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Andrea SPAGGIARI
Professore Associato
Dipartimento di Scienze e Metodi dell'Ingegneria
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Pubblicazioni
- A SYSTEM FOR ELECTRICAL SUPPLY TO ELECTRICAL AND/OR ELECTRONIC DEVICES
[Brevetto]
F., Garlinzoni; Spaggiari, Andrea; Spinella, Igor
abstract
An embodiment of the present invention provides a module (50) for electrical connection of electrical and/or electronic devices to a supply base (10), in which the module (50) comprises a casing (51 ) containing winding means of an extractable electric cable (52), which exhibits an end that exits from the casing (51 ) and to which a connector (53) is associated, which connector (53) is destined to couple with a supply socket of an electrical and/or electronic device; the casing (51 ) being conformed such as to removably insert in a housing (18) of the supply base (10), and in which the casing (51 ) comprises an electrical contact (55) connected to the extractable electric cable (52), which is destined to contact a corresponding electrical contact (19) of the supply base (10), when the casing (51 ) is inserted in the housing (18).
- 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.
2024
- Mechanical properties and failure modes of additively-manufactured chiral metamaterials based on Euclidean tessellations: an experimental and finite element study
[Articolo su rivista]
Mizzi, Luke; Simonetti, Arrigo; Spaggiari, Andrea
abstract
Purpose
The “chiralisation” of Euclidean polygonal tessellations is a novel, recent method which has been used to design new auxetic metamaterials with complex topologies and improved geometric versatility over traditional chiral honeycombs. This paper aims to design and manufacture chiral honeycombs representative of four distinct classes of 2D Euclidean tessellations with hexagonal rotational symmetry using fused-deposition additive manufacturing and experimentally analysed the mechanical properties and failure modes of these metamaterials.
Design/methodology/approach
Finite Element simulations were also used to study the high-strain compressive performance of these systems under both periodic boundary conditions and realistic, finite conditions. Experimental uniaxial compressive loading tests were applied to additively manufactured prototypes and digital image correlation was used to measure the Poisson’s ratio and analyse the deformation behaviour of these systems.
Findings
The results obtained demonstrate that these systems have the ability to exhibit a wide range of Poisson’s ratios (positive, quasi-zero and negative values) and stiffnesses as well as unusual failure modes characterised by a sequential layer-by-layer collapse of specific, non-adjacent ligaments. These findings provide useful insights on the mechanical properties and deformation behaviours of this new class of metamaterials and indicate that these chiral honeycombs could potentially possess anomalous characteristics which are not commonly found in traditional chiral metamaterials based on regular monohedral tilings.
Originality/value
To the best of the authors’ knowledge, the authors have analysed for the first time the high strain behaviour and failure modes of chiral metamaterials based on Euclidean multi-polygonal tessellations.
2023
- 3D printed passive end-effector for industrial collaborative robotic arms
[Articolo su rivista]
Nicolini, L.; Sorrentino, A.; Castagnetti, D.; Spaggiari, A.
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
- Design of isotropic 2D chiral metamaterials based on monohedral pentagonal tessellations
[Articolo su rivista]
Mizzi, Luke; Grasselli, Luigi; Spaggiari, Andrea; Gatt, Ruben; Farrugia, Pierre-Sandre; N Grima, Joseph
abstract
A novel class of transversely-isotropic metamaterials with the potential to exhibit a wide range of Poisson's ratios and stiffnesses is proposed in this work. These metamaterials, which also have the potential to exhibit auxetic behaviour, are formed through the chiralisation of 2D monohedral Euclidean pentagonal tessellations. Through Finite Element simulations and experimental testing on additively manufactured prototypes, we show that these systems can exhibit Poisson's ratios which encompass the entire range of transverse isotropicity, i.e. +1 to -1, and that the mechanical properties of these structures can be tailored considerably through variation of the geometric parameters without a loss of global symmetry and isotropy. The level of versatility observed in these new metamaterials exceeds by far that which is commonly found in traditional and well-known isotropic auxetic systems such as hexachiral honeycombs. In addition, analytical expressions pertaining to the geometric limits which define the realisability of this new class of auxetic metamaterials have also been derived and presented. The findings of this work demonstrate that pentagonal tessellations have considerable potential for the development of novel metamaterials and that the geometric constraints associated with transverse isotropy need not necessarily be an insurmountable barrier for the design of metamaterials with tailorable and versatile mechanical properties.
2023
- Development and prototyping of SMA-metamaterial biaxial composite actuators
[Articolo su rivista]
Mizzi, L; Hoseini, Sf; Formighieri, M; Spaggiari, A
abstract
Shape memory alloys (SMA) are excellent candidates for implementation in actuator systems due to their ability to recover their original shape after high-strain loading through a thermally-induced phase transition. In this work, we propose and develop a novel SMA-metamaterial actuator which is capable of exhibiting a reversible, global elongation in multiple directions induced by the unidirectional contraction upon heating of a single SMA component. This actuator consists of (a) an SMA component, (b) a bias component and (c) the metamaterial geometry, with each component having a distinct function: (a) actuation activation, (b) reversibility of actuation upon deactivation and (c) amplifying and re-directing the uni-directional SMA actuation globally throughout the actuator, respectively. A prototype actuator was designed and tested in various configurations over multiple activation/deactivation cycles in order to demonstrate the functionality and reusability of this system. Furthermore, a theoretical model which predicts the actuation stroke of the system on the basis of the material properties of the SMA and bias components as well as the geometry of the metamaterial system was developed and validated. The findings of this work demonstrate the considerable potential of SMA-metamaterial actuators for implementation in systems requiring a multi-axial actuation output.
2023
- Micro-scale graded mechanical metamaterials exhibiting versatile Poisson’s ratio
[Articolo su rivista]
Dudek, K. K.; Mizzi, L.; Iglesias Martínez, J. A.; Spaggiari, A.; Ulliac, G.; Gatt, R.; Grima, J. N.; Laude, V.; Kadic, M.
abstract
2022
- 3D printed passive end-effector for industrial collaborative robotic arms
[Poster]
Nicolini, Lorenzo; Sorrentino, Andrea; Castagnetti, Davide; Spaggiari, Andrea
abstract
2022
- Bio-inspired auxetic mechanical metamaterials evolved from rotating squares unit
[Articolo su rivista]
Sorrentino, Andrea; Castagnetti, Davide; Mizzi, Luke; Spaggiari, Andrea
abstract
This work investigates the mechanical response of bio-inspired titanium mechanical metamaterials with negative Poisson’s ratio evolved from rotating squares unit. The systems were designed and optimized using finite element analysis, with peculiar focus on the shape profile at the interconnection regions of the rotating units. The proposed solution consists of a combined auxetic rotating/chiral architecture with enhanced mechanical and topological properties which exhibits a 3% of global elastic strain of the structure and a Poisson’s ratio equal to -0.94. Numerical results are in good agreement with those obtained from experimental tests on a 3D printed Onyx prototype. We also examined the effect on the structural response of the metamaterial subject to off-axis mechanical conditions revealing the strong correlation to the geometrically-related anti-tetrachiral honeycombs. The work confirms the great potential of biologically inspired auxetic metamaterials, which can be designed to obtain tailored mechanical properties while improving the elastic strains capabilities of the system.
2022
- Evaluation of polymeric 3D printed adhesively bonded joints: effect of joint morphology and mechanical interlocking
[Articolo su rivista]
Spaggiari, Andrea; Favali, Filippo
abstract
Purpose
The purpose of this paper is to evaluate and exploit the combination of additive manufacturing polymeric technology and structural adhesives. The main advantage is to expand the maximum dimension of the 3D printed parts, which is typically limited, by joining the parts with structural adhesive, without losing strength and stiffness and keeping the major asset of polymeric 3 D printing: freedom of shape of the system and low cost of parts.
Design/methodology/approach
The materials used in the paper are the following. The adhesive considered is a commercial inexpensive acrylic, quite similar to superglue, applicable with almost no surface preparation and fast curing, as time constraint is one of the key problems that affects industrial adhesive applications. The 3D printed parts were in acrylonitrile butadiene styrene (ABS), obtained with a Fortus 250mc FDM machine, from Stratasys. The work first compares flat overlap joint with joints designed to permit mechanical interlocking of the adherends and then to a monolithic component with the same geometry. Single lap, joggle lap and double lap joints are the configurations experimentally characterized following a design of experiment approach.
Findings
The results show a failure in the substrate, due to the low strength of the polymeric adherends for the first batch of typical bonded configurations, single lap, joggle lap and double lap. The central bonded area, with an increased global thickness, never does fail, and the adhesive is able to transfer the load both with and without mechanical interlocking. An additional set of scarf joints was also tested to promote adhesive failure as well as to retrieve the adhesive strength in this application. The results shows that bonding of polymeric AM parts is able to express its full potential compared with a monolithic solution even though the joint fails prematurely in the adherend due to the bending stresses and the notches present in the lap joints.
Research limitations/implications
Because of the 3D printed polymeric material adopted, the results may be generalized only when the elastic properties of the adherends and of the adhesive are similar, so it is not possible to extend the findings of the work to metallic additive manufactured components.
Practical implications
The paper shows that the adhesives are feasible way to expand the potentiality of 3 D printed equipment to obtain larger parts with equivalent mechanical properties. The paper also shows that the scarf joint, which fails in the adhesive first, can be used to extract information about the adhesive strength, useful for the designers which have to combine adhesive and additive manufactured polymeric parts.
Originality/value
To the best of the researchers’ knowledge, there are scarce quantitative information in technical literature about the performance of additive manufactured parts in combination with structural adhesives and this work provides an insight on this interesting subject. This manuscript provides a feasible way of using rapid prototyping techniques in combination with adhesive bonding to fully exploit the additive manufacturing capability and to create large and cost-effective 3 D printed parts.
2022
- Novel chiral honeycombs based on octahedral and dodecahedral Euclidean polygonal tessellations
[Articolo su rivista]
Mizzi, L.; Spaggiari, A.
abstract
In this work, we explored the effect of ‘chiralisation’, i.e. the introduction of geometric chiral characteristics, on the mechanical properties of Euclidean polygonal tessellations containing octahedral or dodecahedral elements. This geometric transformation resulted in the design of three novel auxetic metamaterials which have the potential to exhibit large negative Poisson's ratios (ca. −1) coupled with high levels of in-plane isotropy. We have also examined the influence of the introduction of chiral nodes on the type of geometric arrangement (i.e. whether original or dual) of the base tessellation and also show how the extent of auxeticity may be controlled by tuning the geometric parameters of these systems. This work confirms the potential of Euclidean polygonal tessellations for the design of novel auxetic metamaterials and provides new insights into the deformation mechanisms and geometric conditions which impart this anomalous property.
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
- A Comparison between Rotating Squares and Anti-Tetrachiral Systems: Influence of Ligaments on the Multi-Axial Mechanical Response
[Articolo su rivista]
Mizzi, L; Sorrentino, A; Spaggiari, A; Castagnetti, D
abstract
Rotating unit systems are one of the most important and well-known classes of auxetic
mechanical metamaterials. As their name implies, when loaded, these systems deform
primarily via rotation of blocks of material, which may be connected together either directly
through joints (or ‘joint-like’ connections made by overlapping vertices of the rotating units)
as in the case of rotating rigid polygonal-unit systems or by ligaments/ribs as in the case of
chiral honeycombs. In this work, we used Finite Element Analysis to investigate the effect
which the presence/absence of ligaments has on the on-axis and off-axis mechanical
properties of these systems by analysing two of the most well-known structures which
characterise these two cases: the rotating square system and the anti-tetrachiral honeycomb. It
was found that while the presence of ligaments has a negligible effect on the on-axis
Poisson’s ratio of these systems, it has a profound influence on nearly all other mechanical
properties as well as on the off-axis loading behaviour. Systems with ligaments were found to
exhibit a high level of anisotropy and also a severely reduced level of stiffness in comparison
to their non-ligamented counterparts. On the other hand, the rotating square system suffers
from high localized stress-intensities and has a very low strain-tolerance threshold. In
addition, an optimized ‘hybrid’ geometry which is specifically designed to capture the best
features of both the anti-tetrachiral and rotating square system, was also analysed. This work
shows the main differences between ligament-based and non-ligament-based auxetic
structures and also highlights the importance of considering the off-axis mechanical response
in addition to the on-axis properties when investigating such systems.
2021
- A General Modeling Approach for Shock Absorbers: 2 DoF MR Damper Case Study
[Articolo su rivista]
Lozoya-Santos, J. D. -J.; Tudon-Martinez, J. C.; Morales-Menendez, R.; Sename, O.; Spaggiari, A.; Ramirez-Mendoza, R.
abstract
A methodology is proposed for designing a mathematical model for shock absorbers; the proposal is guided by characteristic diagrams of the shock absorbers. These characteristic diagrams (Force-Displacement, Velocity-Acceleration) are easily constructed from experimental data generated by standard tests. By analyzing the diagrams at different frequencies of interest, they can be classified into one of seven patterns, to guide the design of a model. Finally, the identification of the mathematical model can be obtained using conventional algorithms. This methodology has generated highly non-linear models for 2 degrees of freedom magneto-rheological dampers with high precision (2–10% errors).
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
- Chiralisation of Euclidean polygonal tessellations for the design of new auxetic metamaterials
[Articolo su rivista]
Mizzi, L.; Spaggiari, A.
abstract
Chiral honeycombs are one of the main classes of mechanical metamaterials with the potential to exhibit auxetic behaviour. In this work, we propose a new class of chiral metamaterials based on uniform Euclidean tessellations and their dual counterparts. In total, ten new structures were designed and analysed using Finite Element analysis under periodic boundary conditions, with eight of these systems showing the capability of possessing a negative Poisson's ratio. The relationship between the various geometric parameters defining the systems and the resultant mechanical properties was also studied. We show that ‘chiralisation’, i.e. introduction of chirality and rotational elements within the system, has the ability to transform even complex geometries, which in their original state possess a high positive Poisson's ratio, into auxetic metamaterials and hope that this work can act as a blueprint for the design of auxetic structures with novel topologies.
2021
- Mechanical strength of adhesively bonded joints using polymeric additive manufacturing
[Articolo su rivista]
Spaggiari, A.; Denti, F.
abstract
This paper investigates the combined use of one of the most widespread additive manufacturing techniques, fused deposition molding, with polymeric materials and structural adhesive. The aim is twofold: first, to enhance the adhesive performance exploiting the capability of the additive manufacturing to tailor the bonding surface of the adherend, and second to overcome one of the main limitations of 3D printing, i.e. the quite small printing volume, by means of adhesive bonding. Bonding multiple parts together without loss of performance could open new possibilities for this technology. The present research analyzes, by using a Design of Experiment technique, a wide set of single lap joints with two adhesives and seven different surface morphologies. The results highlight that the adhesive bonding does not undermine the load carrying capacity of the joints as well as their stiffness, and, in some cases, it causes a slight improvement of the peak force. The morphology of the surface plays only a small role in the performance of the system, since it cannot provide a strong mechanical interlocking of the parts due to peel stresses and because of the predominant effect of stress concentrations at the corners, which cause substrate failure.
2021
- Rotating squares auxetic metamaterials with improved strain tolerance
[Articolo su rivista]
Sorrentino, Andrea; Castagnetti, Davide; Mizzi, Luke; Spaggiari, Andrea
abstract
Rotating squares auxetic metamaterials have the peculiar feature of a negative Poisson’s ratio. This work proposes and examines how an innovative variable arcs fillet solution, at the interconnection regions between the rotating units, improves the structural response of a titanium alloy-based rotating squares metamaterial. Through a 2D finite element (FE) model of the auxetic structure, we investigated and optimized two fillet configurations: first, a double circular arcs profile; second, a combined elliptical and circular arc fillet. According to the FE results, the optimal configuration of the combined elliptical and circular arc fillet allows an overall 3% elastic strain of the metamaterial, with a Poisson’s ratio (PR) equal to ca. −1. In order to assess the deformation behavior of the proposed metamaterial, we performed a tensile test on a prototype of the optimal solution, 3D printed in Onyx material. The experimental displacement field of the specimen, measured through digital image correlation, exhibited excellent agreement with the FE predictions, with a PR equal to ca. −1 up to a 3% overall strain.
2021
- Stress concentrations in skew pressurized holes: A numerical analysis
[Articolo su rivista]
Mizzi, Luke; Spaggiari, Andrea
abstract
This work provides a numerical analysis of the stress concentration factor in an elastic solid containing non-aligned and non-concurrent circular holes subjected to an internal pressure. Using Finite Element Analysis, a variety of systems with a range of geometric configurations and loading conditions were simulated and the trends observed were analysed using a qualitative and statistical analysis in order to determine the correlation between these factors and the maximum stress concentration in these systems. Furthermore, simple empirical models were calibrated on the simulation results and used to plot reference graphs which may be employed to predict the stress concentration factor of these systems according to several geometric parameters and loading conditions. The numerical results and the empirical models presented here also show good agreement with previously derived analytical results based on 2D models and are expected to provide a useful tool for the designer of such systems especially for fatigue problems in fluid-power systems, where a straightforward evaluation of the stress concentration factor in pressurized hole systems is needed.
2020
- 2D auxetic metamaterials with tuneable micro-/nanoscale apertures
[Articolo su rivista]
Mizzi, L.; Salvati, E.; Spaggiari, A.; Tan, J. -C.; Korsunsky, A. M.
abstract
Modern advanced manufacturing technologies have made possible the tailored design and fabrication of complex nanoscale architectures with anomalous and enhanced properties, including mechanical and optical metamaterials; structured materials which are able to exhibit unusual mechanical and optical properties that are derived from their geometry rather than their intrinsic material properties. In this work, we fabricated for the first time an ultrathin 2D auxetic metamaterial with nanoscale geometric features specifically designed to deform in-plane by using focused-ion-beam milling to introduce patterned nano-slits within a thin membrane. The system was mechanically loaded in-situ and exhibited in-plane dominated deformation up to 5% tensile strain and a Poisson's ratio of −0.78. Furthermore, the porosity and aperture shape of the metamaterial have been shown to change considerably upon the application of strain, with pore dimensions showing a fourfold increase at 5% strain. This mechanically-controlled tuneability makes this metamaterial system an ideal candidate for use as a reconfigurable nano-filter or a nano light-modulator.
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
- Highly stretchable two-dimensional auxetic metamaterial sheets fabricated via direct-laser cutting
[Articolo su rivista]
Mizzi, L.; Salvati, E.; Spaggiari, A.; Tan, J. -C.; Korsunsky, A. M.
abstract
The design and production of multifunctional materials possessing tailored mechanical properties and specialized characteristics is a major theme in modern materials science, particularly for implementation in high-end applications in the biomedical and electronics industry. In this work, a number of metamaterials with perforated architectures possessing the ability to exhibit a plethora of 2D auxetic responses with negative Poisson's ratios ranging from quasi-zero to large negative values (lower than −3.5), stiffnesses, stretchability and surface coverage properties were manufactured. These systems were produced through the introduction of microstructural cuts in a rubber sheet using direct laser cutting, and analysed using a dual approach involving experimental tests and Finite Element Analysis. In addition to examining the mechanical properties of the perforated metamaterials, the influence of edge effects and material thickness on the deformation behaviour of these systems were investigated, with re-entrant systems shown to possess anomalous deformation profiles which are heavily dominated by the boundary regions. These findings highlight the effectiveness of this method for the fabrication of auxetic metamaterial sheets as well as the large variety of mechanical properties, deformation mechanisms and load responses which may be obtained through what may be effectively described as simply the introduction of patterned cuts in a thin sheet.
2020
- Lightweight mechanical metamaterials designed using hierarchical truss elements
[Articolo su rivista]
Mizzi, Luke; Spaggiari, Andrea
abstract
Rotating unit systems constitute one of the main classes of auxetic metamaterials. In this work, a new design procedure for lightweight auxetic systems based on this deformation mechanism is proposed through the implementation of a hierarchical triangular truss network in place of a full block of material for the rotating component of the system. Using numerical simulations in conjunction with experimental tests on 3D printed prototypes, the mechanical properties of six types of auxetic structures, which include a range of rotating polygons and chiral honeycombs, were analysed under the application of small tensile loads. The results obtained show that there is almost no difference in the Poisson's ratios obtained from the regular, full structures and the ones made from triangular truss systems despite the latter, in some cases, being 80% lighter than the former. This indicates that these systems could be ideal candidates for implementation in applications requiring lightweight auxetic metamaterial systems such as in the aerospace industry.
2020
- Magnetorheological elastomers characterization under shear loading up to failure: A magneto-mechanical multivariate analysis
[Articolo su rivista]
Spaggiari, A.; Bellelli, A.
abstract
This work analyses the shear behavior of magnetorheological elastomers (MRE), a class of smart materials which presents interesting magneto-mechanical properties. In order to determine the effect of several variables at a time, a design of experiment approach is adopted. A set of several samples of MRE was manufactured, by varying the weight fraction of ferromagnetic material inside the viscoelastic matrix and the isotropicity of the material, by adding an external magnetic field while the elastomeric matrix was still liquid. The mechanical behavior of each sample was analyzed by conducting cyclic tests at several shear rates, both with and without an external magnetic field. Moreover, in order to estimate the maximum shear stress, the specimens were loaded monotonically up to failure. Shear stiffness, maximum shear stress and specific dissipated energy were calculated on the basis of the experimental data. The results were analyzed using an Analysis of Variance (ANOVA) to assess the statistical influence of each variable. The experimental results highlighted a strong correlation between the weight fraction of ferromagnetic material in each sample and its mechanical behavior. Moreover, the dissipated energy of the MRE drops down when the magnetic field stiffens the behavior or the shear rate increases. The ultimate failure shear stress is strongly affected by the external magnetic field, increasing it by nearly 50%. The ANOVA on the results provides a simple phenomenological model is built for each output variable and it is compared with the experimental tests. These models produce a fast and fairly accurate prediction of each analyzed response of the MRE under various shear rates and applied magnetic fields.
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
- Analytical design and optimization of an automotive rubber bushing
[Articolo su rivista]
Rivas-Torres, J.; Tudon-Martinez, J. C.; Lozoya-Santos, J. D. -J.; Ramirez-Mendoza, R. A.; Spaggiari, A.
abstract
The ride comfort, driving safety, and handling of the vehicle should be designed and tuned to achieve the expectations defined in the company's design. The ideal method of tuning the characteristics of the vehicle is to modify the bushings and mounts used in the chassis system. To deal with the noise, vibration and harshness on automobiles, elastomeric materials in mounts and bushings are determinant in the automotive components design, particularly those related to the suspension system. For most designs, stiffness is a key design parameter. Determination of stiffness is often necessary in order to ensure that excessive forces or deflections do not occur. Many companies use trial and error method to meet the requirements of stiffness curves. Optimization algorithms are an effective solution to this type of design problems. This paper presents a simulation-based methodology to design an automotive bushing with specific characteristic curves. Using an optimum design formulation, a mathematical model is proposed to design and then optimize structural parameters using a genetic algorithm. To validate the resulting data, a finite element analysis (FEA) is carried out with the optimized values. At the end, results between optimization, FEA, and characteristic curves are compared and discussed to establish the correlation among them.
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
- 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
- Magneto-mechanical characterization of magnetorheological elastomers
[Articolo su rivista]
Bellelli, A.; Spaggiari, A.
abstract
This work analyses the properties and the magneto-mechanical characteristics of magnetorheological elastomers, a class of smart materials not yet broadly investigated. First, set of several samples of this material was manufactured, each one characterized by a different percentage of ferromagnetic material inside the viscoelastic matrix. The specimens were manufactured in order to create isotropic and anisotropic configurations, respectively, with randomly dispersed ferromagnetic particles or with an aligned distribution, obtained through and external magnetic field. Then, the mechanical behaviour of each sample was analysed by conducting a compression test, both with and without an external magnetic field. Moreover, a three-point bending test was also performed on the same specimens. Stiffness, deformation at maximum stress and specific energy dissipated were calculated based on the experimental data. The results were analysed considering the mechanical responses, and an analysis of variance was carried out in order to assess the statistical influence of each variable. The experimental results highlighted a strong correlation between the percentage of ferromagnetic material in each sample and its mechanical behaviour. The anisotropicity of the material, aligned in columnar structures, also affects the stiffness measured in the compression test, while the external magnetic field’s main contribution is to reduce the samples’ maximum deformation. Using analysis of variance results as guidelines, we built a simple phenomenological model which produces quite reliable predictions regarding the mechanical response of the magnetorheological elastomers under compressive stress.
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
- Shear behaviour of magnetorheological elastomers: Viscoelastic and magnetorheological properties
[Relazione in Atti di Convegno]
Spaggiari, A.; Bellelli, A.
abstract
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 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
- Characterization Of Commercial Magnetorheological Fluids At High Shear Rate: Influence Of The Gap
[Articolo su rivista]
Spaggiari, Andrea; Golinelli, Nicola
abstract
This paper reports the experimental tests on the behaviour of a commercial MR fluid at high shear rates and the effect of the gap. Three gaps were considered at multiple magnetic fields and shear rates. From an extended set of almost two hundred experimental flow curves, a set of parameters for the apparent viscosity are retrieved by using the Ostwald de Waele model for non-Newtonian fluids. It is possible to simplify the parameter correlation by making the following considerations: the consistency of the model depends only on the magnetic field, the flow index depends on the fluid type and the gap shows an important effect only at null or very low magnetic fields. This lead to a simple and useful model, especially in the design phase of a MR based product. During the off state, with no applied field, it is possible to use a standard viscous model. During the active state, with high magnetic field, a strong non-Newtonian nature becomes prevalent over the viscous one even at very high shear rate; the magnetic field dominates the apparent viscosity change, while the gap does not play any relevant role on the system behaviour. This simple assumption allows the designer to dimension the gap only considering the non-active state, as in standard viscous systems, and taking into account only the magnetic effect in the active state, where the gap does not change the proposed fluid model.
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
- Effect of Temperature on the Dynamic Response of Adhesively Mounted Accelerometers
[Articolo su rivista]
Spaggiari, Andrea; Cocconcelli, Marco
abstract
This paper focuses on the effect of temperature on the frequency response function (FRF) of three different structural adhesives; namely a two component methylmethacrylate (HBM X60), a modified silane (Terostat 939) and a cyanoacrylate (Loctite 454). The structural adhesives are commonly used in vibration analysis to mount accelerometers on structures or machines. The stiffness of the adhesive can influence the response function on large frequency band, affecting the proportional excitation between the structure and the accelerometer. In the “system structure + adhesive + accelerometer”, the adhesive may acts like a filter between the source and the sink of vibrations. A variation of the dynamic response of the filter could lead to an erroneous analysis. The authors already investigated the relation between the frequency response function and operating conditions of the test. This paper expands the research by considering the temperature effect in order to depict a complete picture of the adhesive behavior on dynamic response of an accelerometer. A design of experiments (DOE) approach was used to test two bonded aluminum bases at different levels of temperature and frequency of the external sinusoidal excitation, supplied by an electromagnetic shaker. The results clearly demonstrate that the adhesive is not able to change the system response, therefore the signal transmission is good in the entire range of temperature regardless the adhesive chosen.
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
- 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.
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
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
- Experimental Validation of a Novel Magnetorheological Damper with Internal Pressure Control
[Articolo su rivista]
Golinelli, Nicola; Spaggiari, Andrea
abstract
In the present article, we have investigated the behaviour of magnetorheological fluids under a hydrostatic pressure of up to 40 bar.We have designed, manufactured and tested a magnetorheological damper with a novel architecture, which provides the control of the internal pressure. The pressurewas regulated by means of an additional apparatus connected to the damper that acts on the fluid volume. The magnetorheological damper was tested under sinusoidal inputs and with several values for the magnetic field and internal pressure. The results show that the new architecture is able to work without a volume compensator and bear high pressures. On the one hand, the influence of the hydrostatic pressure on the yield stress of the magnetorheological fluids is not strong, probably because the ferromagnetic particles cannot arrange themselves into thicker columns. On the other hand, the benefits of the pressure on the behaviour of the magnetorheological damper are useful in terms of preventing cavitation.
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
- Mounting of accelerometers with structural adhesives: experimental characterization of the dynamic response
[Articolo su rivista]
Cocconcelli, Marco; Spaggiari, Andrea
abstract
The use of accelerometers to monitor the vibrations of either complex machinery or simple components 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 an 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 article 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 products have been experimentally compared to assess their transmissivity and the results are reported in this article. A two-component methylmethacrylate (HBM X60), a modified silane (Terostat 737), and a cyanoacrylate (Loctite 454) adhesive have been used to join two aluminum bases, one connected to an accelerometer and the other to the head of electromagnetic shaker. A design of experiment (DOE) approach was used to test the system at several levels of amplitude and frequency of the external sinusoidal excitation supplied by the shaker.
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
- 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 Characterization of Magnetorheological Fluids Using a Custom Searle Magnetorheometer: Influence of the Rotor Shape
[Articolo su rivista]
Golinelli, Nicola; A., Becnel; Spaggiari, Andrea; N., Wereley
abstract
In the present work we investigated the behaviour of magnetorheological fluids (MRFs) by means of a custom Searle magnetorheometer. The Searle measuring system is composed of an outer stationary cylinder and an inner cylinder driven by a motor. The MR fluid is placed in between the two concentric cylinders. While the bob is rotating, the fluid transmits a torque to the outer cylinder, which is related to the velocity profile through the gap and the magnetic field applied. In particular, we wanted to assess the influence of different bob shapes on the shear stress-shear rate curves. Indeed, a non-circular cross section causes cyclic variations on the gap thickness and consequently can squeeze the active MR fluids causing the formation of thicker columns and higher values of shear stresses. This phenomenon known as squeeze-strengthen effect can be exploited to achieve higher energy absorption on magnetorheological devices like brakes and clutches. Two different cross sections were taken into account and then compared to the cylindrical one: elliptical and quadrilobate. In both cases, the gap size varies from 0.25 mm to 0.75 mm. The experimental results showed that with the new bob shapes, the squeeze-strengthen effect does not occur. However, using the elliptical and quadrilobate bobs changes in the slope of the flow curves has been measured. This may suggest that the post yield viscosity can be influenced by more complex factors like non-uniform magnetic field or hydrodynamic phenomena. Further studies such as 3D magnetic simulation and CFD analysis will be taken into account to explain the new phenomena brought up in this work.
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
- 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
- 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 experimental validation of a novel magnetorheological damper with internal pressure control
[Relazione in Atti di Convegno]
Golinelli, N.; Spaggiari, A.
abstract
In the present paper we investigated the behaviour of magnetorheological fluids (MRFs) under a hydrostatic pressure up to 40 bar. We designed, manufactured and tested a magnetorheological damper (MRD) with a novel architecture which provides the control of the internal pressure. The pressure was regulated by means of an additional apparatus connected to the damper that acts on the fluid volume. The MRD was tested under sinusoidal inputs and with several values of magnetic field and internal pressure. The results show that the new architecture is able to work without a volume compensator and bear high pressures. On the one hand, the influence of hydrostatic pressure on the yield stress of MRFs is not strong probably because the ferromagnetic particles cannot arrange themselves into thicker columns. On the other hand, the benefits of the pressure on the behaviour of the MRD are useful in terms of preventing cavitation.
2015
- Design of a novel magnetorheological damper with internal pressure control
[Articolo su rivista]
Golinelli, Nicola; Spaggiari, Andrea
abstract
In this work we designed and manufactured a novel magnetorheological (MR) fluid damper with internal
pressure control. Previous authors’ works showed that the yield stress
τ
B of MR fluids depends both on the magnetic field
intensity and on the working pressure. Since the increase of the magnetic field intensity is limited by considerations like
power consumption and magnetic saturation, an active pressure
control leads to a simple and efficient enhancement of the
performances of these systems. There are three main design
topics covered in this paper about the MR damper design.
First, the design of the magnetic circuit; second the desi
gn of the hydraulic system and third the development of an
innovative pressure control apparatus. The design approach
adopted is mainly analytical and provides the equations
needed for system design, taking into
account the desired force and stroke as
well as the maximum external dimensions.
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
- 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)
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
- 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
- Experimental dynamic characterization of magnetorheological Silly Putty
[Relazione in Atti di Convegno]
Golinelli, Nicola; Spaggiari, Andrea
abstract
In the present study the dynamic behavior of a commercial silicon based magnetorheological elastomer was investigated. This material presents a non-newtonian characteristics whose response depends on the rate at which it is stressed. The damping properties
under dynamic load of these materials have been studied in technical literature, while the
influence of the magnetic field on the dynamic shear modulus is unknown. Hence, the aim
of this paper is to test the change in dynamic shear modulus under a sinusoidal strain with
amplitude of 2 and 4 mm, cyclic frequency of 4 , 8 and 12 Hz and magnetic flux density of 0
and 0.2 T. The approach adopted in this work was based on a design of experiment technique in order to evaluate the influence of the three variables involved and their interactions.
The results highlights a strong dependence of the dynamic shear modulus on the strain rate
while the influence of the magnetic field is weak, especially at the higher frequencies.
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
- 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
- Progettazione di uno smorzatore a fluido magnetoreologico con controllo della pressione
[Relazione in Atti di Convegno]
Golinelli, Nicola; Genta, Giovanni; Spaggiari, Andrea
abstract
Il presente lavoro riguarda la progettazione di uno smorzatore a fluido magnetoreologico (MR) che
prevede la possibilità di controllarne la pressione interna. Precedenti studi degli autori, hanno
evidenziato che la tensione di primo distacco τB di un fluido MR aumenta in funzione non solo
dell'intensità del campo magnetico, ma anche della pressione alla quale si trova. Poiché l'aumento del
campo magnetico è limitato da considerazioni quali la potenza dissipata e la saturazione magnetica,
regolare in maniera attiva la pressione, consente di potenziare le prestazioni di tali sistemi in modo
semplice ed efficiente. Il lavoro descrive la progettazione di dettaglio delle principali funzionalità del
sistema: dimensionamento del circuito magnetico, progettazione del sistema idraulico e sviluppo del
sistema di controllo della pressione. L’approccio è prevalentemente analitico, al fine di fornire le
equazioni necessarie per un dimensionamento di massima del sistema. La metodologia sviluppata
fornisce una traccia per un corretto approccio alla progettazione di un sistema smorzante a fluido MR
sulla base delle caratteristiche di forza e corsa desiderate e degli ingombri disponibili.
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.
2013
- Changes in Length during Free End Torsion of Nitinol Rods
[Relazione in Atti di Convegno]
J. M., Walker; M., Elahinia; Spaggiari, Andrea
abstract
In this experiment, the axial deformation caused during pure torsion in investigated. It was found that axial strains approaching 0.5% are generated when maximum torsional shear strain at the outer radius is 16%. The axial and torsional strains are fully recovered upon unloading. Further study of the micromechanical mechanisms at play is needed to advance the understanding of Nitinol behavior and allow for greater accuracy in modeling and actuator development. Clearly, “pure” torsion (and, conversely, “pure” tension) modes of deformation are impossible to achieve as the two modes are deeply coupled.
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 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
- 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
- Properties and applications of Magnetorheological fluids
[Articolo su rivista]
Spaggiari, Andrea
abstract
This brief introduction describes the mechanical, rheological and magnetic properties of the magnetorheological (MR) fluids for feasible engineering applications. The typical modes of exploiting this technology are shown and discussed. An increasing number of industrial applications illustrate how the MR fluids peculiar properties may be used to provide optimal performance in semi active damping and dissipative devices.
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
- 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
- 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
- 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
- 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
- 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.
2012
- The influence of void morphology and loading conditions on deformation and failure of porous polymers: A combined finite-element and analysis of variance study
[Articolo su rivista]
Spaggiari, Andrea; N., O'Dowd
abstract
This paper presents a combined finite-element and analysis of variance study of polymeric materials containing spherical and ellipsoidal voids. The approach adopted simulates an infinite medium of the material containing an array of voids, using three dimensional finite element analysis. A D-optimal design procedure is used to combine five normalized variables: the stress triaxiality, the ellipsoid ratio, the initial void volume fraction, the void arrangement (number of voids), and the loading angle. A ductile epoxy resin is chosen as reference material and the failure criterion considered is the plasticization of the ligament between two adjacent cells. Results are provided for the normalized equivalent stress and strain at failure, and for the void growth rate. The influence of the variables on the outputs is estimated showing that the response is influenced mainly by stress triaxiality, void volume fraction and void arrangement, in that order.
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
- 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
- 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
- Resistenza in modo misto di adesivo in strato sottile: caratterizzazione sperimentale attraverso un nuovo provino tubolare
[Relazione in Atti di Convegno]
Spaggiari, Andrea; Castagnetti, Davide
abstract
Il presente lavoro riguarda la caratterizzazione di adesivi in strato sottile sottoposti a condizioni di caricamento uniforme e multiassiale. Si utilizza un provino tubolare incollato testa a testa, precedentemente sviluppato dagli autori, che realizza tensioni uniformi nello strato adesivo, sia normali sia tangenziali. L’analisi delle tensioni nel provino mostra che oltre alla tensione assiale e tangenziale, dovute al carico, si instaurano componenti di tensione radiale e circonferenziale dovute all'effetto effetto Poisson combinato al vincolamento prodotto dagli aderendi. Ne deriva un forte stato di triassialità nell'adesivo. Le prove sperimentali, che considerano cinque differenti condizioni di carico mostrano che l'adesivo ha un comportamento migliore a taglio che a trazione. Le tensioni di rottura ricavate sono interpretate utilizzando sia criteri di letteratura sia un criterio sviluppato ad-hoc, che ben si presta all'individuazione di una tensione ideale.
2010
- Caratterizzazione di provini tubolari incollati: regolarizzazione della tensione normale mediante gole schermo
[Relazione in Atti di Convegno]
Castagnetti, Davide; Spaggiari, Andrea
abstract
This paper experimentally investigates bonded tubular specimens, which exhibit uniform stress distribution within the adhesive layer. The mechanical properties of a thin adhesive layer, subject to a singularity-free stress distribution, are immediately applicable to the description of real joint behavior. The proposed specimen consists of a tubular butt joint, with circumferentially machined stress-relief grooves adjacent to the adherend-adhesive interface. The groove geometry, simplified with respect to a previous numerical work from the author, allows significant reduction in edge effects - as confirmed by finite element analyses. The experimental campaign involves three variables: presence of the grooves, adherend material and adhesive thickness. The presence of stress-relief grooves gives higher failure loads for steel adherends, whilst aluminum adherends show strength reduction as adhesive thickness increases.
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
- 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
- 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
- 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
- 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
- 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.
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
- 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.
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
- 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.