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Andrea SORRENTINO
Ricercatore Legge 240/10 - t.det.
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.
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
- 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
- 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
- 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.
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
- 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
- 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.
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
[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
- 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
- Instabilità di pull-in per pinze in nano-tubi di carbonio: formulazione analitica e convalida sperimentale di macro modelli
[Relazione in Atti di Convegno]
Bianchi, Giovanni; Sorrentino, Andrea
abstract
Il presente lavoro investiga il fenomeno dell’instabilità di pull-in di un attuatore NEMS azionato elettrostaticamente, composto da pinze in nano-tubi di carbonio (CNT). Ad una determinata tensione critica, definita tensione di pull-in, la forza di attrazione elettrostatica tra i due nano-tubi causa la chiusura improvvisa del dispositivo definendo il limite di stabilità elastica del sistema. Il lavoro ha l’obiettivo di stimare i limiti inferiore e superiore di pull-in di un dispositivo NEMS CNT tramite l’applicazione di un accurato modello analitico che permette di determinare i valori limite di tensione e deflessione dell’attuatore. Al fine di convalidare il modello analitico, è stato realizzato un prototipo di attuatore in scala millimetrica per la misurazione della tensione critica per differenti configurazioni geometriche del dispositivo. I risultati ottenuti sono ottimi con una differenza tra analitico e sperimentale per la tensione di pull-in in un intervallo tra lo 0.83% ed il 13%.
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
- Modellazione, prototipazione e convalida sperimentale di un nuovo microfono basato su film di PVDF
[Relazione in Atti di Convegno]
Sorrentino, Andrea
abstract
Il presente lavoro si focalizza sulla progettazione, prototipazione e validazione di un nuovo tipo di microfono in stampa 3D di dimensioni millimetriche basato su un film di polivinildenfluoruro (PVDF). Il piezoelettrico PVDF è ampiamente utilizzato per lo sviluppo di sensori in diverse applicazioni grazie alle sue proprietà ferroelettriche e al basso costo. L’obiettivo del lavoro è quello di progettare un sensore acustico ad elevata sensibilità in grado di massimizzare la forza, dovuta all’onda acustica, che si scarica sul film piezoelettrico di PVDF grazie ad un innovativo meccanismo di trasduzione della pressione. Il lavoro presenta un dettagliato modello analitico che descrive il comportamento meccanico del sistema. Tramite un algoritmo di ottimizzazione metaeuristico, è possibile calcolare i parametri geometrici ottimali del sistema che massimizzano la forza acustica sul film piezoelettrico. L’architettura di microfono proposta, realizzata tramite la stampa 3D, possiede un valore di sensibilità dieci volte maggiore rispetto alla configurazione standard di tipo flat in una gamma di frequenze da 10 a 2500 Hz.
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
- 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.
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