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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.

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.

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.

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.

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.

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.

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.

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