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International audience; In order to obtain a fast solution scheme, the trajectory piecewise linear (TPWL) method is applied to the transient elastohydrodynamic (EHD) line contact problem for the first time. TPWL approximates the nonlinearity of a dynamical system by a weighted superposition of reduced linearized systems along specified trajectories. The method is compared to another reduced order model (ROM), based on Galerkin projection, Newton–Raphson scheme and an approximation of the nonlinear reduced system functions. The TPWL model provides further speed-up compared to the Newton–Raphson based method at a high accuracy.

International audience; Rethinking electric mobility in terms of user needs, vehicle characteristics and affordability, as well as actual driving conditions is the motivation for this paper. Studies and experience have highlighted that users' range anxiety may be alleviated by intelligent technological solutions. In this work, a comprehensive investigation of several such solutions and their impact on overall trip time for longdistance journeys has been carried out. In particular, the impact of battery size, driving speed, energy consumption, as well as charging strategy (i.e. sequence of events and charging power) has been evaluated. The goal is to understand how to best influence driving operation (in terms of driving speed and charging strategy) for given physical design parameters (battery size, maximum charging power, etc.) and make long-distance trips feasible even with smaller battery capacities.

International audience; The aim of this work is an extensive experimental mechanical and microstructural characterization of flowing weld lines (WLs) in injection-molded short glass fiber-reinforced polybutylenterephthalate (PBT) using X-ray computed tomography and digital image correlation (DIC). It was found that the induced fiber orientation (FO) in a flowing WL is similar to that induced by flow along a wall. In this test case, the impact of the flowing WL on the FO did not vanish after a flow length of 70 mm. The shape of the inserts, which originated the flowing WLs, only had a marginal effect on the induced FO gradient. By reducing part thickness, the erasing of the FO gradient induced by the WL is reached at shorter flow distances. At the WLs, there is a reduction of the fiber volume fraction in comparison to the regions far from the WL plane. DIC results show a pronounced strain localization at the WL, which can be explained by the FO gradient induced by the WL.

This paper deals with optimal charging versus aging minimization for lithium-ion batteries. The optimal charging strategy proposed involves charging controllers whose design relies on a battery model. The model, especially designed for automotive battery management systems applications, is recalled in this paper. It provides the voltage response of a cell to an input current. It also models side reactions that produce degradation mechanisms and thus decrease battery performance. Side reaction modelling involves taking into account the temperature cell variations, which are thus also modelled. The association of the three above-mentioned sub-models leads to an electro-thermal battery aging model used to design an optimal charging strategy that simultaneously takes into account the minimization of charging time and maximization of battery lifetime. Thus, to achieve a charging controller that manages battery health, an appropriate charging trajectory was computed by solving an optimization problem minimizing aging. Then, a charge control loop was designed. The nonlinear behavior of the battery was taken into account through the linearization of the electro-thermal aging model in different operating conditions. To take into account the resulting linear model family, the CRONE design methodology was used. The principles of this methodology are recapped and the design of the charging control loop is explained. The efficiency of the resulting charge controller is illustrated by several simulations.

International audience; Arithmetic is a key component and is ubiquitous in today's digital world, ranging from embedded to high-performance computing systems. With machine learning at the fore in a wide range of application domains from wearables to automotive to avionics to weather prediction, sufficiently accurate yet low-cost arithmetic is the need for the day. Recently, there have been several advances in the domain of computer arithmetic, which includes high-precision anchored numbers from ARM, posit arithmetic, bfloat16, etc. as an alternative to IEEE 754-2008 compliant arithmetic. Optimizations on fixed-point and integer arithmetic are also being pursued actively for low-power computing architectures. Furthermore, approximate computing and transprecision/mixed-precision computing have been exciting areas of research forever. While academic research in the domain of computer arithmetic has a long history, industrial adoption of some of these new data types and techniques is in its early stages and expected to increase in the future. bfloat16 is an excellent example for this. In this paper, we bring academia and industry together to discuss the latest results and future directions for research in the domain of next-generation computer arithmetic, especially for edge computing.

As new active materials are implemented in commercial cells, so must the mathematical models used in battery management systems (BMS) be updated. This is the case with the use of SiOx (0

International audience; We report the results of a Versailles Project on Advanced Materials and Standards interlaboratory study on the intensity scale calibration of x-ray photoelectron spectrometers using low-density polyethylene (LDPE) as an alternative material to gold, silver, and copper. An improved set of LDPE reference spectra, corrected for different instrument geometries using a quartz-monochromated Al Kα x-ray source, was developed using data provided by participants in this study. Using these new reference spectra, a transmission function was calculated for each dataset that participants provided. When compared to a similar calibration procedure using the NPL reference spectra for gold, the LDPE intensity calibration method achieves an absolute offset of ∼3.0% and a systematic deviation of ±6.5% on average across all participants. For spectra recorded at high pass energies (≥90 eV), values of absolute offset and systematic deviation are ∼5.8% and ±5.7%, respectively, whereas for spectra collected at lower pass energies (

A novel reactor of a natural gas (NG) fueled, 1 kW net power solid oxide fuel cell (SOFC) system with anode off-gas recirculation (AOGR) is experimentally investigated. The reactor operates as pre-reformer, is of the type radial reactor with centrifugal z-flow, has the shape of a hollow cylinder with a volume of approximately 1 L and is equipped with two different precious metal wire-mesh catalyst packages as well as with an internal electric heater. Reforming investigations of the reactor are done stand-alone but as if the reactor would operate within the total SOFC system with AOGR. For the tests presented here it is assumed that the SOFC system runs on pure CH 4 instead of NG. The manuscript focuses on the various phases of reactor operation during the startup process of the SOFC system. Startup process reforming experiments cover reactor operation points at which it runs on an oxygen to carbon ratio at the reactor inlet ( ϕ RI ) of 1.2 with air supplied, up to a ϕ RI of 2.4 without air supplied. As confirmed by a Monte Carlo simulation, most of the measured outlet gas concentrations are in or close to equilibrium.

26th Conference on the Enhanced Safety of Vehicles (ESV), EINDHOVEN, PAYS-BAS, 10-/06/2019 - 13/06/2019; Accidents involving Vulnerable Road Users (VRU) are still a very significant issue for road safety. ŽPROactive Safety for PEdestrians and CyclisTsŽ is a collaborative research project funded by the European Commission. The objective of PROSPECT was to improve significantly the effectiveness of active VRU safety systems compared to those currently on the market by: (i) expanding the scope of urban scenarios addressed (ii) improving the overall Autonomous Emergency Braking (AEB) and Autonomous Emergency Steering (AES) system performance (iii) proposing extensive validation methodologies for consumer testing, simulation and acceptance studies with tools for testing. Concepts for sensors and control systems were shown in three vehicle demonstrators and a mobile driving simulator and tested with novel VRU dummy specimen. Those systems address the well-known barriers of current AEB systems such as limited sensors field-of-view, fuzzy path prediction, unreliable intent recognition and slow reaction times for the actuation. User acceptance tests with the participation of drivers were also crucial in PROSPECT for the success of all active safety systems. Driving simulator studies were then used in a controlled and repeatable environment for the collection of data regarding the interaction between the driver and the safety function. Finally, project consortium implemented a novel benefit estimation methodology that includes an assessment of the combined effect of active and passive safety measures of PROSPECT-like systems.

International audience; Different factors contribute to the weakness of weld lines (WLs) induced by injection molding such as unsuitable fiber orientation (FO), incomplete polymer matrix diffusion, voids and V-notches. This study aims to characterize the contribution of each factor on the weakness of frontal WLs in a short glass fiber-reinforced polybutylene-terephthalate characterized by extensive X-ray computed tomography and mechanical tensile testing assisted with digital image correlation. A reduction of 50% of the stress at break and almost 40% of the strain at break is observed despite the complete matrix healing at the WL interface and the absence of V-notches. Frontal WLs induce a FO gradient starting 2 to 3 mm before the WL plane. The fibers in the WL region mainly orient in transverse-to-flow and thickness direction. This FO gradient localizes the deformations, which leads to failure at a strength near to the one of the unreinforced variant. Voids formation in frontal WLs seems to be driven by large gradients of FO and subsequent anisotropic shrinkage. In addition, this shrinkage behavior at the WL causes an increase of thickness. By applying higher packing pressures, the fibers orient more in flow direction at the core of the WL, leading to a higher tensile strength and a lower content of voids. Finally, we can conclude that the FO is the dominant factor controlling the mechanical performance in frontal WLs.

TRA 2018, Proceedings of 7th Transport Research Arena , Vienne, AUTRICHE, 16-/04/2018 - 19/04/2019; This contribution is based on the European collaborative project TRANSFORMERS (Configurable and adaptable trucks and trailers for optimal transport), which received co-funding from the European Commission. The project has the goal of reducing energy use per tonne.kilometre of goods transported by up to 25%. This is achieved by innovations including: i) Configurable whole vehicle aerodynamics, ii) Improved loading efficiency measures, iii) A distributed, trailer mounted electric driveline known as 'hybrid-on-demand' for truck-semitrailer combinations. The combination of innovations gives the possibility of a semi-trailer combination which can be adapted or re-configured to suit individual transport missions. The paper focuses on providing background to the project, an overview of the innovations developed within the project, and the main conclusions that were drawn from the wide range of work undertaken within the project. It covers both the 'Energy Efficiency' and the 'Load Optimisation' trailers which were developed and tested within the project.

this paper proposes a robust closed-loop control strategy for optimal charging of batteries. Model-based design of the charging controller is performed based on a coupled electro-thermal aging battery model. For developing an optimal charging strategy, besides minimization of charging time, prolonging the lifetime of the battery is of great importance. As the first step towards implementing a health-conscious charging controller, trajectory planning is carried out by solving a nonlinear optimization problem. The aim is to obtain optimal charging profiles while minimizing the aging. By linearization of the nonlinear battery model, a large uncertainty is observed in the behavior of the linear battery model under different operating conditions. In order to address this problem, CRONE control methodology is used. CRONE control scheme is a robust non-conservative control methodology that shows to be a good candidate for achieving the control targets for our case of study. Subsequently, the design and parametrization of the controller is explained. The simulation results are provided to prove the effectiveness of the CRONE controller. Simulation tests show that the developed controller meets the design requirements while tracking the reference signals in presence of model uncertainties.

International audience

International audience; Software Sharing in automotive embedded software development has continuously grown over the last decades and is still getting more importance and attention. Main advantages for Software Sharing, as seen by the OEM, are acceleration of development time and cycle as well as a full flexibility to customize the final product, with introduction of its own software. Although classic software sharing has shown its capabilities in practice, it shows some limitations and need to be extended in order to cover additional use cases. The concept of Model Sharing can help to address those use cases and enhance OEM - Tier1 cooperation. Bosch has established with this approach a five-level classification for Model Sharing between Tier1 and OEM, which starts from "Use of ECU virtualization environment” and goes up to “Joint Development”. Use of Standards for the data description (e.g. ASAM with -MDX, CDF …- and/or AUTOSAR with service libraries, methodology …) as well as standardized interfaces specifications (e.g. as published with AUTOSAR R4.x) can significantly increase the effectiveness of this approach; e.g. by easing labels data management and exchange between development partners through a database as well as exchange of models.

International audience; As a result of the increased complexity of today's power trains, the traditional ways of designing engine control systems essentially through ad hoc methods and experimental tuning will no longer provide the desired level of performance. In this paper, a novel model-based controller is described which accommodatesmany of today's demands on controller development of the automotive industry. The control problem treated here is a boost pressure control of a turbocharged diesel engine with a variable nozzle turbine (VNT). Since the system is essentially nonlinear, a robust nonlinear controller is used. The tracking problem is treated by a control method which combines the Internal Model Control (IMC) structure with the flatness-based approach to design feedforward controllers. The main idea of IMC is to include the model of the plant into the feedback controller. If the model perfectly represents the plant and no disturbances occur, the IMC structure degenerates to a pure feedforward control. Flat systems are characterized by the fact that their input can be expressed explicitly in terms of internal system dynamics which results in a simple method for designing a feedforward controller. In order to extend this concept to nonlinear systems, a flatness-based feedforward controller is proposed as IMC controller. Furthermore, the introduced method allows to explicitly consider input constraints. It is shown that this new concept provides an efficient controller design for certain nonlinear systems and ensures robustness and offset-free tracking. Simulation and testbed results of a controlled air system of a turbocharged diesel engine demonstrate the feasibility of this control scheme which results in impressive control performance.

Part 4: Project Management, Engineering Management, and Quality Management; International audience; In recent years Agile Project Management (APM) and especially the Scrum framework have grown in popularity in order to deal with “vuca” business environments. Scrum has become more and more common practice in software development and has already been tested in a few hardware domains. But is it also applicable outside the development area? The paper aims to show potentials and limitations in the use of Scrum in a purchasing environment and describes implemented customizations.

International audience; In this work a combined heat and power unit (CHP unit) based on the solid oxide fuel cell (SOFC) technology is analysed. This unit has a special feature: the anode offgas is partially recycled to the anode inlet. Thus it is possible to increase the electrical efficiency and the system can be operated without external water feeding. A feed-forward control concept which allows secure operating conditions of the CHP unit as well as a maximization of its electrical efficiency is introduced and validated experimentally. The control algorithm requires a limited number of measurement values and few deterministic relations for its description.

International audience; We propose an SMT-based system synthesis approach where the logic solver performs static binding and routing while the background theory solver computes global time-triggered schedules. In contrast to previous work, we assign additional time to the logic solver in order to refine the binding and routing such that the background theory solver is more likely to find a feasible schedule within a reasonable amount of time. We show by experiments that this coordination of the two solvers results in a considerable reduction of the overall synthesis time.

International audience; Combined heat and power production (CHP) based on solid oxide fuel cells (SOFC) is a very promising technology to achieve high electrical efficiency to cover power demand by decentralized production. This paper presents a dynamic quasi 2D model of an SOFC system which consists of stack and balance of plant and includes thermal coupling between the single components. The model is implemented in Modelica (R) and validated with experimental data for the stack Ul-characteristic and the thermal behavior. The good agreement between experimental and simulation results demonstrates the validity of the model. Different operating conditions and system configurations are tested, increasing the net electrical efficiency to 57% by implementing an anode offgas recycle rate of 65%. A sensitivity analysis of characteristic values of the system like fuel utilization, oxygen-to-carbon ratio and electrical efficiency for different natural gas compositions is carried out. The result shows that a control strategy adapted to variable natural gas composition and its energy content should be developed in order to optimize the operation of the system.

International audience; Software Sharing in automotive embedded software development has continuously grown over the last decades and is still getting more importance and attention. Main advantages for Software Sharing, as seen by the OEM, are acceleration of development time and cycle as well as a full flexibility to customize the final product (with introduction of its own software). Although classic software sharing has shown its capabilities in practice, it shows some limitations and need to be extended in order to cover additional use cases. The concept of model sharing can help to address those use cases and the following paper outline five level of model sharing to enhance customer cooperation. Bosch has identified, from “Use of ECU virtualization environment” up to “Joint Development”. It represents a framework for any contract that has to be established to clearly define fields of responsibilities and guarantees for intellectual properties of each party.

International audience; We present a programmable on-chip Hardware Security Module (HSM) designed as a secure execution environment for security functionality in automotive electronic control units. The HSM contains its own core, dedicated memory and cryptographic components, provides a symmetric cryptography engine and is able to perform asymmetric cryptographic operations in software. HSM is tailored to meet particular requirements of automotive embedded systems, within the limits of security, real-time constraints and cost sensitivity. HSM will enter the market as part of Bosch’s next generation engine control unit hardware platform.

The purpose of this publication is to give an overview of the actual role of multi-layered viscoelastic parts, so called “shims”, to prevent squeal noises of automotive brake systems. Since shear stress is usually used to damp thin structures in their bending modes it is commonly believed to be the largest underwent by shims. To check this assumption and considering that stresses underwent by shims cannot be measured experimentally, the authors have computed them with the help of a detailed and realistic finite element model. Contrary to what shims manufacturers say, this study exhibits the fact that shims are almost uniquely solicited in their normal direction in brake systems. Secondly, the study focuses on the added damping and stiffening induced by the viscoelastic materials. In order to take into account these materials, a realistic frequency dependent viscoelastic behavior has been integrated in the simulations. Finally, the study shows certains eigenmodes for which the viscoelastic behavior of the shims reveals instabilities that would not exist without it. It is shown that this is due to coalescence phenomenon.

International audience; The paper presents the actual results of the TIMMO-2-USE project dedicated to time modeling and analysis in the domain of automotive embedded system design. A first result is the Timing Augmented Description Language (TADL2) that offers capabilities for symbolic time expressions modeling, probabilistic timing information and timing constraints applied on mode definitions. The syntax and semantic of such extensions are presented. These extensions are aligned with EAST-ADL and AUTOSAR timing models. Based on these extensions, new algorithms and tools are developed to analyze and validate TADL2 specifications. Conjointly with these aspects, a new methodology based on industrial use cases is proposed compatible with those of TIMMO, ATESST2 and AUTOSAR. This methodology solves specific issues related to timing in an automotive system design, such as time budgeting. The TIMMO-2-USE work and results are driven by industrial use cases. Use cases are the corner stone of the project as they are used as input for providing requirements for the language, the algorithm development, and the methodology development but also because the same are used for a validation of the results.

Generally speaking, the behaviour of viscoelastic material is more complicated than the behaviour proposed by classical models as Voigt, Maxwell or Zener. The stiffness of such materials is a frequency dependent complex function. Above 1000Hz, classical measurements techniques are unable to achieve accurate measurements of the stiffness. In this paper, a new Dynamical Mechanical Analysis (DMA) tester is presented. It allows the characterization of the shear stiffness of preloaded viscoelastic materials between 200 and 3500Hz and without using frequency-temperature equivalences. Then the Generalized Maxwell model is used to describe behaviours measured with the DMA tester. A new iterative identification method of the parameter of the Generalized Maxwell model is described. This identification method is based on the asymptotes of the model.Copyright © 2011 by ASME

International audience; Handling of large industrial mechanical assemblies implies structure interactions commonly modeled with contact formulations. In cases where component interfaces are discretized using non conforming meshes, classical contact solutions have difficulties producing correct contact pressure fields. The method presented in this paper gives a relevant measure of interface compatibility and shows how it can be exploited to obtain regular contact pressures or limit over-integration in the contact formulation.

International audience; In this work, we studied the hygroscopic equilibrium of cork by the determining the sorption isotherms, this parameter being very important. The obtained results allowed us to know the cork water content at the equilibrium in a given ambient atmosphere and then we will discuss some theoretical models to correlate these data. In the second part, we present the drying kinetics of this material, obtained in a laboratory dryer with controlled aerothermics conditions. The different drying curves obtained, could be reduced by using the concept of characteristic drying curve. This characteristic drying curve which will be useful for calculating the commercial dryers was empirically interpreted by a five degree polynomial.

Brevet mondial

International audience; The present paper investigates the modeling of counterformal elastohydrodynamic lubricated contacts in multi-body system environments. The aim is to obtain a representation of the dynamic behaviour and characteristic values for lifetime calculations. Two contact models are presented for the study of cam-roller tappet and raceway-roller contacts. The first model is a one-dimensional representation of the EHL contact behaviour. It is based on the calculation of the central lubrication film thickness by means of dimensionless values (functions of the operating conditions) and provides a simplified model of the mixed lubrication. The second one, still under development, investigates the modeling of 3D dry and lubricated contacts. This paper proposes, in the latter case, some perspectives and a discussion of its implementation.; L'article suivant concerne la modélisation de contacts élastohydrodynamiques entre semi-espaces dans les environnements de systèmes multi-corps dans le but d'obtenir une représentation du comportement dynamique de mécanismes complexes et d'évaluer les grandeurs caractéristiques nécessaires aux calculs de durée de vie. Deux modèles de contact élastohydrodynamique sont ainsi présentés pour l'étude de systèmes du type came-roulement ou piste-roulement. Le premier modèle, qui est une représentation unidimensionnelle du contact, s'appuie sur le calcul de la hauteur du film de lubrifiant au centre du contact, donnée à partir de coefficients sans dimension dépendant des conditions de fonctionnement. Il inclut une modélisation simplifiée du frottement mixte. Le second, encore en cours de développement, concerne la modélisation 3D de contacts secs et lubrifiés. L'article contient, à cet effet, une discussion ainsi que quelques perspectives quant à son implémentation.

Using Rayleigh surface acoustic waves (SAW), the Young's modulus, the density and the thickness of polycrystalline Silicon-Germanium (SiGe) films deposited on silicon and SiO2 were measured, in excellent agreement with theory. The dispersion curve of the propagating SAW is calculated with a Boundary Element Method (BEM)-Model based on Green's functions. The propagating SAW is generated with a nanosecond laser in a narrowband scheme projecting stripes from a mask on the surface of the sample. For this purpose a glass mask and a liquid crystal display (LCD) mask are used. The slope of the SAW is then measured using a probe beam setup. From the wavelength of the mask and the frequency of the measured SAW, the dispersion curve is determined point by point. Fitting the BEM-Model to the measured nonlinear dispersion curve provides several physical parameters simultaneously. In the present work this is demonstrated for the Young's modulus, the density and the thickness of SiGe films. The results from the narrowband scheme measurement are in excellent agreement with separated measurements of the thickness (profilometer), the density (balance) and the Young's modulus (nanoindenter)., Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions)

This paper describes first results from the AutoMoDe (Automotive Model-Based Development) project. The overall goal of the project is to develop an integrated methodology for model-based development of automotive control software, based on problem-specific design notations with an explicit formal foundation. Based on the existing AutoFOCUS framework, a tool prototype is being developed in order to illustrate and validate the key elements of our approach., Comment: Submitted on behalf of EDAA (http://www.edaa.com/)

International audience; Une étude expérimentale est réalisée sur une série de flammes laminaires d'un prémélange propène-air. La flamme de forme conique est stabilisée sur un brûleur à surface poreuse et entourée par une flamme de méthane pour assurer son isolement. La technique d'incandescence induite par laser (IIL) calibrée par celle de l'extinction du laser, est utilisée pour déterminer la distribution spatiale (2D) de la fraction volumique de la suie pour trois valeurs de la pression, P = 1, 3 et 5 bar à diverses richesses. Pour les flammes à pression atmosphérique, l'investigation est étendue à la détermination de la taille des particules de suie par la mesure du taux de décroissance temporelle du signal IIL(t). Pour ce dernier, la température locale des gaz est mesurée par la technique de diffusion Raman anti-Stokes cohérente (DRASC) décalée indispensable pour les flammes avec suie. Les résultats obtenus sont discutés et constituent une base de données pour valider d'éventuels résultats de modèles théoriques de simulation de la formation de la suie dans une flamme monodimensionnelle.

International audience; A one-dimensional chemistry model is applied to study the stable hydrogen (D) and stable oxygen isotope (17O, 18O) composition of water vapour in stratosphere and mesosphere. In the troposphere, this isotope composition is determined by "physical'' fractionation effects, that are phase changes (e.g. during cloud formation), diffusion processes (e.g. during evaporation from the ocean), and mixing of air masses. Due to these processes water vapour entering the stratosphere first shows isotope depletions in D/H relative to ocean water, which are ~5 times of those in 18O/16O, and secondly is mass-dependently fractionated (MDF), i.e. changes in the isotope ratio 17O/16O are ~0.52 times of those of 18O/16O. In contrast, in the stratosphere and mesosphere "chemical'' fractionation mechanisms, that are the production of HO due to the oxidation of methane, re-cycling of H2O via the HOx family, and isotope exchange reactions considerably enhance the isotope ratios in the water vapour imported from the troposphere. The model reasonably predicts overall enhancements of the stable isotope ratios in H2O by up to ~25% for D/H, ~8.5% for 17O/16O, and ~14% for 18O/16O in the mesosphere relative to the tropopause values. The 17O/16O and 18O/16O ratios in H2O are shown to be a measure of the relative fractions of HOx that receive the O atom either from the reservoirs O2 or O3. Throughout the middle atmosphere, MDF O2 is the major donator of oxygen atoms incorporated in OH and HO2 and thus in H2O. In the stratosphere the known mass-independent fractionation (MIF) signal in O3 is in a first step transferred to the NOx family and only in a second step to HOx and H2O. In contrast to CO2, O(1D) only plays a minor role in this MIF transfer. The major uncertainty in our calculation arises from poorly quantified isotope exchange reaction rate coefficients and kinetic isotope fractionation factors.

The work focuses on potting materials for electronic components. A methodology to analyse the behaviour of cracks initiated in homogeneous materials or at the interface between different materials is addressed. An experimental procedure is described in order to measure the critical stress intensity factor of a homogeneous material. This procedure is then used to compare the crack behaviour in a bimaterial structure and to determine the validity of the results. Hereafter a method is proposed to determine crack growth under subcritical loading conditions. In the case of a crack at the interface of bimaterials, a methodology has been developed to measure the energy release rate necessary to let the crack propagate. With the help of numerical simulations, the corresponding stress intensity factors are computed as well as the resulting mixed mode angle. The whole work realised experimentally and the developed numerical simulations allow us to propose a methodology to analyse the behaviour of a crack placed in a multi-material structure under thermo-mechanical loads.; Ce travail s'articule autour de l'étude de matériaux coulés pour des composants électroniques. Une méthodologie est proposée pour analyser le comportement de fissures initiées dans des matériaux homogènes ou à l'interface entre différents matériaux. Une procédure expérimentale est décrite afin de mesurer le facteur d'intensité de contrainte critique d'un matériau homogène. Cette procédure est ensuite appliquée dans la comparaison du comportement d'une fissure d'un bimatériau et à la détermination du degré de validité des résultats. Une méthode est ensuite proposée pour déterminer la propagation de fissures dans les différents matériaux sous des chargements sous-critiques. Dans le cas d'une fissure à l'interface de bimatériaux, une méthodologie a été développée pour mesurer le taux de restitution d'énergie nécessaire à la propagation de la fissure. Les facteurs d'intensité de contraintes correspondants sont calculés à l'aide de simulations numériques, ainsi que l'angle de mode mixte résultant. L'ensemble des travaux expérimentaux réalisés et des simulations numériques développées permet de proposer une méthodologie d'analyse du comportement d'une fissure située au sein d'un composant multimatériau sollicité sous chargement thermo-mécanique.

The work focuses on potting materials for electronic components. A methodology to analyse the behaviour of cracks initiated in homogeneous materials or at the interface between different materials is addressed. An experimental procedure is described in order to measure the critical stress intensity factor of a homogeneous material. This procedure is then used to compare the crack behaviour in a bimaterial structure and to determine the validity of the results. Hereafter a method is proposed to determine crack growth under subcritical loading conditions. In the case of a crack at the interface of bimaterials, a methodology has been developed to measure the energy release rate necessary to let the crack propagate. With the help of numerical simulations, the corresponding stress intensity factors are computed as well as the resulting mixed mode angle. The whole work realised experimentally and the developed numerical simulations allow us to propose a methodology to analyse the behaviour of a crack placed in a multi-material structure under thermo-mechanical loads.; Ce travail s'articule autour de l'étude de matériaux coulés pour des composants électroniques. Une méthodologie est proposée pour analyser le comportement de fissures initiées dans des matériaux homogènes ou à l'interface entre différents matériaux. Une procédure expérimentale est décrite afin de mesurer le facteur d'intensité de contrainte critique d'un matériau homogène. Cette procédure est ensuite appliquée dans la comparaison du comportement d'une fissure d'un bimatériau et à la détermination du degré de validité des résultats. Une méthode est ensuite proposée pour déterminer la propagation de fissures dans les différents matériaux sous des chargements sous-critiques. Dans le cas d'une fissure à l'interface de bimatériaux, une méthodologie a été développée pour mesurer le taux de restitution d'énergie nécessaire à la propagation de la fissure. Les facteurs d'intensité de contraintes correspondants sont calculés à l'aide de simulations numériques, ainsi que l'angle de mode mixte résultant. L'ensemble des travaux expérimentaux réalisés et des simulations numériques développées permet de proposer une méthodologie d'analyse du comportement d'une fissure située au sein d'un composant multimatériau sollicité sous chargement thermo-mécanique.

International audience; The paper shows that the behaviour of mechanical systems subject to unilateral constraints differs from that of standard systems in subtle, and yet important, ways. Therefore, a proper theoretical formulation is required for simulating their behaviour. After showing that the equilibrium equations for a multibody system subject to unilateral constraints have the same form as the standard Kuhn-Tucker conditions in optimization theory, the first-order equilibrium equations are derived and their integration is discussed. At a general integration step, one has to distinguish between constraints that are strongly active, weakly active and inactive. Whereas strongly active constraints can be treated like bilateral constraints and inactive constraints can be neglected, weakly active constraints need to be constantly re-analysed to determine if they switch to a different state. The outcome is that, in addition to the well-known limit points and bifurcation points, a new type of limit point can exist, where the path is non-smooth and the first-order equilibrium equations-after elimination of any strongly active constraints-non-singular. Such points are called corner limit points. In analogy with common limit points, the degree of instability of the system changes by one at a corner limit point.