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Davide CASTAGNETTI
Professore Ordinario
Dipartimento di Scienze e Metodi dell'Ingegneria
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Pubblicazioni
2024
- Dispositivo antivibrante comprendente un elemento
elastomerico deformabile elasticamente con
proprieta’ piezoelettriche
[Brevetto]
Nicolini, L.; Castagnetti, D.; Sorrentino, A.
abstract
La presente invenzione riguarda l’ambito dei dispositivi antivibranti e in particolare un dispositivo antivibrante comprendente un elemento elastomerico deformabile elasticamente e avente proprietà piezoelettriche. L’invenzione riguarda, inoltre, un metodo di fabbricazione di tale dispositivo antivibrante.
2024
- Geometrically tunable architected materials designed from prismatic rotating units
[Articolo su rivista]
Sorrentino, Andrea; Castagnetti, Davide
abstract
An exotic property of some mechanical metamaterials is their negative Poisson's ratio which is of interest for many applications, from biomedical to aeronautic. This work investigates how a mechanical metamaterial evolved from equilateral triangular rotating prisms changes its Poisson's ratio according to the orientation of the reference units with respect to the tensile loading direction (aligned or 45° rotated, respectively). Different configurations are investigated through kinematic analysis, which describes hinged couplings in the linked vertices of the prisms. The best configurations emerging from the kinematic analysis were converted into chiral architectures: Three-dimensional printed physical prototypes were tested under uniaxial compression and the results compared with finite element predictions. The experimental results showed a remarkably different deformation behaviour between the metamaterial designs, with a good qualitative agreement with the numerical simulations. High values of auxetic response are observed for the configuration whose cells are aligned with the load, while a low auxetic and less sensitive geometry variation behaviour was observed for the rotated cell architecture. This rotated configuration also exhibits the significant achievement of mechanical properties which are approximately independent of the geometry variations.
2024
- Stress distributions around the interference fit between a round pin and a perforated finite plate
[Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract
2023
- 3D printed passive end-effector for industrial collaborative robotic arms
[Articolo su rivista]
Nicolini, L.; Sorrentino, A.; Castagnetti, D.; Spaggiari, A.
abstract
2023
- A SOFT FREE SHAPE CASTED PIEZOELECTRIC ELASTOMER
[Relazione in Atti di Convegno]
Nicolini, Lorenzo; Sorrentino, Andrea; Castagnetti, Davide
abstract
Piezoelectric materials are largely used for sensing and energy harvesting
applications as simple and reliable solutions from piezoelectric accelerometers to vibration
energy harvesters. Most of the applications utilize either piezoceramic materials, exploiting
their high piezoelectric coefficients, or piezoelectric polymers, thanks to their soft response, in
applications where finite displacements are needed.
Actual piezoceramic materials are expensive, brittle and available only in standard and flat
shapes. On the other hand, piezoelectric polymers, like PVDF, are too stiff for many
applications that need softer solutions.
This work presents the study, development and validation of a new soft piezoelectric elastomer,
which can be designed in free shape through a casting process. This study identified a novel
formulation of a cold polymerizable silicone-based elastomer, enhanced with BaTiO3 (barium
titanate) powder.
A detailed procedure of fabrication was defined involving the mixture preparation, curing and
polarization phases of the solution. To obtain disk specimen, we designed and used a dedicated
3D printed acrylonitrile butadiene styren (ABS) mold with a cylindrical cavity. The mold
houses two steel electrodes for the polarization through a high voltage DC converter. This
allows to perform the polarization process at the same time of the polymerization in order to
easily orientate polar BaTiO3 particles in the liquid solution until the polymerization is
completed.
To experimentally evaluate the effect of the main variables on the fabrication procedure and
the piezopolymer response, we conducted a systematic test plan. Specifically, we investigated
both the effect of barium titanate powder concentration and voltage polarization level on the
morphological appearance of the specimen and on its piezoelectric properties. Two quasistatic
cyclic compression tests at different strain levels were performed on small cylindrical samples
cut by the specimens, registering the mechanical behaviours and electric voltage output signals.
The piezoelectric coefficient d33, calculated for all the configurations and for both strain levels,
highlights a remarkable performance of the proposed piezoelectric polymer.
2023
- A soft piezoelectric elastomer with enhanced piezoelastic response
[Articolo su rivista]
Nicolini, Lorenzo; Sorrentino, Andrea; Castagnetti, Davide
abstract
This work aims to study, develop, and validate a soft piezo-polymer with enhanced piezo-elastic
response and easy castable in a free shape through a single and easy process. The work
identified a novel formulation for soft piezopolymers based on ambient temperature
polymerizable silicone rubber, easily fabricable in 3D printed plastic moulds. Combining
polymerizable silicone with a barium titanate (BaTiO3) ceramic powder and defining a detailed
fabrication procedure of casting, curing and high voltage poling, we defined how to obtain a
promising soft piezoelectric elastomer for countless sensing applications. This study includes
information about the mould design used to realize, cure and polarize cylindric elastomeric
specimens. This piezopolymer stands out for its flexibility, softness, easy fabrication at ambient
temperature and obtainability in multiple shapes and bulky 3D geometries. Finally, we
investigated different configurations of the piezopolymer formulation analysing the powder
concentration and voltage polarization effects over the mechanical, piezoelectric and
morphological characteristics. The specimens exhibit a high induced polarization d33 with
values up to 22.5 pC N−1
, comparable with poled β-phase polyvinylidene difluoride. We finally
underlined limits encountered in the most extreme configurations.
2023
- A wideband low frenquency 3D printed electromagnetic energy harvester based on orthoplanar springs
[Articolo su rivista]
Nicolini, Lorenzo; Castagnetti, Davide
abstract
Electromagnetic energy harvesters are commonly known for their high performances in terms of power output
conversion, and they are suitable for low frequency environmental vibrations.
This work reports the study, design, development and experimental validation of a new extremely compact,
low frequency, electromagnetic energy harvester based on two stacked ortho-planar springs, which exploits a
promising magnets disposition.
The device is composed by two stacked ortho-planar springs connected externally by a rigid frame. The two
internal moving parts are connected to each other by a central pivot where an array of magnets is fixed on in a
peculiar disposition: a half has a magnetic field directed upward, while the other half directed downward. A
copper coil is wound into a housing fixed on the external frame. It comes a central massive cursor that axially
moves, exploiting the springs compliance, relatively to the external frame.
The prototype was almost completely realized by using Filament Fused Fabrication (FFF) additive
manufacturing process in Onyx material, carbon fibre reinforced nylon.
In the experimental assessment an oscillating excitation was applied on the external frame in multiple linear
sweep frequency tests with different amplitude signals. The experimental validation shows a large bandwidth,
from 10 to 30 Hz, and consistent output voltage and power signals.
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
- Novel polyhedral mechanical metamaterial exhibiting negative Poisson's ratio
[Articolo su rivista]
Sorrentino, Andrea; Castagnetti, Davide
abstract
The work presents a novel polyhedral mechanical metamaterial based on rotating triangular prisms connected by their corners, which possesses the ability to attain large values of negative Poisson's ratio (NPR). Through a kinematic model of the proposed rotating structure, we evaluate the auxeticity of the system by varying the geometrical parameters of the polyhedrons composing the elementary cell of the structure. The kinematic results highlight the peculiar NPR of the system, whose values are nearly constant over significant strain ranges. Focusing on the most promising auxetic mechanisms we designed chiral architectures that replace the ideal hinges at the corners with curved-shape ligaments, and validated these configurations through 3D printed specimens. The specimens were tested under uniaxial compression and simulated through finite element analyses. Experimental results exhibited an excellent agreement with computational predictions in terms of elastic modulus and auxeticity, showing a value of Poisson's ratio up to -1.3 for one of the designs. Our findings demonstrate the highly auxetic property of rotating polyhedral systems, which allow the design of novel architected materials useful, for example, in biomechanical applications.
2023
- Protesi vertebrale
[Brevetto]
Sorrentino, A.; Castagnetti, D.
abstract
Il brevetto descrive una nuova protesi vertebrale custom made altamente porosa e leggera, in metamateriale auxetico biocompatibile, realizzata in titanio tramite un processo di manifattura additiva ottimizzato, ed impiegabile come elemento di sostituzione ossea in ambito oncologico a seguito di un intervento di vertebrectomia totale.
2023
- RULLO SENSORIZZATO CON RIVESTIMENTO IN ELASTOMERO PIEZOELETTRICO
[Relazione in Atti di Convegno]
Nicolini, Lorenzo; Castagnetti, Davide
abstract
This study reports the realization of a sensed roller with a solid piezoelectric elastomer tread, realized and studied in a previous work of the authors. The device consists in a dedicated metallic rim externally covered by a thick layer of solid elastomer with piezoelectric properties, based on liquid polymerizable silicone combined with 50% by weight of piezoelectric ceramic powder BaTiO3. This application exploits the characteristics of the studied material to provide a voltage signal between the rim wheel and an electrically conductive rolling plain, in order to achieve information about position, velocity and vertical load index applied on the roller. This study describes the device’s working conceptual model, the realization procedure through casting in a dedicated mould and curing process of the external tread, and the testbench set up and working tests of the device.
2023
- Three-dimensional auxetic mechanical metamaterials based on triangular prism architecture
[Relazione in Atti di Convegno]
Sorrentino, A.; Castagnetti, D.
abstract
2023
- Un guscio vertebrale in meta-biomateriale auxetico chirale
[Relazione in Atti di Convegno]
Sorrentino, A.; Genovese, K.; Nicolini, L.; Castagnetti, D.
abstract
Il lavoro si focalizza sulla progettazione, simulazione, prototipazione e convalida sperimentale di un’innovativa struttura a guscio in metamateriale auxetico chirale, realizzata in lega di titanio in stampa 3D. La struttura presenta una morfologia simile a quella delle ossa vertebrali corticali umane e un valore del coefficiente di Poisson negativo. Mediante un sistema di correlazione digitale di immagini (stereo-DIC), il lavoro misura il campo di spostamento e di deformazione del metamateriale sottoposto ad una prova di compressione quasi-statica, e confronta i risultati con quelli ottenuti da un modello 3D agli elementi finiti della struttura. La microstruttura della superficie del prototipo è stata analizzata utilizzando un microscopio elettronico a scansione SEM. L’architettura di metamateriale proposta si distingue per un elevato comportamento auxetico, rimane elastica fino ad uno schiacciamento della struttura del 3%, e si caratterizza per una rigidezza simile a quella dell’osso vertebrale umano.
2022
- 3D printed passive end-effector for industrial collaborative robotic arms
[Poster]
Nicolini, Lorenzo; Sorrentino, Andrea; Castagnetti, Davide; Spaggiari, Andrea
abstract
2022
- A tunable multi-arm electromagnetic pendulum for ultra-low frequency vibration energy harvesting
[Articolo su rivista]
Nicolini, Lorenzo; Castagnetti, Davide; Sorrentino, Andrea
abstract
Autonomous electronic devices and sensors are essential to reduce expensive maintenance,
increasing job security and reliability, avoiding battery replacements and wired systems.
Industrial systems and civil structures vibrate dissipating an important amount of energy that
can be harvested to power small devices. This work continues and extends a previous work from
the authors (Castagnetti 2019 Meccanica 54 749–60). Here we improved that initial
configuration by proposing a tunable multi-arm electromagnetic pendulum for ultra-low
frequency vibrations energy harvesting. This configuration features five electromagnetic
converters and a magnetic spring, each supported by a pendulum arm with different length:
when excited by external vibrations, this six arms frame is free to oscillate around a central
pivot. The paper starts from conceptual design, includes a detailed multiphysics dynamic
simulation implemented with Matlab Simscape software, presents the prototype development
through three-dimensional printing and experimental validation. Systematic experimental tests
investigated different pendulum configurations for three stiffness levels of the magnetic spring
and confirmed both the ultra-low frequency response (from 2 to 10 Hz), as predicted by the
dynamic simulation, and the good voltage and power outputs. Specifically, for the higher
stiffness of the magnetic spring, corresponding to an oscillation frequency of about 9.5 Hz, the
power output was up to 8.4 mW and the output voltage of about 2 Volt.
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
- Electrostatic pull‑in instability for tweezer architectures
[Articolo su rivista]
Bianchi, G.; Sorrentino, A.; Radi, E.; Castagnetti, D.
abstract
The work investigates the static pull-in instability of electrostatically actuated tweezers with tubular electrodes. At a critical voltage, named pull-in voltage, the attraction force between the two electrodes causes the unexpected pull-in of the tubular cantilevers, which defines the limit of the elastic region of the system, especially in the case of carbon-nano tubes (CNTs) applications. The work aims to evaluate the lower and upper bounds of pull-in parameters of a tweezer device with the use of an accurate analytical model which allows to calculate the critical voltage and deflection values of the system. In order to assess the accuracy of the analytical model, we built a prototype and measured the critical pull-in voltage for different geometrical configurations of the device. The experimental results confirm the analytical predictions, with a maximum relative difference between the experimental and analytical values of the pull-in voltage lower than 13%.
2022
- Metamateriale auxetico
[Brevetto]
Sorrentino, A.; Castagnetti, D.
abstract
La presente invenzione concerne un'innovativa struttura cellulare in metamateriale auxetico, i.e. a coefficiente di Poisson negativo.
2022
- Metamateriale auxetico a strutture poliedriche rigide rotanti
[Abstract in Atti di Convegno]
Sorrentino, A.; Castagnetti, D.
abstract
Il presente lavoro descrive la progettazione e validazione sperimentale di uno nuovo metamateriale auxetico tridimensionale (3D) ad elementi rigidi rotanti. I metamateriali auxetici sono strutture di origine artificiale che possiedono un valore del coefficiente di Poisson negativo. Tali strutture presentano proprietà meccaniche estreme e funzionalizzate che dipendono dalla loro peculiare architettura e dalle proprietà elastiche del materiale con le quali vengono realizzate. Le loro funzionalità avanzate non si limitano al solo coefficiente di Poisson negativo, ma includono, tra le altre, un’elevata rigidezza a taglio e resistenza a rottura. I metamateriali auxetici comprendono i sistemi rotanti, le strutture chirali, le strutture rientranti e le strutture pieghevoli. Nello specifico, le strutture ad elementi rotanti consistono di unità rigide collegate tramite elementi cedevoli (equivalenti a cerniere), ordinate secondo una specifica distribuzione topologica. Nel caso di architetture piane (2D), queste sono formate da quadrati, triangoli, rombi, parallelogrammi e da figure a forma irregolare. Analogamente, le strutture rotanti 3D possono essere progettate utilizzando l’elemento base di una geometria piana, realizzando così un metamateriale tridimensionale in grado di manifestare un comportamento auxetico. In questo lavoro viene presentato un originale metamateriale auxetico a poliedri rigidi rotanti. La cella elementare della soluzione proposta è formata da otto prismi a base triangolare, collegati mediante i loro vertici. Tre sono le fasi del lavoro: analisi cinematica, convalida sperimentale e analisi strutturale. In particolare, l’analisi cinematica, svolta su modelli solidi 3D della struttura, ha permesso di valutare la risposta cinematica del metamateriale per differenti configurazioni geometriche della cella elementare: la struttura presenta un comportamento anisotropo ed un’elevata risposta auxetica. Al fine di convalidare questi risultati, sono stati realizzati in stampa 3D con materiale Onyx, i prototipi delle geometrie più promettenti. Queste consistono di unità a poliedri semi-rigidi collegati tramite legamenti di forma variabile: le prove di caratterizzazione svolte hanno confermato valori del coefficiente di Poisson negativi fino ad un minimo di -1.2. Le analisi agli elementi finiti (EF) della struttura hanno confermato i risultati sperimentali, sia relativamente al coefficiente di Poisson, sia relativamente alle proprietà elastiche. In conclusione, il metamateriale proposto si distingue per un evidente comportamento auxetico, calibrabile in funzione della specifica geometria della cella elementare che compone il sistema e permette quindi realizzare nuove architetture auxetiche tridimensionali.
2022
- Modello multifisico di un convertitore elettromagnetico a pendolo per il recupero di energia da vibrazioni ambientali
[Relazione in Atti di Convegno]
Nicolini, Lorenzo; Castagnetti, Davide; Sorrentino, Andrea
abstract
Il lavoro presenta lo sviluppo di un modello multi-fisico che simula il funzionamento di un pendolo per il recupero di energia dalle vibrazioni ambientali a bassa frequenza mediante convertitori elettromagnetici. La dinamica del dispositivo può essere associata a quella di un sistema massa-molla-smorzatore rotante. La molla è caratterizzata da magneti che si attraggono con una legge fortemente non lineare e lo smorzamento è causato dalla conversione di energia. Il modello simulativo è descritto in due parti principali: la dinamica sviluppata in un modello multi-body che include anche la sorgente delle vibrazioni e i segnali di output, e l’analisi EF del campo magnetico generato dai magneti permanenti dei convertitori. Combinando il modello multi-body con i risultati ottenuti nell’analisi agli elementi finiti si ottiene una descrizione completa e accurata del funzionamento del dispositivo, confermata dal confronto con il prototipo reale durante una campagna di test sperimentali.
2022
- Negative Poisson’s ratio lattice for designing vertebral biomaterials
[Articolo su rivista]
Sorrentino, Andrea; Castagnetti, Davide
abstract
This work designs and experimentally validates a novel bone-mimicking biomaterial for human cancellous bone vertebral implants. The lattice architecture here proposed consists of a 3D printed titanium auxetic meta-biomaterial, with a complex micro-structure resembling vertebral trabeculae, and exhibiting a negative Poisson’s ratio. Through finite element analysis, the work finds the optimal geometrical parameters of the unit cells of the lattice and performs the shape optimization of the trabeculae. This leads to a meta-biomaterial with a Poisson’s ratio up to -0.64, and a Young’s modulus of 128.3 MPa, close to that of human vertebral cancellous bones, as the experimental validation confirms. The work demonstrates the great potential of additively manufactured hybrid titanium auxetic metamaterials, which can be designed to obtain peculiar mechanical properties that improve bone tissue regeneration while prevent stress-shielding phenomena.
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
- Predicting the Macroscopic Shear Strength of Tightened-Bonded Joints from the Intrinsic High-Pressure Properties of Anaerobic Adhesives
[Articolo su rivista]
Castagnetti, Davide; Corigliano, Pasqualino; Barone, Calogero; Crupi, Vincenzo; Dragoni, Eugenio; Guglielmino, Eugenio
abstract
This scientific study aims to validate the applicability of a micromechanical model for predicting the static shear strength of hybrid interfaces that are pressure-reinforced and bonded with anaerobic adhesives. To identify the parameters for the micromechanical model, a systematic experimental test plan involving high-strength steel butt specimens bonded with anaerobic adhesive in a finite thickness was performed. The experimental investigation was based on torque tests, which provided the shear strength of two anaerobic adhesives subjected to different values of contact pressure, ranging from 0 up to 1000 MPa. Based on the intrinsic high-pressure properties of the finite-layer adhesives, the formerly developed micromechanical model of hybrid interfaces satisfactorily predicted the macroscopic strength of tightened-bonded joints taken from the literature.
2022
- 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
- Struttura vertebrale in parete sottile in metamateriale auxetico
[Brevetto]
Sorrentino, A.; Castagnetti, D.; Pasquali, A.; Celesti, M.; Manzo, R.
abstract
La presente invenzione si riferisce ad un elemento di protesi ossea, in particolare un guscio vertebrale, realizzato in stampa 3D e avente caratteristiche morfologiche simili a quelle delle ossa vertebrali umane, caratterizzato dal fatto di essere ottenuto sagomando una struttura piana in parete sottile, in metamateriale auxetico.
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
- 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
- Design and Fabrication of a Pillar-based Piezoelectric Microphone exploiting 3D-Printing Technology
[Articolo su rivista]
Ricci, Y.; Sorrentino, A.; La Torraca, P.; Cattani, L.; Cotogno, M.; Cantarella, G.; Orazi, L.; Castagnetti, D.; Lugli, P.; Larcher, L.
abstract
This letter presents a 3-D-printed piezoelectric microphone with enhanced voltage sensitivity. The sensitivity is
improved by a combination of a single-pillar mechanical design and a specific polyvinylidene fluoride (PVDF)-film electrode
patterning. The moving part of the mechanical structure and the chassis are 3D-printed as a single unit and trimmed
by laser cutting, allowing for a simple fabrication of the device. The measured sensitivity of 1 mV/Pa (±6 dB) in the
bandwidth 500–2500 Hz agrees with simulations, showing an improvement over similar pillar-based piezoelectric sensor
solutions. The sensitivity performance is shown to be comparable to existing microphones with different technologies. The
microphone is also characterized by excellent linearity within the measurable range. 3D-printing technique can thus be
adopted for the manufacturing of low cost and highly customizable microphone sensors.
2021
- Measuring the static shear strength of anaerobic adhesives in finite thickness under high pressure
[Articolo su rivista]
Corigliano, P.; Ragni, M.; Castagnetti, D.; Crupi, V.; Dragoni, E.; Guglielmino, E.
abstract
Although anaerobic adhesives are extensively used in addition to mechanical tightening in flanged couplings, interference fits, and threaded connections, their constitutive behaviour still needs to be investigated. According to the micromechanical model proposed by Dragoni and Mauri [Proc. of the IMECHE Part L J. of Mat.: Des. and Appl. 2002; 216: 9–15], the shear strength of the anaerobic adhesives significantly improves with the contact pressure applied to the thin adhesive layer. In order to assess this hypothesis, this work investigates the shear strength of an anaerobic adhesive layer with finite thickness and surface area, subject to a nearly-uniform contact pressure, up to 1000 MPa. The tests involved a head to head bonded specimen, made of high strength steel adherends (39NiCrMo3), with a controlled roughness on the bonding surfaces. Both a weak and a strong anaerobic adhesive (Loctite 243 and Loctite 638) are investigated. A full-field technique, such as the Digital Image Correlation, was used in order to detect the 3D displacement and strain fields, and to evaluate the twist angle of the entire external surface, with particular attention to the interface area. The preliminary results prove the reliability of the test bench and confirms the piezo-resistive response of the anaerobic adhesive.
2021
- Metamateriale auxetico ad elementi rotanti in titanio o tecnopolimero realizzato mediante stampa 3D
[Brevetto]
Sorrentino, Andrea; Castagnetti, Davide; Pasquali, Andrea; Celesti, Mattia; Manzo, Roberto
abstract
Struttura in metamateriale auxetico reticolare altamente porosa per la realizzazione del nucleo di protesi vertebrali.
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
- Struttura reticolare in metamateriale auxetico per protesi ossee vertebrali in stampa 3D
[Relazione in Atti di Convegno]
Sorrentino, A.; Castagnetti, D.
abstract
Il lavoro descrive la progettazione e la validazione sperimentale di una nuova struttura reticolare altamente porosa per protesi vertebrali trabecolari. La soluzione proposta consiste in un originale meta-biomateriale auxetico in titanio, realizzato in stampa 3D, con una complessa micro-struttura simile a quella delle ossa trabecolari umane, avente coefficiente di Poisson negativo. Tramite analisi agli elementi finiti, il lavoro identifica i parametri geometrici ottimali della cella elementare del reticolo ed esegue un’ottimizzazione di forma delle trabecole. La struttura presenta un comportamento anisotropo, una risposta auxetica e proprietà elastiche simili a quelle delle ossa spugnose vertebrali. I test sperimentali confermano le previsioni numeriche. Il lavoro mette in evidenza l’elevato potenziale dei metamateriali auxetici ibridi in stampa 3D, progettati per ottenere specifiche proprietà meccaniche così da ridurre il rischio di ipo-sollecitazione ed assicurare una corretta ricrescita ossea.
2021
- Wideband fractal-inspired piezoelectric energy harvesters
[Articolo su rivista]
Castagnetti, Davide
abstract
Harvesting kinetic ambient energy from vibrations or impact loads to obtain electrical energy useful to supply electronic sensors is still a challenging issue, with a huge number of potential applications, from the industrial field to consumer goods. This work investigates four simple piezoelectric energy harvesters developed from fractal-inspired structures: these structures are square laminas with inner divisions that originate a fractal geometry, since it is obtained by the repetition of a base configuration. Starting from the description of the fractal-inspired structures, the work presents a computational modal analysis highlighting the peculiar wideband frequency response of these structures and thus their applicability as energy converters. Using commercial piezoelectric transducers, we built four energy harvesters and assessed their output voltage and output power performing dynamic tests on a vibrating table. The proposed structures exhibit a wideband frequency response and a good energy conversion, specifically at the fundamental eigenfrequency.
2020
- Experimental and numerical analysis of a liquid aluminium injector for an Al-H2O based hydrogen production system
[Articolo su rivista]
Milani, M.; Montorsi, L.; Storchi, G.; Venturelli, M.; Angeli, D.; Leonforte, A.; Castagnetti, D.; Sorrentino, A.
abstract
This paper investigates pressurised injection system for liquid aluminium for a cogeneration system based on the Al–H2O reaction. The reaction produces hydrogen and heat which is used for super-heating vapour for a steam cycle. The aluminium combustion with water generates also alumina as a byproduct; the aluminium oxide can be recycled and transformed back to aluminium. Thus, aluminium can be exploited as energy carrier in order to transport energy from the alumina recycling plant to the place where the cogeneration system is located. The water is also used in a closed loop; indeed, the amount of water produced employing the hydrogen obtained by the proposed system corresponds to the oxidizing water for the Al/H2O reaction. The development of a specific test rig designed for investigating the liquid aluminium injection is presented in this research study. The injector nozzle is investigated by means of numerical thermal and structural analysis. The calculations are compared and validated against the experimental measurements carried out on ad-hoc developed test rig. A good agreement between the numerical results and the experimental values is found and the new design of the nozzle is devised.
2020
- Experimental characterization of pull-in parameters for an electrostatically actuated cantilever
[Relazione in Atti di Convegno]
Sorrentino, Andrea; Bianchi, Giovanni; Castagnetti, Davide; Radi, Enrico
abstract
Micro-electromechanical systems (MEMS) are a promising research frontier thanks to their multiple physical fields properties. In the field of microcantilever actuators, Radi et al., 2017, proposed an accurate analytical approach for estimating the pull-in characteristics of microcantilever actuators subject to electrostatic actuation. The present work assesses this previous analytical model via experimental tests with the use of a simple millimeter-scale device. The aim of the work is to measure the critical pull-in voltage and the deflection of an actuated cantilever beam for different configurations in order to validate the variation of the pull-in voltage with the geometrical parameters of the device provided by theoretical investigations. Preliminary tests show that the experimental pull-in voltage and deflection are in good agreement with the results provided by the analytical model. Specifically, the relative difference between experimental and analytical values of pull-in voltage is in the range between 0.7% and 10%.
2020
- Experimental characterization of pull-in parameters for an electrostatically actuated cantilever
[Articolo su rivista]
Sorrentino, A.; Bianchi, G.; Castagnetti, D.; Radi, E.
abstract
MEMS-NEMS applications extensively use micro-nano cantilever structures as actuation system, thanks to their intrinsically simple end efficient configuration. Under the action of an electrostatic actuation voltage the can- tilever deflects, until it reaches the maximum value of the electrostatic actuation voltage, namely the pull-in voltage. This limits its operating point and is a critical issue for the switching of the actuator.
The present work aims to experimentally measure the variation of the pull-in voltage and the tip deflection for different geometri- cal parameters of an electrostatically actuated cantilever. First, by relying on a nonlinear differential model from the literature, we designed and built a macro-scale cantilever switch, which can be simply adapted to different configurations. Second, we experimentally investigated the effect of the free length of the suspended electrode, and of the gap from the ground, on the pull-in response. The experimental results always showed a close agree- ment with the analytical predictions, with a maximum relative error lower that 10% for the pull-in voltage, and a relative difference lower than 18% for the pull-in deflection.
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
- A simply tunable electromagnetic pendulum energy harvester
[Articolo su rivista]
Castagnetti, Davide
abstract
A fundamental issue for the advance of self-sustainable electronic systems and remote sensor is the development of energy harvesters able to efficiently convert ambient energy into electrical energy. This paper presents an innovative simply tunable pendulum electromagnetic energy harvester, starting from conceptual design, analysis of the mechanical system and electromagnetic converter, development, and experimental assessment. The proposed system has the peculiar feature of a magnetic spring to enhance the equilibrium whichever the orientation and enabling frequency tuning. A magnetic C-frame gives a constant magnetic field through a gap, which is crossed by the coils fixed to a free end of the pendulum. The prototype, about one cubic decimeter, provides a low frequency and simply tunable modal response, together with a significant output power.
2019
- CONSULENZA TECNICA SU ANALISI STRUTTURALE E PROGETTAZIONE RIDUTTORE DI VELOCITÀ MAZZONI
[Altro]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio; Mizzi, Luke
abstract
Fornire consulenza tecnica per l’analisi strutturale di un riduttore di velocità per accoppiamento di motori endotermici a benzina e pompe acqua a pistoni assiali. Lo studio è finalizzato all’analisi di un riduttore commerciale di riferimento, al fine di valutarne le prestazioni, e allo studio della gamma di riduttori di comune uso presso Mazzoni. Sulla base dei primi due passi si andrà a studiare la fattibilità tecnica per la produzione, da parte del Committente, di una piattaforma di riduttori modulari, adatti alla gamma di prodotti d’interesse.
2019
- CONSULENZA TECNICA SU SISTEMA HEART DAMPER
[Altro]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio; Mizzi, Luke
abstract
La collaborazione riguarda la consulenza tecnica per l’analisi della deformazione e la valutazione della resistenza di un heart damper in Nitinol per la terapia dell’insufficienza cardiaca tramite metodi numerici FEM
2019
- Design and validation of a minimally invasive adjustable titanium prosthesis as a vertebral body replacement
[Abstract in Atti di Convegno]
Sorrentino, A.; Castagnetti, D.; Taddei, F.; Schileo, E.
abstract
Unstable vertebral body compression fractures, spinal tumors and post-traumatic deformities require a vertebral body replacement (VBR). Usually, the reconstruction of the lumbar spinal column requires metallic implants, also called cages, which are inserted after a total corpectomy in combination with an internal spinal fixation device. These implants show several complications, including a low bone fusion rate, localized contact between prosthetic endplates and vertebral endplate, and eventually overload the vertebral body due to the excessive insertional force. Creation of a misalignment between prosthetic and bone endplate sometimes causes the subsidence and collapse of the VBR. Then, the ability of the prosthesis/bone interface to support vertebral loading is crucial to the successful implantation of these devices. Recently developed additive manufacturing techniques (i.e. EBM) allow the production of trabecular titanium structures which provides better biomechanics and customized solutions. Furthermore, most of vertebral body implants are currently designed and produced in batches with standard dimensions, that are not able to meet the patient peculiar features. This work aims to design, optimize and validate a new 3D printed trabecular titanium prosthesis with adjustable height for lumbar VBR. The work focused on the durability of the implant considering the lumbar spinal fatigue loadings acting on the porous cage, with the aims to improve bone ingrowth and, at the same time, to minimize the effects of the surgical treatment on the sagittal alignment of the patient. In order to achieve better performances in terms of spinal stabilization and fatigue life resistance, the design of this new customized prosthesis takes into account the most critical factors of the vertebral body resection, with the aim to ensure minimally invasive surgical procedure.
2019
- Design, prototyping and validation of a new PVDF acoustic sensor
[Relazione in Atti di Convegno]
Sorrentino, A.; Ricci, Y.; Castagnetti, D.; Larcher, L.
abstract
This work focuses on the design, prototyping and testing of a new millimeter-size 3D printed acoustic sensor based on a Polyvinylidene Fluoride (PVDF) film. The piezoelectric PVDF has been widely used for sensors development in many applications due their high sensitivity and low cost. The aim of this work is to design an acoustic sensor that collects the acoustic wave and convey the most part of it as a force on the piezoelectric PVDF film in order to increase the sensitivity of the microphone. The work presents a detailed analytical model describing the mechanical behavior of the system. Through a metaheuristic optimization algorithm, we found the optimal geometric parameters of the system that maximize the acoustic force on the piezoelectric film. Analytical results show that the proposed solution exhibits a good value of sensitivity in the frequency range 10-10000 Hz. The proposed acoustic sensor was manufactured through 3D printing in ABS material and the tests focused on investigating the sensitivity of the system at different frequencies.
2019
- Development of a driveshaft torque transducer for low-cost structural health monitoring of off-highway vehicles
[Articolo su rivista]
Golinelli, Nicola; Spaggiari, Alan; Castagnetti, Davide; Fornari, Lorenzo; Dragoni, Eugenio; Gualdi, G.; Brunazzi, A.
abstract
Mechatronic agricultural machines and equipment are continuously increasing their complexity and cost. In order to ensure their efficiency and reliability and preserve their value, it is important to actively monitor the working loads and register damaging and wear occurring on critical components. This approach needs the introduction of sensors on the machine, which allow continuous monitoring and evaluate the residual life of components. The work presents the development and testing of an innovative low-cost systems for monitoring and diagnostic of off-highway vehicles. The sensor measures the torque of a mechanical power transmissions, and it was designed especially for agricultural machinery. The torque transducer monitors the mechanical power flowing from the tractor into the gearbox and the agricultural implement and is fully integrated with the power take-off driveshaft, thus being generally applicable. The design and development of the transducer was performed following a quality function deployment approach. The system is less expensive considering the typical torque measuring system commercially available and, thanks to its wireless module and integrated power supply, it is reliable and generally applicable to many power take-off to implement combinations.
2019
- Metodologie non distruttive per l’individuazione di difetti su sanitari in ceramica
[Altro]
Castagnetti, Davide; Cocconcelli, Marco; Spaggiari, Andrea; Dragoni, Eugenio; Rubini, Riccardo
abstract
Studio di metodologie per l’individuazione, a fine linea di produzione, di difetti (sfili, cricche) su sanitari in ceramica
2019
- Shape optimization of the fillet under a bolt’s head
[Articolo su rivista]
Sorrentino, Andrea; Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio
abstract
The stress concentration in the fillet under a bolt’s head is a critical issue for the fatigue life of this component. Remembering the variable notch radius solution observed in many biological structures to lower stress concentrations due to normal loads, this work proposes, examines and optimizes a double circular arc fillet, not re-entering the head. The work implements an ad hoc shape optimization procedure that combines a genetic algorithm (the particle swarm optimization) and a parametric, axisymmetric finite-element model of the bolt: by focusing on an M12 bolt, the analysis focuses on two issues: first, the optimization of the radius of each arc in the fillet; second, the optimization of the bolt’s head height and head’s diameter in combination with the fillet radiuses. By comparing the proposed solution with the fillet geometries for the bolt’s heads from the literature, it appears a noticeable stress reduction, about 14% lower than the standard circular fillet, combined with an easy manufacturing.
2019
- Smart materials: Properties, design and mechatronic applications
[Articolo su rivista]
Spaggiari, Andrea; Castagnetti, Davide; Golinelli, Nicola; Dragoni, Eugenio; SCIRE' MAMMANO, Giovanni
abstract
This paper describes the properties and the engineering applications of the smart materials, especially in the mechatronics field. Even though there are several smart materials which all are very interesting from the research perspective, we decide to focus the work on just three of them. The adopted criterion privileges the most promising technologies in terms of commercial applications available on the market, namely: magnetorheological fluids, shape memory alloys and piezoelectric materials. Many semi-active devices such as dampers or brakes or clutches, based on magnetorheological fluids are commercially available; in addition, we can trace several applications of piezo actuators and shape memory-based devices, especially in the field of micro actuations. The work describes the physics behind these three materials and it gives some basic equations to dimension a system based on one of these technologies. The work helps the designer in a first feasibility study for the applications of one of these smart materials inside an industrial context. Moreover, the paper shows a complete survey of the applications of magnetorheological fluids, piezoelectric devices and shape memory alloys that have hit the market, considering industrial, biomedical, civil and automotive field.
2019
- Thermo-mechanical behaviour of an injection nozzle for a cogeneration system based on the aluminum/water reaction
[Relazione in Atti di Convegno]
Angeli, Diego; Castagnetti, Davide; Cingi, Pietro; Leonforte, ADRIANO DAVIDE SERAFINO; Melchionda, Filippo; Milani, Massimo; Montorsi, Luca; Sorrentino, Andrea; Zanni, Davide
abstract
The thermal behaviour of an injection nozzle for a prototype combustion chamber of a cogeneration system based on the reaction of liquid aluminum and water steam, is analyzed. The heat released by the oxidation of aluminum with water is exploited for super-heating the vapor of a steam cycle and simultaneously producing hydrogen. The only by-product is alumina, which can be transformed again into aluminum. From a thermo-mechanical point of view, the most critical part of the system is the injection nozzle, located at the end of a graphite pneumatic needle valve. The head of the injector is made by titanium and includes a Titalox ceramic nozzle characterized by a 0.5 mm calibrated hole. After a warm up cycle, the injector reaches temperatures of the order of 1000°C. During the subsequent cool-down phase, the different strain rates of the two materials could lead to mechanical failure. In this work, the heating and cooling transients of the injection zone are simulated by a Finite Volume approach. Temperature distributions are then transferred to a Finite Element structural solver in order to verify the resulting stresses. Temperature measurements taken during preliminary experimental tests provide a qualitative assessment of the reliability of the numerical predictions.
2018
- A piezoelectric based energy harvester with dynamic magnification: modelling, design and experimental assessment
[Articolo su rivista]
Castagnetti, Davide; Radi, Enrico
abstract
This work presents a simple and innovative piezoelectric energy harvester, inspired by fractal geometry and intrinsically including dynamic magnification. Energy harvesting from ambient vibrations exploiting piezoelectric materials is an efficient solution for the development of self-sustainable electronic nodes. After an initial design step, the present work investigates the eigenfrequencies of the proposed harvester, both through a simple free vibration analysis model and through a computational modal analysis. The experimental validation performed on a prototype, confirms the accurate frequency response predicted by these models with five eigenfrequencies below 100 Hz. Despite the harvester has piezoelectric transducers only on a symmetric half of the top surface of the lamina, the rate of energy conversion is significant for all the investigated eigenfrequencies. Moreover, by adding a small ballast mass on the structure, it is possible to excite specific eigenfrequencies and thus improving the energy conversion.
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
- Experimental validation of a simple shear strength model for hybrid friction-bonded interfaces
[Articolo su rivista]
Ragni, M.; Castagnetti, D.; Dragoni, E.
abstract
The paper deals with the experimental measurement of the shear strength in hybrid interfaces, press fitted and bonded with anaerobic adhesives. The aim is to validate and improve the applicability of a constitutive model, which describes the interface behavior up to complete failure, by combining a cohesive law with a pure friction law. This paper presents an extensive experimental test plan, which deeply investigates the shear strength of two strong anaerobic adhesives, over four nominal contact pressure levels. The tests involve cylindrical specimens, butt bonded and pressure reinforced over an annular surface, and seven replications, giving 56 tests. The experimental torque-rotation curves up to complete failure highlight a similar response between the two adhesives, and confirm that the strain energy up to complete failure sums up a cohesive term and a pure friction term. In addition, the main parameters of the model linearly depend from contact pressure through simple relationships.
2018
- Fornire consulenza tecnica per la analisi preliminare tramite simulazione con metodologia agli elementi finiti di Volante COBO, secondo la norma fornita FZG-11486 Type3
[Altro]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio
abstract
– Predisposizione di un modello CAD per analisi EF in campo elastico, trascurando la cover e l’effetto della temperatura
– Valutazione dei carichi e vincoli agenti sul sistema
– Analisi della “Entire Wheel Skeleton” come da norma fornita FZG-11486, 2.1.2 (Type3)
– Analisi della “Deflection” come da norma fornita FZG-11486, 2.3 (Type3)
– Analisi del “Rim Pull” come da norma fornita FZG-11486, 2.4 (Type3)
2018
- 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
- ATLAS - E’ Così AuTonomus cLeAning System
[Altro]
Castagnetti, Davide; Mistrulli, Michele; Spaggiari, Andrea; Sorrentino, Andrea; Dragoni, Eugenio
abstract
ATLAS - E’ Così AuTonomus cLeAning System
Sviluppo di un robot lavapavimenti autonomo per per ambienti industriali e civili interni di grandi dimensioni.
2017
- CARATTERIZZAZIONE A TORSIONE DI PROVINI DI CONDUTTORE IN CAVO TRASPOSTO UTILIZZATI NEI
TRASFORMATORI SECONDO LA NORMA SOT054
[Altro]
Castagnetti, Davide; Sorrentino, Andrea; Ragni, Marina; Spaggiari, Andrea; Dragoni, Eugenio
abstract
CARATTERIZZAZIONE A TORSIONE DI PROVINI DI CONDUTTORE IN CAVO TRASPOSTO UTILIZZATI NEI
TRASFORMATORI SECONDO LA NORMA SOT054
2017
- Design and experimental assessment of an electromagnetic energy harvester based on slotted disc springs
[Articolo su rivista]
Castagnetti, Davide; Dallari, Federico
abstract
Efficient conversion of ambient energy, being intrinsically variable and in the low frequency range is a fundamental issue for the development of self-powered electronic systems. Simple and reliable solutions are based on piezoelectric or electromagnetic transducers. This work presents an innovative electromagnetic vibration-based energy converter, relying on two counteracting slotted disc springs, which originate a low stiffness mechanical system under a given preload. The electromagnetic converter, involving cylindrical permanent magnets, features coils with a peculiar '8' loop configuration, on opposite sides of the magnets. The prototype was built with commercial components and purposely developed parts, manufactured through rapid prototyping. The experimental validation highlights an excellent response, both in terms of the multi-frequency behaviour and with regard to the significant power output also at low input accelerations.
2017
- Development and Validation of a Numerical Model for the Optimization of a Brace for Lower Limb
[Relazione in Atti di Convegno]
Bellavita, G.; Cocconcelli, Marco; Castagnetti, Davide; Rubini, Riccardo
abstract
The orthopedic prosthesis, known as orthoses, are an external aid used for the correction of diseases which are the cause of a motor malfunction. Nowadays, the classification of different orthoses is performed by grouping them by type of apparatus that is subject to correction and on the basis of the length of the orthosis. In this study we analyze a specific orthosis of composite material, belonging to the AFO (Ankle-Foot-Orthosis) family. Passing through a process of “reverse engineering”, we define a non-linear computational model of the orthosis that describes the large displacement, the composite material, and the contact with the ground. The validation of the model against experimental tests, allows to use it to correlate the stiffness of the orthosis to its geometry, thus providing a useful tool to guide the structural improvements needed for adaptation to the patient.
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
- QUADRIGEN: uso eco-sostenibile dell’alluminio come vettore energetico per la produzione combinata di energia elettrica, termica e idrogeno
[Altro]
Montorsi, Luca; Castagnetti, Davide; Angeli, Diego
abstract
“QUADRIGEN: uso eco-sostenibile dell’alluminio come vettore energetico per la produzione combinata di energia elettrica, termica e idrogeno”
2017
- Shear Strength Characterization of Metal-Elastomer Bonded Joints
[Articolo su rivista]
Ragni, Marina; Castagnetti, Davide; Spaggiari, Andrea; Muccini, Filippo; Dragoni, Eugenio; Milelli, Matteo; Girlando, Simone; Borghi, Pierluigi
abstract
The shear strength characterization of bonded joints involving adherends with a remarkably different stiffness has a peculiar interest in industrial applications. This work proposes and investigates three innovative specimens (an axisymmetric annular, a tensile and a torsional one)
purposely developed to manage dissimilar adherends bonded with adhesive in thin film. A Thick Adherend Shear Test specimen between rigid
adherends is used for the assessment of the adhesive by itself. The work focuses on metal-elastomeric polyurethane bonded joints with a solventbased adhesive. All the tests are performed through an axial dynamometer, using a purposely developed fixture to convert the tensile load in a torque for the torsional specimen. The tensile and the torsional specimens provide the most reliable shear strength characterization.
2017
- Studio e progettazione del dispositivo meccatronico Master Cylinder Locking System con la funzione blocco meccanico basato sulle tecnologie del fluido magnetoreologico o/e piezoelettrico per i sistemi frenanti tipo Brake by Wire
[Altro]
Spaggiari, Andrea; Dragoni, Eugenio; Castagnetti, Davide; Golinelli, Nicola
abstract
Studio e progettazione del dispositivo meccatronico Master Cylinder Locking System con la funzione blocco meccanico basato sulle tecnologie del fluido magnetoreologico o/e piezoelettrico per i sistemi frenanti tipo Brake by Wire
2017
- Sviluppo concettuale e dimensionamento di massima di un sistema meccanico facente parte della sospensione pneumatica di un sedile di guida professionale per macchine off-road
[Altro]
Spaggiari, Andrea; Castagnetti, Davide; Cocconcelli, Marco; Dragoni, Eugenio; Rubini, Riccardo; Panini, Alessandro
abstract
Sviluppo concettuale e dimensionamento di massima di un sistema meccanico facente parte della sospensione pneumatica di un sedile di guida professionale per macchine off-road
2017
- Valvola di azzeramento pressione per sistemi idraulici
[Altro]
Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio
abstract
Analisi e ottimizzazione strutturale di valvola di azzeramento pressione per sistemi idraulici
2016
- Analisi e procedura di collaudo a resistenza di giunzioni incollate con adesivo UV in box doccia
[Altro]
Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio; Ragni, Marina
abstract
Analizzare e definire una procedura di collaudo a resistenza (“Norma Novellini”) delle giunzioni incollate con adesivo UV nei box doccia.
2016
- Calcoli strutturali e valutazione dell’affidabilità funzionale e strutturale del nuovo gruppo di misura per equilibratrici prodotte da Snap-on Equipment
[Altro]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio; Dallari, F.
abstract
SCOPO
Valutazione dell’affidabilità funzionale e strutturale del nuovo gruppo di misura per equilibratrici prodotte da Snap-on Equipment.
ATTIVITÁ
FASE 1: Assistenza per test ISO 21940-21:2012 su nuova macchina equilibratrice
FASE 2: Valutazione strutturale del modello, tramite prove sperimentali accelerate secondo il Metodo Staircase
FASE 3: Applicazione del Metodo Staircase
2016
- Closed-form modal analysis of flexural beam resonators ballasted by a rigid mass
[Articolo su rivista]
Scire' Mammano, Giovanni; Castagnetti, Davide; Dragoni, Eugenio
abstract
The work deals with the study of free flexural vibrations of constant cross-section elastic beams ballasted by a rigid mass with rotary inertia at any longitudinal position. We analyze five sets of boundary conditions of the beam (fixed-free, fixed-fixed, fixed-pinned, pinned-pinned, and free-free) and hypothesize that the structure is perfectly rigid, where the rigid mass is applied. By employing the Euler-Bernoulli beam theory, a single parametric matrix is obtained, which provides the characteristic equation of motion of the structure. When applied to specific configurations, the proposed analytical model predicts the eigenfrequencies and eigenmodes of the beam as accurately as ad-hoc analytical models available in the literature. The accuracy of the results is also confirmed by comparison with detailed two- and three-dimensional finite element analyses of a test case. By means of a 3D finite element model, the applicability of the rigid mass hypothesis to continuous beams with a composite thickened portion is finally assessed.
2016
- Consulenza tecnica per esecuzione di prove sperimentali a taglio per la valutazione del comportamento termomeccanico dell’incollaggio di rivestimenti in poliuretano elastomerico
[Altro]
Castagnetti, Davide; Spaggiari, Andrea; Ragni, Marina; Dragoni, Eugenio
abstract
Svolgimento di prove sperimentali per la caratterizzazione della resistenza a taglio di giunzioni incollate metallo-elastomero al fine di valutare:
a) Effetto della tipologia di sabbiatura degli aderendi, su adesivo Thixon 406;
b) Effetto del condizionamento, sull’adesivo Thixon 406;
c) Effetto del tipo di adesivo: Thixon 406 vs Thixon 422.
2016
- Experimental investigation and model validation of the shear strength of hybrid interfaces up to complete failure
[Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract
The paper experimentally investigates hybrid interfaces pressurereinforced and bonded with anaerobic adhesive. While their static strength has been deeply investigated, their behavior up to complete failure lacks of a constitutive model. This work aims to assess the applicability of a simple model involving a cohesive law and a pure 10 friction law, in order to describe the interface behavior up to complete failure under different contact pressure levels. A systematic experimental campaign investigates the shear strength of cylindrical specimens butt-bonded and pressure reinforced over an annular surface. The tests involve two anaerobic adhesives and 15 four pressure levels. The experimental torque-rotation curves confirm
that the strain energy up to complete failure is given by a cohesive term and a pure friction term, both of them linearly dependent upon the contact pressure.
2016
- 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
- Sviluppo e validazione di un modello numerico per l'ottimizzazione di un'ortesi per arto inferiore
[Capitolo/Saggio]
Bellavita, G.; Cocconcelli, Marco; Castagnetti, Davide; Rubini, Riccardo
abstract
Le protesi ortopediche, note come ortesi, sono un ausilio esterno utilizzato per la correzione di patologie che determinano un malfunzionamento motorio. La suddivisione delle diverse ortesi, ad oggi, viene eseguita mediante un raggruppamento per tipologia di apparato soggetto a correzione e attraverso la lunghezza dell’ortesi. In questo studio si analizza una specifica ortesi in materiale composito, appartenente alla famiglia AFO (Ankle-Foot-Orthosis). Attraverso un processo di “reverse engineering”, si definisce un modello computazionale dell’ortesi che tiene conto delle non linearità geometriche, del materiale e dovute al contatto con il suolo. Dopo aver convalidato il modello con specifiche prove sperimentali, lo si impiega per correlare la rigidezza dell’ortesi alla sua geometria, ottenendo un utile strumento per guidarne le modifiche strutturali necessarie per l’adattamento al paziente.
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.
2016
- Un convertitore di energia da vibrazioni basato su molle coniche: progettazione e convalida sperimentale
[Relazione in Atti di Convegno]
Castagnetti, Davide; Dallari, Federico
abstract
Lo sviluppo di sensori elettronici e circuiti di controllo con consumi sempre più bassi rende possibile la loro autoalimentazione, recuperando energia dall’ambiente circostante. Particolarmente promettente a tale scopo è la conversione di energia cinetica ambientale in energia elettrica mediante materiali piezoelettrici, generatori elettromagnetici o elettrostatici. Per ottenere un’effettiva autonomia energetica del dispositivo, è fondamentale convertire in modo efficiente l’energia ambientale, essenzialmente sviluppando dispositivi multifrequenza in un intervallo di frequenze basso (inferiore ai 200 Hz). Questo lavoro presenta la progettazione, la prototipazione e la convalida sperimentale di un convertitore elettromeccanico. Il sistema si basa su due molle coniche contrapposte e precaricate per realizzare un sistema elastico a bassa rigidezza. Nello specifico, il prototipo sviluppato impiega molle coniche con spacchi radiali, ma può accogliere anche molle coniche continue (Belleville). Il convertitore elettromagnetico, abbinato al sistema elastico, impiega fino a
cinque magneti permanenti cilindrici per la generazione del campo magnetico. Coassiali al pacco dei magneti, su lati opposti, si affacciano due bobine di avvolgimenti. Queste spire, aventi una particolare configurazione ad otto, sono solidali alla parte mobile del sistema elastico e si muovono radialmente rispetto ai magneti. Quando il sistema eccitato dinamicamente entra in risonanza, le spire vedono una variazione di flusso magnetico dovuta al moto relativo rispetto ai magneti e ciò genera una tensione elettrica ai loro capi. Il prototipo è stato interamente realizzato impiegando componenti commerciali e parti realizzate in ABS. Le prove sperimentali svolte hanno messo in luce un ottimo comportamento del sistema, che mostra già con bassa accelerazione (0.35g) una significativa generazione elettrica su un ampio intervallo di frequenze molto al di sotto dei 100 Hz.
2015
- A Belleville-spring-based electromagnetic energy harvester
[Articolo su rivista]
Castagnetti, Davide
abstract
Energy harvesting from kinetic ambient energy is particularly effective to power autonomous sensors. This work proposes an innovative energy converter based on two counteracting
Belleville springs and exploiting their peculiarity, for a height to thickness ratio equal to 1.414, of nearly zero stiffness over a wide deflection range. After analytical and numerical modelling a
prototype is developed and experimentally investigated. The sub-optimal geometry of the commercial springs used in the prototype, together with a non-ideal response, makes the
operating frequency for the prototype higher than in analytical and numerical predictions. Nevertheless, the harvester exhibits a significantly large bandwidth, together with a high output
power, compared to similar solutions in the literature, for all the examined configurations and input excitations.
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
- A piezoelectric based energy harvester with dynamic magnification
[Relazione in Atti di Convegno]
Castagnetti, Davide
abstract
Energy harvesting from ambient vibrations exploiting piezoelectric materials is an efficient solution for the development of self-sustainable electronic nodes. This work presents a simple and innovative piezoelectric energy harvester, intrinsically including dynamic magnification and inspired by fractal geometry. After an initial design step, computational analysis and experimental validation show a very good frequency response with five eigenfrequencies below 100 Hz. Even if the piezoelectric transducers were put only on a symmetric half of the top surface of the structure, the energy conversion is good for all the eigenfrequencies investigated.
2015
- Comparison between a wideband fractal-inspired and a traditional multicantilever piezoelectric energy converter
[Articolo su rivista]
Castagnetti, Davide
abstract
Harvesting energy from ambient vibrations in order to power autonomous sensors is a challenging issue. The aim of this work is to compare the power output from an innovative wideband fractal-inspired piezoelectric converter to that from a traditional multicantilever
piezoelectric energy converter. In a given frequency range, the converters are tuned on the same eigenfrequencies. The effect of the input acceleration and of the resistive load applied to the converters is investigated experimentally for each of the three eigenfrequencies in the range between 0 and 120 Hz. The fractal-inspired converter exhibits a significantly higher specific output power at the first and third of the eigenfrequencies investigated.
2015
- Progetto SAVE WHEEL – Sensorized Anti Vibration Ergonomic Wheel
(Ruota Industriale Innovativa, Ergonomica, Sensorizzata, con recupero di energia)
[Altro]
Spaggiari, Andrea; Castagnetti, Davide; Dragoni, Eugenio; Ragni, Marina; Muccini, Filippo; Spanalatte, Marco
abstract
Progetto SAVE WHEEL – Sensorized Anti Vibration Ergonomic Wheel
(Ruota Industriale Innovativa, Ergonomica, Sensorizzata, con recupero di energia)
2015
- Un semplice modello coesivo con attrito per descrivere interfacce ibride forzate e incollate
[Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio
abstract
Il lavoro studia interfacce ibride forzate meccanicamente e incollate con adesivo anaerobico. Se dal punto di vista della loro resistenza statica sono state ampiamente studiate, altrettanto non è relativamente al loro comportamento fino a completo collasso. Obiettivo di questo lavoro è verificare l’applicabilità di un semplice modello costitutivo, che unisce un legame coesivo con una legge di puro attrito, per descrivere il comportamento dell’interfaccia fino a completo collasso sotto differenti livelli di pressione di contatto. Un’estesa campagna sperimentale esamina la resistenza a taglio di provini cilindrici incollati testa a testa considerando due adesivi anaerobici e quattro livelli di pressione di contatto. Le curve sperimentali confermano che l’energia di deformazione fino a completo collasso del provino è somma di un contributo coesivo e di uno di puro attrito, linearmente dipendenti dalla pressione di contatto.
2014
- A Belleville-Spring Based Piezoelectric or Electromagnetic Energy Harvester
[Relazione in Atti di Convegno]
Castagnetti, Davide
abstract
Energy harvesting from kinetic ambient energy requires converters able to efficiently operate in the low frequency range. A limit of the solutions proposed in the literature, both electromagnetic and piezoelectric, is their operating frequency, which generally ranges from about 50 to 300 Hz. To overcome these limitations, this work proposes an innovative energy harvester exploiting two counteracting Belleville springs. Thanks to the peculiar height to thickness ratio of the springs a highly compliant elastic system is obtained, which can be used either for electromagnetic or piezoelectric harvesting. The harvester is modelled analytically and numerically both with regard to the force-displacement and to the modal response. The experimental validation of the harvester, highlights a noticeable power output but at a higher eigenfrequency than expected.
2014
- A low frequency energy converter for electromagnetic or piezoelectric energy harvesting
[Relazione in Atti di Convegno]
Castagnetti, Davide
abstract
Harvesting kinetic ambient energy usually involves the development of converters which operate in the low frequency range (from 0 to 100 Hz). A limit of the harvesters proposed in the literature is their relatively high operating frequency. This work deals with the development of a very low frequency energy harvester based on two counteracting Belleville springs. For a given height to thickness ratio, Belleville springs have nearly zero stiffness over a wide deflection range, thus giving the possibility to build a low frequency system. Either electromagnetic or piezoelectric transduction but also a hybrid of both can be applied to the proposed converter. A preliminary analytical and computational investigation of this solution is presented in the work showing promising results.
2014
- Adhesively-bonded friction interfaces: Macroscopic shear strength prediction by microscale finite element simulations
[Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract
Anaerobic adhesives are commonly used to enhance the shear strength of clamped friction joints between metal parts. Experimental results show that the total strength of the friction-bonded interface steadily increases with the clamping pressure. However, if weak anaerobics are used in the assembly, its strength is lower than the dry (purely friction) joint0s under high applied pressures. This paper seeks an explanation for this macroscopic behaviour by means of microscale finite-element simulations. The analyses show that the experimental results can be explained by assuming that: (a) however great the clamping pressure, a thin film of adhesive remains trapped between the crests of the mating surfaces; (b) under the high local pressure the shear strength of this film becomes greater than the regular adhesive at no pressure; (c) the stronger adhesives entail a higher increase than the weaker adhesives.
2014
- Closed-form modal analysis of flexural beam resonators ballasted by a rigid mass
[Relazione in Atti di Convegno]
G., Scirè Mammano; Castagnetti, Davide; Dragoni, Eugenio
abstract
The work deals with the study of free flexural vibrations of constant cross-section elastic beams ballasted by a rigid mass with rotary inertia at any longitudinal position. We analyze five sets of boundary conditions of the beam (fixed-free, fixed-fixed, fixed-pinned, pinned-pinned, and free-free) and hypothesize that the structure is perfectly rigid, where the rigid mass is applied. By employing the Euler-Bernoulli beam theory, a single parametric matrix is obtained, which provides the characteristic equation of motion of the structure. When applied to specific configurations, the proposed analytical model predicts the eigenfrequencies and eigenmodes of the beam as accurately as ad-hoc analytical models available in the literature. The accuracy of the results is also confirmed by comparison with detailed two- and three-dimensional finite element analyses of a test case. By means of a 3D finite element model, the applicability of the rigid mass hypothesis to continuous beams with a composite thickened portion is finally assessed.
2014
- Un semplice modello coesivo con attrito per descrivere interfacce ibride forzate e incollate
[Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio
abstract
Il lavoro studia interfacce ibride forzate meccanicamente e incollate con adesivo anaerobico. Se dal punto di vista della loro resistenza statica sono state ampiamente studiate, altrettanto non è relativamente al loro comportamento fino a completo collasso. Obiettivo di questo lavoro è verificare l’applicabilità di un semplice modello costitutivo, che unisce un legame coesivo con una legge di puro attrito, per descrivere il comportamento dell’interfaccia fino a completo collasso sotto differenti livelli di pressione di contatto. Un’estesa campagna sperimentale esamina la resistenza a taglio di provini cilindrici incollati testa a testa considerando due adesivi anaerobici e quattro livelli di pressione di contatto. Le curve sperimentali confermano che l’energia di deformazione fino a completo collasso del provino è somma di un contributo coesivo e di uno di puro attrito, linearmente dipendenti dalla pressione di contatto.
2013
- A fractal-inspired multi-frequency piezoelectric energy converter: design and experimental characterization
[Relazione in Atti di Convegno]
Castagnetti, Davide
abstract
A promising harvesting technique, in terms of simplicity and efficiency, is the conversion of ambient kinetic energy through piezoelectric materials. This work aims to design and investigate a piezoelectric converter conform to a fractal-inspired, multi-frequency structure previously presented by the author. A physical prototype of the converter is built and experimentally examined, up to 120 Hz, in terms of modal response and power output. Three eigenfrequencies are registered and the power output is particularly good at the fundamental eigenfrequency. Also the effect of the resistive load applied to the converter is investigated.
2013
- A wideband fractal-inspired piezoelectric energy converter: design, simulation and experimental characterization
[Articolo su rivista]
Castagnetti, Davide
abstract
In order to develop self-powered wireless sensor nodes, many energy harvesting devices that are able to convert available ambient energy into electrical energy have been proposed in the literature. A promising technique, in terms of simplicity and high conversion efficiency, is the harvesting of ambient kinetic energy through piezoelectric materials. The aim of this work is to design and investigate the modal response and power output of a fractal-inspired, multi-frequency, piezoelectric energy converter. The converter is a square, thin sheet structure, characterized by a fractal geometry obtained through a pattern of cuts in the plate. There are two steps involved. First, a computational analysis of the converter is performed. Second, a physical prototype of the converter is built and its eigenfrequencies and power generation under different resistive loads are experimentally examined in the range from 0 to 120 Hz. The converter exhibits three eigenfrequencies and a good power output, particularly at the first eigenfrequency.
2013
- Confronto sperimentale tra convertitori di energia piezoelettrici multifrequenza: convertitore frattale e convertitore tradizionale
[Relazione in Atti di Convegno]
Castagnetti, Davide
abstract
Il recupero di energia da vibrazioni ambientali per alimentare sensori è un problema di particolare interesse. Obiettivo del lavoro è confrontare la generazione di potenza di un convertitore piezoelettrico innovativo ispirato ad una geometria frattale rispetto a quella di un convertitore tradizionale a mensole indipendenti. I convertitori, realizzati con materiali commerciali, sono progettati in modo da avere le stesse frequenze di risonanza. Si svolge una campagna sperimentale che esamina l’effetto dell’accelerazione e del carico resistivo applicato ai convertitori, per ciascuna delle tre frequenze proprie tra 0 e 120 Hz. I risultati mostrano un’ottima generazione del convertitore frattale rispetto a quello tradizionale alla prima e terza frequenza di risonanza. Maggiore è invece la potenza generata dal convertitore tradizionale alla seconda frequenza di risonanza.
2013
- Experimental Assessment of a Micro-Mechanical Model for the Static Strength of Hybrid Friction-Bonded Interfaces
[Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract
Anaerobic adhesives are thermosetting acrylic polymers commonly used to improve the performance of most metal joints. Researches on the static strength of hybrid joints, available in the technical litera-ture, show scanty and contradictory results that do not explain the effect of anaerobic adhesive on the hybrid joint behaviour. An early study by one of the authors of the present study formulates a micro-mechanical model describing the shear power of anaerobic adhesives as a function of the intimate properties of adherends and adhesive at the interface. According to the micro-mechanical model, the high local pressure acting on the thin film of adhesive trapped between the crests of the mating surfaces improves the film shear strength upon the adhesive’s shear strength at zero pressure. The present work aims to assess this micro-mechanical model through a systematic experimental campaign. The tests are conducted on simple tubular specimens and consider three vari-ables over two levels: adhesive-type (weak and strong anaerobic), pressure level during polymerization (0.5 and 134MPa), and pressure level during failure test (0.5 and 134MPa). The results confirm the proposed micro-mechanical model, and highlight that shear strength slightly differs by applying pressure before or after polymerization.
2013
- Experimental comparison between a fractal-inspired multi-frequency piezoelectric energy converter and a traditional converter
[Relazione in Atti di Convegno]
Castagnetti, Davide
abstract
Harvesting energy from ambient vibrations in order to power autonomous sensors is a challenging issue. The aim of this work is to compare the power output from an innovative multi-frequency fractal-inspired piezoelectric converter to that from a traditional multi-cantilever piezoelectric converter. The converters are designed in order to give the same eigenfrequencies in a given range and a prototype of both is built using commercial materials. The experimental tests investigate both the effect of the acceleration and of the resistive load applied to the converters for each of the three eigenfrequencies in the range between 0 and 120 Hz. The fractal-inspired converter exhibits a significantly higher specific output power at the first and third of the eigenfrequencies investigated.
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
- Stress concentrations in periodic notches: a critical investigation of Neuber's method
[Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract
The work investigates the stress concentrations produced by periodic notches (i. e. uniformly repeated) in elastic solids under different loading conditions. Neuber's criterion, which likens the effect of a periodic notch to a single notch of similar profile but lesser depth, is critically examined. The criterion simply correlates the depth reduction factor to the ratio between the depth and the pitch of the original periodic notch, regardless of its shape. By examining literature results in periodic notches on circular bars and plane strips under torsion or axial loads, the work proves the accuracy of the Neuber's method for the ideal configuration of a sharp and shallow notch under shear stresses. By contrast, for real notches with a large root radius and finite depth, the accuracy is very poor, in particular for normal stresses. However, it is found that by simply ‘repairing’ the expression of the depth reduction factor and distinguishing between notches under shear or normal stresses, the criterion provides very accurate results, and becomes quite useful for real geometries.
2013
- Un sistema di misura della rotazione per la caratterizzazione fino a collasso di interfacce forzate e incollate con adesivi anaerobici
[Relazione in Atti di Convegno]
Castagnetti, Davide; A., Torreggiani; Dragoni, Eugenio
abstract
Le interfacce ibride forzate ed incollate sono diffuse nelle costruzioni meccaniche per migliorare le prestazioni di calettamenti e giunzioni. Questo lavoro ha l’obiettivo mettere a punto un sistema di misura della rotazione semplice ed accurato utile per la caratterizzazione del comportamento elastico e post-elastico di tali interfacce. Il lavoro si articola in due fasi. Nella prima fase si mette a punto un sistema di misura per misurare la rotazione relativa tra le interfacce incollate, basato su un encoder installato direttamente sul provino. Il sistema di misura è stato caratterizzato sia su una barra di torsione sia su un provino con interfaccia a puro attrito mostrando un’ottima accuratezza. Nella seconda fase si svolgono le prime prove della campagna sperimentale che considera due adesivi e quattro livelli di pressione.
2012
- A fractal-inspired multi-frequency piezoelectric energy converter: computational and experimental characterization
[Relazione in Atti di Convegno]
Castagnetti, Davide
abstract
In order to develop self-powered wireless sensor nodes, many energy harvesting devices, able to convert freely available ambient energy into electrical energy, have been proposed in the literature. A promising technique, in terms of simplicity and high conversion efficiency, is the harvesting of ambient kinetic energy through piezoelectric materials.The aim of this work is to design and investigate the modal response and the power output of a fractal-inspired, multi-frequency, piezoelectric energy converter, previously presented by the author. Two are the steps of the work. First, a computational modal analysis of the converter is performed. Second, a physical prototype of the converter is built and its eigenfrequencies and power generation under different resistive loads are experimentally examined in the range between 0 and 120 Hz. The converter exhibits three eigenfrequencies and a good power output, in particular at the first eigenfrequency.
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
- Concentration of torsional shear stresses in axisymmetric bars with deep periodic grooves
[Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract
The torsional stresses in round bars with deep periodic grooves are calculated by means of the formal analogy between the elastic problem and an auxiliary thermal problem. The analogy allows demanding three-dimensional analyses to be replaced with light two-dimensional analyses, easily implemented on general-purpose finite element packages. Following Neuber’s equivalence concept, the stress concentration in each periodically grooved bar is independently calculated by referring to a single groove of like geometry but lesser depth. Neuber’s approach predicts very closely the reference numerical results if supplemented with a heuristic depth correction function formerly developed by the authors for shallow periodic notches under torsion.
2012
- Confronto sperimentale tra un convertitore di energia piezoelettrico frattale multifrequenza ed uno tradizionale
[Relazione in Atti di Convegno]
Castagnetti, Davide
abstract
Il recupero di energia da vibrazioni ambientali per alimentare sensori è un problema di particolare interesse. Obiettivo del lavoro è confrontare la generazione di potenza di un convertitore piezoelettrico innovativo ispirato ad una geometria frattale rispetto a quella di un convertitore tradizionale a mensole indipendenti. I convertitori, realizzati con materiali commerciali, sono progettati in modo da avere le stesse frequenze di risonanza e lo stesso ingombro. Si svolge una campagna sperimentale che esamina l’effetto dell’accelerazione e del carico resistivo applicato al convertitore, per ciascuna delle sue tre frequenze proprie tra 0 e 120 Hz. I risultati mostrano un’ottima generazione del convertitore frattale rispetto a quello tradizionale alla prima e terza frequenza di risonanza. Maggiore è invece la potenza generata dal convertitore tradizionale alla seconda frequenza di risonanza.
2012
- Design and characterization of a fractal-inspired
multi-frequency piezoelectric energy converter
[Articolo su rivista]
Castagnetti, Davide
abstract
A promising harvesting technique, in terms of simplicity and efficiency, is the conversion of ambient kinetic energy through piezoelectric materials. This work aims to design and investigate a piezoelectric converter conform to a fractal-inspired, multi-frequency structure previously presented by the author. A
physical prototype of the converter is built and experimentally examined, up to 120 Hz, in terms of modal response and power output. Three eigenfrequencies are registered and the power output is particularly good at the fundamental eigenfrequency. Also the effect of the resistive load applied to the converter is investigated.
2012
- Experimental modal analysis of fractal-inspired multi-frequency structures for piezoelectric energy converters
[Articolo su rivista]
Castagnetti, Davide
abstract
An important issue in the field of energy harvesting through piezoelectric materials is the design of simple and efficient structures which are multi-frequency in the ambient vibration range. This paper deals with the experimental assessment of four fractal-inspired multi-frequency structures for piezoelectric energy harvesting. These structures, thin plates of square shape, were proposed in a previous work by the author and their modal response numerically analyzed. The present work has two aims. First, to assess the modal response of these structures through an experimental investigation. Second, to evaluate, through computational simulation, the performance of a piezoelectric converter prototype, relying on one of these fractal-inspired structures. The four fractal-inspired structures are examined in the range between 0 and 100 Hz, both with regard to eigenfrequencies and eigenmodes. In the same frequency range, the modal response and power output of the converter prototype are investigated.
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
- Predicting the macroscopic shear strength of adhesively-bonded friction interfaces by microscale finite element simulations
[Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract
Anaerobic adhesives are commonly used to enhance the shear strength of clamped friction joints between metal parts. Experimental results show that the total strength of the friction-bonded interface steadily increases with the clamping pressure. However, if weak anaerobics are used, the combined strength is lower than the in dry (purely friction) joint under high applied pressures. This paper seeks an explanation for this macroscopic behaviour by means of microscale finite-element simulations. The analyses show that the experimental results can be explained by assuming that: a) however great the clamping pressure, a thin film of adhesive remains trapped between the crests of the mating surfaces; b) under the high local pressure the shear strength of this film is greater than the regular adhesive’s at no pressure; c) the stronger adhesives entail a higher increase than the weaker adhesives.
2011
- Appunti di Progettazione Meccanica Assistita
[Monografia/Trattato scientifico]
Dragoni, Eugenio; Castagnetti, Davide
abstract
Il libro raccoglie le lezioni del corso di Progettazione Meccanica Assistita per gli allievi ingegneri meccatronici della Facoltà di Ingegneria di Reggio Emilia. Scopo delle lezioni è introdurre ai principi della progettazione meccanica assistita dal calcolatore, fornendo le basi teoriche e applicative del metodo agli elementi finiti, sia per analisi lineari che non-lineari, statiche e dinamiche, termo-strutturali e modali. La struttura sintetica e la ricchezza di indicazioni metodologiche ed applicative rendono il libro adatto anche alla consultazione in un contesto professionale.
2011
- Concentration of shear stresses in shallow periodic notches
[Articolo su rivista]
Dragoni, Eugenio; Castagnetti, Davide
abstract
The torsional stresses in straight round bars with periodic U-shaped shallow grooves are calculated numerically (boundary elements) taking advantage of a computationally efficientthermal analogy. Neuber’s theory is scrutinized, which equates the stress concentration factor in the periodic notch to the stress concentration factor in the single notch of like profile and lower depth. (Corrected depth = original depth times a depth reduction factor, which is a function of the depth-to-pitch aspect ratio of the periodic notch.) The results disclose a depth correction function in close agreement with Neuber’s theory for ideally sharp notches. For a wide range of rounded notches, which are more likely to occur in practice, the paper shows that Neuber’s depth correction grossly overestimates the stresses. By modifying the expression of the depth correction factor, however, Neuber’s conceptual equivalence works well for engineering purposes. Comparison with former results by the authors indicates that the optimal depth correction function is different for notches affected by shear stresses (as in this paper)or by normal stresses.
2011
- Convalida sperimentale di un modello micromeccanico per la resistenza statica di interfacce ibride forzamento-incollaggio
[Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio
abstract
The paper deals with the investigation of the static strength of friction interfaces supplemented with anaerobic adhesives, by performing a systematic experimental campaign on ad-hoc annular specimens. Aim of the work is to assess a micro-mechanical model, previously proposed by Dragoni et al. [Int. J. Adhes. & Adhes., 20 (2000), 315-321], which correlates the static shear strength of hybrid interfaces to the contact force. The experimental campaign, performed on annular butt specimens, involved three variables: adhesive material, contact pressure along the polymerization and contact pressure along the failure test. The torque tests show that the shear strength of all hybrid interfaces increases with contact pressure. In particular, the strong anaerobic adhesive exhibits a strength that approximately equals the sum of friction and adhesive strength, taken separately.
2011
- Effect of bondline thickness on the static strength of structural adhesives under nearly-homogeneous shear stresses
[Articolo su rivista]
Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio
abstract
An usual experimental observation retrieved in the technical literature is that the strength of an adhesive joint decreases by increasing the adhesive layer thickness. This well known behaviour is still not completely understood. All works found in literature consider a complex stress state in the adhesive with mode mixing, stress concentrations on the midplane and stress singularities at the interface occurring at the same time. This paper aims at estimating the effect of the adhesive thickness on its intrinsic static shear strength and evaluate whether this strength can explain the behaviour of a real bonded joint. A nearly-uniform shear stress distribution is obtained through an ad-hoc tubular butt joint subject to pure torsion. A standard single lap joint is considered as benchmark, due to its complex and singular stress field into the adhesive. The experimental campaign is focused on two brittle adhesives: a modified methacrylate and high strength epoxy. Four levels and three levels of the adhesive thickness were considered in the tubular butt joint and in the single lap joint respectively, all in the range between 0.05 and 0.4 mm. The effect of the adhesive thickness on the static strength of the adhesive is investigated by considering the type of failure and by comparing the structural stresses in the tubular butt joint with the ones on the midplane of the adhesive layer in the single lap joint. Moreover, the stress intensity factor in the single lap joint is calculated.
2011
- Effect of chlorinated water on the oxidative resistance and the mechanical strength of polyethylene pipes
[Articolo su rivista]
Castagnetti, Davide; SCIRE' MAMMANO, Giovanni; Dragoni, Eugenio
abstract
The effect of disinfectants was determined on the mechanical and chemical resistance of high-density polyethylene pipes, commonly used in modern urban networks for water conveyance. A fully monitored test plant was built that was able to simultaneously expose both pipe sections and pre-cut dumbbell specimens to chlorinated and non-chlorinated water. PE100 polyethylene pipes for alimentary use with a nominal diameter DN 32 were tested in two sets of experiments involving both chlorine dioxide (at a constant concentration of 5 ppm), and sodium hypochlorite (at a constant concentration of 2.5 ppm). The effects of these disinfectants were assessed using monotonic tensile tests on dumbbell specimens and oxidation induction time tests. Pressure tests at a constant temperature were also performed to assess any damage in the pipe samples after one year of exposure to chlorine dioxide. The results from the tensile and oxidation induction time tests showed that chlorine dioxide was the most aggressive disinfectant. Nevertheless, the pressure tests at a constant temperature did not show any failure of the pipes after 2000 h of exposure.
2011
- Experimental Modal Analysis of Fractal-Inspired Multi-Frequency Piezoelectric Energy Converters
[Relazione in Atti di Convegno]
Castagnetti, Davide
abstract
An important issue in the field of energy harvesting through piezoelectric materials is the design of simple and efficient structures which are multi-frequency in the ambient vibration range. This paper deals with the experimental assessment of four fractal-inspired multi-frequency structures for piezoelectric energy harvesting. These structures, thin plates of square shape, were proposed and numerically analyzed, with regard to their modal response, in a previous work by the author. The aim of this work is twofold. First, to assess the modal response of these structures through an experimental investigation. Second, to evaluate, through computational simulation, the performance of a piezoelectric converter prototype relying on one of these fractal-inspired structures. The four fractal-inspired structures are examined experimentally in the range between 0 and 100 Hz, both with regard to eigenfrequencies and eigenmodes. In the same frequency range are investigated the modal response and power output of a converter prototype.
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
- Fractal-inspired multi-frequency structures for piezoelectric harvesting of ambient kinetic energy
[Articolo su rivista]
Castagnetti, Davide
abstract
Energy harvesting devices capable of converting freely-available ambient energy into electrical energy have received significant attention recently. Ambient kinetic energy is particularly attractive for conversion since it is almost ubiquitous and easily accessible. Piezoelectric energy harvesting devices are promising due to their simple configuration and high conversion efficiency. This paper studies multifrequency structures for piezoelectric energy harvesting of ambient kinetic energy, inspired by fractal geometry. Identifying such structures that are simple and efficient is challenging. We propose four fractal-inspired structures and we examine them at both micro and macroscales. We calculate their frequency response up to 100 Hz with computational modeling, and we also examine the effect of the fractal geometry iteration level. We use a cantilever plate example as a reference to validate computational results against analytical ones. A quantitative criterion to assess the harvesting efficiency of the proposed structures is introduced using the bending strain associated with each mode shape. Results show that a large number of eigenfrequencies is obtained, evenly distributed below 100 Hz, particularly in the macroscale. In addition, the iteration level of the fractal geometry affects the number and distribution of eigenfrequencies in the range of interest. Comparison with a conventional batch of cantilevers of the same size as the proposed structures shows noticeable improvement in electric charge generation.
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
- Concentration of normal stresses in flat plates and round bars with periodic notches
[Articolo su rivista]
Dragoni, Eugenio; Castagnetti, Davide
abstract
The stress concentrations produced by tensile loading of elastic solids with periodic notches are addressed. The criterion suggested by Neuber, which likens the periodic notch to a single notch of similar shape but smaller depth, is evaluated. According to Neuber, the depth reduction factor only depends on the ratio between the depth and pitch of the periodic notch, regardless of its particular shape. This work benchmarks the criterion against many axially loaded flat plates and round bars with periodic V-notches, which are analysed by means of the boundary element method. The investigation highlights a strong disparity between Neuber’s predictions and numerical findings. However, upon slight adjustment of the depth reduction factor with respect to Neuber’s proposal, a satisfactory agreement is achieved. The good correlation holds true both for shallow notches (notched semi-infinite plate) and for deep notches (notched plates or bars of finite width), which were not covered in Neuber’s work.Excellent correspondence is also found for the stress concentration around an infinite row of equispaced circular holes loaded longitudinally, a solution taken from the literature as a testcase. These results lead to the conclusion that Neuber’s criterion, supplemented with the newly disclosed depth reduction factor, can be applied to periodic notches of whatever geometry under normal stresses.
2010
- 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
- Fractal-inspired multi-frequency structures for piezoelectric harvesting of ambient kinetic energy
[Relazione in Atti di Convegno]
Castagnetti, Davide
abstract
The investigation of energy harvesting devices, able to convert freely-available ambient energy into electrical energy, has significantly improved. To this aim, the most suitable form of ambient energy is the kinetic one, being almost ubiquitous and easily accessible. Among the available conversion technologies, piezoelectric energy harvesting devices are one of the most promising, due to their simple configuration and high conversion efficiency. The most demanding task is to identify simple and efficient multi-frequency structures in the ambient vibration range. To this aim, this work proposes four fractal-inspired structures for piezoelectric energy harvesting. Through computational analysis, their frequency response is calculated up to 100Hz. The structures are examined both in the micro and macro scale and the effect of the iteration level of the fractal geometry is also assessed. By considering the bending strain associated to each mode shape, a quantitative criterion to assess the harvesting efficiency of the proposed structures is introduced.
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.
2010
- Strutture multifrequenza ispirate a geometrie frattali per il recupero piezoelettrico dell’energia cinetica ambientale
[Relazione in Atti di Convegno]
Castagnetti, Davide
abstract
La ricerca su dispositivi per il recupero di energia, che siano in grado di convertire l’energia liberamente disponibile nell’ambiente in energia elettrica, è cresciuta significativamente. A questo scopo, la forma di energia ambientale più adatta è quella cinetica, essendo pressoché ubiqua e facilmente accessibile. Tra le differenti tecnologie di conversione, i dispositivi piezoelettrici per il recupero di energia sono tra i più promettenti, grazie alla loro semplice configurazione ed alta efficienza di conversione. L’attività più complessa riguarda l’individuazione di strutture multifrequenza, semplici ed efficienti, nell’intervallo di vibrazioni ambientali. A questo scopo, questo lavoro propone quattro strutture ispirate a geometrie frattali per il recupero di energia mediante materiale piezoelettrico. Svolgendo delle analisi computazionali, si calcola la loro risposta in frequenza fino a 100Hz. Le strutture sono esaminate sia nella scala micro che in quella macro e si valuta anche l’effetto del livello di iterazione della geometria frattale. Considerando le deformazioni flessionali associate a ciascuna forma modale, si introduce un criterio quantitativo per valutare l’efficienza di recupero energetico delle strutture proposte.
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
- Standard finite element techniques for efficient stress analysis of adhesive joints
[Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract
The paper documents ongoing research in the field of stress analysis of adhesive bonded joints and aimsat developing efficient and accurate finite element techniques for the simplified calculation of adhesivestresses. Goal of the research is to avoid the major limitations of existing methods, in particular theirdependency on special elements or procedures not supported by general purpose analysis packages.Two simplified computational methods, relying on standard modelling tools and regular finite elementsare explored and compared with the outcome of theoretical solutions retrieved from the literature andwith the results of full, computationally intensive, finite element analyses. Both methods reproduce theadherends by means of structural elements (beams or plates) and the adhesive by a single layer of solidelements (plane-stress or bricks). The difference between the two methods resides in the thickness andin the elastic properties given to the adhesive layer. In one case, the adhesive thickness is extended up tothe midplane of the adherends and its elastic modulus is proportionally increased. In the other case, theadhesive layer is maintained at its true properties and the connection to the adherends is enforced bystandard kinematic constraints. The benchmark analyses start from 2D single lap joints and are thenextended to 3D configurations, including a wall-bonded square bracket undergoing cantilever loading.One of the two simplified methods investigated provides accurate results with minimal computationaleffort for both 2D and 3D configurations.
2008
- Calcolo efficiente del comportamento strutturale di costruzioni incollate complesse
[Relazione in Atti di Convegno]
Dragoni, Eugenio; Castagnetti, Davide; Spaggiari, Andrea
abstract
Il lavoro è orientato allo sviluppo di tecniche computazionali efficienti ed accurateper l’analisi semplificata del comportamento elastico e post-elastico di giunzioni e di struttureincollate. L’obiettivo è superare le principali limitazioni dei metodi di calcolo esistenti, inparticolare la loro dipendenza da elementi speciali o da procedure non implementate negliapplicativi commerciali più diffusi. Si propongono due modelli ridotti, entrambi basati sullarappresentazione degli aderendi mediante elementi strutturali (travi o gusci) e dell’adesivo permezzo di un singolo strato di elementi solidi (tensione piana o esaedri). La differenza tra i duemodelli risiede nel fatto che in un caso lo spessore dell’adesivo è esteso fino al piano dimezzeria degli aderendi e le proprietà elastiche sono incrementate proporzionalmente.Nell’altro caso, invece, lo strato adesivo mantiene le sue proprietà reali e la connessione agliaderendi è realizzata mediante vincoli cinematici convenzionali. Le analisi di verificariguardano il campo elastico ed il campo post-elastico. In entrambi i casi si effettua ilconfronto tra modelli ridotti e modelli completi, computazionalmente onerosi. Per l’analisipost-elastica si fa riferimento anche a prove sperimentali. Le analisi in campo elastico sonocondotte su una serie di configurazioni bidimensionali (giunto a sovrapposizione semplice) esono poi estese a due configurazioni tridimensionali (giunto a sovrapposizione semplice emensola a squadretta). In campo post-elastico il modello ridotto che ha fornito i miglioririsultati in campo elastico è applicato ad una giunzione T-Peel sollecitata fino a collasso perla quale il criterio che regola il cedimento dell’adesivo è basato sul concetto delle tensioni“regolarizzate”. Nel complesso, i risultati mostrano un buon accordo tra i modelli ridotti ed imodelli completi nella previsione sia delle tensioni elastiche nell’adesivo che delcomportamento post-elastico fino a collasso. Si riscontra inoltre, a favore dei metodi ridotti,una drastica diminuzione dei tempi di calcolo, in particolare per geometrie tridimensionali.
2008
- Contact force distribution in the interference fit between a helical spring and a cylindrical shaft
[Relazione in Atti di Convegno]
Castagnetti, Davide; Spinella, Igor; Dragoni, Eugenio
abstract
This paper deals with the analysis of the contact forces developed by a helical spring shrink fitted on acircular shaft. This interference fit is an effective, fast to apply, reversible and inexpensive fastener. An analyticalsolution able to predict the contact forces distribution and the maximum thrust which the system can withstand hasbeen developed. The analytical results have been compared with a finite element analysis confirming theeffectiveness of the developed formulas.
2008
- Elastostatic contact model of rubber-coated truck wheels loaded to the ground
[Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio; Scire' Mammano, Giovanni
abstract
The solid wheels often foundonindustrial trucksmaybe subject to failure of the wheels’rubber coating under certain load conditions. To date, there has been no adequate analyticalmodel to predict these conditions and the design of these wheels has been based on costlytrial and error. In this work, an elastostatic analytical model is developed, which describes theinteraction of the wheel with the rigid ground in terms of relative approach, contact width,and contact pressure for a given load applied to the wheel. This model has been validated bycomparison with both experimental measurements and finite-element analyses, showing strongagreement for all three parameters. The results of the proposed model are more accurate thanthose of previous analytical models reported in the literature for rubber-coated rotary equipment.The new model can be used to design against creep or excessive deformation of the wheel coating.
2007
- Analisi del contatto elastico tra corpi assialsimmetrici parzialmente conformi
[Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio; SCIRE' MAMMANO, Giovanni
abstract
Il lavoro presenta un’attività di ricerca volta a verificare l’applicabilità della soluzione hertziana a configurazioni di contatto tra corpi assialsimmetrici, non direttamente riconducibili alle geometrie studiate da Hertz. Si considerano quattro configurazioniassimilabili a casi frequenti nella pratica industriale e se ne esaminano in particolare due: sfera su cono e toro su cono. L’analisi, condotta col metodo dell’elemento finito, è svolta informa sistematica facendo variare tutte le grandezze geometriche e di materiale che, secondo il modello di Hertz, influiscono sul contatto. Per ciascuna configurazione sivalutano tre differenti livelli dell’angolo di pressione del contatto. I risultati ottenuti numericamente mostrano una buona corrispondenza con la previsione analitica del modelloclassico di Hertz, confermandone l’applicabilità. Si presentano infine formule pratiche per una diretta applicazione delle formule hertziane a tali casistiche assialsimmetriche ed unaindagine che individua il dimensionamento ottimale dei membri a contatto per minimizzarne la sollecitazione a parità di carico totale applicato alla coppia.
2007
- Dynamic modelling of composite acoustic boxes for automotive applications
[Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio; Rubini, Riccardo
abstract
Abstract: Automotive components must withstand shock loads and random vibrations during service which heavily affect their structural integrity. In this paper, an automotive acoustic box supporting two speakers for a car radio system is analysed. The box is made of talc-reinforced polypropylene, an injection-mouldable polymer. Shock load analysis and random response analysis are performed.
2007
- Metodi efficienti agli elementi finiti per l’analisi a collasso di strutture incollate
[Relazione in Atti di Convegno]
Castagnetti, Davide; Spaggiari, Andrea; Dragoni, Eugenio
abstract
Il presente lavoro verifica l’applicabilità di un modello computazionale ridotto perl’analisi a collasso di giunzioni strutturali incollate. Il modello, basato sullarappresentazione degli aderendi mediante elementi strutturali di tipo trave e dell’adesivoper mezzo di un singolo strato di elementi in tensione piana, è stato precedentementeverificato per la previsione delle tensioni elastiche in un giunto a semplice sovrapposizione.Lo stesso modello viene ora applicato ad una configurazione T-Peel, sollecitata oltre illimite elastico. Il cedimento dell’adesivo è condizionato dal confronto tra le tensionimassime di tipo “regolarizzato”, calcolate nell’adesivo, ed una tensione critica propria diquest’ultimo. Il modello numerico, risolto sia in forma implicita che in forma esplicita, èconfrontato con un modello computazionale completo e con risultati sperimentali diletteratura. Dal confronto emerge un buon accordo dei risultati, sia in termini di forzamassima all’inizio del collasso che di evoluzione del carico durante il collasso. Grazie allesemplificazioni adottate, il metodo ridotto ha permesso di ridurre l’onere di calcolo da 350ad oltre 2100 volte rispetto al modello numerico completo, senza apprezzabile perdita diaccuratezza dei risultati.
2007
- Robust set up of experimental procedure for monotonic tensile test on polyethylene specimens
[Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio; SCIRE' MAMMANO, Giovanni
abstract
Polyethylene pipes for water conveyance may present sensitivity to disinfectants employed to assure water potability. In particular, chlorine based disinfectants could affect their structural properties, which are mainly assessed through monotonic tensile test. A systematic experimental plan, performed to investigate the effects of chlorine based disinfectant on the mechanical properties of PE pipes, emphasized the high variability of the measured parameters, in particular with regard to percentage elongation at fracture. A research aimed at identifying whichfactors affect the outcome of the monotonic tensile test, and which combination of such factors provides a robust setup of the experimental procedure, is presented here. A systematic approach has been adopted considering a fullfactorial experimental plan, and varying each factor between two levels. From the outcome of the experimental results the influence of the test speed, the cutting die, the cutting direction and the pipe diameter has been assessed.
2006
- Analisi efficiente delle tensioni in giunzioni incollate mediante tecniche agli elementi finiti
[Relazione in Atti di Convegno]
Castagnetti, D; Dragoni, Eugenio
abstract
2006
- Efficient stress analysis of adhesively bonded joints by finite elements techniques
[Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio
abstract
The paper documents ongoing research on the field ofstress calculations in the adhesive layer of bonded joints andbonded structures. Aim of the research is to develop simple,general, portable, efficient and accurate finite elementtechniques for adhesive stress analysis and strength assessmentof the joint. Among four methods envisioned, two methods arepresented for 2D configurations and applied to a referencesingle-lap configuration. In both methods, the adherends aredescribed by means of beam elements and the adhesive layer bya single string of plane-stress solid elements. The plane-stresselements have either the original thickness of the true adhesivelayer or an expanded thickness up to the offset betweenadherends. Beams and plane-stress elements are connected bystandard constraining techniques (tied mesh) offered by thepackage employed (ABAQUS). The stress results provided bythe two methods are compared step by step with the predictionsof analytical models retrieved from the literature and with theoutcome of a full, computationally-intensive finite elementmodel using solid plane-stress elements for both adhesive andadherends. The simplified method using a single layer of planestress elements with the same thickness and properties as the true adhesive layer provides very promising results in terms of stress accuracy and computational efficiency.
2006
- Simulazione dinamica e sintesi strutturale per il contenimento delle vibrazioni di un cogeneratore termoelettrico
[Relazione in Atti di Convegno]
Benetti, Matteo; Castagnetti, Davide; Dragoni, Eugenio; Rubini, Riccardo; E., Zanichelli
abstract
This paper deals with the design and the vibration analysis of a small-size (30 kVA) cogeneration unit, which can produce electric and thermal energy both for domestic and industrial appliances. To optimize the machine unsatisfactory dynamic behaviour (vibrations and noise), a discrete system approach was at first considered, also employing the design of experiments (DOE) technique to easily attain the best solution, then FEM analysis and measures with accelerometers on a prototype were performed. The solutions obtained allowed a significant improvement of the cogenerator behaviour, without adding any costs, being the final structure of the machine almost equal to the original version.
2005
- Kinematic analysis of universal split heads for milling machines
[Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio; SCIRE' MAMMANO, Giovanni
abstract
Most milling machines are equipped with split heads aimed at orienting the tool at any angle with respect to the workpiece. Typical examples are given in Fig. 1. The general geometry of these heads can be reduced to the linkage shown in Fig. 2. Each particular architecture is achieved by choosing angle θ between the member axis and by selecting the orientation of the tool with respect to the final member. The head features two degrees of freedom, embodied by the joint rotations α and β, through which the configuration can be changed to adjust the orientation ofthe tool. The kinematic analysis of the head can be posed in two ways: a) direct analysis if the values of the joint rotations, α and β, are given and the orientation of the tool axis with respect to the machine frame is sought; b) inverse analysis if the desired orientation of the tool axis is given and the joint rotations, α and β, are sought that enforce that orientation. This paper provides the analytical solution of both direct and inverse problems. The work falls within a research program carried out with the partnership of a renowned machine tool manufacturer of Reggio Emilia.
2005
- Modello elastostatico del contatto al suolo di ruote con rivestimento elastomerico
[Relazione in Atti di Convegno]
Castagnetti, Davide; Dragoni, Eugenio; SCIRE' MAMMANO, Giovanni; P., Borghi
abstract
The paper deals with the elastostatic analisis of rubber-layered wheels for industrial trucks. An analytical model is developed which describes the interaction of the wheel with the rigid ground in terms of relative approach, contact width and contact pressure for a given load applied to the wheel. The comparison is favourable against experimental measurements and finite element analyses for all three parameters. The analytical model is a good tool for the prediction of fatigue failures and ofthermomechanical failures of the wheels undergoing heavy service conditions.
2005
- Optimal aspect ratio of interference fits for maximum load transfer capacity
[Articolo su rivista]
Castagnetti, Davide; Dragoni, Eugenio
abstract
The stress state in frictional interference fits under torsional and axial loading is examined. The optimal ratio between the inside and outside diameters of the hub is calculated, which maximizes the load transmitted by the joint. Design formulae and charts are provided, giving the most efficient aspect ratio of the hub for all practical situations. It is found that the maximum load capacity is achieved for an aspect ratio in the range from 0.5 to 0.7, regardless of the frictional coefficient (up to 1), of the kind of loading (torsional or axial), and of the material response (brittle or ductile).
2004
- Development and testing of an inflatable capsule for the YES2 project
[Relazione in Atti di Convegno]
Benetti, M.; Castagnetti, D.; Dragoni, E.; Van Der Heide, E. J.
abstract
The YES2 project features a lightweight (about 10 kg), single-stage, inflatable reentry capsule. This paper describes the development, the manufacturing and the testing of the first capsule prototype. The prototype capsule is a 1.5 m diameter sphere-cone. Rigidity is provided by 5 stacked inflatable tori, connected together for single-stage inflation. A laminated solution is used for each torus, comprising two layers of surface-treated Kapton® film for air tightness, and a single layer of Zylon® fabric for structural strength. Design trade-offs involving the location of the valves and the connections to the thermal protection system are addressed and future steps for optimization and testing are discussed. The flight design contains an ablative foam nose and an Alumina-Nextel flexible insulating cover. The design of the capsule is driven by the following aims: a) high stability during reentry, both in the hypersonic and in the subsonic phase; b) low stresses in the inflatable structure; c) high ratio of drag area to total weight; d) affordable thermal loads; e) simple manufacturability, foldability and deployment; f) single-stage inflation already in space for inherent safety, allowing the capsule to land in mainland Europe for the first time in history. Samples of the materials employed have been prepared and tested. Adhesively-bonded Kapton® samples have been tested only for durability at high temperatures (200°C), since the Kapton® layer undergoes no structural loads. Zylon® samples (both bonded and sewn) have been tested under load at high temperatures (200°C). The samples were in the form of cylinders inflated at 250 kPa, which is the maximum expected gas pressure during re-entry. A prototype of the inflatable capsule has been manufactured and assembly technologies are discussed in the paper. The model will be submitted to aerodynamic tests for shape stability (fluttering). The capsule is designed specifically for Earth entry (sample return), but the advantages of the innovative inflatable concept introduced can readily be exploited for future interplanetary missions.
2003
- Concept selection and design of the inherently safe re-entry capsule for YES2
[Relazione in Atti di Convegno]
Kruijff, M.; Heide, E. J. V. D.; Dragoni, E.; Castagnetti, D.; Ferretti, S.
abstract
The design and concept selection of the inherently safe re-entry capsule for the 2 nd Young Engineers' Satellite (YES2) are discussed. A significant investment to evaluate, combine and analyze first the simple ideas is made. The steps define the YES2 concept selection logic include, reduce classes, strip the concept from attributes, merging all the options, and options evaluation and initial design. Material tests were performed and simulation tools were developed for re-entry, heat flux, CFD, FEM, stability, and pressure-shape interaction.