Dragoni, E.
abstract

CONSULENZA TECNICA SU RESISTENZA STRUTTURALE DI VOLANTE C.O.B.O S.P.A


2018 - CONSULENZA TECNICA SU SISTEMA DI BLOCCO PER SCAPOLARE SEDILE C.O.B.O S.P.A [Altro]
Spaggiari, Andrea; Dragoni, Eugenio; Panini, Alessandro
abstract

# Definizione di bisogni cliente e specifiche tecniche # Analisi funzionale del sistema # Generazione di 2/3 concetti di blocco/sblocco automatico alternativi all’attuale versione COBO # Valutazione dei concetti e selezione condivisa del concetto campione # Elaborazione di Concept CAD 3D del concetto campione # Relazione finale con portafoglio concetti, procedura di selezione del concetto campione, file CAD 3D


2018 - Experimental validation of a simple shear strength model for hybrid friction-bonded interfaces [Articolo su rivista]
Ragni, M.; Castagnetti, D.; Dragoni, E.
abstract

The paper deals with the experimental measurement of the shear strength in hybrid interfaces, press fitted and bonded with anaerobic adhesives. The aim is to validate and improve the applicability of a constitutive model, which describes the interface behavior up to complete failure, by combining a cohesive law with a pure friction law. This paper presents an extensive experimental test plan, which deeply investigates the shear strength of two strong anaerobic adhesives, over four nominal contact pressure levels. The tests involve cylindrical specimens, butt bonded and pressure reinforced over an annular surface, and seven replications, giving 56 tests. The experimental torque-rotation curves up to complete failure highlight a similar response between the two adhesives, and confirm that the strain energy up to complete failure sums up a cohesive term and a pure friction term. In addition, the main parameters of the model linearly depend from contact pressure through simple relationships.


2018 - Fornire consulenza tecnica per la analisi preliminare tramite simulazione con metodologia agli elementi finiti di Volante COBO, secondo la norma fornita FZG-11486 Type3 [Altro]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio
abstract

– Predisposizione di un modello CAD per analisi EF in campo elastico, trascurando la cover e l’effetto della temperatura – Valutazione dei carichi e vincoli agenti sul sistema – Analisi della “Entire Wheel Skeleton” come da norma fornita FZG-11486, 2.1.2 (Type3) – Analisi della “Deflection” come da norma fornita FZG-11486, 2.3 (Type3) – Analisi del “Rim Pull” come da norma fornita FZG-11486, 2.4 (Type3)


2018 - Modeling and simulation of a compact push–pull rubber actuator energized by an outer coil of shape memory wire [Articolo su rivista]
Dragoni, Eugenio; Scirè Mammano, Giovanni
abstract

This paper introduces the concept and develops the theory for a push–pull actuator made by winding a thin shape memory wire on a solid rubber cylinder. The incompressibility of the rubber converts the thermomechanical contraction of the heated wire in twice as much axial strain available in the rubber core. The intrinsic elastic backup provided by the core allows push–pull action of the device. Based on the assumption of both material and geometric linearity, a simple theoretical model is developed, which culminates in a simple closed-form equation for the output stroke of the actuator. The theoretical predictions closely agree with refined finite element simulations, anticipating a net stroke of about 5–6% of the overall actuator length, depending on the outer load applied. The working principle of the actuator and the accuracy of the model are validated by tests on a proof-of-concept prototype.


2018 - Progettazione di una innovativa barella EMS meccatronica [Altro]
Spaggiari, A.; Castagnetti, D.; Dragoni, E.; Lusetti, M.
abstract

La ricerca consiste nello sviluppare concettualmente e proporzionare un sistema meccatronico di caricamento, sollevamento e riscaldamento di pazienti il soccorso e il trasporto in ambulanza, applicando i risultati ottenuti ad un’innovativa barella EMS meccatronica, quale esemplare su cui applicare le tecnologie sviluppate


2018 - Rapid evaluation of notch stress intensity factors using the peak stress method: Comparison of commercial finite element codes for a range of mesh patterns [Articolo su rivista]
Meneghetti, G.; Campagnolo, A.; Avalle, M.; Castagnetti, Davide; Colussi, M.; Corigliano, P.; DE AGOSTINIS, Massimiliano; Dragoni, E.; Fontanari, V.; Frendo, F.; Goglio, L.; Marannano, G.; Marulo, G.; Moroni, F.; Pantano, A.; Rebora, A.; Scattina, A.; Spaggiari, Andrea; Zuccarello, B.
abstract

The peak stress method (PSM) is an engineering, finite element (FE)‐oriented method to rapidly estimate the notch stress intensity factors by using the singular linear elastic peak stresses calculated from coarse FE analyses. The average element size adopted to generate the mesh pattern can be chosen arbitrarily within a given range. Originally, the PSM has been calibrated under pure mode I and pure mode II loadings by means of Ansys FE software. In the present contribution, a round robin between 10 Italian universities has been carried out to calibrate the PSM with 7 different commercial FE codes. To this aim, several two‐dimensional mode I and mode II problems have been analysed independently by the participants. The obtained results have been used to calibrate the PSM for given stress analysis conditions in (i) FE software, (ii) element type and element formulation, (iii) mesh pattern, and (iv) criteria for stress extrapolation and principal stress analysis at FE nodes.


2017 - ANALYTICAL MODELLING OF ROLAMITE MECHANISM MADE OF SHAPE MEMORY ALLOY FOR CONSTANT FORCE ACTUATORS [Articolo su rivista]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

This article analyses the Rolamite architecture exploiting shape-memory alloys as power element to obtain a solid-state actuator. The Rolamite mechanism was discovered in the late 1960s, initially as precision and low friction linear bearing. The most common Rolamite configuration consists of a flexible thin metal strip and two rollers mounted between two fixed parallel guide surfaces. The system can roll back and forth without slipping guided by the plates along its so-called sensing axis. The system presents another relevant advantage in addition to low friction coefficient, which is the possibility to provide force generation in a quite simple way. In the original literature works, the force was provided, thanks to cut-outs of various shapes in the strip, although this method does not allow the Rolamite to be considered a proper actuator, but only a force generator. In this article, we developed the idea of exploiting the shape-memory alloy as Rolamite power element, and therefore, to use the shape-memory effect to change the elastic properties of the strip and to provide the actuation force. The mechanical analysis, where the martensite–austenite transition is modelled in a simplified way, shows that this application is feasible, mainly thanks to the initial precurvature of the shape-memory alloy strip. The discussion of the results highlights some important merits of this architecture such as long stroke, constant force and compactness.


2017 - ATLAS - E’ Così AuTonomus cLeAning System [Altro]
Castagnetti, Davide; Mistrulli, Michele; Spaggiari, Andrea; Sorrentino, Andrea; Dragoni, Eugenio
abstract

ATLAS - E’ Così AuTonomus cLeAning System Sviluppo di un robot lavapavimenti autonomo per per ambienti industriali e civili interni di grandi dimensioni.


2017 - CARATTERIZZAZIONE A TORSIONE DI PROVINI DI CONDUTTORE IN CAVO TRASPOSTO UTILIZZATI NEI TRASFORMATORI SECONDO LA NORMA SOT054 [Altro]
Castagnetti, Davide; Sorrentino, Andrea; Ragni, Marina; Spaggiari, Andrea; Dragoni, Eugenio
abstract

CARATTERIZZAZIONE A TORSIONE DI PROVINI DI CONDUTTORE IN CAVO TRASPOSTO UTILIZZATI NEI TRASFORMATORI SECONDO LA NORMA SOT054


2017 - Design and Characterization of a Continuous Rotary Minimotor Based on Shape-Memory Wires and Overrunning Clutches1 [Articolo su rivista]
Scirè Mammano, Giovanni; Dragoni, Eugenio
abstract

An attractive but little explored field of application of the shape-memory technology is the area of rotary actuators, in particular for generating endless motion. This paper presents a miniature rotary motor based on shape-memory alloy (SMA) wires and overrunning clutches, which produces high output torque and unlimited rotation. The concept features an SMA wire tightly wound around a low-friction cylindrical drum to convert wire strains into large rotations within a compact package. The seesaw motion of the drum ensuing from repeated contraction-elongation cycles of the wire is converted into unidirectional motion of the output shaft by an overrunning clutch fitted between drum and shaft. Following a design process developed in a former paper, a six-stage prototype with size envelope of 48 × 22 × 30 mm is built and tested. Diverse supply strategies are implemented to optimize either the output torque or the speed regularity of the motor with the following results: maximum torque = 20 Nmm; specific torque = 6.31 × 10-4 Nmm/mm3; rotation per module = 15 deg/cycle; and free continuous speed = 4.4 rpm.


2017 - Mechanical behaviour of magnetic Silly Putty: Viscoelastic and magnetorheological properties [Articolo su rivista]
Golinelli, Nicola; Spaggiari, Andrea; Dragoni, Eugenio
abstract

In this work the mechanical and viscoelastic properties of magnetic Silly Putty are investigated. Silly Putty is a non-Newtonian material whose response depends on the rate at which it is deformed. For a rapid deformation, it behaves as an elastic solid, while over a relatively long time scale, the polymer molecules can be untangled and it flows as a fluid. The purpose of this article is to study the behaviour of this material firstly under a quasi-static compression and shear loading, and secondly under dynamic shear loading. The Silly Putty under study has a volume fraction of ferromagnetic particles. Hence, both quasi-static and dynamic stress are coupled with several strengths of magnetic field in order to assess the influence of the magnetisation on the mechanical and viscoelastic properties of the material. The approach adopted in this work followed the Design of Experiment method so that evaluating the influence of the variables and their interactions on the system response is possible. The results highlight a strong dependence on the deformation rate, while the influence of the magnetic field is weak, especially under dynamic shear tests in which the viscous components are predominant.


2017 - Mechanical design of buckled beams for low-stiffness elastic suspensions: Theory and application [Articolo su rivista]
SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

Axially compressed buckled beams have been used for several decades as elastic suspensions characterized by high static stiffness and low dynamic stiffness. The most comprehensive mathematical modelling of buckled beams is based on the elastica theory, a rational framework that seeks the equilibrium configuration for arbitrarily large deflections and rotations. The use of the elastica model is straightforward for analysis purposes but is rather awkward for design tasks because it requires handling of elliptic functions. This paper presents approximate equations developed from the elastica solution to facilitate the structural synthesis of buckled-beam suspensions starting from high-level engineering specifications. The step-by-step design procedure is illustrated by means of a case study and the theoretical predictions are validated against test data and finite element results.


2017 - Optimal design of tapered roller bearings for maximum rating life under combined loads [Articolo su rivista]
Dragoni, Eugenio
abstract

Using the relationships of the ISO 281 standard, this paper optimizes the internal dimensions of tapered roller bearings for maximum rating life. The bearing system addressed contains two identical bearings subjected to an arbitrary combination of centred radial and axial forces. It is shown that the basic rating life increases more than quadratically with the roller infill and the aspect ratio of the rollers, increases with the sixth power of the pitch diameter of the roller set and decreases with the third power of the applied radial force. Further, for any given ratio of axial to radial force, an optimal contact angle exists which maximizes the rating life of the bearing pair, irrespective of the actual bearing size and ratio of roller diameter to pitch diameter. The optimization procedure can either be used to design custom-made bearings or to select from manufacturers’ catalogues the bearing with the best contact angle for any assigned loading condition.


2017 - Progettazione di un banco prova per ruote con rivestimento in poliuretano elastomerico e sviluppo di un modello previsionale del comportamento in esercizio [Altro]
Castagnetti, Davide; Spaggiari, Andrea; Barone, Calogero; Dragoni, Eugenio
abstract

Progettazione di un banco prova per ruote con rivestimento in poliuretano elastomerico e sviluppo di un modello previsionale del comportamento in esercizio


2017 - Shear Strength Characterization of Metal-Elastomer Bonded Joints [Articolo su rivista]
Ragni, Marina; Castagnetti, Davide; Spaggiari, Andrea; Muccini, Filippo; Dragoni, Eugenio; Milelli, Matteo; Girlando, Simone; Borghi, Pierluigi
abstract

The shear strength characterization of bonded joints involving adherends with a remarkably different stiffness has a peculiar interest in industrial applications. This work proposes and investigates three innovative specimens (an axisymmetric annular, a tensile and a torsional one) purposely developed to manage dissimilar adherends bonded with adhesive in thin film. A Thick Adherend Shear Test specimen between rigid adherends is used for the assessment of the adhesive by itself. The work focuses on metal-elastomeric polyurethane bonded joints with a solventbased adhesive. All the tests are performed through an axial dynamometer, using a purposely developed fixture to convert the tensile load in a torque for the torsional specimen. The tensile and the torsional specimens provide the most reliable shear strength characterization.


2017 - Studio e progettazione del dispositivo meccatronico Master Cylinder Locking System con la funzione blocco meccanico basato sulle tecnologie del fluido magnetoreologico o/e piezoelettrico per i sistemi frenanti tipo Brake by Wire [Altro]
Spaggiari, Andrea; Dragoni, Eugenio; Castagnetti, Davide; Golinelli, Nicola
abstract

Studio e progettazione del dispositivo meccatronico Master Cylinder Locking System con la funzione blocco meccanico basato sulle tecnologie del fluido magnetoreologico o/e piezoelettrico per i sistemi frenanti tipo Brake by Wire


2017 - Sviluppo concettuale e dimensionamento di massima di un sistema meccanico facente parte della sospensione pneumatica di un sedile di guida professionale per macchine off-road [Altro]
Spaggiari, Andrea; Castagnetti, Davide; Cocconcelli, Marco; Dragoni, Eugenio; Rubini, Riccardo; Panini, Alessandro
abstract

Sviluppo concettuale e dimensionamento di massima di un sistema meccanico facente parte della sospensione pneumatica di un sedile di guida professionale per macchine off-road


2017 - Valvola di azzeramento pressione per sistemi idraulici [Altro]
Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio
abstract

Analisi e ottimizzazione strutturale di valvola di azzeramento pressione per sistemi idraulici


2016 - Analisi e procedura di collaudo a resistenza di giunzioni incollate con adesivo UV in box doccia [Altro]
Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio; Ragni, Marina
abstract

Analizzare e definire una procedura di collaudo a resistenza (“Norma Novellini”) delle giunzioni incollate con adesivo UV nei box doccia.


2016 - Calcoli strutturali e valutazione dell’affidabilità funzionale e strutturale del nuovo gruppo di misura per equilibratrici prodotte da Snap-on Equipment [Altro]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio; Dallari, F.
abstract

SCOPO Valutazione dell’affidabilità funzionale e strutturale del nuovo gruppo di misura per equilibratrici prodotte da Snap-on Equipment. ATTIVITÁ FASE 1: Assistenza per test ISO 21940-21:2012 su nuova macchina equilibratrice FASE 2: Valutazione strutturale del modello, tramite prove sperimentali accelerate secondo il Metodo Staircase FASE 3: Applicazione del Metodo Staircase


2016 - Closed-form modal analysis of flexural beam resonators ballasted by a rigid mass [Articolo su rivista]
Scire' Mammano, Giovanni; Castagnetti, Davide; Dragoni, Eugenio
abstract

The work deals with the study of free flexural vibrations of constant cross-section elastic beams ballasted by a rigid mass with rotary inertia at any longitudinal position. We analyze five sets of boundary conditions of the beam (fixed-free, fixed-fixed, fixed-pinned, pinned-pinned, and free-free) and hypothesize that the structure is perfectly rigid, where the rigid mass is applied. By employing the Euler-Bernoulli beam theory, a single parametric matrix is obtained, which provides the characteristic equation of motion of the structure. When applied to specific configurations, the proposed analytical model predicts the eigenfrequencies and eigenmodes of the beam as accurately as ad-hoc analytical models available in the literature. The accuracy of the results is also confirmed by comparison with detailed two- and three-dimensional finite element analyses of a test case. By means of a 3D finite element model, the applicability of the rigid mass hypothesis to continuous beams with a composite thickened portion is finally assessed.


2016 - Consulenza tecnica per esecuzione di prove sperimentali a taglio per la valutazione del comportamento termomeccanico dell’incollaggio di rivestimenti in poliuretano elastomerico [Altro]
Castagnetti, Davide; Spaggiari, Andrea; Ragni, Marina; Dragoni, Eugenio
abstract

Svolgimento di prove sperimentali per la caratterizzazione della resistenza a taglio di giunzioni incollate metallo-elastomero al fine di valutare: a) Effetto della tipologia di sabbiatura degli aderendi, su adesivo Thixon 406; b) Effetto del condizionamento, sull’adesivo Thixon 406; c) Effetto del tipo di adesivo: Thixon 406 vs Thixon 422.


2016 - Experimental investigation and model validation of the shear strength of hybrid interfaces up to complete failure [Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract

The paper experimentally investigates hybrid interfaces pressurereinforced and bonded with anaerobic adhesive. While their static strength has been deeply investigated, their behavior up to complete failure lacks of a constitutive model. This work aims to assess the applicability of a simple model involving a cohesive law and a pure 10 friction law, in order to describe the interface behavior up to complete failure under different contact pressure levels. A systematic experimental campaign investigates the shear strength of cylindrical specimens butt-bonded and pressure reinforced over an annular surface. The tests involve two anaerobic adhesives and 15 four pressure levels. The experimental torque-rotation curves confirm that the strain energy up to complete failure is given by a cohesive term and a pure friction term, both of them linearly dependent upon the contact pressure.


2016 - Measuring the shear strength of structural adhesives with bonded beams under antisymmetric bending [Articolo su rivista]
Spaggiari, Andrea; Dragoni, Eugenio; H., Brinson
abstract

Standard tests for adhesive bond characterization suffer from several deficiencies. The simplest specimens to make and test are lap joint geometries (e.g. single, double, symmetric, etc.) that generate complex stress distributions with irregularities and even singularities of the stress state. Those with the stress state closer to pure shear (e.g. napkin ring or Arcan) are difficult to make and require special test fixtures. This paper examines the stress state in the adhesive of a simple beam specimen obtained by bonding two flat plates upon one another and loading the final sandwich in four-point antisymmetric bending. This test improves over a previously investigated sandwich test performed in three-point bending. A simple analytical model is used to optimize the specimen for piece-wise constant shear stresses along the adhesive. The accuracy of the model is validated by finite element analyses, showing good agreement for thin layers of relatively stiff adhesives. A Digital Image Correlation technique is exploited to verify the analytical and the finite element models and the first results confirm the applicability of the method for assessing the shear strength of glassy adhesives.


2016 - Modeling and optimization of the sandwich beam specimen in three-point bending for adhesive bond characterization [Articolo su rivista]
Dragoni, Eugenio; H. F., Brinson
abstract

Standard tests for adhesive bond characterization suffer for several deficiencies. The simplest specimens to make and test are lap joint geometries (e.g. single, double, symmetric, etc.) that generate complex stress distributions with irregularities and even singularities of the stress state. Those with the stress state closer to pure shear (e.g. napkin ring or Arcan) are difficult to make and require special test fixtures. This paper examines the stress state in the adhesive of a simple beam specimen obtained by bonding two flat plates one upon the other and loading the final sandwich in three-point bending. An elementary theory is used to optimize the specimen for in-situ measurements of either shear strength or shear modulus of the adhesive. The accuracy of the model is validated with finite element analyses, showing good agreement between the analytical and finite element model and also providing suggestions for the best geometry to be adopted for practical implementation of the test.


2016 - Modelling and validation of a continuous rotary motor combining shape memory wires and overrunning clutches [Articolo su rivista]
SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

This article presents the conceptual design, modelling, prototyping and testing of a novel rotary motor featuring shape memory alloy wires and overrunning clutches. The device comprises a shape memory alloy wire wound around a low-friction cylindrical drum contrasted by a backup beam spring and fitted to the output shaft through an overrunning clutch. Electrical heating produces a contraction of the wire, hence a rotation of the drum which is transferred to the shaft. Thanks to the overrunning clutch, during the recoiling phase, the drum rotates backward while the shaft does not move. Spurious backward movements of the shaft are contrasted by a second overrunning clutch linking the shaft to the frame. This article develops a model for the quasi-static simulation of the motor and the experimental characterization of a prototype device featuring three active drums, a rotary sensor and an angular brake to apply the external load. Despite the low degree of optimization, the tested motor performs well in terms of specific stroke, specific output torque and specific output work per cycle. Winding of the wire on the drum impairs somewhat the fatigue life with respect to publish data on straight wires, a drawback which calls for further design refinements.


2016 - Progettazione e validazione di materiali compositi attivi rinforzati con fibra SMA per strutture adattative, nell’ambito del progetto Prin 2015 n. 2015RT8Y45-PE8 dal titolo Smart Composite Laminates [Altro]
Spaggiari, A.; Castagnetti, Davide; Dragoni, E.; Mizzi, Luke
abstract

Smart materials such as piezoelectrics and shape memory alloys (SMA) are receiving increasing attention due to their possible application in actuators technology, shape morphing structures, energy harvesters, and vibration control. However, their practical diffusion is limited due to restrictions associated with scarce mechanical properties, low electro-mechanical conversion rates, or difficulties in the modulation of their morphed shape while actuated. Overarching objective of this project is developing and characterizing innovative smart structures which can either serve as conductors, energy harvesters, or selectively modulate their shape (shape morphing) by combining innovative piezoelectric materials with SMAs to form a new class of smart structural composites. Final effort of this project is not only the development of innovative smart composite materials, but also the development of prototypal energy harvester and shape morphing structures to assess their effective smart capabilities. The proper development of such a technology involves a broad range of expertises. First, the development, optimization, and characterisation of such smart composite materials. Second, the formulation of tools capable of predicting the complex thermo-electro-mechanical behaviour of the envisioned structures to aid the optimization of their design. Third, the development of mechatronic techniques for the autonomous implementation of the morphing process, which passes through the creation of a robust control policy capable of selectively actuate the morphing structure as a function of its application. To tackle such a challenging process, we here envisage developing smart structures by utilizing both SMAs and innovative piezoelectric nanofibers. In particular, the piezoelectric polymeric nanofibers production technology has been recently developed by members of the proposed research team. These offer the twofold advantage of significantly increase the electromechanical conversion rate with respect to traditional piezoelectric materials, whereby their morphology allows their introduction into composite laminates at the production stage, resulting into a piezoelectric structural material. Similarly, SMA fibers will be utilized as reinforce for the composite. These allow for higher actuation loads and larger deformations, extending the application ranges. Analytical and numerical models of the thermo-electro-mechanical response will be developed and utilised for the optimisation of the active structures. Results from the proposed research will be finally applied to specific case studies, e.g. a micro-actuator, a energy harvester from a broadband excitation, and plates with shape morphing capabilities under selective control. The potential impact and importance of these goals on materials science, and for a wide spectrum of industrial applications, high-tech industry, and finally in actuating and sensing technology is indeed of extreme interest.


2016 - Sviluppo di viti ad altissima resistenza per applicazione su motori endotermici altamente performanti e settore aerospace [Altro]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio; Marmiroli, M.
abstract

Stato dell’arte sull’effetto delle variabili geometriche (raccordi sottotesta, forma filetto, giochi, …) e delle condizioni di installazione (precarico, rigidezza delle parti serrate, presenza di sistemi antisvitamento, numero di filetti in presa …) sulla resistenza a fatica a temperatura ambiente. Individuazione di geometrie e forme, compatibili con la funzionalità delle viti, in grado di aumentare la resistenza a fatica; Selezione dei parametri geometrici e di montaggio più promettenti per l’aumento a fatica dei prodotti e delle tipologie di collegamento VIMI ai fini della successiva campagna sperimentale. o Individuazione di best practice di carattere progettuale delle viti; Definizione di best practice e di linee guida di supporto alla progettazione geometrica della vite. In particolare, a seguito delle successive prove sperimentali e dell’analisi statistica dei risultati, saranno individuate le migliori soluzioni di disegno e di installazione per massimizzare la vita a fatica della vite. Assistenza per la scelta e l’utilizzo di applicativi commerciali FEM per l’analisi elastoplastica e la previsione a fatica a temperatura ambiente di viti e collegamenti filettati. Affiancamento e formazione a personale VIMI per la costruzione di modelli FEM efficienti e attendibili


2016 - The use of the theory of critical distance and the stress-gradient approach in the fatigue life estimation of notched components [Articolo su rivista]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio; Bulleri, S.
abstract

Fatigue life prediction for machine components is a fundamental factor in the industrial world, and therefore several methods can be traced in technical literature to estimate life of notched components. The present paper correlates the classical stress-gradient approach, or support factor method, proposed by Siebel, Neuber and Petersen with the more recent theory of critical distance approach by Tanaka and Taylor. On one hand, the main asset of the support factor method is the punctual information about the stresses needed to estimate the effective stress, namely the maximum stress and stress gradient at the hot spot. By contrast, the theory of the critical distance needs the calculation of the stress distribution for a finite depth inside the material. The main drawback of the support factor method is that the material parameter * is available only for a limited series of materials. In order to overcome this limitation, the paper investigates the correlation between the material parameter * and the critical distance L by relying on a parametric stress function. The proposed correlation aims at giving a simple method for the industrial engineers, which often needs straightforward methods to tackle practical problems. A comparison between the two methods is carried out by considering three different benchmark geometries: a typical V-notched specimen, a vessel under internal pressure and a complex industrial hydraulic control valve. In the first two benchmarks, the effective stresses are analytically retrieved and compared using both methods while an elastic finite element analysis is performed for the last one. The close match of the fatigue life prediction between the methods supports the possibility to exploit the data available in literature for the critical distance in order to estimate the effective stresses with the support factor method.


2015 - A novel ball joint wear sensor for low-cost structural health monitoring of off-highway vehicles [Articolo su rivista]
Castagnetti, Davide; Bertacchini, Alessandro; Spaggiari, Andrea; Lesnjanin, A.; Larcher, Luca; Dragoni, Eugenio; Arduini, M.
abstract

Mechatronic agricultural machines and equipment are continuously increasing their complexity and cost. In order to ensure their efficiency and reliability and preserve their value, it is important to actively monitor damaging and wear occurring on critical components. This approach needs the introduction of sensors on the machine, which allow continuous monitoring of the residual life of components. This work presents the development and testing of a wear sensor for a ball joint which can be applied for monitoring and diagnostic in off-highway vehicles, automotive and the industrial fields. Many peculiar features make this sensor innovative and contribute to the advance of the technology in the sector: there are no other active sensors for this specific and safety-critical joint; it has an ultra-low power consumption and can be self-powered through energy harvesting; it implements wireless connectivity; it is simple, small size and low cost. This wear sensor for the ball joint is firstly aimed at monitoring the damage of the ball joint placed between the steering actuator and the wheel spindle, since failure of the joint leads to complete loss of steering action. However, the sensor can be applied to any application involving a safety-critical ball joint (e.g. the front suspension of a vehicle). The present work describes the conceptual design and development of the whole mechatronic sensor, which includes the mechanical joint sensor and the electronic board which manages the system. Validation of the ball joint wear sensor, which was performed on an agricultural tractor through tests on a track, proved the reliability of the proposed solution.


2015 - American Society of Mechanical Engineers 2013 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, Symposium on Modeling, Simulation and Control [Articolo su rivista]
Dragoni, E.; Kiefer, B.; Koo, J. -H.
abstract


2015 - Analytical modelling of rolamite mechanism made of shape memory alloy for constant force actuators [Relazione in Atti di Convegno]
Spaggiari, A.; Dragoni, E.
abstract

This paper analyses the Rolamite architecture exploiting shape memory alloys as power element to obtain a solid state actuator. The Rolamite mechanism was discovered in the late sixties, initially as precision and low friction linear bearing. The most common Rolamite configuration consists of a flexible thin metal strip and two rollers mounted between two fixed parallel guide surfaces. The system can roll back and forth without slipping guided by the plates along its so called sensing axis. The system presents another relevant advantage in addition to low friction coefficient, which is the possibility to provide force generation in a quite simple way. In the original literature works the force was provided thanks to cutouts of various shape in the strip, though this method does not allow the Rolamite to be considered a proper actuator, but only a force generator. In this paper we developed the idea of exploiting the shape memory alloy as Rolamite power element and therefore to use the shape memory effect to change the elastic properties of the strip and to provide the actuation force. The mechanical analyses and the equations where the martensite-Austenite transition is modelled in a simplified way, show that this application is feasible, mainly thanks to the initial precurvature of the SMA strip. The discussion of the results highlights some important merits of this architecture such as long stroke, constant force and compactness.


2015 - Design and characterization of a continuous rotary minimotor based on shape memory wires and overrunning clutches [Relazione in Atti di Convegno]
Mammano, G. S.; Dragoni, E.
abstract

An attractive but little explored field of application of the shape memory technology is the area of rotary actuators, in particular for generating endless motion. This paper presents a miniature rotary motor based on SMA wires and overrunning clutches which produces high output torque and unlimited rotation. The concept features a SMA wire tightly wound around a low-friction cylindrical drum to convert wire strains into large rotations within a compact package. The seesaw motion of the drum ensuing from repeated contractionelongation cycles of the wire is converted into unidirectional motion of the output shaft by an overrunning clutch fitted between drum and shaft. Following a design process developed in a former paper, a six-stage prototype with size envelope of 48×22×30 mm is built and tested. Diverse supply strategy are implemented to optimize either the output torque or the speed regularity of the motor with the following results: maximum torque = 20 Nmm; specific torque = 6.31×104 Nmm/mm3; rotation per module = 15 deg; free continuous speed = 4 rpm.


2015 - Effect of Stress, Heating Rate, and Degree of Transformation on the Functional Fatigue of Ni-Ti Shape Memory Wires [Articolo su rivista]
SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

Shape memory alloys, particularly in the form of thin wires, are becoming increasingly attractive in the industrial field for the construction of compact actuators with high-power density. The structural and functional fatigue behavior of shape memory alloys undergoing thermomechanical cycling has been investigated only partially in the technical literature. In particular, the effects of operating parameters like the degree of martensite-austenite transformation and the heating rate on the fatigue life of the alloy have received very little attention so far. This paper explores the effect of these two parameters on the fatigue response of commercial SMA wires exposed to two linear stress-strain profiles during cycling. The results show the beneficial effects of partial transformation on the structural and functional life of the wires, with negligible loss of performance in terms of useful stroke. Though less markedly, the heating rate also has an effect on the structural and functional response, with the sine waveform supply performing better than the square profile.


2015 - Enhanced properties of magnetorheological fluids: Effect of pressure [Articolo su rivista]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

Magnetorheological fluids are extensively used in the industrial world to produce dissipative systems in an easily adjustable or even self-adaptive way. Sometimes their intrinsic rheological properties fail to meet system requirements in terms of available forces or yield stress for a given design space. In technical literature, previous works show a dependency of the shear strength of magnetorheological fluids on the internal pressure of the fluid, called squeeze strengthen effect. This work aims at the experimental validation of the behaviour of the magnetorheological fluids in both flow and shear modes under a given compressive state. Two specific ad hoc experimental test rigs are used for the campaign. The systems are designed in order to apply the magnetic field and the pressure at the same time and the tests are carried out following a design of experiment method. The magnetic parts of the system are designed with the help of a magnetic finite element simulation software, then the experiments are performed and the results are collected. The output is analysed through an analysis of variance approach, a statistical procedure that shows the influence of multiple variables on the system outputs. The outcome of the experimental tests confirms the beneficial effect of the pressure in both flow and shear modes, with performances up to three times compared with the datasheet values, where no pressure is considered.


2015 - Experimental characterization and modelling validation of shape memory alloy Negator springs [Articolo su rivista]
Spaggiari, Andrea; Dragoni, Eugenio; Tuissi, A.
abstract

This article is aimed at the experimental characterization and modelling validation of shape memory alloy Negator springs. A Negator spring is a spiral spring made of strip of metal wound on the flat with an inherent curvature such that, in repose, each coil wraps tightly on its inner neighbour. The main feature of a Negator springs is the nearly constant force–displacement behaviour in the unwinding of the strip, mounted on a rotating drum. Moreover, the stroke is very long, theoretically infinite as it depends only on the length of the initial strip. A Negator spring made of shape memory alloy is built and experimentally tested to demonstrate the feasibility of this actuator. The shape memory Negator spring behaviour is predicted both with an analytical model and with a finite element software. In both cases, the material is modelled as elastic in austenitic range while an exponential continuum law is used to describe the martensitic behaviour. The experimental results confirm the applicability of this kind of geometry to the shape memory alloy actuators, and the analytical model is confirmed to be a powerful design tool to dimension and predict the spring behaviour both in martensitic and austenitic ranges, as well as the finite element model developed.


2015 - Formulation of a three-dimensional shear-flexible bimaterial beam element with constant curvature [Articolo su rivista]
Dragoni, Eugenio; Bagaria, W. J.
abstract

This paper presents the closed-form formulation for a three-dimensional curved beam element with round bimaterial section. The formulation includes the effects of shear forces on displacements and stresses and of the beam curvature on the distribution of bending and torsional stress over the cross section. The element is coherent with the well-known theory for straight beams, which is obtained exactly as the curvature radius becomes infinite. The numerical predictions for a test case compare favourably with published analytical and experimental results and with the outcome of a purposely developed, large-scale FE brick model.


2015 - Modelling, simulation and characterization of a linear shape memory actuator with compliant bow-like architecture [Articolo su rivista]
SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

The design of shape memory alloy actuators typically compromises between force and stroke, the two properties being inversely proportional to one another for any given shape memory alloy element. This article presents a bow-like compliant actuator aimed at improving the specific performance of shape memory wires on both accounts. Conceptually, the actuator is formed by two straight elastic beams mutually hinged at the ends with a pre-stretched shape memory alloy wire in between. Heating of the alloy shortens the wire, which in turn makes the beams to buckle outwards in a symmetric double-arched configuration. The transverse displacement of the beams amplifies the contraction of the wire while producing a favourable output force. This article develops a simple, though accurate, analytical model of the actuator upon which a step-by-step design procedure is built. The theoretical findings are compared with the outcome of a finite element simulation for a case study and with the test data gathered from a physical prototype actuator.


2015 - Optimal design of paired tapered roller bearings under centred radial and axial static loads [Articolo su rivista]
Dragoni, Eugenio
abstract

Based on the relationships from the ISO 76 standard, this paper optimizes the internal dimensions of tapered roller bearings for maximum static load capacity. A bearing system formed by two identical bearings is assumed, subjected to whatever combination of centred radial and axial forces. It is shown that the static capacity increases linearly with the roller infill, with the ratio of roller length to roller diameter and with the square of the pitch diameter of the roller set. Further, given the ratio of axial to radial force, an optimal contact angle exists which maximizes the static capacity of the bearing pair, regardless of the actual bearing size and ratio of roller diameter to pitch diameter. The optimization procedure can either be used to design custom-made bearings or to pick from manufacturersʼ catalogues the bearing with the best contact angle for any assigned loading condition.


2015 - Optimization and testing of a continuous rotary motor based on shape memory wires and overrunning clutches [Relazione in Atti di Convegno]
Scire Mammano, G.; Dragoni, E.
abstract

A relatively unexplored but extremely attractive field for the application of the shape memory technology is the area of rotary actuators, especially for generating continuous rotations. This paper deals with a novel design of a rotary motor based on SMA wires and overrunning clutches which features high output torque and boundless angular stroke in a compact package. The concept uses a long SMA wire wound round a low-friction cylindrical drum upon which the wire can contract and extend with minimum effort and limited space demand. Fitted to the output shaft by means of an overrunning clutch the output shaft rotates unidirectionally despite the sequence of contractions-elongation cycles of the wire. Following a design procedure developed in a former paper, a six-stage miniature prototype is built and tested showing excellent performance in terms of torque, speed and power density. Characteristic performances of the motor are as follows: size envelope = 48×22×30 mm3; maximum torque = 20 Nmm; specific torque = 6.31×10-4 Nmm/mm3; rotation per module = 15 deg; continuous speed (unloaded) = 4 rpm.


2015 - Progetto SAVE WHEEL – Sensorized Anti Vibration Ergonomic Wheel (Ruota Industriale Innovativa, Ergonomica, Sensorizzata, con recupero di energia) [Altro]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio; Ragni, Marina; Muccini, Filippo; Spanalatte, Marco
abstract

Progetto SAVE WHEEL – Sensorized Anti Vibration Ergonomic Wheel (Ruota Industriale Innovativa, Ergonomica, Sensorizzata, con recupero di energia)


2015 - Special issue on modeling and control of adaptive dynamic systems and structures [Articolo su rivista]
Dragoni, E.; Harne, R. L.; Daqaq, M. F.
abstract


2015 - Un semplice modello coesivo con attrito per descrivere interfacce ibride forzate e incollate [Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio
abstract

Il lavoro studia interfacce ibride forzate meccanicamente e incollate con adesivo anaerobico. Se dal punto di vista della loro resistenza statica sono state ampiamente studiate, altrettanto non è relativamente al loro comportamento fino a completo collasso. Obiettivo di questo lavoro è verificare l’applicabilità di un semplice modello costitutivo, che unisce un legame coesivo con una legge di puro attrito, per descrivere il comportamento dell’interfaccia fino a completo collasso sotto differenti livelli di pressione di contatto. Un’estesa campagna sperimentale esamina la resistenza a taglio di provini cilindrici incollati testa a testa considerando due adesivi anaerobici e quattro livelli di pressione di contatto. Le curve sperimentali confermano che l’energia di deformazione fino a completo collasso del provino è somma di un contributo coesivo e di uno di puro attrito, linearmente dipendenti dalla pressione di contatto.


2014 - Adhesively-bonded friction interfaces: Macroscopic shear strength prediction by microscale finite element simulations [Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract

Anaerobic adhesives are commonly used to enhance the shear strength of clamped friction joints between metal parts. Experimental results show that the total strength of the friction-bonded interface steadily increases with the clamping pressure. However, if weak anaerobics are used in the assembly, its strength is lower than the dry (purely friction) joint0s under high applied pressures. This paper seeks an explanation for this macroscopic behaviour by means of microscale finite-element simulations. The analyses show that the experimental results can be explained by assuming that: (a) however great the clamping pressure, a thin film of adhesive remains trapped between the crests of the mating surfaces; (b) under the high local pressure the shear strength of this film becomes greater than the regular adhesive at no pressure; (c) the stronger adhesives entail a higher increase than the weaker adhesives.


2014 - Analytical and numerical modeling of shape memory alloy Negator springs for constant-force, long-stroke actuators [Articolo su rivista]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

This article explores the merits of shape memory alloy Negator springs as powering elements for solid-state actuators. A Negator spring is a spiral spring made of strip of metal wound on the flat with an inherent curvature such that, in repose, each coil wraps tightly on its inner neighbor. The unique characteristic of Negator springs is the nearly constant force needed to unwind the strip for very large, theoretically infinite deflections. Moreover, the flat shape, having a high area-over-volume ratio, grants improved bandwidth compared to any solution with solid wires or helical springs. The shape memory alloy material is modeled as elastic in austenitic range while an exponential continuum law is used to describe the martensitic behavior. The mathematical model of the mechanical behavior of shape memory alloy Negator springs is provided, and their performances as active elements in constant-force, long-stroke actuators are assessed. The shape memory alloy Negator spring is also simulated in a commercial finite element software, ABAQUS, and its mechanical behavior is estimated through finite element analyses. The analytical and the numerical predictions are in good agreement, both in martensitic and in austenitic ranges.


2014 - Closed-form modal analysis of flexural beam resonators ballasted by a rigid mass [Relazione in Atti di Convegno]
G., Scirè Mammano; Castagnetti, Davide; Dragoni, Eugenio
abstract

The work deals with the study of free flexural vibrations of constant cross-section elastic beams ballasted by a rigid mass with rotary inertia at any longitudinal position. We analyze five sets of boundary conditions of the beam (fixed-free, fixed-fixed, fixed-pinned, pinned-pinned, and free-free) and hypothesize that the structure is perfectly rigid, where the rigid mass is applied. By employing the Euler-Bernoulli beam theory, a single parametric matrix is obtained, which provides the characteristic equation of motion of the structure. When applied to specific configurations, the proposed analytical model predicts the eigenfrequencies and eigenmodes of the beam as accurately as ad-hoc analytical models available in the literature. The accuracy of the results is also confirmed by comparison with detailed two- and three-dimensional finite element analyses of a test case. By means of a 3D finite element model, the applicability of the rigid mass hypothesis to continuous beams with a composite thickened portion is finally assessed.


2014 - Combined squeeze-shear properties of magnetorheological fluids: Effect of pressure [Articolo su rivista]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

Several applications of magnetorheological fluids are nowadays present in the industrial world; however, sometimes material properties are not sufficient to meet the system requirements. Among the technical literature, there is experimental evidence of the squeeze-strengthen effect, which is a pressure dependency of the yield stress of the magnetorheological fluid. Since many magnetorheological systems are rotary devices, such as brakes and clutches, this article investigates the behaviour of magnetorheological fluids under pressure when a rotation is applied to shear the fluid. The system is designed to apply both the magnetic field and the pressure following a design of experiment method. The experimental apparatus comprises a cylinder in which a piston applies both pressure and a prescribed rotation. The magnetic circuit is designed to provide a tunable, nearly constant magnetic induction field inside the fluid. The experimental apparatus measures the torque produced by the magnetorheological fluid as a function of the variables considered, and consequently, the yield shear stress is evaluated. A statistical analysis of the results finds a positive interaction between the magnetic field and the pressure, which enhances the magnetorheological fluid performances, measured in terms of yield stress, up to more than two times the manufacturer’s datasheet values.


2014 - Design of a Dielectric Elastomer Cylindrical Actuator With Quasi-Constant Available Thrust: Modeling Procedure and Experimental Validation [Articolo su rivista]
Berselli, Giovanni; G., Scirè Mammano; Dragoni, Eugenio
abstract

A novel design for a dielectric elastomer (DE) actuator is presented. The actuator is obtained by coupling a cylindrical DE film with a series of slender beams axially loaded beyond their buckling limit. Similar to previous published solutions, where different actuator geometries were coupled with compliant mechanisms of various topologies, the elastic beams are designed so as to provide a suitable compensating force that allows obtaining a quasi-constant available thrust along the entire actuator stroke. Whilst the elastic beam are sized on the basis of an analytical procedure, the overall system performance is evaluated by means of multiphysics finite element (FE) analysis, accounting for the large deflection of the buckled-beam springs (BBSs) and for the DE material hyperelasticity. Numerical and experimental results are finally provided, which demonstrate the prediction capabilities of the proposed modeling method and confirm that well behaved cylindrical actuators can be conceived and produced.


2014 - Effects of Loading and Constraining Conditions on the Thermomechanical Fatigue Life of NiTi Shape Memory Wires [Articolo su rivista]
G., Scirè Mammano; Dragoni, Eugenio
abstract

The availability of engineering strength data on shape memory alloys (SMAs) under cyclic thermal acti-vation (thermomechanical fatigue) is central to the rational design of smart actuators based on these materials. Test results on SMAs under thermomechanical fatigue are scarce in the technical literature, and even the few data that are available are mainly limited to constant-stress loading. Since the SMA elements used within actuators are normally biased by elastic springs or by antagonist SMA elements, their stress states are far from being constant in operation. The mismatch between actual working conditions and laboratory settings leads to suboptimal designs and undermines the prediction of the actuator lifetime. This paper aims at bridging the gap between experiment and reality by completing an experimental campaign involving four fatigue test conditions, which cover most of the typical situations occurring in practice: constant stress, constant-strain, constant stress with limited maximum strain, and linear stress-strain variation with limited maximum strain. The results from the first three test settings, recovered from the previously published works, are critically reviewed and compared with the outcome of the newly performed tests under the fourth arrangement (linear stress-strain variation). General design recommendations emerging from the experimental data are put forward for engineering use.


2014 - Elastic compensation of linear shape memory alloy actuators using compliant mechanisms [Articolo su rivista]
G., Scire Mammano; Dragoni, Eugenio
abstract

This article presents a modular architecture for shape memory alloy actuators elastically compensated by thin beams loaded axially beyond their buckling limit. Starting from the exact equations for the elastic curve of the beams, an approximate procedure is developed for the engineering design of the entire compensating system. The theory of the compensator is validated successfully against a finite element model and experimental results. The experimental charac-terization of a complete prototype actuator shows that the forces generated by the compensated actuator are constant for both instroke and outstroke over the full range of displacements. The actuator concept proposed lends itself to modular assembly to multiply either the stroke covered (series combination) or the force generated (parallel combination).


2014 - Functional fatigue of Ni–Ti shape memory wires under various loading conditions [Articolo su rivista]
SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

The rational design of smart actuators based on shape memory alloys requires reliable strength data from the thermo-mechanical cycling of the material (functional fatigue). Functional tests results do not abound in the technical literature and the few data available are mostly limited to the condition of constant applied stress, which is hardly achieved in operation. The disagreement between actual working condi-tions and laboratory conditions leads to suboptimal designs and undermines the prediction of the life of the actuator. To bridge the gap between experiment and reality, this paper envisions four cyclic tests spanning the range of loadings which can occur in practice: constant-stress, constant-strain, constant-stress with limited maximum strain and linear stress–strain cycle. Commercial NiTi wires (0.15 mm diameter) are tested under constant-stress, constant-strain and constant stress with limited maximum strain conditions using a custom machine and the disclosed results are critically discussed.


2014 - MECHANICAL BEHAVIOUR OF MAGNETIC SILLY PUTTY: VISCOELASTIC AND MAGNETORHEOLOGICAL PROPERTIES [Relazione in Atti di Convegno]
Golinelli, Nicola; Spaggiari, Andrea; Dragoni, Eugenio
abstract

In this work the mechanical and viscoelastic properties of the magnetic Silly Putty are investigated. Silly Putty is a non-Newtonian material whose response depends on the rate at which it is deformed. For a rapid deformation it behaves as an elastic solid while over a relatively long time scale stress, the polymer molecules can be untangled and it flows as a fluid. The purpose of this paper is to study the behaviour of this material firstly under a quasi-static compression and shear and secondly under a dynamic shear loading. The Silly Putty under study presents a volume fraction of ferromagnetic particles. Hence, both quasi-static and dynamic stress are coupled with several values of magnetic field in order to assess the influence on the mechanical and viscoelastic properties of magnetic Silly Putty. The approach adopted in this work was based on a Design of Experiment technique so that evaluating the influence of the variables involved and their interactions is possible. The results highlight a strong dependence on the deformation rate while the influence of the magnetic field is weak especially under dynamic shear tests in which the highest deformation are predominant. (doi:10.1115/SMASIS2014-7438)


2014 - Modelling and validation of a rotary motor combining shape memory wires and overrunning clutches [Relazione in Atti di Convegno]
Mammano, Giovanni; Dragoni, E.
abstract

The paper presents the conceptual design, modeling and prototyping of a novel rotary motor based on shape memory alloy (SMA) wires. The basic architecture of the device capitalizes on a SMA wire wound around a low-friction cylindrical drum. The backup force to the SMA wire is provided by a beam spring which generates a nearly-constant force tangential to the drum. The electrical activation of the wire produces a contraction of the wire, hence a rotation of the drum fitted to the shaft through an overrunning clutch (free wheel). Thanks to the overrunning clutch, during the backup phase (recoiling of the wire), the drum rotates backward while the shaft does not move. Spurious backward movements of the shaft are contrasted by a second overrunning clutch linking the shaft to the frame. The paper presents a model for the quasistatic simulation of the motor and the experimental characterization of a prototype device featuring three active drums, a rotary sensor and an angular brake to apply the external load.


2014 - NiTi Alloy Negator Springs for Long-Stroke Constant-Force Shape Memory Actuators: Modeling, Simulation and Testing [Articolo su rivista]
Spaggiari, Andrea; Dragoni, Eugenio; A., Tuissi
abstract

This work aims at the experimental characterization and modeling validation of shape memory alloy (SMA) Negator springs. According to the classic engineering books on springs, a Negator spring is a spiral spring made of strip of metal wound on the flat with an inherent curvature such that, in repose, each coil wraps tightly on its inner neighbor. The main feature of a Negator springs is the nearly constant force displacement behavior in the unwinding of the strip. Moreover the stroke is very long, theoretically infinite, as it depends only on the length of the initial strip. A Negator spring made in SMA is built and experimentally tested to demonstrate the feasibility of this actuator. The shape memory Negator spring behavior can be modeled with an analytical procedure, which is in good agreement with the experimental test and can be used for design purposes. In both cases, the material is modeled as elastic in austenitic range, while an exponential continuum law is used to describe the martensitic behavior. The experimental results confirms the applicability of this kind of geometry to the shape memory alloy actuators, and the analytical model is confirmed to be a powerful design tool to dimension and predict the spring behavior both in martensitic and austenitic range.


2014 - Regularization of torsional stresses in tubular lap bonded joints by means of functionally graded adhesives [Articolo su rivista]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

This paper describes the analytical stress analysis of a tubular single lap joint under torsion with a functionally graded modulus adhesive (FGA). The adhesive technology offers several advantages in structural applications, such as bonding dissimilar materials, but suffers from severe stress concentrations in the bondline which often act as a trigger for fracture phenomena. To overcome these problems, FGA with nanoparticles distributed inside the polymer can be used, as proposed recently in technical literature. The aim of the work is to retrieve which is the optimal stiffness of the adhesive layer to regularize the stresses. The peculiar geometry analyzed permits a straightforward analytical approach since pure torsion on tubes do not cause any bending and no Poisson’s effect creates peel stress in the adhesive, therefore only shear stress are to be considered. The work first develops the equations which govern the shear stress distribution in the adhesive and then by forcing the shear stress to be constant is able to find out which is the stiffness profile along the bondline. The axial distribution of the stiffness of the FGA layer along the overlap is provided and the dependence on the elasto-geometrical parameters is discussed. The findings of the paper can be used to tailor the reinforcement distribution, under the hypothesis of a continuously changing adhesive stiffness.


2014 - Special Issue: 2012 ASME conference on smart materials, adaptive structures, and intelligent systems [Articolo su rivista]
Smith, R.; Wereley, N. M.; Myers, O.; Dragoni, E.; Ruggiero, E.; Loh, K. J.
abstract


2014 - Un semplice modello coesivo con attrito per descrivere interfacce ibride forzate e incollate [Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio
abstract

Il lavoro studia interfacce ibride forzate meccanicamente e incollate con adesivo anaerobico. Se dal punto di vista della loro resistenza statica sono state ampiamente studiate, altrettanto non è relativamente al loro comportamento fino a completo collasso. Obiettivo di questo lavoro è verificare l’applicabilità di un semplice modello costitutivo, che unisce un legame coesivo con una legge di puro attrito, per descrivere il comportamento dell’interfaccia fino a completo collasso sotto differenti livelli di pressione di contatto. Un’estesa campagna sperimentale esamina la resistenza a taglio di provini cilindrici incollati testa a testa considerando due adesivi anaerobici e quattro livelli di pressione di contatto. Le curve sperimentali confermano che l’energia di deformazione fino a completo collasso del provino è somma di un contributo coesivo e di uno di puro attrito, linearmente dipendenti dalla pressione di contatto.


2013 - Adhesive stresses in axially-loaded tubular bonded joints – Part I: Critical review and finite element assessment of published models [Articolo su rivista]
Dragoni, Eugenio; L., Goglio
abstract

Adhesive bonding of overlapping coaxial tubes of either conventional or composite materials is a joining solution often encountered in engineering structures. This paper reviews the underlying assumptions and assesses the accuracy offive published theoretical models for the adhesive stresses produced by axial loading of the tubular joint. The models scrutinized are those by Lubkin and Reissner (1956)[1], Shi and Cheng (1993)[3], Nayeb-Hashemi et al. (1997) [4], Pugno and Carpinteri (2003) [5] and Nemeşet al. (2006)[6]. Comparison of the model results with the outcome of ad-hoc finite element analyses onfive joint configurations shows that: (1) all models predict correctly the shear stresses; (2) only Lubkin and Reissner's model gives correct peel stress distributions; and (3) the axial and the hoop stresses are close to each other and are about one half of the peel stresses. The usefulness of an explicit closed-form solution, not provided by Lubkin and Reissner's theory, is recognized.


2013 - DESIGN AND MODELING OF A DIELECTRIC ELASTOMER CYLINDRICAL ACTUATOR WITH QUASI-CONSTANT AVAILABLE THRUST [Relazione in Atti di Convegno]
Berselli, Giovanni; G., Scirè Mammano; Dragoni, Eugenio
abstract

A novel design for a Dielectric Elastomer (DE) actuator is presented. The actuator is obtained by coupling a cylindrical DE film with a series of slender beams axially loaded beyond their buckling limit. Similarly to previous published solutions, where different actuator geometries were coupled with compliant mechanisms of various topologies, the elastic beams are designed so as to provide a suitable compensating force that allows obtaining a quasi-constant available thrust along the entire actuator stroke. The overall system performance are subsequently evaluated by means finite element analysis, accounting for the large deflection of the buckled-beam springs and for the DE material hyperelasticity. Final results confirm that compact and better behaved constant force cylindrical actuators can be obtained, which potentially outperform similar devices in terms of achievable stroke.


2013 - Design and testing of an enhanced shape memory actuator elastically compensated by a bistable rocker arm [Articolo su rivista]
SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

This article presents the design, the prototype construction, and the experimental testing of a shape memory actuator implementing the concept of elastic compensation put forward in a previous publication by the authors. A two-shape memory alloy actuator, compensated by a spring-assisted bistable rocker arm, is designed theoretically to provide nearly constant output forces and then it is built and characterized experimentally under laboratory conditions. The test results closely agree with the theoretical predictions and show that for given output force, the compensated actuator produces net strokes from 2.5 to 22 times greater than a twin uncompensated actuator. The stroke improvement increases dra-matically with the generated output force. Weaknesses of the compensated design are the heavier average stress sus-tained by the shape memory alloy springs, which could impair the fatigue life, and a higher response time.


2013 - Design equations for binary shape memory actuators under arbitrary external forces [Articolo su rivista]
Spaggiari, Andrea; Spinella, Igor; Dragoni, Eugenio
abstract

This article presents the design equations for an on–off shape memory alloy actuator working against an external system of arbitrary constant forces. A binary shape memory alloy actuator is considered where a cursor is moved against both conservative and dissipative forces, which may be different during the push or pull phase. Three cases are analysed and differentiated in the way the bias force is applied to the primary shape memory alloy spring: using a constant force, a conventional spring or a second shape memory alloy spring. Closed-form dimensionless design equations are developed, which form the basis of a step-by-step procedure for an optimal design of the whole actuator.


2013 - Effect of Mechanical Surface Treatment on the Static Strength of Adhesive Lap Joints [Articolo su rivista]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

This work deals with an experimental investigation on the effect of mechanical surface treatments of adhesive bonded joints. The behaviour of an adhesively bonded joint can be considered good if cohesive failure is achieved, while when interfacial failure occurs the performances are normally much worse. A key parameter which drives the failure type is the surface treatment applied to the adherends. This work analyzes, by means of a structured experimental campaign, which surface mechanical treatment gives the best performance. The design of the experimental approach used involves different materials, joint geometries, and surface treatments. The results are investigated in terms of force, energy, and stresses in the joints and the performance of the several mechanical treatments tested is assessed, showing that a simple correlation with the surface roughness is not sufficient to predict the best joint performances. The reliable results obtained prove that sandpapering or sandblasting the adherends gives a strong improvement in terms of performance and leads to a higher probability of cohesive failure.


2013 - Effect of pressure on the physical properties of magnetorheological fluids [Articolo su rivista]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

To date, several applications of magnetorheological (MR) fluids are present in the industrial world, nonetheless system requirements often needs better material properties. In technical literature a previous work shows that MR fluids exhibit a pressure dependency called squeeze strengthen effect. Since a lot of MR fluid based devices are rotary devices, this paper investigates the behaviour of MR fluids under pressure when a rotation is applied to shear the fluid. The system is designed in order to apply both the magnetic field and the pressure and follows a Design of Experiment approach. The experimental apparatus comprises a cylinder in which a piston is used both to apply the pressure and to shear the fluid. The magnetic circuit is designed to provide a nearly constant induction field in the MR fluid. The experimental apparatus measures the torque as a function of the variables considered and the yield shear stress is computed. The analysis of the results shows that there is a positive interaction between magnetic field and pressure, which enhances the MR fluid performances more than twice.


2013 - Experimental Assessment of a Micro-Mechanical Model for the Static Strength of Hybrid Friction-Bonded Interfaces [Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract

Anaerobic adhesives are thermosetting acrylic polymers commonly used to improve the performance of most metal joints. Researches on the static strength of hybrid joints, available in the technical litera-ture, show scanty and contradictory results that do not explain the effect of anaerobic adhesive on the hybrid joint behaviour. An early study by one of the authors of the present study formulates a micro-mechanical model describing the shear power of anaerobic adhesives as a function of the intimate properties of adherends and adhesive at the interface. According to the micro-mechanical model, the high local pressure acting on the thin film of adhesive trapped between the crests of the mating surfaces improves the film shear strength upon the adhesive’s shear strength at zero pressure. The present work aims to assess this micro-mechanical model through a systematic experimental campaign. The tests are conducted on simple tubular specimens and consider three vari-ables over two levels: adhesive-type (weak and strong anaerobic), pressure level during polymerization (0.5 and 134MPa), and pressure level during failure test (0.5 and 134MPa). The results confirm the proposed micro-mechanical model, and highlight that shear strength slightly differs by applying pressure before or after polymerization.


2013 - Experimental characterization and modelling validation of shape memory alloy Negator springs [Relazione in Atti di Convegno]
Spaggiari, A.; Dragoni, E.; Tuissi, A.
abstract

This paper is aimed at the experimental characterization and modelling validation of shape memory alloy (SMA) negator springs. A Negator spring is a spiral spring made of strip of metal wound on the flat with an inherent curvature such that, in repose, each coil wraps tightly on its inner neighbour. The main feature of a Negator springs is the nearly-constant force displacement behaviour in the unwinding of the strip. Moreover the stroke is very long, theoretically infinite as it depends only on the length of the initial strip. A Negator spring made in SMA is built and experimentally tested to demonstrate the feasibility of this actuator. The shape memory Negator spring behaviour is predicted both with an analytical model and with a a finite element software. In both cases the material is modelled as elastic in austenitic range while an exponential continuum law is used to describe the martensitic behaviour. The experimental results confirms the applicability of this kind of geometry to the shape memory alloy actuators and the analytical model is confirmed to be a powerful design tool to dimension and predict the spring behaviour both in martensitic and austenitic range, as well as the finite element model developed. Copyright © 2013 by ASME.


2013 - Functional fatigue of NiTi Shape Memory wires for a range of end loadings and constraints [Articolo su rivista]
SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

The availability of engineering strength data on shape memory alloys (SMAs) under cyclic thermal activation (functional fatigue) is central to the rational design of smart actuators based on these materials. Test results on SMAs under functional fatigue are scarce in the technical literature and the few data available are mainly limited to constant-stress loading. Since the SMA elements used within actuators are normally biased by elastic springs or by another SMA element, their stress state is far from constant in operation. The mismatch between actual working conditions and laboratory arrangements leads to suboptimal designs and undermines the prediction of the actuator lifetime. This paper aims at bridging the gap between experiment and reality. Four test procedures are planned, covering most of the typical situations occurring in practice: constant-stress, constant-strain, constant-stress with limited maximum strain and linear stress-strain variation with limited maximum strain. The paper describes the experimental apparatus specifically designed to implement the four loading conditions and presents fatigue results obtained from commercial NiTi wires tested under all those protocols.


2013 - Lezioni di progetto di sistemi meccatronici [Monografia/Trattato scientifico]
Dragoni, Eugenio; Giovanni Scirè, Mammano
abstract

Questo libro raccoglie le lezioni del corso di Progetto di Sistemi Meccatronici tenuto dagli autori agli allievi ingegneri meccatronici presso la Facoltà di Ingegneria di Reggio Emilia. Il corso ha come oggetto il processo di progettazione del prodotto industriale, con particolare riferimento alle seguenti fasi: - Raccolta e interpretazione dei bisogni del cliente - Definizione di specifiche tecniche oggettive e misurabili - Generazione di soluzioni concettuali ai problemi tecnici - Confronto critico di concetti alternativi - Scelta del concetto migliore - Trasformazione del concetto in un prodotto concreto - Progettazione della sicurezza e dell’affidabilità del prodotto Grazie alla struttura sintetica e all’esposizione sistematica di casi reali applicativi, il testo è indicato anche per i progettisti e per le aziende che vogliono intraprendere la progettazione strutturata di prodotto in ottica cliente.


2013 - Mixed-Mode Strength of Thin Adhesive Films: Experimental Characterization through a Tubular Specimen with Reduced Edge Effect [Articolo su rivista]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio
abstract

The present work deals with the characterization of adhesives in thin film under uniform and multi-axial loading conditions. The tests are carried out with a tubular butt bonded specimen, previously developed by the authors, which ensures both shear and normal uniform stress fields inside the adhesive layer. Stress analysis is performed analytically and shows that, in addition to the axial stress, both radial and circumferential stress components are present in the adhesive layer due to Poisson's effect. This leads to a high level of stress triaxiality especially when only axial loading is considered. The experimental tests performed on eight different loading modes show that the adhesive behaves better under shear stress rather than under normal tensile stress, and its strength increases under compressive mixed mode loading. Among literature criteria for equivalent stress, the Stassi D'Alia criterion provides a clear equivalent failure stress value for the adhesive here examined, regardless of the stress triaxiality.


2013 - Modeling, simulation and characterization of a linear shape memory actuator with compliant bow-like architecture [Relazione in Atti di Convegno]
Mammano, Giovanni.; Dragoni, E.
abstract

The design of shape memory alloy (SMA) actuators typically compromises between force and stroke, the two properties being hard to achieve simultaneously. This paper presents a bow-like compliant SMA actuator aimed at improving the performance on both sides. Conceptually, the actuator is formed by two straight elastic beams hinged at the ends with an SMA wire pre-stretched in between. Heating of the alloy shortens the wire, which in turn makes the beams to buckle outward in a symmetric double-arched configuration. The transverse displacement of the beams amplifies the contraction of the wire while producing a favourable output force. The paper develops a simple, though accurate, analytical model of the actuator upon which a step-by-step design procedure is built. The numerical results for a case study are compared with the outcome of a finite element simulation. Copyright © 2013 by ASME.


2013 - Numerical and experimental validation of a theoretical model for bimaterial helical springs [Articolo su rivista]
Dragoni, Eugenio; W. J., Bagaria
abstract

This article deals with the numerical and experimental validation of a theoretical elastic model for bimaterial helical springs developed by the authors in a recently published article. The numerical validation is performed on finite element models involving one half turn of several springs identified by three spring indices (c=D/d= 3, 5, 10) and three section types (solid homogeneous, solid bimaterial and thin hollow). The experimental validation involves compression tests on two polymer (acrylonitrile butadiene styrene) spring configurations produced by rapid prototyping and cladded by ionic infiltration with CrNiCo alloy. For the larger prototype spring, the stresses are measured on the outside of the coil by means of miniature strain gauges. The numerical results confirm the theoretical stress concentration factors within an error of 5%. The experimental results closely agree with the predicted spring rates of all springs, either fully polymeric or bimaterial. In addition, the strain gauge measurements on the instrumented spring correlate well with the theoretical stresses calculated for that particular geometry.


2013 - Optimal design of radial cylindrical roller bearings for maximum load-carrying capacity [Articolo su rivista]
Dragoni, Eugenio
abstract

The design of compact and inexpensive mechanical drives and gearboxes can take advantage from the use of custom rolling bearings in which the rolling elements are directly in contact with the shaft and the housing containing them. The custom construction is particularly convenient for the case of roller bearings, either cylindrical or tapered, because these elements are easily manufactured and provide a remarkable loading capacity. Starting from the standard load rating equations available in the literature (ISO standards), this paper develops a step-by-step design procedure for the geo-metric optimization of radial bearings with cylindrical rollers. The procedure includes constraints on the geometry and leads to the optimal bearing with the maximum static and dynamic load ratings compatible with the space available.


2013 - Optimal mechanical design of tetrahedral truss cores for sandwich constructions [Articolo su rivista]
Dragoni, Eugenio
abstract

Lattice truss cores are an emerging family of synthetic periodic materials that can add multifunctional capabilities to lightweight sandwich constructions while maintaining high standards of strength and stiffness. Recent strides in prototyping technologies allow efficient monolithic truss cores to be built from advanced metals without the nuisances of assembled constructions. Based on published models for these materials, this paper tackles the optimal design of tetrahedral truss cores for minimum density under prescribed constraints on strength and stiffness. A closed-form, single-pass algorithm is developed, which finds the optimum after a finite number of steps. The method shows that the best tetrahedral truss core depends on the initial con-ditions, though 45-degree orientations are most likely to occur and squatter shapes are rarely convenient. A numerical example demonstrates that optimized aluminium tetra-hedral cores outperform high-profile polymer foams and compete favourably with commercial-grade aluminium honeycombs of equal density. The general approach disclosed can be applied to the mechanical optimization of other types of truss core (e.g. pyramidal or kagome, single- or multilayered) and classical periodic design (e.g. corrugated cores), which so far have been analyzed in a less general way.


2013 - Stress concentrations in periodic notches: a critical investigation of Neuber's method [Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract

The work investigates the stress concentrations produced by periodic notches (i. e. uniformly repeated) in elastic solids under different loading conditions. Neuber's criterion, which likens the effect of a periodic notch to a single notch of similar profile but lesser depth, is critically examined. The criterion simply correlates the depth reduction factor to the ratio between the depth and the pitch of the original periodic notch, regardless of its shape. By examining literature results in periodic notches on circular bars and plane strips under torsion or axial loads, the work proves the accuracy of the Neuber's method for the ideal configuration of a sharp and shallow notch under shear stresses. By contrast, for real notches with a large root radius and finite depth, the accuracy is very poor, in particular for normal stresses. However, it is found that by simply ‘repairing’ the expression of the depth reduction factor and distinguishing between notches under shear or normal stresses, the criterion provides very accurate results, and becomes quite useful for real geometries.


2013 - Un sistema di misura della rotazione per la caratterizzazione fino a collasso di interfacce forzate e incollate con adesivi anaerobici [Relazione in Atti di Convegno]
Castagnetti, Davide; A., Torreggiani; Dragoni, Eugenio
abstract

Le interfacce ibride forzate ed incollate sono diffuse nelle costruzioni meccaniche per migliorare le prestazioni di calettamenti e giunzioni. Questo lavoro ha l’obiettivo mettere a punto un sistema di misura della rotazione semplice ed accurato utile per la caratterizzazione del comportamento elastico e post-elastico di tali interfacce. Il lavoro si articola in due fasi. Nella prima fase si mette a punto un sistema di misura per misurare la rotazione relativa tra le interfacce incollate, basato su un encoder installato direttamente sul provino. Il sistema di misura è stato caratterizzato sia su una barra di torsione sia su un provino con interfaccia a puro attrito mostrando un’ottima accuratezza. Nella seconda fase si svolgono le prime prove della campagna sperimentale che considera due adesivi e quattro livelli di pressione.


2012 - Analytical and Numerical Modelling of Shape Memory Alloy Negator Springs for Long-Stroke Constant-Force Actuators [Relazione in Atti di Convegno]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

Analytical and Numerical Modelling of Shape Memory Alloy Negator Springs for Long-Stroke Constant-Force Actuators PDF Andrea Spaggiari and Eugenio Dragoni SMASIS2012-7964 pp. 353-361; 9 pages doi: 10.1115/SMASIS2012-7964 This paper explores the merits of shape memory Negator springs as powering elements for solid state actuators. A Negator spring is a spiral spring made of strip of metal wound on the flat with an inherent curvature such that, in repose, each coil wraps tightly on its inner neighbour. The unique characteristic of Negator springs is the nearly-constant force needed to unwind the strip for very large, theoretically infinite deflections. Moreover the flat shape, having a high area over volume ratio, grants improved bandwidth compared to any solution with solid wires or helical springs. The SMA material is modelled as elastic in austenitic range while an exponential continuum law is used to describe the martensitic behaviour. The mathematical model of the mechanical behaviour of SMA Negator springs is provided and their performances as active elements in constant-force, long-stroke actuators are assessed. The SMA Negator spring is also simulated in a commercial finite element software, ABAQUS, and its mechanical behaviour is estimated through FE analyses. The analytical and the numerical prediction are in good agreement, both in martensitic and in austenitic range.


2012 - Assessment of the Cohesive Contact method for the analysis of thin-walled bonded structures [Articolo su rivista]
Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio
abstract

Several finite element (FE) techniques for the structural analysis of bonded joints and structures have been proposed in the literature. This paper deals with the assessment of a new surface interaction technique that models the adhesive as a pure contact with cohesive properties. This technique is a new feature of the FE software ABAQUS. The work has two objectives. Firstly, to assess the applicability, efficiency and accuracy of this Cohesive Contact (CC) method in the analysis of three dimensional, thin-walled bonded structures. Secondly, to compare the CC method with a similar technique, called Tied Mesh (TM) method, previously proposed by the authors. By considering as benchmark standard and ad hoc bonded joints and structures, the CC method is checked against a full FE model in the elastic field and with the outcome of experimental tests in the post-elastic field. Also, the TM method is implemented for all these geometries, in order to obtain a comparison. The results show that the CC method gives a fair prediction both in the elastic and post-elastic field, with lower accuracy than the TM method.


2012 - Combined squeeze-shear properties of magnetorheological fluids: Effect of pressure [Relazione in Atti di Convegno]
Spaggiari, A.; Dragoni, E.
abstract

Several applications of magnetorheological (MR) fluids are nowadays present in the industrial world, however sometimes system requirements require better material properties. In technical literature an interesting previous work shows that MR fluids exhibit a pressure dependency called squeeze strengthen effect. Since a lot of MR fluid based devices are rotary devices, this paper investigates the behaviour of MR fluids under pressure when a rotation is applied to shear the fluid. The system is designed in order to apply both the magnetic field and the pressure following a Design of Experiment method. The experimental apparatus comprises a cylinder in which a piston is used both to apply the pressure and to apply a prescribed rotation. The magnetic circuit is designed to provide a nearly constant induction field in the MR fluid. The experimental apparatus measures torque as a function of the variables considered and the yield shear stress is computed. A statistical analysis of the results shows that there is a positive interaction between magnetic field and pressure, which enhance the MR fluid performances more than two times. Copyright © 2012 by ASME.


2012 - Concentration of torsional shear stresses in axisymmetric bars with deep periodic grooves [Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract

The torsional stresses in round bars with deep periodic grooves are calculated by means of the formal analogy between the elastic problem and an auxiliary thermal problem. The analogy allows demanding three-dimensional analyses to be replaced with light two-dimensional analyses, easily implemented on general-purpose finite element packages. Following Neuber’s equivalence concept, the stress concentration in each periodically grooved bar is independently calculated by referring to a single groove of like geometry but lesser depth. Neuber’s approach predicts very closely the reference numerical results if supplemented with a heuristic depth correction function formerly developed by the authors for shallow periodic notches under torsion.


2012 - Effect of internal pressure on flow properties of magnetorheological fluids [Relazione in Atti di Convegno]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

Magnetorheological (MR) fluids have a lot of applications in the industrial world, but sometimes their properties are not performing enough to meet system requirements. It has been found that in shear mode MR fluids exhibits a pressure dependency called squeeze strengthen effect. Since a lot of MR fluid based devices work in flow mode (i.e. dampers) this paper investigates the behaviour in flow mode under pressure. The system design is articulated in three steps: hydraulic system design, magnetic circuit design and design of experiment. The experimental apparatus is a cylinder in which a translating piston displaces the fluid without the use of standard gear pumps, incompatible with MR fluids. The experimental apparatus measures the MR fluid yield stress as a function of pressure and magnetic field allowing the yield shear stress to be calculated. A statistical analysis of the results shows that the squeeze strengthen effect is present in flow mode as well and the presence of internal pressure is able to enhance the performance of MR fluid by nearly ten times.


2012 - Effect of Pressure on the Flow Properties of Magnetorheological Fluids [Articolo su rivista]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

Magnetorheological (MR) fluids are widely used in the industrial world; however, sometimes their properties fail to meet system requirements. In shear mode, MR fluids have been found to exhibit a pressure dependency called squeeze strengthen effect. Since a lot of MR fluid based devices work in flow mode (i.e., dampers), this paper investigates the behavior in flow mode under pressure. The system design consists of three steps: the hydraulic system, the magnetic circuit, and the design of experiment method. The experimental apparatus is a cylinder in which a piston displaces the fluid without the use of standard gear pumps, which are incompatible with MR fluids. The experimental apparatus measures the yield stress of the MR fluid as a function of the pressure and magnetic field, thus, enabling the yield shear stress to be calculated. A statistical analysis of the results shows that the squeeze strengthen effect is also present in flow mode, and that the internal pressure enhances the performance of MR fluids by nearly five times.


2012 - Efficient dynamic modelling and characterization of a magnetorheological damper [Articolo su rivista]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

The present work is about the dynamic modelling and the experimental testing of magnetorheological (MR) dampers, especially at low frequency. The main improvement of this work over former models is the identification of dynamic parameters which are independent of the working conditions and vary only as a function of the current. A simple model is built on the basis of the literature and of a systematic experimental campaign, with the aim of simplifying the effort in retrieving the parameters and in controlling the system. The excitation current is introduced in the model as a variable, not only reducing the amount of test needed to assess the parameters, but also obtaining a faster model useful in motion control. A second order polynomial relationship between the applied current and the three variable parameters is found, showing a saturation effect at high currents. A verification test shows the reliability and the performance of the proposed model.


2012 - Elastic compensation of linear shape memory alloy actuators using compliant mechanisms [Relazione in Atti di Convegno]
Mammano, G. S.; Dragoni, E.
abstract

The paper presents a modular architecture for SMA actuators elastically compensated by thin beams loaded axially beyond their buckling limit. Starting from the exact equations for the elastic curve of the beams, an approximate procedure is developed for the engineering design of the entire compensating system. The theory of the compensator is validated successfully against a finite element model and experimental results. The experimental characterization of a complete prototype actuator shows that the forces generated by the compensated actuator are constant for both instroke and outstroke over the full range of displacements. The actuator concept proposed lends itself to modular assembly to multiply either the stroke covered (series combination) or the force generated (parallel combination). Copyright © 2012 by ASME.


2012 - Experimental tests on tubular bonded butt specimens: effect of relief grooves on tensile strength of the adhesive [Articolo su rivista]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio
abstract

This paper investigates experimentally a tubular bonded butt specimen with relief grooves carved close to the adherend-adhesive interface. The specimen is used to assess the strength of a thin adhesive layer, as usually occurs in structural bonded joints. Hence, this configuration overcomes the problems related to the differences in chemical and mechanical properties which could occur in bulk adhesive tests. The aim is to verify experimentally the reduction of the stress concentrations at the interface given by the presence of the grooves, observed in a previous numerical work of the authors. Finite element analyses show that the groove geometry adopted here, although slightly simplified with respectto the optimum shape previously proposed, produces a strong reduction of the edge effects. This work performs an indirect assessment by comparing tensile strength of bonded specimens with and without relief grooves. A two-level factorial experimental campaign is performed, according to Design of Experiment criteria. The variables are: presence of the grooves, adherends material, and adhesive thickness. The response of the tests is the maximum tensileload carried by the specimen which is found to depend strongly on the adherends’ materials. In the case of steel joints, the relief grooves near the adherend-adhesive interface lead to higher loads regardless of the adhesive thickness. In the case of aluminium joints the relief grooves play a minor role, while tensile strength decreases as the adhesive thickness increases.


2012 - MODELLING OF SHAPE MEMORY ALLOY NEGATOR SPRINGS FOR LONG-STROKE CONSTANT-FORCE ACTUATORS [Relazione in Atti di Convegno]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

The paper deals with the analytical modelling of a shape memory alloy Negator spring. Negator springs are spiral springs made of strip metal wound on the flat with an inherent curvature such that, in repose, each coil wraps tightly on its inner neighbour. This configuration allows a constant force mechanical response and very long strokes, limited mainly from the total length of the spring. The authors investigate the behaviour of the spring made of a shape memory alloy (SMA). The intrinsic characteristic of SMA is to have two different elastic moduli at different temperatures. This difference can be exploited in order to have a net actuation force for the entire very long stroke, overcoming the two major drawbacks of the SMA actuators, short strokes and output force which varies linearly during the travel.


2012 - Mounting of accelerometers with structural adhesives: experimental characterization of the dynamic response [Capitolo/Saggio]
Cocconcelli, Marco; Spaggiari, Andrea; Rubini, Riccardo; Dragoni, Eugenio
abstract

The use of accelerometers to monitor the vibrations of either complex machinery or simple component involves some considerations about the mounting of the sensor to the structure. Different types of mounting solutions are commonly used but in all cases they can be classified in one of these categories: stud mounting, screw mounting, adhesive mounting, magnetic mounting and probe sensing. Indeed each of them has a specific field of application depending on e.g. the mounting surface conditions, the temperature, the accessibility to the specific mounting point, etc. The choice of the mounting solution has a important effect on the accuracy of the usable frequency response of the accelerometer, since the higher the stiffness of the fixing, the higher the low-pass frequency limit of the mounting. This paper specifically focuses on adhesive mounting of accelerometers, which includes a great number of different products from the temporary adhesives like the beeswax to the permanent ones like cyanoacrylate polymers. Among the variety of commercial adhesives, three specific glues have been experimentally compared to assess their transmissivity and the results are reported in this paper. A two component methylmethacrylate (HBM X60), a modified silane (Terostat 737) and a cyanoacrylate (Loctite 401) adhesives have been used to joint two aluminium bases, one connected to an accelerometer and the other to the head of electromagnetic shaker. A design of experiments (DOE) approach was used to test the system at several levels of amplitude and frequency of the external sinusoidal excitation supplied by the shaker.


2012 - Optimum Mechanical Design of Binary Actuators Based on Shape Memory Alloys [Capitolo/Saggio]
Spaggiari, Andrea; SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

This chapter describes the optimum mechanical design of shape memory based actuators. The authors show how to exploit the Shape Memory Alloy (SMA) to design silent, compact and light binary actuators. Two simple mechanical models are considered to describe the SMA behaviour and design equations are provided for two classes of actuators. First SMA actuators are analyzed and designed on the basis of the backup element needed to recover the stroke. Second SMA actuators are improved by adding a compensator system to enhance the output mechanical response, especially in terms of available stroke. Useful design procedures are provided to help the engineer in the synthesis of SMA actuators. Starting from the design specifications, a step by step procedure is built to define the mechanical dimension of the SMA active elements, of the backup system and of the compensator.


2012 - Predicting the macroscopic shear strength of adhesively-bonded friction interfaces by microscale finite element simulations [Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract

Anaerobic adhesives are commonly used to enhance the shear strength of clamped friction joints between metal parts. Experimental results show that the total strength of the friction-bonded interface steadily increases with the clamping pressure. However, if weak anaerobics are used, the combined strength is lower than the in dry (purely friction) joint under high applied pressures. This paper seeks an explanation for this macroscopic behaviour by means of microscale finite-element simulations. The analyses show that the experimental results can be explained by assuming that: a) however great the clamping pressure, a thin film of adhesive remains trapped between the crests of the mating surfaces; b) under the high local pressure the shear strength of this film is greater than the regular adhesive’s at no pressure; c) the stronger adhesives entail a higher increase than the weaker adhesives.


2012 - REGOLARIZZAZIONE DELLE TENSIONI TORSIONALI IN GIUNZIONI TUBOLARI INCOLLATE A SINGOLA SOVRAPPOSIZIONE CON ADESIVI FUNZIONALIZZATI [Relazione in Atti di Convegno]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

Il presente lavoro ha come obiettivo la regolarizzazione delle tensioni torsionali in giunzioni tubolari incollate a singola sovrapposizione. Le tensioni negli adesivi sono tipicamente caratterizzate da andamenti disuniformi, a volte singolari, che agiscono come inneschi preferenziali per la propagazione di cricche. Nella recente letteratura scientifica sono presenti particolari adesivi "funzionalizzati" che, grazie a nanorinforzi dispersi al loro interno, possono essere dotati di caratteristiche elastiche non costanti. Attraverso uno studio analitico delle tensioni nello strato adesivo è fornita la soluzione analitica in forma chiusa dell'andamento del modulo elastico tangenziale dell'adesivo in direzione assiale che consente di avere una tensione costante nello strato incollato. La distribuzione del modulo elastico adimensionalizzato è mostrata in funzione delle caratteristiche elasto-geometriche del giunto, sia in termini di rigidezza degli aderendi che in termini di rapporto di forma dello strato incollato.


2011 - Accelerometri MEMS: caratterizzazione dinamica e confronto con i sensoripiezoelettrici [Capitolo/Saggio]
G., Scirè Mammano; Cocconcelli, Marco; Rubini, Riccardo; Dragoni, Eugenio
abstract

Gli accelerometri di tipo piezoelettrico sono probabilmente i più diffusi sensori diaccelerazione attualmente in commercio per l’ambito industriale. Hanno infatti un’ampiabanda dinamica di linearità,sono influenzati in modo trascurabile da rumore etemperatura, e possono misurare elevati valori di accelerazione. Negli ultimi anni sonostati proposti sul mercato dei nuovi tipi di accelerometri di tipo MEMS (Micro Electro-Mechanical Systems) che hanno la caratteristica di essere molto meno costosi deipiezoelettrici sia per i materiali impiegati sia per il processo di fabbricazione di massa. Sefino a poco tempo fa la qualità degli accelerometri MEMS non era paragonabile a quelladei piezoelettrici, la continua evoluzione tecnologica ha estremamente ridotto le differenzetra le due tipologie di sensori. Lo scopo di questo articolo è di confrontare le prestazionidinamiche di alcuni accelerometri di tipo piezoelettrico e di tipo MEMS, per valutarne ledifferenze, qualità e difetti, e fornire un’introduzione alle problematiche che nascono nelpassaggio da una tecnologia all’altra


2011 - Appunti di Progettazione Meccanica Assistita [Monografia/Trattato scientifico]
Dragoni, Eugenio; Castagnetti, Davide
abstract

Il libro raccoglie le lezioni del corso di Progettazione Meccanica Assistita per gli allievi ingegneri meccatronici della Facoltà di Ingegneria di Reggio Emilia. Scopo delle lezioni è introdurre ai principi della progettazione meccanica assistita dal calcolatore, fornendo le basi teoriche e applicative del metodo agli elementi finiti, sia per analisi lineari che non-lineari, statiche e dinamiche, termo-strutturali e modali. La struttura sintetica e la ricchezza di indicazioni metodologiche ed applicative rendono il libro adatto anche alla consultazione in un contesto professionale.


2011 - Concentration of shear stresses in shallow periodic notches [Articolo su rivista]
Dragoni, Eugenio; Castagnetti, Davide
abstract

The torsional stresses in straight round bars with periodic U-shaped shallow grooves are calculated numerically (boundary elements) taking advantage of a computationally efficientthermal analogy. Neuber’s theory is scrutinized, which equates the stress concentration factor in the periodic notch to the stress concentration factor in the single notch of like profile and lower depth. (Corrected depth = original depth times a depth reduction factor, which is a function of the depth-to-pitch aspect ratio of the periodic notch.) The results disclose a depth correction function in close agreement with Neuber’s theory for ideally sharp notches. For a wide range of rounded notches, which are more likely to occur in practice, the paper shows that Neuber’s depth correction grossly overestimates the stresses. By modifying the expression of the depth correction factor, however, Neuber’s conceptual equivalence works well for engineering purposes. Comparison with former results by the authors indicates that the optimal depth correction function is different for notches affected by shear stresses (as in this paper)or by normal stresses.


2011 - Convalida sperimentale di un modello micromeccanico per la resistenza statica di interfacce ibride forzamento-incollaggio [Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio
abstract

The paper deals with the investigation of the static strength of friction interfaces supplemented with anaerobic adhesives, by performing a systematic experimental campaign on ad-hoc annular specimens. Aim of the work is to assess a micro-mechanical model, previously proposed by Dragoni et al. [Int. J. Adhes. & Adhes., 20 (2000), 315-321], which correlates the static shear strength of hybrid interfaces to the contact force. The experimental campaign, performed on annular butt specimens, involved three variables: adhesive material, contact pressure along the polymerization and contact pressure along the failure test. The torque tests show that the shear strength of all hybrid interfaces increases with contact pressure. In particular, the strong anaerobic adhesive exhibits a strength that approximately equals the sum of friction and adhesive strength, taken separately.


2011 - Design and testing of an enhanced shape memory actuator elastically compensated by a bi-stable rocker-arm [Relazione in Atti di Convegno]
Mammano, G. S.; Dragoni, E.
abstract

This paper presents the design, the prototype construction and the experimental testing of a shape memory actuator implementing the concept of elastic compensation put forward in a previous publication by the authors. A two-SMA actuator, compensated by a spring-assisted bistable rocker-arm, is designed theoretically to provide nearly-constant output forces, then it is built and characterized under laboratory conditions. The test results are in good agreement with the theoretical predictions and show that, for given output force, the compensated actuator produces net strokes from 2.5 to 22 times greater than an identical uncompensated actuator. The stroke improvement increases dramatically with the generated output force. Weaknesses of the compensated design are the heavier average stress sustained by the SMA springs, which could impair the fatigue life, and a higher response time. © 2011 by ASME.


2011 - Design equations for binary shape memory actuators under arbitrary external forces [Relazione in Atti di Convegno]
Spaggiari, Andrea; Spinella, Igor; Dragoni, Eugenio
abstract

The paper presents the design equations for an on-off shape memory alloy actuator under an arbitrary system of external constant forces. A binary SMA actuator is considered where a cursor is moved against both conservative and dissipative force which may be different during the push or pull phase. Three cases are analyzed and differentiated in the way the bias force is applied to the primary SMA spring, using a constant force, a traditional spring, or a second SMA spring. Closed-form dimensionless design equations are developed, which form the basis of a step-by-step procedure for an optimal design of the whole actuator


2011 - Design of a Telescopic Linear Actuator Based on Hollow Shape Memory Springs [Articolo su rivista]
Spaggiari, Andrea; Spinella, Igor; Dragoni, Eugenio
abstract

Shape memory alloys (SMAs) are smart materials exploited in many applications to build actuators with high power to mass ratio. Typical SMA drawbacks are: wires show poor stroke and excessive length, helical springs have limited mechanical bandwidth and high power consumption. This work is focused on the design of a large-scale linear SMA actuator conceived to maximize the stroke while limiting the overall size and the electric consumption. This result is achieved by adopting for the actuator a telescopic multi-stage architecture and using SMA helical springs with hollow cross-section to power the stages. The hollow geometry leads to reduced axial size and mass of the actuator and to enhanced working frequency while the telescopic design confers to the actuator an indexable motion, with a number of different displacements being achieved through simple on-off control strategies. An analytical thermo-electro-mechanical model is developed to optimize the device. Output stroke and force are maximized while total size and power consumption are simultaneously minimized. Finally, the optimized actuator, showing good performance from all these points of view, is designed in detail.


2011 - Effect of bondline thickness on the static strength of structural adhesives under nearly-homogeneous shear stresses [Articolo su rivista]
Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio
abstract

An usual experimental observation retrieved in the technical literature is that the strength of an adhesive joint decreases by increasing the adhesive layer thickness. This well known behaviour is still not completely understood. All works found in literature consider a complex stress state in the adhesive with mode mixing, stress concentrations on the midplane and stress singularities at the interface occurring at the same time. This paper aims at estimating the effect of the adhesive thickness on its intrinsic static shear strength and evaluate whether this strength can explain the behaviour of a real bonded joint. A nearly-uniform shear stress distribution is obtained through an ad-hoc tubular butt joint subject to pure torsion. A standard single lap joint is considered as benchmark, due to its complex and singular stress field into the adhesive. The experimental campaign is focused on two brittle adhesives: a modified methacrylate and high strength epoxy. Four levels and three levels of the adhesive thickness were considered in the tubular butt joint and in the single lap joint respectively, all in the range between 0.05 and 0.4 mm. The effect of the adhesive thickness on the static strength of the adhesive is investigated by considering the type of failure and by comparing the structural stresses in the tubular butt joint with the ones on the midplane of the adhesive layer in the single lap joint. Moreover, the stress intensity factor in the single lap joint is calculated.


2011 - Effect of chlorinated water on the oxidative resistance and the mechanical strength of polyethylene pipes [Articolo su rivista]
Castagnetti, Davide; SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

The effect of disinfectants was determined on the mechanical and chemical resistance of high-density polyethylene pipes, commonly used in modern urban networks for water conveyance. A fully monitored test plant was built that was able to simultaneously expose both pipe sections and pre-cut dumbbell specimens to chlorinated and non-chlorinated water. PE100 polyethylene pipes for alimentary use with a nominal diameter DN 32 were tested in two sets of experiments involving both chlorine dioxide (at a constant concentration of 5 ppm), and sodium hypochlorite (at a constant concentration of 2.5 ppm). The effects of these disinfectants were assessed using monotonic tensile tests on dumbbell specimens and oxidation induction time tests. Pressure tests at a constant temperature were also performed to assess any damage in the pipe samples after one year of exposure to chlorine dioxide. The results from the tensile and oxidation induction time tests showed that chlorine dioxide was the most aggressive disinfectant. Nevertheless, the pressure tests at a constant temperature did not show any failure of the pipes after 2000 h of exposure.


2011 - Failure analysis of complex bonded structures: experimental tests and efficient finite element modelling by tied mesh method [Articolo su rivista]
Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio
abstract

This paper aims at assessing the accuracy and applicability of an efficient finite element (FE) computational method for the prediction of the post-elastic response of large and complex bonded structures. In order to overcome the limitations found in the technical literature, such as the use of user defined elements, the present work assesses the applicability of a reduced computational technique, named Tied Mesh (TM) method previously presented by the authors. The method is based on standard modelling tools, describes the adherends by semi-structural elements (plates or shells), and the adhesive by means of a single layer of cohesive elements. The benchmarks for the TM method are the force-displacement curves obtained by experimental tests on a complex, industrial-like structure. A square thin-walled beam is considered, made of two different portions butt joined by overlapping thin plates on each side. Two different geometries of the beam are loaded by a three point bending fixture up to failure, thus originating a complex stress field on the bonded region. The comparison with the experimental data shows a good accuracy of the proposed TM method in terms of structural stiffness, maximum load (error below 10%) and post-elastic behaviour up to the collapse of the structure. The numerical precision and the computational speed make the TM method very useful for the efficient analysis of complex bonded structure, both in research and industrial world.


2011 - Fatigue life prediction of notched components: a comparison between the theory of critical distance and the classical stress-gradient approach [Relazione in Atti di Convegno]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio; S., Bulleri
abstract

Fatigue life prediction for machine components is a key factor in the industrial world and several methods can be traced in technical literature to estimate life of notched components. The paper correlates the classical stress-gradient approach, here after called support factor (SF) method, proposed by Siebel, Neuber and Petersen with the modern theory of critical distance (TCD) approach by Tanaka and Taylor. On the one hand, the main asset of the SF method is that it relies only on the knowledge of the maximum stress and stress gradient in the hot spot. By contrast, the TCD needs the calculation of the stress distribution for a finite depth inside the material. On the other hand, the main drawback of the SF method is that the material parameter ρ* is available only for a limited collection of materials and moreover the experimental procedure to retrieve this parameter is not clearly defined in the technical literature. In order to overcome this limitation, the paper investigates the correlation between the material parameter ρ* and the critical distance L of the TCD by relying on a specific stress function. A comparison between the SF method and the TCD is then performed by considering three different benchmark geometries: a general V-notch in a plate, a pressure vessel and an industrial oleo-hydraulic distributor. Effective stresses are analytically retrieved and compared using both methods for the first two benchmarks and with the help of an elastic finite element analysis for the last one. The results appear good in terms of fatigue life prediction, especially for the industrial case study.


2011 - Functional fatigue of shape memory wires under constant-stress and constant-strain loading conditions [Relazione in Atti di Convegno]
SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

Shape memory alloys (SMAs) are increasingly used for the construction of simple solid-state actuators characterized by outstanding power density. The rational design of these actuators requires reliable data on the fatigue strength of the alloy under cyclic thermal activation (functional fatigue). The technical literature shows scanty test results for SMAs under functional fatigue. Furthermore, the few data available are mainly limited to the condition of constant stress applied to the material. Since the SMA elements used within actuators are normally biased by conventional springs or by another SMA element, their stress condition is far from constant in operation. The disagreement between actual working conditions and laboratory conditions leads to suboptimal designs and undermines the prediction of the life of the actuator. This paper aims at bridging the gap between experiment and reality. Four characteristic test conditions are envisioned, covering most of the actual situations occurring in practice: constant-stress, constant-strain, constant-stress with controlled maximum strain and cyclic-stress with controlled maximum strain. The paper presents the experimental apparatus specifically designed to implement the four test conditions. Fatigue results on a commercial NiTi wire (0.15 mm diameter) tested under constant-stress and constant-strain loading are also presented and discussed.


2011 - Increasing stroke and output force of linear shape memory actuatorsby elastic compensation [Articolo su rivista]
SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

Shape memory actuators are a class of very interesting actuators due to the high power to weight ratio, plus the fact that they can work in harsh environments and can be easily constructed. The main defects of this technology are the short strokes and the non-uniformity of the useful force over the stroke. This paper aims to limit these two problems by introducing a passive system of elastic compensation. We first develop a functional design procedure of the active elements and of the compensation system in order to obtain the force and stroke desired. We also show two compensation mechanisms that are able to execute the laws required, and we provide expressions for the kinematic design. A numerical example for an actuator with a single shape memory element shows that, all other conditions being equal, the elastic compensation produces increases in stroke (for equal useful force) or useful force (for the same stroke) that are more than 2.5 times greater. A proof-of-concept actuator including a rocker-arm compensating mechanism is also built and tested to confirm the theoretical predictions.


2011 - Mechanical design of bimaterial helical springs with circular cross-section [Articolo su rivista]
Dragoni, Eugenio; W. J., Bagaria
abstract

This paper presents an approximate theoretical model for the mechanical behaviour of helical springs with circular cross-section formed by an inner elastic core encased in an outer annulus of dissimilar elastic properties. Closed-form equations are developed for stresses and deflection in the spring undergoing either bending or axial end loads. For both loading conditions, the model takes into account the stress concentrations arising in the cross-section due to curvature of the spring axis. The disclosed equations are specialized for bimaterial springs with a polymer core and a thin nanometal cladding, a solution reflecting a unique technology recently brought onto the market by a leading polymer manufacturer. In this special case, the cladding performs as an efficient thin-walled tube under torsion with the soft core preventing the danger of wall instability. A design procedure is exemplified, showing that this construction leads to lighter and smaller springs than all-metal or allpolymer counterparts.


2011 - Modeling of Wire-on-Drum Shape Memory Actuators for Linear and Rotary Motion [Articolo su rivista]
SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

The article presents the analytical model of a linear/rotary solid-state actuator formed by a shape memory wire wound over a cylindrical drum. The model assumes a bilinear w temperature) and a linear elastic response in the austenitic state (high temperature). Based on simple equilibrium conditions, the model calculates the stress and strain distributions in the wire when subjected to a constant external backup force and undergoing frictional sliding forces at the contact with the drum. Closed-form expressions are supplied for the stroke produced by whatever actuator geometry and are validated numerically against finite element results. For a particular actuator configuration, the analytical forecasts are also checked experimentally on a proof-of-concept prototype. The analytical model shows that large strokes (up to one-half of the drum’s diameter) are achieved if the frictional coefficient is kept below 0.01. Rolling-contact architectures or sonic-pulse excitations of the drum are discussed as technical solutions to obtain such low friction values.


2011 - Multiphysics Modeling and Design of Shape Memory Alloy Wave Springs as Linear Actuators [Articolo su rivista]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

This paper explores the merits of shape memory wave springs as powering elements of solid state actuators. Advantages and disadvantages of the wave construction in comparison to the traditional helical shape are presented and discussed by means of dimensionless functions. The main assets of the wave springs are the higher electrical resistance (leading to simpler electrical drives) and the lower cooling time (leading to enhanced working frequency). The wave geometry is also superior in purely mechanical terms to the helical counterpart when axial space is at a premium. A step-by-step design procedure is proposed, leading to the optimal wave spring meeting the multiphysics design specifications and constraints. A case study is finally reported, showing the application of shape memory wave springs to the design of a telescopic linear actuator.


2011 - Multiscale modelling of porous polymers using a combined finite element and D-optimal design of experiment approach [Articolo su rivista]
Spaggiari, Andrea; N., O'Dowd; Dragoni, Eugenio
abstract

This paper presents a general numerical procedure for the analysis of polymeric materials containing spherical voids. The multiscale approach implemented simulates, via three dimensional finite element analysis, an infinite medium of the material containing discrete voids. A D-optimal design procedure is used to combine the seven normalized variables considered in the problem: the material strength and ductility, the hardening ratio, the void volume fraction, the void arrangement (number of voids), the stress triaxiality and the Lode parameter. The failure criterion considered is based on a critical distance approach, considering a brittle epoxy resin as a reference material. Results are provided for the normalized equivalent stress and strain at failure, the void growth rate and the equivalent failure strain. The influence of the variables on the outputs is estimated and design equation coefficients are calculated.


2011 - Science of Friction–Adhesive Joints [Capitolo/Saggio]
Dragoni, Eugenio; P., Mauri
abstract

This chapter addresses the fundamental properties of hybrid friction–adhesive joints which combine any form of mechanical tightening (stimulus for friction forces) with anaerobic adhesives. By filling the voids around the microareas of true metal-to-metal contact between the mating parts, anaerobic adhesives allow the full area involved by the engagement to be usefully exploited. Advantages ranging from sealing action, fretting suppression, noise reduction and enhanced strength derive from this combination. The focus of the chapter is on predicting the mechanical strength of these joints. The literature covering the static and the fatigue strength is reviewed showing that proper choice of the adhesive can increase the overall strength of the joint well above the strength of the purely mechanical joint based on friction only. Simple equations are also provided for the strength calculation of practical engineering assemblies.


2010 - Analysis and design of hollow helical springs for shape memory actuators [Articolo su rivista]
Spinella, Igor; Dragoni, Eugenio
abstract

The shape memory alloys (SMAs) can be exploited successfully to reduce the complexity and the weight of actuators, but the main drawbacks that limit the use of SMAs are the low bandwidth, the poor energetic efficiency and the unsatisfactory stroke. This paper contributes to enhancing the mechanical, the thermal and the electric performances of SMA actuators by providing analysis and design equations for helical springs with hollow round section. Emptied of the inefficient material from its centre, the hollow section features a lower mass, a lower cooling time and a lower heating energy than its solid counterpart for given strength, stiffness and deflection. The advantages of the hollow construction over solid springs are presented and discussed by means of dimensionless functions. A step by step procedure leading to the optimal design of hollow springs with minimum energy consumption is finally proposed.


2010 - Attuatore a memoria di forma [Articolo su rivista]
Spinella, Igor; Dragoni, Eugenio
abstract

L’attuatore lineare telescopico basato su molle cave a memoria di forma unisce i pregi dei fili e delle molle SMA (Shape Memory Alloy). Le prestazioni del sistema risultano ottime se comparate con attuatori lineari a memoria di forma, ma ancora non sono sufficienti per far competere l’attuazione SMA con quella elettrica convenzionale in campi differenti dalla microattuazione.


2010 - Concentration of normal stresses in flat plates and round bars with periodic notches [Articolo su rivista]
Dragoni, Eugenio; Castagnetti, Davide
abstract

The stress concentrations produced by tensile loading of elastic solids with periodic notches are addressed. The criterion suggested by Neuber, which likens the periodic notch to a single notch of similar shape but smaller depth, is evaluated. According to Neuber, the depth reduction factor only depends on the ratio between the depth and pitch of the periodic notch, regardless of its particular shape. This work benchmarks the criterion against many axially loaded flat plates and round bars with periodic V-notches, which are analysed by means of the boundary element method. The investigation highlights a strong disparity between Neuber’s predictions and numerical findings. However, upon slight adjustment of the depth reduction factor with respect to Neuber’s proposal, a satisfactory agreement is achieved. The good correlation holds true both for shallow notches (notched semi-infinite plate) and for deep notches (notched plates or bars of finite width), which were not covered in Neuber’s work.Excellent correspondence is also found for the stress concentration around an infinite row of equispaced circular holes loaded longitudinally, a solution taken from the literature as a testcase. These results lead to the conclusion that Neuber’s criterion, supplemented with the newly disclosed depth reduction factor, can be applied to periodic notches of whatever geometry under normal stresses.


2010 - Designing bonded joints by means of the jointcalc software [Articolo su rivista]
Dragoni, Eugenio; L., Goglio; F., Kleiner
abstract

This paper describes the theoretical framework, the experimental background and the software implementation of the computer package JointCalc for the strength analysis and design of adhesively bonded joints. Developed by Henkel AG in collaboration with three Italian Universities, JointCalc was designed to be accessible to non-experts, intuitive for occasional users and also general enough to include most of the joint configurations encountered in practice. For the calculation of adhesive stresses, JointCalc implements the analytical elastic solutions available in the literature for the fundamental joint geometries (single and double-lap joints, single and double-strap joints, peel joints and cylindrical joints). A key aspect of JointCalc is the experimental failure criterion adopted, represented by an admissible region in the peel-shear stress plane. The implementation required the creation of an experimental database, specifically built for the set of 14 adhesives (mostly epoxies) considered. A distinguished asset of JointCalc is its intuitive graphical interface that enables the user to choose the desired joint configuration, input the data and examine the results in a straightforward way. Since its appearance in 2003, JointCalc has been applied to the design of bonded assemblies covering a wide spectrum of industrial applications. Three of those applications (a seat back mounting, a shear punch solenoid and a screening device) are presented at the end of the paper as case studies. The disclosed data show that, provided that thoughtful engineering judgement is applied to idealize the real joints, JointCalc strength predictions closely match the experimental findings.


2010 - Failure analysis of bonded T-peel joints: Efficient modelling by standard finite elements with experimental validation [Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio; Spaggiari, Andrea
abstract

The paper describes an efficient procedure, based on standard finite element techniques, for the failure analysis of bonded structures. Modelled with structural elements, the adherends are attached by means of standard kinematic constraints to a single layer of solid elements reproducing the adhesive. The work assesses the accuracy of the proposed method in the prediction of the post-elastic response of adhesive joints by applying a singularity-free stress failure criterion. Benchmarks for the model are the load–deflection curves obtained by an ad-hoc experimental campaign on steel and aluminium T-peel joints. The accuracy of the model appears very good with respect to the experimental results, both in terms of maximum force and post-elastic behaviour. The failure criterion adopted appears well-founded and the CPU time needed for the analysis is minimum thus corroborating this efficient procedure for the analysis of very complex structures.


2010 - Modeling, Prototyping, and Testing of Helical Shape Memory Compression Springs With Hollow Cross Section [Articolo su rivista]
Spinella, Igor; Dragoni, Eugenio; F., Stortiero
abstract

Shape memory alloys (SMAs) are used in many applications as actuators. The main drawbacks that limit the use of the SMAs in the field of mechanical actuation are the low mechanical bandwidth (up to a few Hertzs) and the unsatisfactory stroke (several millimeters). This paper contributes to enhancing the performances of SMA actuators by proposing a new SMA helical spring with a hollow section. The hollow spring is modeled, then it is constructed, and finally it is tested in compression to compare its performances with those of a spring with a solid cross section of equal stiffness and strength. Emptied of the inefficient material from its center, the hollow spring features a lower mass (37% less) and an extremely lower cooling time (four times less) than its solid counterpart. These results demonstrate that helical springs with a hollow construction can be successfully exploited to build SMA actuators for higher operating frequencies and improved strokes.


2010 - Modelling of wire-on-drum shape memory actuators for linear and rotary motion [Relazione in Atti di Convegno]
Mammano, G. S.; Dragoni, E.
abstract

The paper presents the analytical model of a linear/rotary solid-state actuator formed by a shape memory wire wound over a cylindrical drum. The model assumes a bilinear stress-strain behaviour of the wire in the martensitic state (low temperature) and a linear elastic response in the austenitic state (high temperature). Based on simple equilibrium conditions, the model calculates the stress and strain distributions in the wire subjected to a constant backup force and to frictional sliding forces at the contact with the drum. Closed-form expressions are supplied for the stroke produced by whatever actuator geometry. The model shows that large strokes (up to one half of the drum diameter) are achieved if the frictional coefficient is kept below 0.01. Rolling-contact architectures or sonic-pulse excitation of the drum are discussed as technical solutions to obtain such low friction values. Copyright © 2010 by ASME.


2010 - Multiphysics modelling and design of shape memory alloy wave springs as linear actuators [Relazione in Atti di Convegno]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

This paper explores the merits of shape memory wave springs as powering elements of solid state actuators. Advantages and disadvantages of the wave construction in comparison to the traditional helical shape are presented and discussed by means of dimensionless functions. The main assets of the wave springs are the higher electrical resistance (leading to simpler electrical drives) and the lower cooling time (leading to enhanced working frequency). The wave geometry is also superior in purely mechanical terms to the helical counterpart when axial space is at a premium. A step-by-step design procedure is proposed, leading to the optimal wave spring meeting the multiphysics design specifications and constraints. A case study is finally reported, showing the application of shape memory wave springs to the design of a telescopic linear actuator.


2010 - Robust shape optimization of tubular butt joints for characterizing thin adhesive layers under uniform normal and shear stresses [Articolo su rivista]
Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio
abstract

Thin-walled tubular joints, bonded end to end, are commonly used specimens to measure the mechanical properties of thin adhesive layers subjected to uniform shear stress distributions. Unfortunately, the application of an axial loading to this geometry leads to strong stress concentrations at the edges of the adherend–adhesive interface. This drawback undermines the use of this test for characterizing adhesives under biaxial stress conditions. With the aim of removing these stress concentrations, this paper suggests the introduction of stress relieving grooves on the internal and external surfaces of the tubular adherends.The optimal shape of the groove is identified following the Taguchi robust optimization technique. Via finite element analyses, the stress concentrations at the edges of the adherend–adhesive interface are calculated. Many geometries are examined for different adherend and adhesive properties (noise factors) in order to identify the groove shape that minimizes the stress concentrations for all experimental conditions.The analysis shows that a shallow V-shaped groove close to the adherend–adhesive interface smoothes significantly the stress peaks due to axial loading.With this simple modification, a tubular butt joint becomes a universal specimen for applying any combinations of reasonably uniform shear and normal stresses to thin adhesive layers.


2009 - Conceptual design and simulation of a compact shape memory actuator for rotary motion [Articolo su rivista]
Spinella, Igor; SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

This work describes the conceptual design, the modelling, the optimization, the detail design and the virtual testing of a shape memory actuator purposely conceived to maximize torque and angular stroke while limiting overall size and electric consumption. The chosen design, achieved by means of a Quality Function Deployment approach, features a fully modular concept in which an arbitrary number of identical modules are assembled to produce the desired angular stroke and output torque. The basic module contains shape memory springs that actuate the device and also a conventional spring that reduces the torque ripple. Following the concept generation stage, a thermo-electromechanical model is developed and a numerical optimization performed, aimed at minimizing the electrical consumption of the actuator. Finally, the device is designed in detail and the actuator is tested virtually. Thanks to the proposed modular construction and the use of a conventional balancing spring, the device shows better performances than known rotary shape memory actuators in terms of rotation, torque and customization.


2009 - Control-Oriented Dynamic Modeling and Characterization of Magnetorheological Dampers [Relazione in Atti di Convegno]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

experimental testing of magnetorheological (MR) dampers. The main improvement of this work over former models is the identification of dynamic parameters that are independent of the working conditions and that vary only as a function of the current. A simple model is built on the basis of the literature with the aim of simplifying the effort in retrieving the parameters and in controlling the system. The excitation current is introduced in the model as a variable, not only reducing the amount of test needed to assess the parameters, but also obtaining a faster model that can be profitably used in motion control. A second order polynomial relationship between the applied current and the three variable parameters is found, showing a saturation effect at high currents.


2009 - Design equations for binary shape memory actuators under dissipative forces [Articolo su rivista]
Spinella, Igor; Dragoni, Eugenio
abstract

An analytical procedure to design binary shape memory actuators is described. Ageneric actuator is considered where a cursor is moved against dissipative forces using an elasticsystem containing a primary shape memory spring and a bias (backup) element. Three typicalcases are analysed and differentiated in the way the bias force is applied to the primary shapememory spring, using a constant force, a conventional spring, or a second shape memory spring.Dimensionless, closed-form relationships are developed, which form the basis of a step-by-stepprocedure for an optimal design of the whole actuator (primary active spring and bias element).Specific formulas regarding the detailed design of the shape memory elements of the actuator inthe formof straight wires and wire helical springs are also presented.


2009 - Efficient post-elastic analysis of bonded joints by standard finite element techniques [Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio; Spaggiari, Andrea
abstract

A simplified finite element approach based on reduced models with minimum degrees of freedom was applied to the post-elastic analysis of bonded joints. The reduced model describes the adherends by means of structural elements (beams or shells) and the adhesive by a single strip of solid elements (plane-stress or brick). Internal kinematic constraints were applied to link the adherends and adhesive meshes. The accuracy and the efficiency of the reduced models in providing the force–displacement curve of T-peel joints were evaluated through a numerical test campaign by comparison with full finite element analyses. The test campaign was designed as a 2-level factorial experiment involving four variables: the skew angle of the T-peel (45 and 90◦), the thickness of the adherends (2 and 3 mm), the material of the adherends (aluminium and steel) and the stress–strain behaviour of the adhesive (brittle and perfectly plastic). The results show that the reduced model reproduces with fair accuracy the load–displacement curves of the joints at a fraction of the computational cost of the full model. The elastic stiffness, the yield load and the deformation energy were predicted within an error of 7%, 15% and 36%, respectively, with processing times that were typically 50 times shorter than the full model.


2009 - Materiali meccatronici [Articolo su rivista]
Dragoni, Eugenio
abstract

Liquidi che solidificano se esposti al campo magnetico, metalli che si deformano se percorsi da corrente elettrica, elastomeri che si contraggono come muscoli per effetto del campo elettrico. È l’affascinante mondo dei materiali meccatronici, fonte di curiosità scientifica e ispiratore di nuovi prodotti.


2009 - Mechatronic Design of a shape memory alloy actuator for automotive tumble flaps: a case study [Articolo su rivista]
Bellini, Alberto; Colli, Marcello; Dragoni, Eugenio
abstract

The continuous advance in mechatronics has long attracted researchers toward the development of new highly integrated actuators for automotive applications where reduced space and low weight are common constraints. In this context, Shape Memory Alloys (SMAs) offer many peculiar characteristics that make this technology very attractive for the construction of miniature mechatronic actuators. This paper presents the design, the prototype fabrication, and the functional testing of a case study, where an SMA binary actuator is used for automotive tumble flaps. The innovative solid-state actuation system is proposed as an alternative to electromagnetic and pneumatic effectors, traditionally used to drive the tumble shaft of an air intake manifold for internal combustion engines. Original features of the linear actuator involve the mechanical architecture and the control structure. On the mechanical side, two contrasting sets of SMA springs are used to actively generate the net actuating force during both outstroke and instroke. On the control side, a current feedback is exploited for sensorless real-time monitoring of the working temperature of the SMA springs during electrical supply. Major shortcomings of the proposed solution are a low response time and a power consumption higher than pneumatic and electromagnetic counterparts.


2009 - Modellazione efficiente agli elementi finiti per l’analisi a collasso di strutture incollate complesse [Relazione in Atti di Convegno]
Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio
abstract

Il lavoro verifica l’applicabilità di un modello semplificato agli elementi finiti per l’analisi a collasso post elastico di strutture incollate complesse in parete sottile. Al fine di superare le limitazioni dei modelli di letteratura come l’uso di elementi speciali, il lavoro sfrutta un modello ridotto già presentato dagli autori in campo elastico. Tale modello è basato sulla rappresentazione degli aderendi mediante elementi semistrutturali (piastre o gusci) e dell’adesivo per mezzo di speciali elementi coesivi. La continuità strutturale tra aderendi e adesivo è ottenuta mediante vincoli interni (tied mesh) che accomunano i gradi di libertà dei nodi mutuamente affacciati di aderendi ed adesivo. La struttura analizzata è un simulacro di incollaggio industriale e produce nella strato adesivo una sollecitazione complessa, analizzabile solo con modelli numerici. Si considera una struttura tubolare in parete sottile a sezione quadrata, fatta di due spezzoni posti testa a testa e incollati con fazzoletti di lamiera sui quattro lati. La struttura è sottoposta a flessione a tre punti fino al cedimento e la zona incollata posta disassata rispetto al punto di applicazione del carico riceve una sollecitazione indiretta. I risultati dell’analisi FEM, confrontati direttamente con le curve sperimentali forza-spostamento, evidenziano una buona accuratezza del metodo, in termini di rigidezza, forza massima e comportamento post elastico della struttura, accompagnati da ridotte dimensioni del modello e tempi di calcolo molto contenuti. Grazie a questi vantaggi, la procedura si presta ad effettuare l’analisi di strutture incollate complesse, altrimenti ingestibili se affrontate con una modellazione agli elementi finiti tradizionale.


2009 - Modelling, prototype construction and testing of helical shape memory springs with hollow cross-section [Relazione in Atti di Convegno]
Spinelia, I.; Dragoni, E.; Stortiero, F.
abstract

Shape memory alloys (SMAs) are used in many applications as actuators. The main drawbacks that limit the use of the SMAs in the field of micro-actuation are the low bandwidth and the unsatisfactory stroke. This paper contributes to enhancing the performances of SMA actuators by proposing a new SMA helical spring with hollow section. The hollow spring is modelled, then it is constructed and finally it is tested, comparing its performances with those of a spring with solid cross-section of equal stiffness and strength. Emptied of the inefficient material from its centre, the hollow spring features a lower mass (37% less) and an extremely lower cooling time (four times less). These results demonstrate that helical springs with hollow construction can be successfully exploited to realize SMA actuators with high bandwidth and stroke. Copyright © 2009 by ASME.


2009 - SISTEMA DI CARATTERIZZAZIONE PER FLUIDI MAGNETOREOLOGICI: EFFETTO DELLA PRESSIONE IN MODALITA’ SCORRIMENTO [Relazione in Atti di Convegno]
Spaggiari, Andrea; Dragoni, Eugenio
abstract

Il presente lavoro descrive l’ apparecchiatura sperimentale per la caratterizzazione di fluidi magnetoreologici (MR) in modalità scorrimento, sottoposti a pressione. Lavori di letteratura riportano indicazioni sull’effetto della pressione sui fluidi MR a taglio, ma oiché molti dispositivi commerciali lavorano in modalità scorrimento è interessante investigare questo aspetto. La progettazione del sistema è sviluppata in tre fasi: progetto del sistema meccanico, progetto del circuito magnetico, progetto della campagna sperimentale. L’attrezzatura effettua la misura della tensione di snervamento apparente del fluido MR in funzione di pressione, campo magnetico e velocità del fluido. Il circuito magnetico, progettato con un software FEM è stato verificato con un gaussmetro, evidenziando un ottimo accordo numerico-sperimentale. Il sistema sviluppato si pone come strumento per valutare se la pressione del fluido MR possa essere usata come strumento per potenziare gli attuali sistemi semiattivi basati su fluidi MR, come smorzatori e dissipatori lineari.


2009 - Standard finite element techniques for efficient stress analysis of adhesive joints [Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract

The paper documents ongoing research in the field of stress analysis of adhesive bonded joints and aimsat developing efficient and accurate finite element techniques for the simplified calculation of adhesivestresses. Goal of the research is to avoid the major limitations of existing methods, in particular theirdependency on special elements or procedures not supported by general purpose analysis packages.Two simplified computational methods, relying on standard modelling tools and regular finite elementsare explored and compared with the outcome of theoretical solutions retrieved from the literature andwith the results of full, computationally intensive, finite element analyses. Both methods reproduce theadherends by means of structural elements (beams or plates) and the adhesive by a single layer of solidelements (plane-stress or bricks). The difference between the two methods resides in the thickness andin the elastic properties given to the adhesive layer. In one case, the adhesive thickness is extended up tothe midplane of the adherends and its elastic modulus is proportionally increased. In the other case, theadhesive layer is maintained at its true properties and the connection to the adherends is enforced bystandard kinematic constraints. The benchmark analyses start from 2D single lap joints and are thenextended to 3D configurations, including a wall-bonded square bracket undergoing cantilever loading.One of the two simplified methods investigated provides accurate results with minimal computationaleffort for both 2D and 3D configurations.


2009 - Stress concentrations around a pressurized hole close to a uniformly loaded boundary [Articolo su rivista]
SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract

The elastic stresses arising around a pressurized circular hole close to a free or uniformly loaded boundary are examined. The boundary near to the hole can represent the periphery of a circular disc, the straight edge of a half-plane, or the contour of a second circular hole. All three configurations are modelled with the same general geometry, described by means of bipolar coordinates, from which each particular shape is obtained by assigning a suitable value to the curvature of the adjacent boundary. An exact solution found in the literature, covering the cases of a pressurized hole cut in a disc or in a half-plane, is developed semi-analytically to solve the third case of two arbitrary, loaded, adjacent holes. For the three cases examined, closed-form expressions are derived for the stress distributions along the contour of the hole and along the nearby edge. These expressions hold true for any geometry and for arbitrary combinations of uniform loadings on the two boundaries. For the special case of a pressurized hole close to a free edge, readily accessible charts of stress concentration factors are also provided.


2008 - Calcolo efficiente del comportamento strutturale di costruzioni incollate complesse [Relazione in Atti di Convegno]
Dragoni, Eugenio; Castagnetti, Davide; Spaggiari, Andrea
abstract

Il lavoro è orientato allo sviluppo di tecniche computazionali efficienti ed accurateper l’analisi semplificata del comportamento elastico e post-elastico di giunzioni e di struttureincollate. L’obiettivo è superare le principali limitazioni dei metodi di calcolo esistenti, inparticolare la loro dipendenza da elementi speciali o da procedure non implementate negliapplicativi commerciali più diffusi. Si propongono due modelli ridotti, entrambi basati sullarappresentazione degli aderendi mediante elementi strutturali (travi o gusci) e dell’adesivo permezzo di un singolo strato di elementi solidi (tensione piana o esaedri). La differenza tra i duemodelli risiede nel fatto che in un caso lo spessore dell’adesivo è esteso fino al piano dimezzeria degli aderendi e le proprietà elastiche sono incrementate proporzionalmente.Nell’altro caso, invece, lo strato adesivo mantiene le sue proprietà reali e la connessione agliaderendi è realizzata mediante vincoli cinematici convenzionali. Le analisi di verificariguardano il campo elastico ed il campo post-elastico. In entrambi i casi si effettua ilconfronto tra modelli ridotti e modelli completi, computazionalmente onerosi. Per l’analisipost-elastica si fa riferimento anche a prove sperimentali. Le analisi in campo elastico sonocondotte su una serie di configurazioni bidimensionali (giunto a sovrapposizione semplice) esono poi estese a due configurazioni tridimensionali (giunto a sovrapposizione semplice emensola a squadretta). In campo post-elastico il modello ridotto che ha fornito i miglioririsultati in campo elastico è applicato ad una giunzione T-Peel sollecitata fino a collasso perla quale il criterio che regola il cedimento dell’adesivo è basato sul concetto delle tensioni“regolarizzate”. Nel complesso, i risultati mostrano un buon accordo tra i modelli ridotti ed imodelli completi nella previsione sia delle tensioni elastiche nell’adesivo che delcomportamento post-elastico fino a collasso. Si riscontra inoltre, a favore dei metodi ridotti,una drastica diminuzione dei tempi di calcolo, in particolare per geometrie tridimensionali.


2008 - Contact force distribution in the interference fit between a helical spring and a cylindrical shaft [Relazione in Atti di Convegno]
Castagnetti, Davide; Spinella, Igor; Dragoni, Eugenio
abstract

This paper deals with the analysis of the contact forces developed by a helical spring shrink fitted on acircular shaft. This interference fit is an effective, fast to apply, reversible and inexpensive fastener. An analyticalsolution able to predict the contact forces distribution and the maximum thrust which the system can withstand hasbeen developed. The analytical results have been compared with a finite element analysis confirming theeffectiveness of the developed formulas.


2008 - CONTROL-ORIENTED DYNAMIC MODELLING AND EXPERIMENTAL CHARACTERIZATION OF MAGNETORHEOLOGICAL DAMPERS [Relazione in Atti di Convegno]
Spaggiari, Andrea; R. L., Andriatinavola; Dragoni, Eugenio
abstract

This work is about the dynamic modelling and the experimental testing of magnetorheological (MR) dampers. The main improvement of this work over former models is the identification of dynamic parameters that are independent of the working conditions (speed, stroke) and that vary only as a function of the current. The excitation current is introduced in the model as a variable, not only reducing the amount of test needed to asses the parameters, but also obtaining a faster model that can be profitably used in motion control. A second order polynomial relationship between the applied current and the three variable parameters is found, showing a saturation effect at high current.


2008 - Design of adhesive joints based on peak elastic stresses [Articolo su rivista]
L., Goglio; M., Rossetto; Dragoni, Eugenio
abstract

The paper is focused on the static strength of adhesively bonded structural joints and seeks a simplecalculation rule that can assist the designer in everyday engineering practice. The work encompassesthree steps. In the first step, an experimental campaign is carried out on an assortment of customizedbonded joints (single lap and T-peel) made of steel strips bonded by an acrylic structural adhesive. Thedimensions of the joints are chosen so as to produce a wide range of combinations of shear and peelstresses in the adhesive layer. In the second step, the stress analysis of the joints is performed by meansof a sandwich model that describes the variability of shear and peel stresses over the overlap length butdisregards the stress singularities at the corners. In the third step, a design rule is inferred by notingthat, in a chart having as axes the peak values of the peel and shear components in the adhesive atfailure, the points—calculated for each joint at the 2% (deviation from linearity) proof load—define alimit zone. The inferred design rule is that the adhesive withstands the load if the representative pointof the stress state lies inside this zone. For the tested case, the envelope of the limit zone has anapproximately rectangular shape. This criterion predicts the failure load of the joints far better than thesimplistic approach based on the nominal stress calculated as the ratio of the load to the bonded area.The paper also discusses the response which is obtained by applying, to the same experimental data,the traditional calculation based on the mean stress (force to area ratio), and the more sophisticatedapproach based on the stress intensity factor, which accounts for the singularity of the stress field.Applied to our experimental data, the performance of both has been unsatisfactory.


2008 - Elastostatic contact model of rubber-coated truck wheels loaded to the ground [Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio; Scire' Mammano, Giovanni
abstract

The solid wheels often foundonindustrial trucksmaybe subject to failure of the wheels’rubber coating under certain load conditions. To date, there has been no adequate analyticalmodel to predict these conditions and the design of these wheels has been based on costlytrial and error. In this work, an elastostatic analytical model is developed, which describes theinteraction of the wheel with the rigid ground in terms of relative approach, contact width,and contact pressure for a given load applied to the wheel. This model has been validated bycomparison with both experimental measurements and finite-element analyses, showing strongagreement for all three parameters. The results of the proposed model are more accurate thanthose of previous analytical models reported in the literature for rubber-coated rotary equipment.The new model can be used to design against creep or excessive deformation of the wheel coating.


2007 - Analisi del contatto elastico tra corpi assialsimmetrici parzialmente conformi [Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio; SCIRE' MAMMANO, Giovanni
abstract

Il lavoro presenta un’attività di ricerca volta a verificare l’applicabilità della soluzione hertziana a configurazioni di contatto tra corpi assialsimmetrici, non direttamente riconducibili alle geometrie studiate da Hertz. Si considerano quattro configurazioniassimilabili a casi frequenti nella pratica industriale e se ne esaminano in particolare due: sfera su cono e toro su cono. L’analisi, condotta col metodo dell’elemento finito, è svolta informa sistematica facendo variare tutte le grandezze geometriche e di materiale che, secondo il modello di Hertz, influiscono sul contatto. Per ciascuna configurazione sivalutano tre differenti livelli dell’angolo di pressione del contatto. I risultati ottenuti numericamente mostrano una buona corrispondenza con la previsione analitica del modelloclassico di Hertz, confermandone l’applicabilità. Si presentano infine formule pratiche per una diretta applicazione delle formule hertziane a tali casistiche assialsimmetriche ed unaindagine che individua il dimensionamento ottimale dei membri a contatto per minimizzarne la sollecitazione a parità di carico totale applicato alla coppia.


2007 - DESIGN OF A COMBINED PNEUMATIC AND MAGNETORHEOLOGICAL ACTUATOR FOR PROPORTIONAL MOTION CONTROL [Relazione in Atti di Convegno]
Spaggiari, Andrea; Dragoni, Eugenio; N., Bellato; F., Lancioni; M., Pecora
abstract

This paper shows a solution based on the use of magnetorheological fluids, aimed at conferring proportional controllability to standard on-off pneumatic actuators. The central idea is based on adding a magnetorheological fluid brake on a standard pneumatic device, in order to achieve position control of the system. The goal is to design a small and cheap magnetorheological fluid brake for automotive applications . Several concept of brake are presented, using the fluid in shear and flow mode. The final configuration involves not only mechanical architecture, but also an investigation on the coil shape and the related magnetic field.


2007 - Dynamic modelling of composite acoustic boxes for automotive applications [Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio; Rubini, Riccardo
abstract

Abstract: Automotive components must withstand shock loads and random vibrations during service which heavily affect their structural integrity. In this paper, an automotive acoustic box supporting two speakers for a car radio system is analysed. The box is made of talc-reinforced polypropylene, an injection-mouldable polymer. Shock load analysis and random response analysis are performed.


2007 - Lezioni di costruzione di macchine [Monografia/Trattato scientifico]
Dragoni, Eugenio
abstract

Il libro raccoglie le lezioni del corso di Costruzione di Macchine tenute dall'autore agli allievi ingegneri meccatronici presso la Facoltà di Ingegneria di Reggio Emilia. Il corso ha lo scopo di: introdurre ai principi della progettazione meccanica; abituare alla critica economica delle scelte costruttive; orientare la scelta di materiale e disegno alla fabbricazione; fornire gli strumenti per la verifica dei componenti; affrontare semplici problemi di progetto; comunicare con efficacia i risultati.Grazie alla struttura sintetica ed alla ricca serie di formule di calcolo, diagrammi e tabelle, il testo si presta anche per l’uso pratico come manuale di pronta consultazione in un contesto professionale.


2007 - Metodi efficienti agli elementi finiti per l’analisi a collasso di strutture incollate [Relazione in Atti di Convegno]
Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio
abstract

Il presente lavoro verifica l’applicabilità di un modello computazionale ridotto perl’analisi a collasso di giunzioni strutturali incollate. Il modello, basato sullarappresentazione degli aderendi mediante elementi strutturali di tipo trave e dell’adesivoper mezzo di un singolo strato di elementi in tensione piana, è stato precedentementeverificato per la previsione delle tensioni elastiche in un giunto a semplice sovrapposizione.Lo stesso modello viene ora applicato ad una configurazione T-Peel, sollecitata oltre illimite elastico. Il cedimento dell’adesivo è condizionato dal confronto tra le tensionimassime di tipo “regolarizzato”, calcolate nell’adesivo, ed una tensione critica propria diquest’ultimo. Il modello numerico, risolto sia in forma implicita che in forma esplicita, èconfrontato con un modello computazionale completo e con risultati sperimentali diletteratura. Dal confronto emerge un buon accordo dei risultati, sia in termini di forzamassima all’inizio del collasso che di evoluzione del carico durante il collasso. Grazie allesemplificazioni adottate, il metodo ridotto ha permesso di ridurre l’onere di calcolo da 350ad oltre 2100 volte rispetto al modello numerico completo, senza apprezzabile perdita diaccuratezza dei risultati.


2007 - Robust set up of experimental procedure for monotonic tensile test on polyethylene specimens [Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio; SCIRE' MAMMANO, Giovanni
abstract

Polyethylene pipes for water conveyance may present sensitivity to disinfectants employed to assure water potability. In particular, chlorine based disinfectants could affect their structural properties, which are mainly assessed through monotonic tensile test. A systematic experimental plan, performed to investigate the effects of chlorine based disinfectant on the mechanical properties of PE pipes, emphasized the high variability of the measured parameters, in particular with regard to percentage elongation at fracture. A research aimed at identifying whichfactors affect the outcome of the monotonic tensile test, and which combination of such factors provides a robust setup of the experimental procedure, is presented here. A systematic approach has been adopted considering a fullfactorial experimental plan, and varying each factor between two levels. From the outcome of the experimental results the influence of the test speed, the cutting die, the cutting direction and the pipe diameter has been assessed.


2006 - Analisi efficiente delle tensioni in giunzioni incollate mediante tecniche agli elementi finiti [Relazione in Atti di Convegno]
Castagnetti, D; Dragoni, Eugenio
abstract


2006 - Efficient stress analysis of adhesively bonded joints by finite elements techniques [Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio
abstract

The paper documents ongoing research on the field ofstress calculations in the adhesive layer of bonded joints andbonded structures. Aim of the research is to develop simple,general, portable, efficient and accurate finite elementtechniques for adhesive stress analysis and strength assessmentof the joint. Among four methods envisioned, two methods arepresented for 2D configurations and applied to a referencesingle-lap configuration. In both methods, the adherends aredescribed by means of beam elements and the adhesive layer bya single string of plane-stress solid elements. The plane-stresselements have either the original thickness of the true adhesivelayer or an expanded thickness up to the offset betweenadherends. Beams and plane-stress elements are connected bystandard constraining techniques (tied mesh) offered by thepackage employed (ABAQUS). The stress results provided bythe two methods are compared step by step with the predictionsof analytical models retrieved from the literature and with theoutcome of a full, computationally-intensive finite elementmodel using solid plane-stress elements for both adhesive andadherends. The simplified method using a single layer of planestress elements with the same thickness and properties as the true adhesive layer provides very promising results in terms of stress accuracy and computational efficiency.


2006 - Fatigue behavior of bolts and nuts treated with anaerobic thread locking adhesive [Articolo su rivista]
Mauri, P.; Dragoni, E.
abstract


2006 - Simulazione dinamica e sintesi strutturale per il contenimento delle vibrazioni di un cogeneratore termoelettrico [Relazione in Atti di Convegno]
Benetti, Matteo; Castagnetti, Davide; Dragoni, Eugenio; Rubini, Riccardo; E., Zanichelli
abstract

This paper deals with the design and the vibration analysis of a small-size (30 kVA) cogeneration unit, which can produce electric and thermal energy both for domestic and industrial appliances. To optimize the machine unsatisfactory dynamic behaviour (vibrations and noise), a discrete system approach was at first considered, also employing the design of experiments (DOE) technique to easily attain the best solution, then FEM analysis and measures with accelerometers on a prototype were performed. The solutions obtained allowed a significant improvement of the cogenerator behaviour, without adding any costs, being the final structure of the machine almost equal to the original version.


2006 - System design of a shape memory alloy actuator for automotive tumble flaps [Relazione in Atti di Convegno]
Colli, M.; Dragoni, E.; Bellato, N.
abstract

The continuous advance in mechatronics has long attracted researchers towards the development of new highly integrated actuators for automotive applications. Shape Memory Alloys (SMAs) offer many favourable characteristics that make this technology very attractive for mechatronic actuators. This paper presents the design, the prototype fabrication and the functional testing of an SMA binary actuator for automotive tumble flaps. The innovative solid-state actuation system is proposed as an alternative to traditional electric or pneumatic effectors used to drive tumble flaps of an air intake manifold for internal combustion engines. Copyright © 2006 SAE International.


2005 - Kinematic analysis of universal split heads for milling machines [Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio; SCIRE' MAMMANO, Giovanni
abstract

Most milling machines are equipped with split heads aimed at orienting the tool at any angle with respect to the workpiece. Typical examples are given in Fig. 1. The general geometry of these heads can be reduced to the linkage shown in Fig. 2. Each particular architecture is achieved by choosing angle θ between the member axis and by selecting the orientation of the tool with respect to the final member. The head features two degrees of freedom, embodied by the joint rotations α and β, through which the configuration can be changed to adjust the orientation ofthe tool. The kinematic analysis of the head can be posed in two ways: a) direct analysis if the values of the joint rotations, α and β, are given and the orientation of the tool axis with respect to the machine frame is sought; b) inverse analysis if the desired orientation of the tool axis is given and the joint rotations, α and β, are sought that enforce that orientation. This paper provides the analytical solution of both direct and inverse problems. The work falls within a research program carried out with the partnership of a renowned machine tool manufacturer of Reggio Emilia.


2005 - Modello elastostatico del contatto al suolo di ruote con rivestimento elastomerico [Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio; SCIRE' MAMMANO, Giovanni; P., Borghi
abstract

The paper deals with the elastostatic analisis of rubber-layered wheels for industrial trucks. An analytical model is developed which describes the interaction of the wheel with the rigid ground in terms of relative approach, contact width and contact pressure for a given load applied to the wheel. The comparison is favourable against experimental measurements and finite element analyses for all three parameters. The analytical model is a good tool for the prediction of fatigue failures and ofthermomechanical failures of the wheels undergoing heavy service conditions.


2005 - Optimal aspect ratio of interference fits for maximum load transfer capacity [Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract

The stress state in frictional interference fits under torsional and axial loading is examined. The optimal ratio between the inside and outside diameters of the hub is calculated, which maximizes the load transmitted by the joint. Design formulae and charts are provided, giving the most efficient aspect ratio of the hub for all practical situations. It is found that the maximum load capacity is achieved for an aspect ratio in the range from 0.5 to 0.7, regardless of the frictional coefficient (up to 1), of the kind of loading (torsional or axial), and of the material response (brittle or ductile).


2004 - Development and testing of an inflatable capsule for the YES2 project [Relazione in Atti di Convegno]
Benetti, M.; Castagnetti, D.; Dragoni, E.; Van Der Heide, E. J.
abstract

The YES2 project features a lightweight (about 10 kg), single-stage, inflatable reentry capsule. This paper describes the development, the manufacturing and the testing of the first capsule prototype. The prototype capsule is a 1.5 m diameter sphere-cone. Rigidity is provided by 5 stacked inflatable tori, connected together for single-stage inflation. A laminated solution is used for each torus, comprising two layers of surface-treated Kapton® film for air tightness, and a single layer of Zylon® fabric for structural strength. Design trade-offs involving the location of the valves and the connections to the thermal protection system are addressed and future steps for optimization and testing are discussed. The flight design contains an ablative foam nose and an Alumina-Nextel flexible insulating cover. The design of the capsule is driven by the following aims: a) high stability during reentry, both in the hypersonic and in the subsonic phase; b) low stresses in the inflatable structure; c) high ratio of drag area to total weight; d) affordable thermal loads; e) simple manufacturability, foldability and deployment; f) single-stage inflation already in space for inherent safety, allowing the capsule to land in mainland Europe for the first time in history. Samples of the materials employed have been prepared and tested. Adhesively-bonded Kapton® samples have been tested only for durability at high temperatures (200°C), since the Kapton® layer undergoes no structural loads. Zylon® samples (both bonded and sewn) have been tested under load at high temperatures (200°C). The samples were in the form of cylinders inflated at 250 kPa, which is the maximum expected gas pressure during re-entry. A prototype of the inflatable capsule has been manufactured and assembly technologies are discussed in the paper. The model will be submitted to aerodynamic tests for shape stability (fluttering). The capsule is designed specifically for Earth entry (sample return), but the advantages of the innovative inflatable concept introduced can readily be exploited for future interplanetary missions.


2003 - Concept selection and design of the inherently safe re-entry capsule for YES2 [Relazione in Atti di Convegno]
Kruijff, M.; Heide, E. J. V. D.; Dragoni, E.; Castagnetti, D.; Ferretti, S.
abstract

The design and concept selection of the inherently safe re-entry capsule for the 2 nd Young Engineers' Satellite (YES2) are discussed. A significant investment to evaluate, combine and analyze first the simple ideas is made. The steps define the YES2 concept selection logic include, reduce classes, strip the concept from attributes, merging all the options, and options evaluation and initial design. Material tests were performed and simulation tools were developed for re-entry, heat flux, CFD, FEM, stability, and pressure-shape interaction.


2003 - Fatigue testing of taper press fits bonded with anaerobic adhesives [Articolo su rivista]
Dragoni, Eugenio
abstract

This article compares the static strength and the fatigue strength (under repeated stress) of axially loaded taper press fits, either dry or bonded with an anaerobic adhesive. A general increase of both static and fatigue strength with the contact pressure is observed, the strength buildup being greater for the dry joints than for the bonded ones. No significant difference between the static and the fatigue strength is measured for the dry joints. For the bonded joints, the fatigue strength decay is nearly independent (in absolute terms) of the assembly contact pressure.


2002 - Cumulative static strength of tightened joints bonded with anaerobic adhesives [Articolo su rivista]
Dragoni, Eugenio; P., Mauri
abstract

This paper deals with the static strength of mechanically tightened joints augmented with anaerobic adhesives. Tests were performed on a variety of specimens distinguished by fairly homogeneous (annular butt joint) or realistically inhomogeneous (threaded, cylindrical and double lap joints) working conditions over the bondline. For each geometry, the strength of the dry (unbonded) joint was compared with the strength of the joint bonded with an assortment of anaerobics. The results indicate that the strength of all joints (bonded and unbonded) increases with the contact force. When strong adhesives (retainers) are used, the overall strength approximately equals the sum of friction and adhesive strengths, taken separately. When weak adhesives (threadlockers) are adopted, the superimposition of effects grossly overestimates the measured strength. A micromechanical model is proposed that explains the observed macroscopic behaviour.


2001 - Designing the cross-section of curved beams for equal magnitude of peak bending stresses [Articolo su rivista]
Dragoni, Eugenio
abstract

The paper discusses the problem of designing the cross-section of curved beams to achieve any desired ratio of the stress arising at the inner radius to that arising at the outer radius. A general design equation is developed which identifies the cross-sectional profiles enforcing that condition when the beam undergoes flexural and axial loads. Based on Winkler's theory for circumferential stresses, the equation shows the extent to which trapezoidal and triangular cross-sections can develop equal peak stresses for an assortment of loading conditions. Several three-dimensional finite element analyses of reference configurations are performed that confirm the theoretical findings.


2000 - Intrinsic static strength of friction interfaces augmented with anaerobic adhesives [Articolo su rivista]
Dragoni, Eugenio; P., Mauri
abstract

The paper is focused on the static strength of friction joints supplemented with anaerobic adhesives. Through torsional tests on the annular interface between tubular steel specimens, the friction and the adhesive contributions to the overall strength are determined as a function of the clamping force. The analysis shows no interaction of the component strengths, with the frictional strength proportional to and the adhesive strength independent of the clamping force as if the underlying mechanisms were acting separately. This cumulative performance, intrinsic of the interface in the homogeneous test conditions attained, should be exploited to the full when designing efficient real joints based on this hybrid technology.


2000 - La resistenza dei forzamenti incollati [Articolo su rivista]
Dragoni, Eugenio; P., Mauri
abstract

Gli adesivi anaerobici sono impiegati da tempo nel settore industriale per potenziare le prestazioni dei collegamenti meccanici tradizionali. L'articolo prende in esame l'incremento di resistenza che essi apportano agli accoppiamenti per attrito in condizioni ideali di funzionamento. Attraverso prove di torsione su giunzioni anulari assortite, si determinano le quote di resistenza imputabili singolarmente all'attrito e all'adesivo per diverse pressioni di contatto. L'indagine rivela la sostanziale indipendenza dei due contributi simultanei. La componente d'attrito e quella adesiva risultano, rispettivamente, proporzionale e insensibile alla pressione, come se le due cause agissero separatamente. Il risultato costituisce un utile riferimento per il razionale proporzionamento dei giunti reali basati su questa tecnologia ibrida.


1999 - Effect of anaerobic threadlockers on the fatigue strength of threaded connections [Articolo su rivista]
Dragoni, Eugenio
abstract

The paper deals with the fatigue behaviour of threaded connections bonded with anaerobic threadlockers. Fatigue tests are described involving rolled ISO M10 bolts of property class 10.9 loaded under constant amplitude at the load levels 11+/- 10 kN and 8.8 +/- 8 kN. The number of cycles to failure consequent to treatment with anaerobics is significantly longer than without treatment, the ratio between the corresponding lives being about 3.5 at the higher load (11 +/- 10 kN) and about 2 at the lower load (8.8 +/- 8 kN). The reduced effect with the lower load discloses a common endurance limit. The behaviour is attributed to elimination of fretting damage between the contacting threads of the bonded connections. This interpretation suggests an important role of the mean test load and fosters further investigation.


1998 - Design of a single-sided composite rear swing arm for racing motorcycles [Articolo su rivista]
Dragoni, Eugenio; F., Foresti
abstract

The single-sided rear swing arm for a racing motorcycle is redesigned with composite materials to further improve on an existing successful cast metal version. Capitalizing on the distinguished properties of carbon epoxy laminates and sandwich constructions, the new design is optimized numerically for reduced weight and like stiffness in comparison with the metal counterpart. The goal is achieved with the best composite arm leading to slightly increased torsional stiffness (+10%) and substantially reduced mass (-30%) and mass moment of inertia (-40%). The construction of a non-structural fibreglass model is finally described which provides considerable insight into the actual fabrication process.


1998 - I frenafiletti anaerobici alleviano la fatica nelle viti [Articolo su rivista]
Dragoni, Eugenio
abstract

I frenafiletti anaerobici sono adesivi acrilici che vengono interposti, al serraggio, tra vite e madrevite col fine primario di mantenere il precarico tra le parti in ogni condizione d'esercizio. Sotto carichi esterni fortemente variabili, ciò giova alla resistenza del collegamento perchè, grazie ai noti meccanismi di ripartizione delle forze, la vite risente solo in misura minima della variabilità del carico. Il lavoro dimostra attraverso prove di fatica che a questo aumento indiretto della resistenza a fatica del collegamento si aggiunge anche un beneficio diretto sul limite di fatica della vite.


1997 - Defect detection in bonded joints by acoustic emission [Articolo su rivista]
V., Dal Re; Dragoni, Eugenio
abstract

The paper explores the merits of the acoustic emission analysis as a means for non destructive evaluation of adhesively bonded joints. The technique is used to inspect sound and defective single lap joints undergoing incremental or monotonic tensile loads. Simple processing of acoustic emission characteristics allows early detection of faulted joints both as a stand-alone method or, most effectively, as a supplement to proof testing.


1997 - Effect of thread pitch on the fatigue strength of steel bolts [Articolo su rivista]
Dragoni, Eugenio
abstract

The paper explores the effect of the thread pitch on the fatigue strength of ISO steel bolts fitted with standard nuts. By means of boundary element analyses and cross-comparison with theory and photoelasticity, the load capacity of the bolt is ultimately related to a comprehensive notch factor which embodies both stress concentration and notch sensitivity dependencies. The notch factor is conveniently plotted as a function of nominal diameter and thread pitch for a selection of steel grades. The charts show that the endurance load slightly increases as the pitch is decreased for small bolts of low-grade steel. Conversely, the endurance load markedly increases with the pitch (improvements above 40 per cent can be achieved) for large bolts of high-grade steel.


1997 - Una sospensione monobraccio in carbonio per moto da competizione [Articolo su rivista]
Dragoni, Eugenio; F., Foresti
abstract

Le analisi agli elementi finiti possono offrire un importante riscontro per valutare l'affidabilità strutturale dei veicoli a due ruote: nel presente articolo viene mostrata un'applicazione a una moto di elevate prestazioni.


1996 - Analisi numerica di una guarnizione elastomerica O-R montata in cava a coda di rondine [Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract

Per il loro corretto funzionamento gli O-ring sono normalmente alloggiati all'interno di cave. Le forme di queste ultime possono essere diverse, ma la più comune è la forma a cosiddetta "coda di rondine". Ma qual è la forma ideale della sezione trapezoidale di tale cava e quali sono i comportamenti della guarnizione all'interno di essa. Ecco i risultati di uno studio condotto dagli autori di questo articolo.


1996 - Influenza del passo di filettatura sulla resistenza a fatica delle viti [Articolo su rivista]
Dragoni, Eugenio
abstract

Sono più resistenti a fatica le filettature a passo grosso o quelle a passo fine? Il presente lavoro cerca una risposta esauriente a questa comune domanda nel caso di accoppiamento tra vite e dado a filettatura metrica.


1996 - The radial compaction of a hyperelastic tube as a benchmark in compressible finite elasticity [Articolo su rivista]
Dragoni, Eugenio
abstract

The stress solution to the radial compaction of a hyperelastic tube is developed analytically for both incompressible and slightly compressible material response. The solution is explicit for the incompressible behaviour and implicit for the compressible one. It is shown that proper combination of tube geometry and total compaction leads to stress results very sensitive to small variations of Poisson's ratio. This makes the problem a good benchmark for the performance of numerical methods in the area of compressible finite elasticity. As an example, the commercial finite element code ABAQUS is applied to a demanding tube configuration for Poisson's ratios in the range from 0.49 to 0.5.


1995 - Fatigue testing of metric bolts fitted with lip-type nuts [Articolo su rivista]
Dragoni, Eugenio
abstract

The paper addresses the effect of the external shape of lip-type nuts on the fatigue strength of commercial M10 bolts loaded in tension. Evolving from the standard configuration, six nut geometries are compared, characterized by lips of different shape (cylindrical or tapered) and length. Testing and statistical treatment of the data are performed in accordance with a JSME standard involving 14 specimens for each geometry. Within the class of merely cylindrical lips, only limited advantages over the standard assembly are detected. In particular, the bolt strength remains mostly unaffected by lengthening of the lip beyond one-third of the nut height. Conversely, tapering of the lip end so as to thin its wall around the entry section of the bolt results in substantial improvements. In this case, the strength increase is roughly proportional to the taper length. Adoption of a tapered lip covering two-thirds of the nut height enhances the bolt strength by about one-fourth with respect to the standard geometry.


1995 - Mechanical analysis of a thin solid circular plate deflected by transverse periphery forces and by a central load [Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract

A thin, solid, circular plate deflected by a number of transverse, concentrated, periphery forces, not necessarily angularly equispaced or equally oriented, and sustaining a central, transverse, equilibrating lead, is mechanically anaoysed via a purely flexural model. This problem is interpreted as a angularly dephased combination of a relatively simple model. This fundamental scheme consists of a plate loaded by a single periphery force, by a central load of equal intensity and opposite direction, and by a sinusoidal periphery line loading whose wavelength equals the plate border and whose intensity render the plate loading self-equilibrated. When a sequence of basic schemes, possibly referring to loads is different intensity, is combined, respecting the condition that the resultant of the periphery loads is equilibrated by a central force alone, the sinusoidal load effects vanish and the title problem is recovered. A series solution in terms of plate deflections is obtained for the basic model, whose coefficients are analytically evaluated via a computer algebra package. The series sum is expressed in finite terms involving the dilogarityhmic function, valid over the whole plate region. In particular, the series is summed in analytical form for the whole plate periphery, along which the boundary deflections are expressed in closed form.


1995 - Simply supported annular plates transversely loaded by a concentrated force applied at an arbitrary point [Articolo su rivista]
Strozzi, Antonio; Dragoni, Eugenio; V., Ciavatti
abstract

An analysis is performed for a thin, annular plate, simply supported at its inner boundary, free at its periphery, and loaded by a concentrated force applied at any plate position. A purely flexural model is adopted, for which a series solution is obtained with the aid of an algebraic manipulator. Experimental tests are carried out for a specific plate geometry and the results obtained are compared to the analytical forecasts. A diagram is presented which summarizes the plate theoretical deflection by the loaded point for a wide range of aspect ratios of the annular plate and of normalized loaded positions.


1995 - Structural evaluation of ceramic femoral heads: effect of taper friction, support conditions and trunnion compliance [Articolo su rivista]
Dragoni, Eugenio; Andrisano, Angelo Oreste
abstract

The outcome of a nonlinear finite element stress analysis of ceramic heads for artificial hip joints is presented. The analysis mainly covers the influence of taper friction, support conditions and trunnion modulus of elasticity on the hoop stress distribution at the surface of the head bore. The paper quantifies how much the maximum tensile stress decreases with increasing frictional coefficient, with stiffening of the support and with stiffening of the trunnion material. An appreciable rise of the maximum tensile upon unloading of the head is also shown for the case of cup support. The computational results are found in close correspondence with photoelastic measurements of taper pressures and encourage the use, for preliminary design purposes, of an approximate theoretical model retrieved from the literature.


1994 - Effect of thread pitch and frictional coefficient on the stress concentration in metric nut-bolt connections [Articolo su rivista]
Dragoni, Eugenio
abstract

By means of the finite element method, this paper establishes how much the stress state within standard metric nut-bolt connections is affected by variations of the thread pitch and of the frictional coefficient. Following a validated simplified approach, the actual three-dimensional geometry of each connection is replaced by an axisymmetric model which recreates the outline of the joint on an appropriate meridional section. The numerical data prove that, for prescribed nominal thread diameter and bolt load, The peak stress in the screw monotonically increases as the pitch decreases. Further, as far as complete sticking between nut and bolt is not achieved, the stress level linearly increases with the coefficient of friction, the rate of variations being higher at the lowest pitches.


1994 - Effect of thread shape on screw stress concentration by photoelastic measurements [Articolo su rivista]
Dragoni, Eugenio
abstract

The screw stress concentration for six nut-bolt connections embodying three different thread profiles and two nut shapes is measured photoelastically. Buttress (nearly zero flank angle), trapezoidal (15-deg flank angle), and triangular (30-deg flank angle) thread forms are examined in combination with standard and lip-type nuts. The effect of the thread profile on the screw stress concentration appears to be dependent upon the kind of nut considered. If the fastening incorporates a standard nut, the buttress thread is stronger than the triangular one, which, in turn, behaves better than the trapezoidal contour. The improvement is roughly a 20-percent reduction in the stress concentration factor from the trapezoidal to the buttress thread. In the case of lip nut, conversely, this tendency is somewhat reversed, with the trapezoidal thread performing slightly (but not decidedly) better than the other two shapes. Finally, averaged over all three thread forms, the lip nut exhibits a stress concentration factor which is about 50 percent lower than that of the standard nut.


1994 - Fatigue testing of metric bolts fitted with lip-type nuts [Relazione in Atti di Convegno]
Dragoni, E.
abstract

The paper addresses the effect of the external shape of lip-type nuts on the fatigue strength of commercial M10 bolts loaded in tension. Evolving from the standard configuration, six nut geometries are compared, characterized by lips of different shape (cylindrical, tapered or both) and length. Testing and statistical treatment of the data are performed in accordance with a JSME standard involving 14 specimens for each geometry. Within the class of merely cylindrical lips, only limited advantages over the standard assembly are detected. In particular, the bolt strength remains mostly unaffected by lengthening of the lip beyond one third of the nut height. Conversely, tapering of the lip end so as to thin its wall around the entry section of the bolt results in substantial improvements. In this case, the strength increase is roughly proportional to the taper length. Adoption of a tapered lip covering two thirds of the nut height enhances the bolt strength by about one fourth with respect to the standard geometry.


1993 - Effect of thread shape on screw stress concentration by photoelastic measurements [Relazione in Atti di Convegno]
Dragoni, E.
abstract

The screw stress concentration for six nut-bolt connections embodying three different thread profiles and two nut shapes is measured photoelastically. Saw-toothed (nearly zero flank angle), trapezoidal (15-degree flank angle) and triangular (30-degree flank angle) thread forms are examined in combination with standard and lip-type nuts. The effect of the thread profile on the screw stress concentration appears to be dependent upon the kind of nut considered. If the fastening incorporates a standard nut, the saw-toothed thread is stronger than the triangular one which, in turn, behaves better than the trapezoidal contour. The improvement is roughly a 20 per cent reduction in the stress concentration factor from the trapezoidal to the saw-toothed thread. In the case of lip nut, conversely, this tendency is somewhat reversed, with the trapezoidal thread performing slightly (but not decidedly) better than the other two shapes. Finally, averaged over all three thread forms, the lip nut exhibits a stress concentration factor which is about 50 per cent lower than the standard nut's.


1992 - Effect of nut geometries on screw thread stress distribution: photoelastic results [Articolo su rivista]
Dragoni, Eugenio
abstract

The structural merits of lip-type nuts engaging with ordinary bolts are assessed experimentally by means of frozen-stress photoelasticity. Thread pitch, lip radial thickness, and lip length are selected as design variables and scanned for possible effect on the maximum stress within the connection. In this respect, the length of lip is shown to play a major role while the other parameters have no decided effect. It is found that a nut with a lip covering 60 percent of total height reduces the stress concentration in the screw by nearly 40 percent with respect to a standard nut of equal height and outside diameter. This improvement is achieved without producing higher stresses in the nut than in the screw.


1992 - Effect of thread pitch and frictional coefficient on the stress concentration in metric nut-bolt connections [Relazione in Atti di Convegno]
Dragoni, E.
abstract

By means of the finite element method, this paper establishes how much the stress state within standard metric nut-bolt connections is affected by variations of the thread pitch and of the frictional coefficient. Following a validated simplified approach, the actual three-dimensional geometry of each connection is replaced by an axisymmetric model which recreates the outline of the joint on an appropriate meridional section. The numerical data prove that, for prescribed nominal thread diameter and bolt load, the peak stress in the screw monotonically increases as the pitch decreases. Further, as far as complete sticking between nut and bolt is not achieved, the stress level linearly increases with the coefficient of friction, the rate of variations being higher at the lowest pitches.


1992 - Finite element redesign of reciprocating 'PTFE' rod seals [Capitolo/Saggio]
Botto, P.; Dragoni, E.; Strozzi, A.
abstract

The paper deals with a non-linear Finite Element analysis of the mechanical behaviour of a reciprocating rod seal assembly, composed of a PTFE Edge-seal and of an elastomeric O-ring. As a first step, a widely spread commercial version of this composite seal is numerically analyzed and the predictions are compared with published experimental data. Next, following the indications of an oversimplified model of the seal, several geometric parameters of the Edge-seal section are tentatively adjusted for improved performance and checked by means of refined Finite Element analyses. (from Authors)


1992 - Mechanical analysis of an annular plate transversely loaded at an arbitrary point by a concentrated force [Articolo su rivista]
V., Ciavatti; Dragoni, Eugenio; Strozzi, Antonio
abstract

An annular plate clamped at the inner rim, free at the outer edge and loaded at an arbitrary point by a concentrated force is mechanically analyzed via a purely flexural model. A series solution is achieved, whose coefficients are analytically evaluated with the aid of an algebraic manipulator. A series acceleration technique is also developed. Experimental data are obtained for a particular plate geometry, and the results retrieved in terms of deflections and stresses are compared to the analytical forecasts. A technically relevant diagram detailing the theoretical deflection of the plate at the loading point for a variety of plate proportions and load locations is also presented.


1992 - Stresses in Universal Ceramic Heads for Total Hip Replacement: Effect of Stem Elastic Modulus and Frictional Coefficient [Relazione in Atti di Convegno]
Andrisano, Angelo Oreste; F., Bertuzzi; Dragoni, Eugenio
abstract

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1991 - Mechanical analysis of an annular plate subject to a concentrated radial moment [Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract

An annular plate loaded by a concentrated radial moment applied to one of its contours and simply supported along the other boundary is mechanically analysed via a series solution. The sensitivity of the plate deflections to modifications of the Poisson's ratio is examined numerically. Several useful tables and interpolating expressions are reported which describe the deflections of the plate loaded edge for various geometries. Finally, the case of a uniform radial moment applied to an arc of the plate periphery is also studied.


1990 - A Photoelastic analysis of ceramic heads for total hip replacements [Articolo su rivista]
Andrisano, Angelo Oreste; V., Ciavatti; Dragoni, Eugenio; Strozzi, Antonio
abstract

The main stress features in a hip joint replacement are studied photoelastically. In particular, the load transfer mechanism and the outcome of pressure peaks are examined and interpreted. An improved solution which permits a reduction of the stress level to be achieved is also investigated photoelastically. Some joint design directives are included.


1990 - Axisymmetric mechanical analysis of ceramic heads for total hip replacement [Articolo su rivista]
Andrisano, Angelo Oreste; Dragoni, Eugenio; Strozzi, Antonio
abstract

An axisymmetric, mechanical analysis of conical press-fit ceramic heads is performed. The head strength and its fracture modes are assessed experimentally. The stress field is examined by finite element, strain gauge and photoelastic methods. An alternative head design, characterized by a cylindrical engagement with the stem, is analysed with the same techniques and its merits are explored.


1990 - Effect of nut compliance on screw thread load distribution [Articolo su rivista]
Dragoni, Eugenio
abstract

A well-known theoretical equation for the distribution of contact load along threads in standard nut-bolt connections is generalized to incorporate the case of axially variable Young's moduli of the threaded elements. The influence of the material selection for homogeneous bolt and nut on the thread load concentration factor is initially addressed. The theoretical possibility of equalising the thread load distribution over the whole engagement by a convenient axial variation of the nut Young's modulus is then examined.


1989 - Analisi fotoelastica di una protesi d’anca in ceramica. Parte I: Metodologia [Relazione in Atti di Convegno]
Andrisano, Angelo Oreste; V., Ciavatti; Dragoni, Eugenio; Strozzi, Antonio
abstract

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1989 - Analisi fotoelastica di una protesi d’anca in ceramica. Parte II: Risultati [Relazione in Atti di Convegno]
Andrisano, Angelo Oreste; V., Ciavatti; Dragoni, Eugenio; Strozzi, Antonio
abstract

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1989 - Measuring the load eccentricity in helical compression springs [Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract

An experimental device able to detect the load eccentricity in helical compression springs is described. The theory underlying the resolution of measured bending strains of the apparatus into effective load eccentricity is discussed. Laboratory results are offered for heavy duty springs and compared to theoretical estimates retrieved from the literature.


1989 - Mechanical analysis of a simply supported annular plate loaded by a periphery force [Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract

An annular plate subject to a concentrated force applied to one of its edges and simply supported along the other contour is mechanically analised. A series solution method is employed, the analytical expressions of the series coefficients are derived and the series convergence is accelerated via a simple, yet effective, technique. An approximate analytical expression for the loaded edge deflection is derived via a Taylor expansion of the series coefficients. The sensitivity of the plate deflection to modifications of the Poisson's ratio is examined numerically. Various practically relevant diagrams are presented which describe the deflections of the plate loaded edge for several geometries. Finally, the case of a uniform linear force applied to an arc of the plate periphery is also examined.


1989 - Mechanisches Verhalten von durch ein konzentriertes Radialmoment belasteten Kreisringplatten [Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract

In dieser Arbeit wird der Fall einer an einem Rand durch ein konzentriertes Radialmoment belasteten, am anderen Rand eingespannten Ringplatte behandelt. Die Verschiebung der Platte wird durch eine unendliche konvergente Reihe ausgedrückt, deren Koeffizienten ausgerechnet werden. Es wird gezeigt, wie die Reihenkonvergenz verbessert werden kann. Verschiedene Kurvenbilder der Durchbiegung längs des belasteten Plattenrandes und Näherungsausdrücke der Verschiebung am Belastungspunkt werden geliefert. Schließlich werden verschiedene Kurvenbilder auch für den Fall eines längs eines Randbogens gleichförmig verteilten Radialmomentes dargestellt.


1989 - Theoretical analysis of an unpressurized, elastomeric O-ring seal inserted into a rectangular groove [Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract

Based on linear elasticity, a theoretical model is developed which is able to describe the mechanical behaviour of an unpressurized, elastomeric O-ring seal inserted into a rectangular groove. First, the analytical tools employed to handle the unilateral contact problem and to improve the pressure profile regularity are discussed in detail. Next, an assessment of the model is performed for a laterally free seal, for which a variety of studies exist in the literature. Finally, the model is applied to the analysis of a seal installed into several grooves of different width, and the results retrieved are compared with the few data available. The model response to a perturbation of Poisson ratio of the elastomer is also critically examined.


1988 - A contribution to wave spring design [Articolo su rivista]
Dragoni, Eugenio
abstract

An analytical model for stamped ring wave springs is proposed, based on the theory for circular beams loaded normal to the plane of curvature. The model profits from the adoption of Castigliano's theorem as a tool for mathematical treatment. Closed-form expressions for both load—deflection and load—stress relationships are presented. Because of the particular shape of the spring in the undeformed configuration, the load—deflection curve is found to be appreciably bilinear in character. A similar but less pronounced behaviour is displayed also by the relationship between load and internal stresses. The analytical results are compared to earlier theoretical findings and are shown to correlate well with experimental measurements.


1988 - Analisi meccanica di testine in ceramica per protesi d’anca [Articolo su rivista]
Andrisano, Angelo Oreste; Dragoni, Eugenio; Strozzi, Antonio
abstract

Il lavoro è rivolto all'analisi meccanica di testine di ceramica comunemente impiegate in protesi d'anca ed alla definizione di una nuova geometria della testina. La ricerca si articola in quattro parti. La prima parte riguarda l'analisi geometrica (errori di forma) delle superfici interessate al collegamento testina-stelo. La seconda parte è dedicata alla determinazione sperimentale dei carichi e dei modi di rottura delle testine. Nella terza parte viene svolta l'analisi delle sollecitazioni nelle testine, condotta con metodi sperimentali (fotoelasticità) e numerici (elemento finito). La quarta parte propone un disegno alternativo delle testine per ottenere una resistenza maggiore rispetto a quelle esistenti.


1988 - Analysis of an unpressurized, laterally restrained, elastomeric O-ring seal [Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract

An unpressurized, elastomeric O-Ring seal inserted into a rectangular groove is analysed numerically and experimentally. The salient parameters characterizing the seal deformed geometry and stress field are investigated. The results gathered are confronted to those holding for a laterally unrestrained toroidal seal. Based on such a comparison, an analytical model is developed which accounts for the lateral restraining effect.


1988 - Fracture toughness evaluation of natural rubber [Articolo su rivista]
Dragoni, Eugenio; G., Medri
abstract

A method for estimating the fracture toughness of rubbur-like materials is presented. Experimental data of a notched natural rubber sheet is analysed by application of the path-independent J-integral. A finite element code for large elastic deformations is used to evaluate the deformed shape of the rubber at crack growth initiation. Discussed is a stability criterion based on the existence of a critical value of J in relation with the experimental results.


1988 - Mechanical Analisys of Ceramic Total Hip Replacements Heads [Relazione in Atti di Convegno]
Andrisano, Angelo Oreste; Dragoni, Eugenio; Strozzi, Antonio
abstract

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1987 - Design of an end face seal assembly for lubricated rotary joints [Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract

A novel end face seal assembly composed of a rubber load ring, a metal stiffening ring, and a rubber seal ring serially connected together is presented. The design procedures adopted to achieve good operational effectiveness and long wear life are discussed in detail. Particular attention is focused on obtaining a load ring exhibiting a linear load-deflection relationship, and a seal ring capable of producing a semi-elliptical pressure profile at the sealing lip. These requirements are met by acting on the cross sectional shape of the rings. A comparison between well-correlating theoretical, numerical, and experimental results is given for both the elastomeric components.


1986 - Analysis of a split ring inserted into a circular housing [Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract

The internal forces and contact zones of a split ring inserted into a circular housing are examined analytically, numerically, and experimentally. The mechanical components which can be likened to such a configuration are illustrated. The results obtained show that only one third of the ring periphery is in contact with the housing and that the effects of the shear strain on the contact pressure profile are appreciable.


1983 - L’importanza di alcuni parametri geometrici in guarnizioni elastomeriche di sezione rettangolare: studio numerico [Articolo su rivista]
Dragoni, Eugenio; G., Medri; Strozzi, Antonio
abstract

Con l'impiego di un programma di calcolo agli elementi finiti, viene esaminata l'influenza di alcuni parametri geometrici sull'andamento della pressione di contatto al bordo interno di una guarnizione dinamica, di sezione circa rettangolare, realizzata in materiale elastomerico. E' evidenziata la possibilità di modificare tale andamento in maniera più agevole di quanto possa avvenire negli anelli di tenuta O-Ring. E' proposta una formula empirica che fornisce l'influenza della curvatura della guarnizione sulla pressione di contatto massima. Essa consente di correggere i risultati ottenibili nell'ipotesi semplificativa che la sezione dell'organo di tenuta si trovi in condizioni di deformazione piana.


1983 - The importance of some geometrical parameters for rectangular section elastomeric seals: numerical study [Articolo su rivista]
Dragoni, E.; Medri, G.; Strozzi, A.
abstract

The influence of geometrical factors on the variation of contact pressure at the inner edge of an approximately rectangular cross section dynamic sealing ring was studied using finite-element techniques. The possibility of varying the contact pressure distribution between the seal and the moving element was demonstrated and shown to be easier than for O-rings. An empirical formula is proposed which allows the calculation of curvature on maximum contact pressure. This permits the correction of results obtained by assuming conditions of plans deformation of the seal cross-section, and is particularly useful for the study of wear. (C.C.B.)