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International audience; Youla-Kucera (YK) parametrization was formulated decades ago for obtaining the set of controllers stabilizing a linear plant. This fundamental result of control theory has been used to develop theoretical tools solving many control problems ranging from stable controller switching, closed-loop identification, robust control, disturbance rejection, adaptive control to fault tolerant control.This paper collects the recent work and classifies the maccording to the use of YK parametrization, Dual YK parametrization or both, providing the latest advances with main applications indifferent control fields. A final discussion gives some insights on the future trends in the field.

International audience; o meet forthcoming Euro 6 Diesel engines NOx emissions legislation; highly efficient after-treatment systems are required. The use of urea or ammonia SCR is a well-established solution for high NOx abatement for diesel engines. The combination of a Cu-Zeolite SCR catalyst and a diesel particulate filter has been widely investigated in recent years to respond to the European NOx emissions regulations especially for those on light-duty vehicles. The after-treatment systems are preferred to be durable during the entirety of vehicle use. Indeed, the SCRF system must withstand the temperature resulting from the active regeneration of the particulate filter continuously. A 160,000 km vehicle aged SCRF catalyst which has endured more than 91 hours at temperatures superior to 600°C during the regeneration of the particulate filter was compared to an SCRF catalyst aged in the laboratory oven for 16 hours at 800°C with 10% H2O. The vehicle aged SCR has not only been exposed to the hydrothermal ageing generated by the diesel particulate regeneration but also has seen chemical elements from urea decomposition, soot accumulation, engine oil and fuel residues. In this paper, deeper comprehension of the behaviour the SCRF catalyst during vehicle ageing was exposed. It is evident that the loss of NOx activity is not only due to the regeneration of the particulate filter but also to the possible contamination from the urea injection and the elements present in the diesel fuel and engine oil. XRF results demonstrate that the concentrations of poisoning elements coming from the engine oil or fuel are concentrated mainly at the outlet of vehicle aged SCRF catalyst. Also, results reveal that the poisoning elements have affected the SCR activity of the vehicle aged SCRF catalyst. Finally, it was possible to establish a correlation between a 160,000 km vehicle aged SCRF catalyst and an equivalent SCRF aged for 16 hours at 800°C.

International audience; Self-vehicle localization is one of the fundamental tasks for autonomous driving. Most of current techniques for global positioning are based on the use of GNSS (Global Navigation Satellite Systems). However, these solutions do not provide a localization accuracy that is better than 2-3 m in open sky environments [1]. Alternatively, the use of maps has been widely investigated for localization since maps can be pre-built very accurately. State of the art approaches often use dense maps or feature maps for localization. In this paper, we propose a road sign perception system for vehicle localization within a third party map. This is challenging since third party maps are usually provided with sparse geometric features which make the localization task more difficult in comparison to dense maps. The proposed approach extends the work in [2] where a localization system based on lane markings has been developed. Experiments have been conducted on a Highway-like test track using GNSS/INS with RTK corrections as ground truth (GT). Error evaluations are given as cross-track and along-track errors defined in the curvilinear coordinates [3] related to the map.

Gray cast iron age strengthening is a phenomenon known as a modification of the alloy's structure by iron nitride precipitation during few days after casting. It generates an evolution of cast iron mechanical properties as a gain of hardness and Young's modulus. In a first time, this article presents the possibility to monitor the aging time and the intensity of age strengthening using two nondestructive methods: nonstandard Rockwell hardness and inert frequencies measurement. In a second time, the study shows the influence of the alloying elements on this phenomenon and particularly the influence of free nitrogen amount, which is a first-order parameter to control aging. Finally, a prediction model of the time and the intensity of age strengthening has been elaborated using the results of the two different monitoring described Convention CIFRE Renault-LaBoMaP

International audience; Accurate localization is very important to ensure performance and safety of autonomous vehicles. In particular, with the appearance of High Definition (HD) sparse geometric road maps, many research works have been focusing on the deployment of accurate localization systems in a previously built map. In this paper, we solve a localization problem by matching road perceptions from a 3D LIDAR sensor with HD map elements. The perception system detects High Reflective Landmarks (HRL) such as: lane markings, road signs and guard rail reflectors (GRR) from a 3D point cloud. A particle filtering algorithm estimates the position of the vehicle by matching observed HRLs with HD map attributes. The proposed approach extends our work in [1] and [2] where a localization system based on lane markings and road signs has been developed. Experiments have been conducted on a highway-like test track using GNSS/INS with RTK corrections as a ground truth (GT). Error evaluations are given as cross-track (CT) and along-track (AT) errors defined in the curvilinear coordinates [3] related to the map. The obtained accuracies of our localization system is 18 cm for the cross-track error and 32 cm for the along-track error.

International audience; This paper presents the design and implementation of a novel lateral control approach. The proposed control strategy is based on Youla-Kucera parametrization to switch gradually between controllers that are designed separately for big and small lateral errors. The present approach studies the critical problem of initial lateral error in line following. It ensures smooth and stable transitions between controllers and provides a smooth vehicle response regardless of the lateral error. For an initial validation the present work was tested in simulation, implementing a dynamic bicycle model. It has also been tested in real platforms implementing an electric Renault ZOE, with good results when activating the system at different lateral errors. autonomous vehicles Switched controllers parametrization.

IV 2017 - IEEE Intelligent Vehicles Symposium, Redondo Beach, Los Angeles, ETATS-UNIS, 11-/06/2017 - 14/06/2017; For several years, researches dedicated to autonomous driving are growing and a great number of applications and algorithms have been developed for embedded ADAS. In a part of these very critical applications, the tracking of the road's obstacles is one of the key elements. The tracking is built around a stage of measurement to track association. It consists in assessing the similarity between two sets of multi-dimensional state vectors characterizing the track and the measurement. For this application, but not only, we propose in this work a multi-criteria similarity operator based on Belief Theory allowing to take into account uncertainties and imperfections on the data. Partial data availability, conflict and ambiguities between state vectors are managed. The output of this operator provides not only the similarity but also the dissimilarity level, the amount of conflict and ambiguity. This operator is applied to relevant use-cases to highlight its benefits over the standard similarity operators.

International audience; This paper discusses the different approaches that can be used to determine the strain energy density of a given rubber-like material based on tension–torsion experimental results. More precisely, the aim is to answer the question: how to handle the measured macroscopic quantities, i.e. load and torque, to determine the constitutive equation with the less possible assumptions? The method initially proposed by Penn and Kearsley [Trans. Soc. Rheol. 20 (1976) 227–238] is adopted: the strain energy derivatives with respect to kinematical quantities have to be calculated in terms of the measured load and torque. Here, we propose to consider different sets of kinematical quantities to overcome the incoherence encountered with the classical Cauchy–Green strain invariants I1 and I2. Two new sets are considered: the principal stretch ratios and two specific invariants of the logarithmic (true) Hencky strain tensor. The corresponding derivations coupled with new experimental results permit (i) to calculate the Cauchy stress tensor on the outer surface of the cylindrical samples, and (ii) to demonstrate that a well- conditioned set of kinematical quantities must be adopted to determine the strain energy density. It is proved here that the principal stretch ratios are good candidates to express and determine the strain energy density with tension–torsion experiments.

This thesis deals with multi-objective optimization for expensive evaluation functions and its application for the tuning of vehicle monitoring and driver assistance systems in the context of automotive engineering. After the presentation of a state of the art on multi-objective optimization methods, a new algorithm based on a double kriging strategy is proposed in order to reduce the number of objective function evaluations. The first application of the optimization algorithm concerns the tuning of an indirect tire-pressure monitoring system (without sensor). In addition to the tuning of high number of parameters, the optimization is constrained by the use of a large database, containing measurements obtained in realdriving situations, and has to provide an optimal tuning in a limited processing time. The second application falls within lateral control of an autonomous driving system in a traffic jam situation. The current solution used by Renault/Nissan is based on a Kalman filter. In order to reduce the number of tuning parameters, solutions based on nonlinear approaches (high gain and sliding mode) are proposed. The tuning of the gains appearing in all these observers has been performed by using the proposed optimization algorithm, and by taking into account real driving data with measurements contained in a large database.; Cette thèse est dédiée à l’optimisation globale multi-objectif de fonctions coûteuses, avec des applications de mise au point de systèmes de surveillance et d’aide à la conduite automobile. Après avoir présenté un état de l’art du domaine, un nouvel algorithme basé sur une stratégie de double krigeage est proposé afin de réduire le nombre d’évaluations dela fonction objectif. La première application de l’algorithme concerne l’optimisation des paramètres de mise en oeuvre d’un système de surveillance de la pression des pneumatiques sans capteur de pression.En plus du nombre important de paramètres à optimiser, cette mise au point est soumise à des contraintes de test sur une très grande base de données de roulage, dans différents scénarios et à un temps de calcul limité. La seconde applicationconcerne un système de conduite automatique dans une situation d’embouteillage. Le travail est focalisé sur l’utilisation d’observateurs pour le contrôle latéral. La solution actuellement utilisée par Renault/Nissan est fondée sur un filtre de Kalman. Afin de réduire le nombre de paramètres de réglage, des solutions basées sur des approches non linéaires (grand gain et mode glissant) ont été proposées. Les gains de ces observateurs ont été réglés en utilisant le nouvel algorithme d’optimisation et en tenant compte d’essais sur route dont les mesures ont généré une grande base de données.

This thesis deals with multi-objective optimization for expensive evaluation functions and its application for the tuning of vehicle monitoring and driver assistance systems in the context of automotive engineering. After the presentation of a state of the art on multi-objective optimization methods, a new algorithm based on a double kriging strategy is proposed in order to reduce the number of objective function evaluations. The first application of the optimization algorithm concerns the tuning of an indirect tire-pressure monitoring system (without sensor). In addition to the tuning of high number of parameters, the optimization is constrained by the use of a large database, containing measurements obtained in realdriving situations, and has to provide an optimal tuning in a limited processing time. The second application falls within lateral control of an autonomous driving system in a traffic jam situation. The current solution used by Renault/Nissan is based on a Kalman filter. In order to reduce the number of tuning parameters, solutions based on nonlinear approaches (high gain and sliding mode) are proposed. The tuning of the gains appearing in all these observers has been performed by using the proposed optimization algorithm, and by taking into account real driving data with measurements contained in a large database.; Cette thèse est dédiée à l’optimisation globale multi-objectif de fonctions coûteuses, avec des applications de mise au point de systèmes de surveillance et d’aide à la conduite automobile. Après avoir présenté un état de l’art du domaine, un nouvel algorithme basé sur une stratégie de double krigeage est proposé afin de réduire le nombre d’évaluations dela fonction objectif. La première application de l’algorithme concerne l’optimisation des paramètres de mise en oeuvre d’un système de surveillance de la pression des pneumatiques sans capteur de pression.En plus du nombre important de paramètres à optimiser, cette mise au point est soumise à des contraintes de test sur une très grande base de données de roulage, dans différents scénarios et à un temps de calcul limité. La seconde applicationconcerne un système de conduite automatique dans une situation d’embouteillage. Le travail est focalisé sur l’utilisation d’observateurs pour le contrôle latéral. La solution actuellement utilisée par Renault/Nissan est fondée sur un filtre de Kalman. Afin de réduire le nombre de paramètres de réglage, des solutions basées sur des approches non linéaires (grand gain et mode glissant) ont été proposées. Les gains de ces observateurs ont été réglés en utilisant le nouvel algorithme d’optimisation et en tenant compte d’essais sur route dont les mesures ont généré une grande base de données.

International audience

IEEE Intelligent Vehicles Symposium 2015 (IV 2015), Seoul, COREE, REPUBLIQUE DE, 28-/06/2015 - 01/07/2015; This paper aims to present how the Belief Theory (also known as the Dempster-Shafer theory) can be relevant to implement powerful tracking systems. As the Belief theory belongs to the group of information-theories, it is very suitable for solving the track-to-target association problem which is one of the main issue of tracking systems. The data association problem is about associating the measurement at a given time-stamp with the objects that are being tracked along the time. In this paper, we present two methods based on the belief theory that can be used to improve the data association reliability. After that we propose as an example of tracking implementation and discuss the effect of using a multi-criteria track-to-target association algorithm.

International audience; This paper describes a novel technique to control the air fraction in the intake of dual-loop exhaust gas recirculation (EGR) Diesel engines. This control strategy enables to efficiently regulate the air fraction while satisfying a desired EGR proportion (between low-pressure EGR and high-pressure EGR). Based on a modified physical model of the air fraction dynamics along the engine air-path, a linear parameter varying (LPV) linear quadratic regulator (LQR) control is designed to ensure the stability of the air fraction while minimizing a quadratic performance index. The controllability of the system, necessary for the LPV-LQR control design, is verified by defining a convex parameter set using a polytopic approach. The controller is evaluated under strong transient conditions using an engine model that has been experimentally validated as a reference.; Este artículo describe una nueva técnica para controlar la fracción de aire fresco en el colector de admisión de motores Diesel con doble circuito de recirculación de gases de escape (RGE). Esta estrategia de control permite regular eficientemente la fracción de aire, satisfaciendo al mismo tiempo una proporción deseada entre las RGEs de alta y baja presión. Basado en un modelo físico de la dinámica de la fracción de aire a lo largo del sistema de aire del motor, un regulador lineal cuadrático a parámetros variables (LPV-LQR) es diseñado para asegurar la estabilidad de la fracción de aire y minimizar un índice de desempeño cuadrático. La controlabilidad del sistema, necesaria para garantizar la existencia del controlador LPV-LQR, se verifica mediante la definición de un subespacio convexo de parámetros utilizando un enfoque politópico. El controlador es evaluado bajo fuertes condiciones transitorias utilizando como referencia, un modelo del motor validado experimentalmente.

International audience; In a motor vehicle, the cowl box is a volume located at the bottom of the windshield. It collects rainwater and drains it to provide clean dry air to the passenger compartment through the ventilation system. When rainwater accumulates in the box, a bathtub vortex forms above the drain pipe. This vortex sucks up air into the pipe and creates an air core that decreases the water drain rate in the pipe. This increases the water level in the box and can cause a water overflow into the ventilation system. The behavior of this bathtub vortex was experimentally studied using a simplified geometry representative of a real cowlbox. The inlet water flow rate was controlled and a capacitive probe measured the water level in the box. The flow was studied using Particle Image Velocimetry to measure the velocity field around the vortex. The flow pattern is described using these data. Due to geometry and inlet conditions, the upstream flow forces the vortex counter-clockwise. It also shifts the vortex axis away from the drain axis. In this configuration, the upstream flow is strongly asymmetric and feeds the vortex using less than half the width of the box. Based on these observations, a device was tested in order to reduce the vortex intensity and consequentlythe water level. Resulting velocity fields showed a better distribution of the upstream flow. The vortex intensity decreased by up to 55% and the water level by up to 53%. While there was still a vortex with an air core, the water level was therefore significantly reduced. These results are particularly interesting for cowl box design: as this device can guarantee a lower water level, the cowl box depth can be reduced and space can be saved.

The purpose of this thesis is to develop a method for characterizing and modelling the behavior of elastomeric engine mounts. Loading conditions undergone by these parts are decomposed in two steps, which are a large preload caused by the weight of the engine, considered as quasi-static, and some superimposed displacements caused by road conditions. During both steps, loading conditions are likely to be multiaxial. For this goal, following steps have been developed:1. Determination of the range of strain undergone by an engine mount through experiments on vehicles. Using original strain invariants allows to quantify the strain amplitude as well as its multiaxiality;2. Development of an experimental method of tension-torsion on elastomers. An almost cylindrical specimen is specially designed for this type of test. Thanks to stereo-digital image correlation tests, displacements and angles imposed on the specimen are linked to the strain field in its cylindrical zone;3. Hyperelastic modelling based on tension-torsion large strain quasi-static tests. A specific attention is paid on the method of post-treating this kind of test, studying the relevance of calculating some mechanical quantities;4. Viscoelastic modelling based on tests of small oscillations in tension or torsion superimposed on a large tension-torsion static preload. The influence of the preload on the dynamic properties is considered, and the ability of two linearized viscoelastic models to take into account this influence is studied and discussed;5. Simulation of the behaviour of an engine mount through finite elements, using both hyperelastic and viscoelastic models previously identified. Results of this simulation are compared with experiments on the engine mount.; L'objectif de cette thèse est de développer une méthode de caractérisation et de modélisation du comportement de pièces de suspension moteur en élastomères. En service, les chargements que subissent ces pièces peuvent être décomposés en deux parties à savoir une grande précharge due au poids du moteur, considérée comme quasi-statique et des débattements dus aux conditions de route qui se superposent à la précharge précédente. Lors de ces deux étapes, la multiaxialité des sollicitations peut être importante. Dans ce but, les travaux suivants ont été mis en œuvre :1. Détermination de l'enveloppe de déformations subies par une pièce de suspension par des essais sur véhicule. L'utilisation d'invariants originaux de la déformation permet de quantifier d'une part l'amplitude de la déformation et d'autre part sa multiaxialité ;2. Mise en place d'une méthodologie expérimentale de traction-torsion sur élastomères. Une éprouvette quasi-cylindrique est spécialement conçue pour ce type d'essais. Des essais de stéréo-corrélation d'images permettent de relier les déplacements et angles imposés à l'éprouvette au champ de déformation ;3. Modélisation hyperélastique identifiée sur des essais quasi-statiques en traction-torsion en grandes déformations. Une attention particulière est portée sur la méthodologie de post-traitement de ce type d'essais en étudiant la pertinence du calcul de certaines grandeurs mécaniques ;4. Modélisation viscoélastique identifiée sur des essais de petites oscillations en traction ou torsion, superposée à une grande précharge statique en traction-torsion. L'influence de la précharge sur les propriétés dynamiques du matériau est considérée. La prise en compte ou non de cette influence par deux modèles viscoélastiques linéarisés est étudiée et discutée ;5. Simulation du comportement d’une suspension moteur par éléments finis. Les résultats de cette simulation sont comparés avec des essais sur pièce.

International audience; For automotive field, the vehiclevibrations induce movements of connector systems,composed of a female part system (springs) which isconnected and tighten up with the male part system(pin). There is relative movement of the contact zonebetween spring and pin which can lead to the frettingcorrosion phenomena.Several studies have been performed to investigatevibration consequences on electrical connectors. Thiswork aims to address the influence of a variety of factorssuch as fretting amplitude, frequency and current on theperformance of automotive connectors. An originalbench has been designed in order to measure the threedimensional displacements of the connector and theelectric contact characteristics at the same time. Thevelocity is measured with a laser Doppler vibrometer within the excitation-axis and the displacements within the two other axes are measured with laser displacement while a vibration is applied to the system. In this study, a measurement of induced relative displacements for different types of connector systems is undertaken as an analysis of the influence of the connector shapes and the dynamic parameters on the contact area damage and on the connector threshold of use.

National audience

International audience; AUTOSAR (AUTomotive Open System Architecture) is the most recent standard for automotive embedded systems. A major drawback of AUTOSAR lies in its lack of flexibility. Software-wise, ECUs (Electronic Control Unit) are tested, validated and uploaded; these three steps are performed in a monolithic process. Adding adaptability features into the standard is a major challenge in this context, and may result in consequent savings of time and money. On-line adaptation allows the inclusion of new functionalities in an efficient way. In this paper, we first extract relevant features from AUTOSAR for allowing dynamic software updates. Then, we define our approach for performing updates, and provide an evaluation of our approach on a RISC micro controller.

L'invention concerne un système de traitement des gaz d'échappement 2, comprenant un dispositif de réduction catalytique sélective 13 des oxydes d'azote et un moyen d'estimation 18 apte à estimer la quantité d'agent réducteur stockée dans le dispositif 13, le débit d'oxydes d'azote alimentant le dispositif 13 et les débits d'oxydes d'azote et d'agent réducteur sortant du dispositif 13. Le système comprend un unique capteur 15 apte à mesurer le débit global d'oxydes d'azote et d'agent réducteur, ledit capteur 15 étant monté en aval du dispositif 13. Le moyen d'estimation 18 est également apte à corriger lesdites estimations en fonction de l'écart entre le débit global mesuré par ledit capteur 15 et les débits estimés d'oxydes d'azote et d'agent réducteur sortant du dispositif 13. L'invention concerne également le procédé correspondant.

International audience; The effects of bias current in the sensing layer of resistive Metal-Oxide (MOX) sensors toward gases have been investigated. The behavior of a WO3 thin film deposited by sputtering has been studied. In a first time, while the working temperature is kept constant, it has been found that tuning the polarization of the MOX layer induces changes on its sensitivity. Besides, the behavior of sensitivity versus bias current depends on the nature of the gas. For example, the response to NH3-10ppm hugely increases with the bias rise; at the opposite, the polarization has no effect on NO2-10ppm responses. In a second time, the effect of the working temperature changing added to the polarization has been studied. Thus, an optimized temperature-modulated profile has been established and it has been associated with a multivariate analysis in order to quickly and easily discriminate several gases and mixtures. It has been shown this method allows discriminating two gases (NH3 and NO2) at two concentrations (5 and 10 ppm) alone and mixed. These results open a new way to increase the selectivity of MOX sensors.

La présente invention est relative à une méthode d'estimation de la résistance au roulement d'un train de roues d'un véhicule en mouvement et des rayons effectifs des roues dudit train, ledit véhicule étant muni d'au moins deux roues (1) équipées de pneumatiques, la méthode comprenant : - la mesure ou l'estimation de la valeur de la vitesse angulaire Omega de rotation de chacune des roues (1) du train, - la mesure ou l'estimation de la valeur du couple moteur tau appliqué au train de roues, caractérisée par le fait que la méthode utilise un observateur de la dynamique de la roue basé sur la théorie des modes glissants dont les signaux d'entrée sont la valeur de la vitesse angulaire Omega de chaque roue (1) du train ainsi que la valeur du couple moteur tau appliqué au train de roues (1).

La présente invention est relative à un dispositif d'amélioration du signal délivré par un capteur de vitesse monté sur une roue, ledit capteur comportant une partie mobile liée à la roue, se présentant sous la forme d'une roue d'impulsions (2) comportant des éléments spécifiques (1) régulièrement répartis, ainsi qu'une partie fixe (4) disposée en vis-à-vis desdits éléments spécifiques, ladite partie fixe (4) délivrant un signal au passage des éléments spécifiques (1), caractérisé en ce que le dispositif comporte des moyens d'estimation et de mémorisation des irrégularités de répartition angulaire deltatheta des éléments spécifiques sur la roue d'impulsions (2).

Procédé de détection du sens de rotation d'une roue d'un véhicule automobile en utilisant : -un capteur de vitesse de rotation de roue non signé, -une unité de contrôle électronique. Caractérisé en ce que le capteur de vitesse comporte des irrégularités de fabrication et en ce que le procédé comprend une étape d'estimation desdites irrégularités en temps réel et une étape de détermination du sens de rotation lors de laquelle lesdites irrégularités sont comparées à des irrégularités de référence en fonction de la vitesse moyenne.

Sheet metal forming processes involve multi-axial strain paths. For the numerical simulation of such processes, an appropriate constitutive model that properly describes material behavior at large strain is required. For accurate and time-effective simulations, it is crucial to use plasticity models based on physics, as material macroscopic behavior is closely related to the evolution of the associated microstructures. Accordingly, a large strain work-hardening phenomenological model that incorporates the intragranular microstructure evolution through a dislocation density approach is proposed. The model is defined by a yield criterion and hardening laws that are all grain-size dependent. The classical Hill criterion in which grain-size dependency was introduced is proposed. Hardening laws are given by a combination of kinematic and isotropic contributions that respectively take into account the evolution with strain of cell blocks formed by geometrically necessary boundaries (GNBs) and individual dislocation cells delineated by incidental dislocation boundaries within cell blocks (IDBs). On the one hand, IDBs evolution contribution is described by a modified Rauch et al. isotropic model, which is able to describe work-hardening stagnation and work-softening. On the other hand, GNBs evolution contribution is described by a grain-size dependent tensorial back-stress expression proposed by Aouafi et al. [2007] to describe the plastic anisotropy and Bauschinger effect. Moreover, the proposed model aims to accurately predict steel behavior through an innovative approach by only changing few “simply measurable” microstructure data (e.g. chemical composition, grain size…). The predictive capabilities of the model are assessed for interstitial free (IF) and dual phase (DP) steels with grain sizes varying respectively in the 8-40 µm and 1-10 µm value range. Different loading paths are analyzed, namely the uniaxial tensile test, reversal simple shear and orthogonal tests.; International audience; Sheet metal forming processes involve multi-axial strain paths. For the numerical simulation of such processes, an appropriate constitutive model that properly describes material behavior at large strain is required. For accurate and time-effective simulations, it is crucial to use plasticity models based on physics, as material macroscopic behavior is closely related to the evolution of the associated microstructures. Accordingly, a large strain work-hardening phenomenological model that incorporates the intragranular microstructure evolution through a dislocation density approach is proposed. The model is defined by a yield criterion and hardening laws that are all grain-size dependent. The classical Hill criterion in which grain-size dependency was introduced is proposed. Hardening laws are given by a combination of kinematic and isotropic contributions that respectively take into account the evolution with strain of cell blocks formed by geometrically necessary boundaries (GNBs) and individual dislocation cells delineated by incidental dislocation boundaries within cell blocks (IDBs). On the one hand, IDBs evolution contribution is described by a modified Rauch et al. isotropic model, which is able to describe work-hardening stagnation and work-softening. On the other hand, GNBs evolution contribution is described by a grain-size dependent tensorial back-stress expression proposed by Aouafi et al. [2007] to describe the plastic anisotropy and Bauschinger effect. Moreover, the proposed model aims to accurately predict steel behavior through an innovative approach by only changing few “simply measurable” microstructure data (e.g. chemical composition, grain size…). The predictive capabilities of the model are assessed for interstitial free (IF) and dual phase (DP) steels with grain sizes varying respectively in the 8-40 µm and 1-10 µm value range. Different loading paths are analyzed, namely the uniaxial tensile test, reversal simple shear and orthogonal tests.

International audience; ABSTRACT: A general procedure is proposed to develop relevant multiaxial tension-torsion experiments that mimic the complex loading conditions undergone by engine mounts in service. First, displacements and forces exerted on the engine mount are measured on an instrumented vehicle. For several loading conditions, the displacements are introduced in a finite element model of the engine mount to determine the corresponding strain fields. To characterize and compare these strain fields, we consider the invariants of the Hencky strain tensor. For a given set of invariants, we determine displacements and angles that must be applied on the samples to reproduce the deformation of the engine mount. The present work focuses on the subsequent experimental campaign. Firstly, a new rubber specimen is designed for simultaneous tension-torsion tests. Its principal re- quirement is that the finite element strain field must be as close as possible to the analytical solution of the simultaneous extension and torsion of a cylinder. The geometry of the new sample is validated with the help of stereo digital images correlation (SDIC) on the lateral surface of the specimen. From SDIC results, rela- tionships between global axial displacement and local extension λ on the one hand, and between global angle and local angle per unit of height τ on the other hand are established. This validated method will be consid- ered in a next future to perform multiaxial quasi-static and dynamic experiments, leading to identification of a visco-hyperelastic model.

La présente invention est relative à une méthode d'estimation de la résistance au roulement d'une roue d'un véhicule en mouvement, ledit véhicule étant muni d'au moins deux roues (1) équipées de pneumatiques, la méthode comprenant : -la mesure ou l'estimation de la valeur de la vitesse angulaire Omega de rotation d'au moins une roue (1), -la mesure ou l'estimation de la valeur du couple tau appliqué à ladite roue (1), caractérisée par le fait que la méthode utilise un observateur de la dynamique de la roue (1) basé sur la théorie des modes glissants dont les signaux d'entrée sont la valeur de la vitesse angulaire Omega de roue (1) ainsi que la valeur du couple tau appliqué à la roue (1).

This paper investigates a recently developed elasto-plastic constitutive model. For this purpose, the model was implemented in a commercial finite element code and was used to simulate the cross-die deep drawing test. Deep drawing experiments and numerical simulations were conducted for five interstitial-free steels and seven dual-phase steels, each of them having a different thickness and strength. The main interest of the adopted model is a very efficient parameter identification procedure, due to the physical background of the model and the physical significance of some of its parameters and state variables. Indeed, the dislocation density, grain size, and martensite volume fraction explicitly enter the model’s formulation, although the overall approach is macroscopic. For the dual-phase steels, only the chemical composition and the average grain sizes were measured for the martensite and ferrite grains, as well as the martensite volume fraction. The mild steels required three additional tensile tests along three directions, in order to describe the plastic anisotropy. Information concerning the transient mechanical behavior after strain-path changes (reverse and orthogonal) was not collected for each material, but for only one material of each family of steels (IF, DP), based on previous works available in the literature. This minimalistic experimental base was used to feed the numerical simulations for the twelve materials that were confronted to deep drawing experiments in terms of thickness distributions. The results suggested that the accuracy of the numerical simulations is very satisfactory in spite of the scarce experimental input data. Additional investigations indicated that the modeling of the transient behavior due to strain-path changes may have a significant impact on the simulation results, and that the adopted approach provides a simple and efficient alternative in this regard.; International audience; This paper investigates a recently developed elasto-plastic constitutive model. For this purpose, the model was implemented in a commercial finite element code and was used to simulate the cross-die deep drawing test. Deep drawing experiments and numerical simulations were conducted for five interstitial-free steels and seven dual-phase steels, each of them having a different thickness and strength. The main interest of the adopted model is a very efficient parameter identification procedure, due to the physical background of the model and the physical significance of some of its parameters and state variables. Indeed, the dislocation density, grain size, and martensite volume fraction explicitly enter the model’s formulation, although the overall approach is macroscopic. For the dual-phase steels, only the chemical composition and the average grain sizes were measured for the martensite and ferrite grains, as well as the martensite volume fraction. The mild steels required three additional tensile tests along three directions, in order to describe the plastic anisotropy. Information concerning the transient mechanical behavior after strain-path changes (reverse and orthogonal) was not collected for each material, but for only one material of each family of steels (IF, DP), based on previous works available in the literature. This minimalistic experimental base was used to feed the numerical simulations for the twelve materials that were confronted to deep drawing experiments in terms of thickness distributions. The results suggested that the accuracy of the numerical simulations is very satisfactory in spite of the scarce experimental input data. Additional investigations indicated that the modeling of the transient behavior due to strain-path changes may have a significant impact on the simulation results, and that the adopted approach provides a simple and efficient alternative in this regard.

International audience; The effects of bias current on sensitivity and selectivity of resistive Metal-Oxide (MOX) sensors toward gases have been investigated. While the working temperature is kept constant, it has been found that tuning the polarization of the MOX thin film induces changes on its sensitivity toward gases. Besides, the behavior of sensitivity versus bias current depends on the nature of the gas and of the thin sensing film, meaning it is possible to enhance the selectivity by adjusting the polarization of different sensitive layers. This underutilized parameter provides a new way of improving easily gas sensors sensitivity and above all selectivity. It would then be interesting to polarize individually each sensor of a multi-sensor device in order to optimize the whole system performances, which may represent a breakthrough in the development of smart E-Nose.

La présente invention est relative à une méthode d'estimation de paramètres d'un véhicule en mouvement, ledit véhicule étant muni de roues équipées de pneumatiques, la méthode comprenant : -la mesure ou l'estimation de la valeur de la vitesse angulaire de rotation d'au moins une roue, -la mesure ou l'estimation de la valeur du couple appliqué à ladite roue, caractérisée par le fait que la méthode utilise un observateur de la dynamique de la roue basé sur la théorie des modes glissants dont les signaux d'entrée sont la valeur de la vitesse angulaire de roue ainsi que la valeur du couple appliqué à la roue, et les variables estimées sont la vitesse longitudinale v de la roue, ainsi que le rayon dynamique R de la roue.

With a view to environmental, economic and safety concerns, car manufacturers need to design lighter and safer vehicles in ever shorter development times. In recent years, High Strength Steels (HSS) like Interstitial Free (IF) steels which have higher ratios of yield strength to elastic modulus, are increasingly used for sheet metal parts in automotive industry to meet the demands. Moreover, the application of sheet metal forming simulations has proven to be beneficial to reduce tool costs in the design stage and to optimize current processes. The Finite Element Method (FEM) is quite successful to simulate metal forming processes but accuracy largely depends on the quality of the material properties provided as input to the material model. Common phenomenological models roughly consist in the fitting of functions on experimental results and do not provide any predictive character for different metals from the same grade. Therefore, the use of accurate plasticity models based on physics would increase predictive capability, reduce parameter identification cost and allow for robust and time-effective finite element simulations. For this purpose, a 3D physically based model at large strain with dislocation density evolution approach was presented in IDDRG2009 by the authors [1]. This model allows the description of work-hardening's behavior for different loading paths (i.e. uni-axial tensile, simple shear and Bauschinger tests) taking into account several data from microstructure (i.e. grain size, texture, etc...). The originality of this model consists in the introduction of microstructure data in a classical phenomenological model in order to achieve work-hardening's predictive character for different metals from the same grade. Indeed, thanks to a microstructure parameter set for an Interstitial Free steel, it is possible to describe work-hardening behavior for different loading paths of other IF steels by only changing the mean grain size and the chemical composition. During sheet metal forming processes local material points may experience multi-axial and multi-path loadings. Before simulating actual industrial parts, automotive manufacturers use validation tools - e.g. the Cross-Die stamping test. Such typical stamping tests enable the evaluation of a complex distribution of strains. The work described is an implementation [2] of a 3D dislocation based model in ABAQUS/Explicit and its validation on a Finite Element (FE) Cross-Die model. In order to assess the performance and relevance of the 3D dislocation based model in the simulation of industrial forming applications, the results of thinning profiles predicted along several directions and the strain distribution were obtained and compared with experimental results for IF steels with grain sizes varying in the 8-22 μm value range.; International audience; With a view to environmental, economic and safety concerns, car manufacturers need to design lighter and safer vehicles in ever shorter development times. In recent years, High Strength Steels (HSS) like Interstitial Free (IF) steels which have higher ratios of yield strength to elastic modulus, are increasingly used for sheet metal parts in automotive industry to meet the demands. Moreover, the application of sheet metal forming simulations has proven to be beneficial to reduce tool costs in the design stage and to optimize current processes. The Finite Element Method (FEM) is quite successful to simulate metal forming processes but accuracy largely depends on the quality of the material properties provided as input to the material model. Common phenomenological models roughly consist in the fitting of functions on experimental results and do not provide any predictive character for different metals from the same grade. Therefore, the use of accurate plasticity models based on physics would increase predictive capability, reduce parameter identification cost and allow for robust and time-effective finite element simulations. For this purpose, a 3D physically based model at large strain with dislocation density evolution approach was presented in IDDRG2009 by the authors [1]. This model allows the description of work-hardening's behavior for different loading paths (i.e. uni-axial tensile, simple shear and Bauschinger tests) taking into account several data from microstructure (i.e. grain size, texture, etc...). The originality of this model consists in the introduction of microstructure data in a classical phenomenological model in order to achieve work-hardening's predictive character for different metals from the same grade. Indeed, thanks to a microstructure parameter set for an Interstitial Free steel, it is possible to describe work-hardening behavior for different loading paths of other IF steels by only changing the mean grain size and the chemical composition. During sheet metal forming processes local material points may experience multi-axial and multi-path loadings. Before simulating actual industrial parts, automotive manufacturers use validation tools - e.g. the Cross-Die stamping test. Such typical stamping tests enable the evaluation of a complex distribution of strains. The work described is an implementation [2] of a 3D dislocation based model in ABAQUS/Explicit and its validation on a Finite Element (FE) Cross-Die model. In order to assess the performance and relevance of the 3D dislocation based model in the simulation of industrial forming applications, the results of thinning profiles predicted along several directions and the strain distribution were obtained and compared with experimental results for IF steels with grain sizes varying in the 8-22 μm value range.

International audience; In many global optimization problems motivated by engineering applications, the number of function evaluations is severely limited by time or cost. To ensure that each of these evaluations usefully contributes to the localization of good candidates for the role of global minimizer, a stochastic model of the function can be built to conduct a sequential choice of evaluation points. Based on Gaussian processes and Kriging, the authors have recently introduced the informational approach to global optimization (IAGO) which provides a one-step optimal choice of evaluation points in terms of reduction of uncertainty on the location of the minimizers. To do so, the probability density of the minimizers is approximated using conditional simulations of the Gaussian process model behind Kriging. In this paper, an empirical comparison between the underlying sampling criterion called conditional minimizer entropy (CME) and the standard expected improvement sampling criterion (EI) is presented. Classical test functions are used as well as sample paths of the Gaussian model and an industrial application. They show the interest of the CME sampling criterion in terms of evaluation savings.

International audience; We consider an estimator $\hbbeta_n(\param)$ defined as the element $\bphi\in\bPhi$ minimizing a contrast process $\pencontrast(\bphi,\param)$ for each $\param$. We give some general results for deriving the weak convergence of $\sqrt{n}(\hbbeta_n-\bbeta)$ in the space of bounded functions, where, for each $\param$, $\bbeta(\param)$ is the $\bphi\in\bPhi$ minimizing the limit of $\pencontrast(\bphi,\param)$ as $n\to\infty$. These results are applied in the context of penalized M-estimation, that is, when $\pencontrast(\bphi,\param)=M_n(\bphi)+\param J_n(\bphi)$, where $M_n$ is a usual contrast process and $J_n$ a penalty such as the $\ell^1$ norm or the squared $\ell^2$ norm. The function $\hbbeta_n$ is then called a \emph{regularization path}. For instance we show that the central limit theorem established for the lasso estimator in Knight and Fu (2000) continues to hold in a functional sense for the regularization path. Other examples include various possible contrast processes for $M_n$ such as those considered in Pollard (1985).

International audience; This paper describes a novel technique to control the air fraction in the intake of dual-loop exhaust gas recirculation (EGR) Diesel engines. This control strategy enables to efficiently regulate the air fraction while satisfying a desired EGR proportion (between low-pressure EGR and high-pressure EGR). Based on a modified physical model of the air fraction dynamics along the engine air-path, a linear parameter varying (LPV) linear quadratic regulator (LQR) control is designed to ensure the stability of the air fraction while minimizing a quadratic performance index. The controllability of the system, necessary for the LPV-LQR control design, is verified by defining a convex parameter set using a polytopic approach. The controller is evaluated under strong transient conditions using an engine model that has been experimentally validated as a reference.; Este artículo describe una nueva técnica para controlar la fracción de aire fresco en el colector de admisión de motores Diesel con doble circuito de recirculación de gases de escape (RGE). Esta estrategia de control permite regular eficientemente la fracción de aire, satisfaciendo al mismo tiempo una proporción deseada entre las RGEs de alta y baja presión. Basado en un modelo físico de la dinámica de la fracción de aire a lo largo del sistema de aire del motor, un regulador lineal cuadrático a parámetros variables (LPV-LQR) es diseñado para asegurar la estabilidad de la fracción de aire y minimizar un índice de desempeño cuadrático. La controlabilidad del sistema, necesaria para garantizar la existencia del controlador LPV-LQR, se verifica mediante la definición de un subespacio convexo de parámetros utilizando un enfoque politópico. El controlador es evaluado bajo fuertes condiciones transitorias utilizando como referencia, un modelo del motor validado experimentalmente.

International audience; We propose a new a reference model for Steerby- Wire applications. The model accounts for force reflection and vehicle dynamics interaction. In particular, a Bicycle model including the front axle kinematic and lateral contact forces, are explicitly accounted during the model tuning. The model is completed with a virtual feedback force, designed from an optimal feedback control loop, that aims at imposing a particular steering behavior improving the vehicle handling characteristics. This results in a model that is (vehicle) velocity dependent with good stability properties. The model keeps such good properties even in presence of unmodelled tire-road dynamics, and under certain parameter variation.