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Small-scale energy harvesting to power self-powered electronic devices is tremendously increasing. In this context, the ability to combine thermal and mechanical energy harvesting using smart materials deserves more attention for further study. We have presented the feasibility of using P(VDF-TrFE) piezoelectric polymer coupled with NiTi shape memory alloy (SMA) to harvest both mechanical and thermal energy in simple scalable devices. A novel hybrid composite consisting of SMA, and P(VDF-TrFE) has been developed without any complex composites or patterned structures, which couples the piezoelectric effect of the poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) and the shape memory effects of NiTi SMA. We have also fabricated a multi-layer SMA/PEN/P(VDF-TrFE) device using epoxy as an interface and bonding layer. During bending, the P(VDF-TrFE) device with an active area of 3.68 cm2 generated an output voltage of 8 V and an output power of 6.25 µW. When coupled with NiTi SMA to create a hybrid composite thermoelectric material, the device can convert the phase change associated with SMA, and thus thermal energy is converted to mechanical energy and finally into electrical energy. The SMA/P(VDF-TrFE) hybrid composite produced an output voltage of ∼2 V for one cyclic heating and cooling of the device. This is a promising approach for the further development of coupled hybrid energy harvester devices for the powering of small-scale electronic devices such as sensors, MEMS, or biomedical devices.

Hydrogen containers type IV should stand for severe operational conditions, such as temperature variations from −40 °C to 85 °C, and depressurisation from high-pressure above 95 MPa to near atmospheric pressure. There are experimental studies showing that container's liner, usually a thermoplastic material, can suffer blistering and buckling during depressurisation process. It has also been proved that elastomers under high-pressure conditions, which are submitted to a rapid depressurisation, can suffer the formation of cavities because of the dissolved gas. The formation of microscopic defects in thermoplastic materials because of rapid depressurisation is less common in scientific literature. In this paper, we evaluate by numerical means the maximum depressurisation rate a polymer sample can stand before cavitation occurs. By studying the influence of geometrical and pressure conditions, so as material's properties, we obtain algebraic equations that define maximal depressurisation rate. Results of present work serve to estimate performance of liner materials, with the scope of safe and fast container discharge.

The present study deals with the modeling of a single intermetallic powder particle likely to form reversibly a hydride material while submitted to hydrogen gas. These materials that make part of the so-called hydrogen solid storage family are one of the most employed media used in order to store hydrogen. During hydrogenation cycling, the initially coarse powder expanses due to hydrogen absorption and shrinks over hydrogen desorption. The powder granularity also decreases with the number of cycles but seems to stabilize to reach a mechanical limit. One plausible explanation is that large particles decrepitate into smaller ones because, only due to their geometry, they are less able to accommodate large volume changes and thus, internal stresses are higher than in small particles. This is the hypothesis we intend to discuss in the present work, hypothesis that has never been investigated, in our knowledge, from a mechanical point of view. Within the framework of a simple analytical model, several parameters (initial particle size, material behavior parameters …) are varied in order to evaluate their influence on the propensity of the particle to decrepitate. After introducing the context, the model that allows describing the fragile elastic mechanical response of a single spherical particle submitted to hydrogen is presented. Computed stress and strain along the radius of particles with different size or elastic properties lead to the main conclusion: considering a spherical particles made of an undamaged uniform elastic brittle two phase material is insufficient to evidence dependency of the mechanical response on the particle size. Consequently, this primary model is unable to validate our hypothesis, according which the limit size of decrepitating is driven by the mechanical accommodation of volume changes. This implies that a description of heterogeneities or geometric irregularities must be introduced to account for the phenomenon of particle size stabilization during decrepitating. After results are presented and discussed, opportunities to deepen the present analysis are proposed to account for physical observations of the decrepitating phenomenon, and are to be developed in forthcoming publications.

International audience; Design has an important influence on mechanical response of endodontic instruments made of shape memory alloys. The experimental and numerical prediction of their thermomechanical response is necessary to improve their behavior during operating inside root canal. Due to the curved and tapered shape of the dental canal, endodontic files are subjected to rotating bending during the root canal preparation phase. These rotative bending could ever be combined with torsion when the instruments are engined in the root canal. Bending and torsion tests available in the standard ISO 3630-1 do not take into account this combined loading leading to a response different from the one obtained by superposition of separated bending and torsion loadings. This article details the design and the realization of bending–torsion testing device particularly adapted to shape memory alloy endodontic files. It allows to control the torsion and the bending rotations in a separate or a combined way. Qualification tests using this bending–torsion testing device on NiTi wires showed a good agreement between the experimental and the simulated responses. Finally, this bending–torsion testing device allowed to analyze the response of various NiTi endodontic files, currently used in endodontics, subjected to bending, torsion, and combined bending–torsion loadings. Obtained results showed clearly that combined bending–torsion loading changes significantly the shape memory alloy file response.

Polymer materials subjected to gases at high-pressure can have issues during decompression. For instance, a sudden decompression can promote the formation of cavities inside the material. This phenomenon is known as cavitation or eXposive Decompression Failure (XDF). There is a body of scientific articles discussing different aspects of cavitation phenomenon, which indicate that the degree of damage is proportional to saturation pressure, depressurisation rate, and material thickness, among other parameters. In this article we propose a general approach by non-dimensional parameters to estimate the risk of cavitation. Numerical results were validated with bibliographic evidence of cavitation in polymers, for both thermoplastics and elastomers. Present results can be used as guidelines for design of systems involving polymers under high pressure, such as o-rings or liners in type IV hydrogen containers.

The flexibility of NiTi based endodontic files is improved by heat treatment, leading to lower risk of failure, ledges, and canal transportation during the preparation of curved root canals. The aim of this study is to investigate and clearly highlight the influence of every parameter of heat treatment on the flexibility of NiTi wires and thus of endodontic instruments. A full factorial Design of Experiment (DoE) and a designed bending–torsion bench following the ISO 3630-1 standard were used for this investigation. Temperature, holding time, and cooling method were selected as contributing factors, while maximum bending moment, hysteresis size, and stiffness during martensitic transformation were selected as outputs. Regression analysis was performed to estimate the relationship between contributing and output variables to assess how the experimentation fits with the model. The experimental results showed that wires heated at 425 °C for 30 min are more flexible. Moreover, heat treatment temperature is the most critical factor influencing the flexibility and hysteresis size of the NiTi wire followed by the holding time, while the cooling method has a negligible effect. The regression analysis showed that the model is effective at predicting the relationship between contributing factors, bending moment response, and hysteresis size.

International audience; Energy harvesting is one of the most promising research areas to produce sustainable power sources from the ambient environment. Which found applications to attain the extensive lifetime self-powered operations of various devices such as MEMS wireless sensors, medical implants and wearable electronic devices. Piezoelectric nanogenerators can efficiently convert the vastly available mechanical energy into electrical energy to meet the requirements of low-powered electronic devices. Among the piezoelectric materials, poly (vinylidene fluoride) (PVDF) and its copolymers are extensively studied for the development of energy harvesting devices. Due to the outstanding properties such as high flexibility, ease of processing, long-term stability, biocompatibility makes them a promising candidate for piezoelectric generators. Nevertheless, compared to piezoceramic materials, PVDF based generators produce lower piezoresponse. Over the last decades, tremendous research activities have been reported to endorse the performance of PVDF based energy harvesters. This review article mainly focused on the recent progress in the performance improvement with processing methods, piezoelectric materials, different filler loading. The new developments and design structures will lead to an increase in piezoelectricity, alignment of dipoles, dielectric properties and subsequently enhance the output performance of the device. Electronic circuits play a vital role in energy harvesting to efficiently collect the developed charge from the device. Here, we have proposed a detailed description of the electronic circuits. Also, in the application part deals with the recent progress in flexible, biomedical and hybrid generators based on PVDF polymers.

Hydrogen storage at high pressure is currently attained by the use of different materials, such as elastomers in sealing joints, thermoplastics and thermosetting polymers in high-pressure containers, and metallic tube connections. Hydrogen containers type IV use a thermoplastic polymer for hydrogen tightness and composite materials for mechanical resistance, usually made with thermosetting resins and carbon or glass fibre. International standards impose a wide range of operative temperatures for such containers, from −40 °C to 85 °C. Once saturated with hydrogen at high pressure, a fast depressurisation process can create stress in the polymeric materials, causing its degradation by the formation of cavities. In a previous work, we were able to make a generalization of cavitation risk by the use of non-dimensional parameters, based on a simplified mechanical failure model. We observed that for the model, material's hydrogen diffusivity and yield strength are of upmost importance. In present work, we analyse the effect of temperature on these two properties, as they have an inverse evolution with temperature. Results confirm the pertinence of considering temperature in the whole application range of technology under analyse.

The share of renewable energies in the energy mix is gradually increasing. This transition brings many challenges in the management of electricity grids, especially because of the fluctuating and intermittent nature of renewable energies. Therefore, hydrogen represents one of the keystones for the sustainable exploitation of our energy resources. Hydrogen allows storing in the long term not consumed but available electricity, and hydrogen is a ‘fuel’ for mobile, nomadic and remote site applications. Once produced and awaiting consumption, the hydrogen must be stored in optimal conditions of safety and efficiency with regard to the application and its location. The most mature solution to date is the storage under the compressed form, which consists in keeping the hydrogen gas in a container at increasing pressures in order to increase the energy density; cryogenic storage is now well controlled but generally reserved for very specific applications for reasons inherent to the technology and because of significant costs; and finally the so-called ‘solid storage’, to which the scientific community has been showing a marked interest for several decades in the hope of identifying a lasting solution likely to replace advantageously other solutions. In this paper, these storage media are introduced by evoking their technological characteristics and their fields of application often justified by inherent limitations of the technology. We will also discuss the challenges still posed by these storage solutions today by linking them with the research work carried out in the Department of Applied Mechanics in FEMTO ST Institute.

We present an analytical model to analyze the bending of a bimorph beam comprising of piezoelectric material (PM) and shape memory alloy (SMA) thin layers. The model starts from the governing equations of the bending beam based on the Euler-Bernoulli beam theory. The PM and SMA layers are supposed to be perfectly bonded. The linear constitutive equations of PMs are used. Using this approach, we investigate thermal energy conversion into electricity by mean of the SMA-PM bimorph. Particularly, the model takes into account cyclic thermal energy harvesting by coupling the direct piezoelectric effect and the two-way shape memory effect. In this case, the SMA is assumed to be trained prior to assembling the bimorph so that it can deform in a cyclic way upon cyclic thermal loading without applying any external stress. The thermal-to-electrical conversion is achieved from the induced strain within the SMA layer upon heating which induces stress into the PM layer so that it produces an electrical potential.

The end of life of carbon fibre-reinforced polymer (CFRP) structures represents a major challenge to the aerospace industry, as new European regulations are demanding recycling solutions that can be complicated and expensive to apply. This study aims to address new practical ways to recycle CFRP materials. CFRP materials with a polyether ether ketone (PEEK) matrix were fragmented via electrodynamical fragmentation, which exhibits several benefits compared to mechanical shredding processes, especially for composites commonly found in the aerospace industry. The fragments are characterized and reused to produce new CFRP aerospace parts. Structural testing of recycled composite parts revealed a 17% decrease of the mechanical properties compared to the novel material. The combination of these manufacturing and recycling techniques closes the cradle to cradle loop of thermoplastic CFRP.

Objectives The purpose of this study was to study the effects on Young's modulus and conversion degree of variations in polymerization conditions during the 3-point bending test of composite samples in accordance with the ISO 4049 standard. Methods Three nanocomposites were used in the 3-point bending test based on the conditions described in the ISO 4049 standard. Samples of 2 mm × 2 mm x 25 mm were fabricated and tested with a different number of irradiation points and irradiation time. Conversion degree of the samples were also measured by micro-Raman spectroscopy and correlated with the Young's modulus values obtained for each one. Results The variations in curing protocol during specimen's realization influenced the Young's modulus and degree of conversion of all composites. These two properties correlated well. The ISO 4049 standard defines the conditions for performing the properties tests of composites to allow reproducibility and comparison of different studies. Concerning the 3-point bending test, even a minimal change in the state causes differences in the results obtained. The standard should thus clarify the tools that can be used when producing samples in order to minimize discrepancies. Significance The influence of the parameters surrounding the design of the samples should be controlled and defined so as not to include bias in the studies carried out. This will allow literature studies to be compared with more accuracy.

International audience; This paper presents an experimental characterization of the damping capacity of the Fe-30Mn-6Si-5Cr subjected to cyclic tensile tests. Fe-SMA specimens underwent a specific heat treatment to improve their properties. At room temperature, the studied Fe-SMA showed different microstructures depending on the applied heat treatment. In order to define the best initial properties guaranteeing maximum pseudoelastic damping capacity (PDC), different types of initial microstructures were investigated: purely austenitic state and biphased states (austenite + stress induced and/or thermal martensite). The alloy was studied under different parameters such as loading-unloading frequencies, prestrain amount and operating temperatures. Experimental results were analyzed by computing the energy dissipated from hysteresis loops areas as well as the associated loss factor. Consequently, the beneficial role of the stress-induced martensite (${M}^{\sigma}$) was demonstrated and quantified. Furthermore, it was found that the PDC seems to have slightly improved by the presence of thermal martensite (Mth) and increased with temperature increase. As a result, an economical and efficient initial microstructure for damping application of the studied SMA has been defined.

International audience; Shape memory alloys (SMA) are good candidates especially for being used as passive dampers. In order to develop the use of these alloys in structural vibrations control, the dynamical behavior of a NiTi helical spring is led, and the damping effect investigated. First, compression tests on the spring are carried out. These tests allow us to notice the effect of the maximal compression displacement, the cyclic behavior and the compression rate on its mechanical behavior. A finite element model analysis of the compression tests is then proposed. In consequence, the materials parameters have been identified after a numerical convergence test. In order to characterize the dynamical behavior of the spring, the innovative tool called equivalent complex stiffness is developed and used. Finally, the one degree of freedom vibration equation is solved with this equivalent complex stiffness. The solution of this equation clearly shows the non linear dynamical behavior of the SMA spring and its damping potential.

This paper focuses on the mechanical behaviour of PP/MWCNT composites. The Young’s modulus and the rupture strain versus nanotubes content are investigated. Four grades are made: 1 wt%, 2 wt%, 4 wt%, 8 wt%. The achievement of the tensile test samples require three phases: the mixing stage, the identification of the rheological behaviour stage and the injection molding stage. In the mixing stage, one must be careful that there’s a good dispersion of the MWCNT in the polymer matrix. The rheological behaviour of the PP/MWCNT composite show that the useful injection molding parameters of the neat PP can be reinvestigated for the PP/MWCNT composites. Results of the mechanical experiments clearly show a high dependence of the Young’s modulus and the rupture strain with the CNT content.

Shape memory alloys (SMAs) are good candidates for being used as passive dampers, strain sensors, stiffness or shape drivers. To design these structures, an implementation which takes into account the obvious asymmetry between tension–compression and the thermomechanical coupling taken into account with the introduction of the heat equation is required. We present in this paper an implementation of a phenomenological model based on the R L model (Raniecki and Lexcellent [B. Raniecki, C. Lexcellent, Eur. J. Mech. A/Solids 17 (2) (1998) 185–205]) in a finite element code called COMSOL© which allows to build automatically many loading cases in force or displacement. The results clearly show the influence of the temperature on the pseudoelastic behavior of SMA and on the asymmetry between tension and compression. This implementation could be useful to simulate complex three dimensional SMA structures as dynamical devices.

International audience; This study aims to describe the response of a Hydrogen solid storage cylindrical tank, which is filled by a metal hydride alloy (FeTi-X) and subjected to several types of solicitations, such as: pressure, external temperature, and inlet and outlet flow. The model used in this work is classified as a macro scale model [1-2] it describes the Hydrogen absorption and desorption processes, and predicts the time-space profile of: local temperature, local reaction rate, local equilibrium pressure, local heat generated/needed, and then the homogeneous temperature, equilibrium pressure and reaction rate temporal profiles can be computed. In addition, the effect of cycling (absorption/desorption) on thereaction rate is monitored in order to optimize the operation and get at the same time a sufficient outlet flux coupled with a high reaction rate.

Sintered bulk ceramics, such as PZT are brittle materials. This macroscopically implies a statistical distribution of the ultimate strengths, because defects, such as pores or cracks are responsible for the initiation of the specimen failure. Another aspect of this fracture phenomenon is the crack propagation inside the material, along grain boundaries or through the grains themselves. An experimental study was carried out on hard and soft PZT by means of a scanning electron microscopy (SEM) quantitative analysis of tensile fractured areas. This reveals that the fracture mode is mixed, although it seems to be rather intragranular for hard ceramics and more intergranular for soft ones. Further investigations deal with the characterization of the residual porosity, which has to be distinguished from the population of critical defects. This porosity is located at grain boundaries and likely acts also as a stress concentrator and has an effect on the fracture mode and mechanical properties. For doped hard and soft PZT, a careful analysis of the microstructure is thus achieved through transmission electron microscopy (TEM) micrographs. Furthermore, domain structure is analysed for hard and soft PZT.

International audience; The aim of the present paper is the development of endodontic Cu-based single crystal Shape Memory Alloy (SMA) instruments in order to eliminate the antimicrobial and mechanical deficiencies observed with the conventional Nickel-Titane (NiTi) SMA files. A thermomechanical constitutive law, already developed and implemented in a finite element code by our research group, is adopted for the simulation of the single crystal SMA behavior. The corresponding material parameters were identified starting from experimental results for a tensile test at room temperature. A computer-aided design geometry has been achieved and considered for a finite element structural analysis of the endodontic Cu-based single crystal SMA files. They are meshed with tetrahedral continuum elements to improve the computation time and the accuracy of results. The geometric parameters tested in this study are the length of the active blade, the rod length, the pitch, the taper, the tip diameter, and the rod diameter. For each set of adopted parameters, a finite element model is built and tested in a combined bending-torsion loading in accordance with ISO 3630-1 norm. The numerical analysis based on finite element procedure allowed purposing an optimal geometry suitable for Cu-based single crystal SMA endodontic files. The same analysis was carried out for the classical NiTi SMA files and a comparison was made between the two kinds of files. It showed that Cu-based single crystal SMA files are less stiff than the NiTi files. The Cu-based endodontic files could be used to improve the root canal treatments. However, the finite element analysis brought out the need for further investigation based on experiments.

Resume Cette etude concerne le developpement de transducteurs piezocomposites destines au controle de forme de structures. Deux technologies de fabrication de piezocomposites a connectivite 0–3 sont presentees. La premiere est basee sur l'utilisation de la force centrifuge, la seconde est un procede de moulage sous pression. L'etude de deux resines et plusieurs poudres piezoceramiques permet de comparer les proprietes dielectriques et piezoelectriques des echantillons fabriques et de donner ainsi le domaine de validite des deux technologies utilisees. Les valeurs experimentales obtenues sont comparees avec des modeles issus de la litterature.

Power applications generate high stresses which can damage piezoceramic components. In this study tensile fracture of several types of PZT (hard/soft) is investigated. After validation of the specimen geometry by means of numerical simulation, samples are led to failure using a specific device. Weibull law parameters enable the characterisation of the tensile strength distribution and highlight clear differences between soft and hard ceramics. A fractographic approach emphasises the specificities of the fracture mode and the fracture origin for each type of samples.

The aim of this work is to characterize the interface between a shape memory alloy wire (SMA) and a resin epoxy matrix. More precisely, we want to associate the roughness of the wire with the adhesion between the fiber/matrix. The effect of various surface treatments applied to SMA NiTi wires on the quality of the fiber/matrix interface is presented and discussed. First, a profilometric study is carried out on the different wires. The parameters, which characterize the vertical distribution of the roughness and the wire morphology, are determined. The topographic study reveals that the surface treatments which are applied strongly modify the external surface of the wire. In the second part of this work the adhesion fiber/matrix is quantified by using a pull-out test. These experimental results are analyzed and compared with the roughness parameters. This comparative study enables us to determine the wire morphology which will guarantee the best adhesion fiber/matrix. The roughness parameters are sufficient for the choice of the wire which will be embedded into the resin.

A new phase transformation zone around a crack tip is proposed for shape memory materials. The present analysis integrates the asymmetry between tension and compression in its yield criterion. A comparison with a previous experimental investigation performed on NiTi alloys is done.

International audience; The filament winding process faces up limiting fabrication inconveniences when designing complex geometries of composite structures. Even the complete coverage of a cylindrical mandrel requires introducing deviation from geodesic trajectories. As a consequence, models for non-geodesic paths have been developed. The present research aims to establish, to solve and to validate a generic mathematical model that contributes either to wind complex shapes, or to solve common filament winding disadvantages, on the basis of an integrated strategy. This so-called unified approach leads to benefit of composite structures made by filament winding despite the limitations of the manufacturing process. Based on the mathematical description of the mandrel geometry, the theory of surfaces leads to express the local curvatures. Considering the slippage tendency of the fiber tow over the surface, a local stability criterion involving mathematical parameters of the mandrel surface is established, and a general fiber path equation can be formulated. A numerical tool is developed and applied to predict the evolution of the filament winding angle of the fiber tow placed over the surface of two axisymmetric geometries: a convex and a concave one. Experimental validation is carried out by manufacturing these geometries using a four axis filament winding machine.

International audience; The paper presents a new damage model for predicting stiffness loss due to creep loading and cyclic fatigue. The model, developed within a continuum damage mechanics framework, is based on the idea of a time-dependent damage spectrum, some elements of which occur rapidly and others slowly. The use of this spectrum allows a single damage kinematic to model creep and fatigue damage and to take into account the effect of stress amplitude, R ratio, and frequency. The evolution equations are based on similar equation than the one describing the viscoelasticity model and are relatively easy to implement. The new model is compared to the experimental results on carbon fiber/epoxy tubes. Quasi-static, creep and fatigue tests are performed on filament-wound tubular specimens to characterize the elastic, viscoelastic and plastic behavior of the composite 2 material. Varying amounts of damage are observed and discussed depending on stress level and R ratio. The experimental work aims to develop and validate the damage model for predicting stiffness loss due to creep loading and cyclic fatigue.

Objectives The study dealt with full dental prosthetic reconstruction on four implants. The aim was to analyse the influence of material parameters on the mechanical behaviour of the restored mandible compared to the natural mandible. Methods A finite element model of an edentulous mandible with prosthetic rehabilitation was established. Four materials were investigated for the framework of the prosthesis (zirconia, titanium, gold and nickel-titanium (NiTi)), as well as three cortical bone thicknesses. Various muscles were employed to simulate the main stages of mastication. Three distinct phases of mastication were modelled: maximum intercuspation, incisal clench and unilateral molar clench. Results The zirconia framework demonstrated the highest stresses and NiTi the weakest. The highest stresses in the framework were obtained during maximum intercuspation. The highest stresses at the bone-implant interface were recorded on the working axial implant during unilateral molar clench and on tilted implants during maximum intercuspation. The influence of the framework's material stiffness on the stresses at the bone-implant interface was insignificant for axial implants (except the right implant during unilateral molar clench) and slightly more significant for tilted implants. Mandibular flexion decreased with an increase of the cortical bone thickness and the stiffness of the prosthetic framework's material. Conclusions Among all materials, NiTi allowed a better preservation of the mandibular flexure, during all the mastication stages. Compared to stiffer materials, NiTi also permitted physiological mechanical conditions at the bone/implant interface, in almost all mastication stages.

International audience; Composite material components will be an essential part of ocean energy recovery devices, and their long term durability in sea water must be guaranteed. Despite extensive experience for boat structures and wind turbines few data exist to design structures subjected to a combination of mechanical loads and sea water immersion. This paper presents the first results from an experimental study, performed jointly with fibremanufacturers, and a resin supplier, to fill this gap. The experimental study is completed by numerical modelling to simulate the coupling between water absorption and mechanical behaviour. Sea water ageing is shown to result in a drop in quasi–static mechanical properties and a change in flexural mode from compression to tension at longer ageing times, which is consistent with results from the numerical simulations.

Composites will play an essential role in the development of ocean energy conversion systems, and their long term durability is critical to the success of these structures. Composites have been widely used in marine applications and in structures highly loaded in fatigue such as wind turbine blades. However, very few data are available to evaluate their performance under conditions which combine long term immersion in sea water and sustained cyclic loading. In this study composites reinforced with three different types of glass fibre and the same epoxy resin have been tested under these conditions, and the influence of aging on both static and fatigue behaviour has been quantified. Fibre type, resin and fibre/resin interface all influence the fatigue behaviour of these materials in sea water., Les matériaux composites joueront un rôle essentiel dans le développement de systèmes de conversion d’énergie marine renouvelable, et pour cette application compte tenu des contraintes liées à la maintenance une excellente durabilité à long terme s’avère indispensable. On dispose d’une bonne expérience de ces matériaux en milieu marin, et pour des applications, telles les éoliennes, où ils sont soumis à un chargement cyclique, mais on ne trouve que très peu d’informations sur leur comportement sous sollicitation cyclique dans l’eau de mer. Cet article adresse cette lacune, et présente les résultats d’une étude du comportement sous chargement quasi-statique et cyclique de composites renforcés de différentes fibres de verre et sollicités dans l’eau de mer. Pour ces conditions de chargement couplé, le type de fibre, la résine et l’interface fibre/matrice influent tous sur la durée de vie.

International audience; This paper focuses on the numerical simulation of the polypropylene / multi-walled carbon nanotubes (PP/MWCNT) flow into a twin screw mixer, during the mixing phase. The PP/MWCNT behavior obeys an innovating Carreau law enriched temperature built on the rheological properties carried out previously. The polypropylene was mixed with different MWCNTs contents (1, 2, 4 and 8 wt% of MWCNT content) and the rheological tests were performed at shear rate ranges from 10 to 210 s at four temperatures (180, 200, 220 and 240 °C). Thus the effects of the temperature and the MWCNTs content on the rheological properties of the PP/MWCNT composites were investigated. The finite element (FEM) analysis of the PP/MWCNT flow allows to compute the velocity, the shear rate and the temperature during the mixing phase period. A good agreement between the experimental measured torque on the screw and the calculated one is shown. Therefore, one can consider that the physical flow is generally well described, awaiting a numerical simulation of the PP/MWCNT mixing phase.

September; International audience

May 21-24; International audience

May 21-24; International audience

Shape memory alloys (SMAs) are good candidates for being used as passive dampers, strain sensors, stiffness or shape drivers. In order to develop the use of these alloys in structural vibration control, we present in this paper an implementation of a phenomenological model based on the Rl model (Raniecki et al 1992 Arch. Meh. 44 261–84) in a finite element code called COMSOL© which allows one to build automatically many loading cases in force or displacement. This implementation is used to simulate internal loops in order to characterize the stiffness and the damping effect by an equivalent complex Young's modulus approach under static strain offsets. The results clearly show the influence of the initial static strain offset and the amplitude of vibration on the damping and stiffness properties.

June 11-14; International audience

December 10-11; International audience

Electrical boundary conditions influence the nonlinear electromechanical behavior of ferroelectric materials. In this study, a hard and a soft PZT are tested under tensile loading in short and open circuit. Depolarization of the specimen or evolution of the electric field due to the piezoelectric effect is recorded. Nonlinear stress–strain curves are greatly affected by the electric field which appears in open circuit and reduces ferroelastic domain switching.

The compressive creep behaviour of a soft PZT has been studied. The effect of polarisation is measured and simulated by means of a viscoplastic-type model. The creep strain is linked to the amount of ferroelectric domains available to 90° ferroelastic switching. A temperature rise is found to reduce the anelastic strain but increase the creep strain itself.

The aim of this work is to collect a database from uniaxial experiments and model the material behavior. A soft PZT is tested in compression; the influence of stress rate seems to be negligible and the material accommodates to cyclic mechanical loadings. These responses are simulated by means of a phenomenological model taking into account the coupling between remnant strain and polarization thanks to a mechanically induced depolarization function.

The aim of this paper is to model the one-dimensional behaviour of a soft PZT tested in compression. Thanks to a viscoplastic formulation, the effects of cyclical loading and loading rates are also taken into account. The coupling between remnant strain and polarisation is achieved through a mechanically induced depolarisation function.

This paper presents an experimental and numerical study showing that single crystal shape memory alloy (SMA) Cu-based endodontic instruments can lead to equivalent mechanical performances compared to NiTi-based instruments besides their interesting biological properties. Following a previous finite element analysis (FEA) of single crystal CuAlBe endodontic instruments (Vincent et al 2015 J. Mater. Eng. Perform. 24 4128–39), prototypes with the determined geometrical parameters were machined and experimentally characterized in continuous rotation during a penetration/removal (P/R) protocol in artificial canals. The obtained mechanical responses were compared to responses of NiTi endodontic files in the same conditions. In addition, FEA was conducted and compared with the experimental results to validate the adopted modeling and to evaluate the local quantities inside the instrument as the stress state and the distribution of volume fraction of martensite. The obtained results highlight that single crystal CuAlBe SMA prototypes show equivalent mechanical responses to its NiTi homologous prototypes in the same P/R experimental conditions.

10-11 mai

Composite materials, and especially sandwich structures, have been studied for decades. Indeed, the association between lightness and resistance of these structures leads to the development of their use. Their manufacturing method and their characterization remain as essential points in most studies. This work is part of the FUI SOLLICITERN project, which aims to design a composite water treatment tank for vehicles intended for this purpose. As a first step, and based on the classical filament winding principal, we aim to search designs that are best adapted to the fabrication of a curved sandwich material on a cylindrical mandrel, while respecting the process parameters of and their influence on structural properties. Since an optimal solution was validated, the constituent materials were studied by measuring mechanical properties. The objective is to help our industrial partner to validate a manufacturing solution and verify that such properties are the expected ones. For that, several static and dynamic characterizations were carried out on curved samples manufactured by the optimized process designed for our application. This part includes various experimental tests in order to validate the structure behavior with the most appropriate dimensions and material combinations, taking into account the manufacturing process. At the end, the best structural configuration is retained for the first tank prototype fabrication.; Les matériaux composites, et en particulier les sandwichs, sont très étudiés depuis des décennies. En effet, l'alliance entre légèreté et résistance de ces structures entraîne le développement de leur utilisation. Leur méthode de fabrication et éventuellement leur caractérisation restent des points essentiels dans la plupart des études. Ce travail s’inscrit dans le projet FUI SOLLICITERN qui vise à développer une citerne routière en matériau composite sandwich pour un véhicule d’hydrocurage. Comme première étape, et à partir du principe de l’enroulement filamentaire classique, l’objectif consiste à chercher des conceptions qui sont les mieux adaptées à l’enroulement d’un matériau sandwich sur un mandrin cylindrique, tout en respectant les paramètres de l’enroulement et leur influence sur la structure et les propriétés. La solution optimale étant validée, les matériaux constitutifs ont été étudié en mesurant de nombreuses propriétés mécaniques. L’objectif est de pouvoir aider le bureau d’étude à valider une solution de fabrication et de vérifier que les propriétés sont celles attendues. Pour ce faire, des caractérisations statique et dynamique ont menée sur des échantillons incurvés fabriqués par le procédé optimisé pour notre application. Cette partie comporte notamment différents essais expérimentaux dans le but de valider le comportement de la structure visée avec les dimensions et les combinaisons de matériaux les plus appropriées, en tenant compte du processus de fabrication. La meilleure configuration structurelle est retenue à la fin pour la fabrication de la citerne routière prototype.

Many advances have been made in terms of instrumental geometry, working motion and manufacturing processes of endodontic files. However, since the discovery of Nickel-Titanium (NiTi) shape memory alloys (SMA), few research has been carried out on new SMAs. In this context, this work aims to develop an endodontic instrument machined from a new SMA with very promising mechanical and antimicrobial properties: the single crystal CuAlBe. Following a finite element analysis in order to determine adequate geometric parameters for a single crystal CuAlBe SMA endodontic instrument, prototypes were machined and tested following a continuous rotation penetration / removal (P/R) protocol in artificial canals. Endodontic files made of NiTi SMA, already commercialized, were also tested with the same protocol. The aim of this researches is to show that CuAlBe endodontic instruments could lead equivalent mechanical performances to NiTi instruments in addition of their antimicrobial properties, De nombreuses avancées ont été réalisées en termes de géométries instrumentales, mouvements de travail et procédés de fabrication des limes endodontiques. Cependant, peu de recherches se sont tournées vers l’utilisation d’alliages à mémoire de forme (AMF) autres que le Nickel-Titane (NiTi). Ce travail se propose de développer un instrument endodontique constitué d’un nouvel AMF aux propriétés mécaniques et antimicrobiennes très prometteuses : le CuAlBe monocristallin. Après une première analyse par éléments finis des paramètres géométriques adéquats pour une lime endodontique en AMF monocristallin à base de CuAlBe, plusieurs prototypes ont été fabriqués puis testés en rotation continue selon un protocole de pénétration / retrait (P/R) dans des canaux artificiels. Des limes endodontiques en NiTi, déjà commercialisées, ont été également testées avec le même protocole. L’objectif de ces recherches était de montrer que les instruments endodontiques en CuAlBe monocristallin présentaient des performances mécaniques équivalentes à ceux en NiTi, en plus de leurs propriétés antimicrobiennes