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The carburizing of tantalum samples under different carbon flow rates has highlighted the influence of the carbon flow rate on the structure of tantalum carbides. XRD analyses enabled the identification of surface structures that were revealed by optical micrographs. Four carbon flow rates were tested. The lowest carbon flow rate produced a Ta2C layer that grew epitaxially on the tantalum substrate according to the relationship: {View the MathML source101¯}Ta// View the MathML source{1¯101}Ta2C; View the MathML source〈101¯〉Ta// View the MathML source〈17¯17010〉Ta2C. An increase in the carbon flow rate resulted in the appearance of TaC nuclei through the carbon enrichment of the Ta2C layer. These nuclei appeared in the form of islets and highly oriented needles. EBSD (Electron Back Scattered Diffraction) analyses and pole figures revealed that the carbide layers grew epitaxially towards their substrates. The Ta2C layer grew according to the relationship View the MathML source{101¯}Ta// View the MathML source{1¯101}Ta2C while the TaC structures nucleated according to the following relationships: {111}TaC//{0001}Ta2C; 〈111〉TaC//〈0001〉Ta2C; {100}TaC// View the MathML source{202¯3}Ta2C; 〈100〉TaC// View the MathML source〈909¯8〉Ta2C and {110}TaC// View the MathML source{101¯3}Ta2C; 〈110〉TaC// View the MathML source〈909¯16〉Ta2C. The highest carbon flow produced stoichiometric TaC grains at the surface, which appeared to be equiaxed. The diversity of the TaC crystallographic orientations stems from the underlying Ta2C layer, the TaC grains having nucleated epitaxially from the Ta2C layer. This misorientation of the Ta2C grains with respect to Ta is governed by the exceeding of a carbon flow limit. CEA and the Regional Council of Burgundy

International audience; In this paper a computational fluid dynamics (CFD) code is applied to three-dimensional simulations of windage power loss generated by spur gears rotating in air. Emphasis is placed on the simplification which can be made in the numerical approach in order to gain cost and time needed for reaching a converged solution when using both fine mesh and important angular velocity. It appears that the similarity of the flows which are observed in the vicinity of both gear and disk sides is helpful. It is finally possible to compute the flow pattern near the teeth without simulating the contribution of the sides when appropriate boundary conditions are applied at the inlet of a truncated computational domain. The predictions of windage power losses using this original method are satisfying.

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International audience; The collaborative robot (cobot) is a technology contributing to the industrial revolution Industry 4.0. Indeed, cobots’ flexibility and their easy-to-use solutions fill a gap with traditional robots to robotize manufacturing of products with low volume and high mix profiles. Parts needed to manufacture a product must first be presented to the cobot, so that afterwards it can perform operations such as assembly. The paper classifies the current part presenters. Then, a methodology is proposed to select the best presenter based on the characteristics of the parts and the workstation. To be aligned with markets requiring a high mix of products frequently renewed, the development times for part presenter design and for cobot programming are new data to select the best presenter. Indeed, at every part redesign, the part presenter changes and the cobot is reprogrammed. These two times are depreciated based on the lifespan quantity of the part. Lifespan quantity is the number of the same parts, which are dropped-off on the part presenter during the part’s lifespan, i.e. until its redesign. A concrete industrial use case is explained to test the methodology. Results conclude that a tray pattern is the best part presenter, except for parts with low lifespan quantity. Lifespan quantity of the part appears to be a significant parameter when deciding the best part presenter.

Cette note de synthèse décrit une méthode pour l'élaboration d'échantillons piézoélectriques amincis en sel de Rochelle avec électrodes. Les propriétés du sel de Rochelle sont rappelées et certaines astuces de mises en œuvres sont données.

International audience; Parts made by metal additive manufacturing processes assisted by sintering suffer from embrittlement due to binder/powders interactions. Using a core-shell approach, we modelled the diffusion of carbon and oxygen from the binder into the metallic powders. The model was assessed by measuring the interstitials content upon various debinding/sintering steps. The diffusion/precipitation phenomena during these non-isothermal treatments lead to either a saturated solid solution or the precipitation of titanium carbides. The consequences on the mechanical behavior of single 3D printed filaments were quantified by bending tests, highlighting a transition from brittle to ductile fracture depending on the debinding parameters. This approach can be applied to understand the role of fast diffusing interstitial elements into various powders systems in order to optimise the chemical composition and the mechanical properties of 3D printed metallic parts.

The thermal stability of magnetron-sputtered Zr-Cu-Ag thin films, presenting key-antibacterial properties against E. coli and S. aureus, is studied by using an in situ multiscale approach. This study is carried out to better understand the general evolution of these amorphous films under thermal constraint, and to determine their limit of use in aggressive conditions. The general crystallization behavior and structural stability are investigated by in situ X-ray diffraction (XRD) in heating mode, and completed at micro- and nano-scale by complementary electron microscopy characterizations. The global crystallization temperature of films, determined by XRD, is found between 200 °C and 400 °C depending on the composition. The in situ HT-ESEM (High Temperature – Environmental Scanning Electron Microscope) observations show that, for the composition with the lowest Zr/(Cu + Ag) ratio (Zr33Cu35Ag32), the crystallization process is followed by a total dewetting of the thin film. The Zr73Cu16Ag11 film is a thin film metallic glass (TFMG), and was also investigated at the nanoscale. In situ HT-TEM (High Temperature – Transmission Electron Microscope) allows observing the progressive crystallization of the TFMG, describing the different steps of transformation from the amorphous as-deposited structure, the individual formation of intermetallics and to the whole crystalline state.

Given the large contribution of the transport sector in the global level of Greenhouse Gases (GHG) emissions, developing and adopting more carbon-efficient transport mode is crucial. Many discrepancies exist in the literature comparing modal transport emissions since their scope, geographic perimeter, calculation methods and sets of assumptions strongly vary. This paper reviews some CO2 and GHG emissions data from the literature analyzing air, road, and rail transport, and shows that similar patterns of contributors can be found within each mode. It allows the identification of some important parameters to focus on for further development of multimodal comparative Life Cycle Assessments.

We manufactured eco-friendly piezoelectric transducers that are promising for several technological applications within an eco-design paradigm. Taking into account the environmental, eco-design and energetic constrains, two eco-friendly piezoelectric salts were investigated in this work: Rochelle Salt (KNaC4H4O6.4H2O) and Ammonium Dihydrogen Phosphate (NH4H2PO4). The piezoelectric resonance and temperature stability of these two salts were compared. Furthermore these two salt crystals were integrated into biodegradable structural material in order to obtain several eco-friendly piezoelectric devices such as resonating cantilevers, energy harvesters, and bulk acoustic wave (BAW) filters. These three types of devices were successfully fabricated and characterized, demonstrating the potential of these piezoelectric materials. The intrinsic performance of the devices might be unbeatable taking into account the fabrication costs and ecological aspects.

In this communication, we report the manufacturing process of green piezoelectric samples that can easily be produced in any Fablab. The method combines conventional 3D printing of a polymer matrix with liquid phase epitaxial grown of a piezoelectric salt. Piezoelectric resonators enhancing high coupling factors were successfully fabricated using this process. These composite transducers composed of Polylactic acid (PLA) and Rochelle Salt (RS) (or other piezoelectric salt) are promising for low energy budget or eco-friendly applications., Dans cette communication, nous abordons le processus de fabrication d'échantillons piézoélectriques verts qui peuvent facilement être produits dans n'importe quel Fablab. Le procédé combine l'impression 3D conventionnelle d'une matrice polymère, avec une croissance épitaxiale en phase liquide d'un sel piézoélectrique. Des résonateurs piézoélectriques avec des facteurs de couplage élevés ont été fabriqués avec succès en utilisant ce procédé. Ces transducteurs composites composés d'acide polylactique (PLA) et de sel de Rochelle (RS) (ou autre sel piézoélectrique) sont prometteurs pour des applications à faible budget énergétique ou respectueuses de l'environnement.

International audience; This paper deals with the analysis of a class of offline state estimators for LTI discrete-time systems in the presence of an arbitrary measurement noise which can potentially take any value. The considered class of estimators is defined as the solution of an optimization problem involving a performance function which can be interpreted as a generalization of cost functions used in the Maximum Correntropy Criterion. The conclusion of the analysis is that if the system is observable enough, then the considered class of estimators is resilient, which means that the obtained estimation error is independent from the highest values of the measurement noise. In the case of systems with a bounded process noise, the considered class of estimators provides a bounded estimation error under the appropriate conditions despite not being designed for this scenario.

International audience; This paper proposes to analyze the resilient properties of a specific state estimator for LTI discrete-time systems. The dynamic equation of the system is assumed to be affected by a bounded process noise. As to the available measurements, they are potentially corrupted by a noise of both dense and impulsive natures. In this setting, we define an estimator as the map which associates to the measurements, the minimizing set of an appropriate (convex) performance function. It is then shown that the proposed estimator enjoys the property of resilience, that is, it induces an estimation error which, under certain conditions, is independent of the extreme values of the (impulsive) measurement noise. Therefore, the estimation error may be bounded while the measurement noise is virtually unbounded. Moreover, the expression of the bound depends explicitly on the degree of observability of the system being observed and on the considered performance function. Finally, a few simulation results are provided to illustrate the resilience property.

International audience; This article deals with the Windage Power Losses (WPL) of pinion-gear pairs rotating in air. The WPL of several disks, spur and helical gears have been measured using a dedicated test rig developed from a WPL measurement system initially used for one single pinion or disk. In practice, several gears are in mesh and the windage losses for coupled pinion-gear systems need to be addressed. It is experimentally confirmed that, although some couplings can be identified between two rotating gears, the total WPL can be estimated as the sum of that of each individual member.

International audience; The electronic conductivity, at the multiscale, of lithium-ion positive composite electrodes based on LiNi_{1/3}Mn_{1/3}Co_{1/3}O_2 and/or carbon-coated LiFePO_4, carbon black and poly(vinylidene fluoride) mixture is modeled. The electrode microstructures are acquired numerically in 3D by X-ray tomography and FIB/SEM nanotomography and numerically segmented to perform electrostatic simulations using Fast Fourier Transform (FFT) method. Such simulations are easy and quick to perform because they are directly computed on the grid represented by the voxels in the 3D volumes. Numerical results are compared with experimental measurements of the multiscale electronic conductivity by broadband dielectric spectroscopy (BDS). A good prediction is realized for the bulk conductivities of the C/LiFePO_4 phase and the CB/PVdF mixture. The combination of X-ray and FIB/SEM tomography, FFT simulation method, and BDS is thus well adapted to understand the influence of the electrode composition and microstructure on its electronic conductivity.

International audience; Gear unit condition monitoring is a key factor for mechanical system reliability management. When they are subjected to failure, gears and bearings may generate excessive vibration, debris and heat. Vibratory, acoustic or debris analyses are proven approaches to perform condition monitoring. An alternative to those methods is to use temperature as a condition indicator to detect gearbox failure.The review focuses on condition monitoring studies which use this thermal approach. According to the failure type and the measurement method, it exists a distinction whether it is contact (e.g. thermocouple) or non-contact temperature sensor (e.g. thermography). Capabilities and limitations of this approach are discussed. It is shown that the use of temperature for condition monitoring has a clear potential as an alternative to vibratory or acoustic health monitoring.

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International audience; Metallization of polymers is important for several technological and industrial applications. In this work, we demonstrate the influence of metallization bath parameters on LCP Vectra® 820i polymer samples prepared by incorporation of a small amount (

This paper deals with recent experimental and numerical research in the possible reduction of windage power losses (WPL). It is accepted that these load-independent losses become prominent over other sources in mechanical transmissions with peripheral speeds above 100 m/s as is the case in energy production, aeronautics and electric vehicles. So far, the majority of the experiments and models deal with WPL evaluation for one single rotating pinion. The unique test rig designed at INSA Lyon makes it possible to measure both the WPL of a single pinion or a non-meshing pinion-gear pair. A number of comparisons between experimental and numerical results are presented and commented upon. It is shown, that the gear environment changes the airflow and, in depending on the cases, it can either reduce or increase WPL. Finally, the influence of pinion-gear couplings on WPL is discussed as well as the interest of shrouds and deflectors.

The objective of this study is to examine the sudden drop in properties of aluminum, titanium and chromium thin films prepared by the glancing angle deposition method. The thin films were deposited by DC magnetron sputtering under identical deposition conditions. A substrate-holder with seven different orientations with respect to the target normal was used. The thickness and the column tilt angles (β) of the thin films were determined by scanning electron microscopy. The residual stress of the thin films was evaluated using the wafer curvature technique and calculated by the Stoney's formula. The thickness variation and column tilt angle versus the orientation of the substrate indicated that the critical point is around 60° for all metallic materials and a critical angle of 60° is also found for the residual stress. Simulations of the particles transport are compared to the experimental data and moderate the critical angles analyses. Frnch Ministry of Higher Education and Research

International audience; This paper describes a model developed to simulate the evolution of carbide layers (TaC/Ta2C) formed during carburizing and annealing treatments of tantalum. The model is based on a parabolic evolution of the layer thickness during the growth, and on the carbon conservation during the annealing. In order to validate this model a MATLAB® program was developed. It enables the prediction of the evolution of the tantalum carbide layers (nature and thickness) for a desired treatment defined by a temperature, a carburizing and an annealing duration.

International audience; The Stoney formula, based on the measurement of the substrate curvature, is often used for the determination of the thin films' residual stress. In this study, titanium nitride coatings were deposited by DC reactive magnetron sputtering on silicon substrates. An optical profiler was used to determine the curvature of the surface before and after coating. Two radii were then obtained, along the principal perpendicular directions of the surface curvature. A simple and efficient method to determine the experimental error on the stress calculation was developed taking into account the film thickness dispersion and the radii dispersion. Using constant deposition parameters, some samples' characteristics were tested: film and substrate thickness, size, shape and crystallographic orientations of the substrates. With the help of the developed error method, we analyzed what can be conclude about the influence of these characteristics on the calculated stress values, obtained from the experimental measurements.

International audience; Human Robot Collaboration is seen as a significant feature of Industry 4.0 implementation. Collaborative robots (cobots) are supposed to deliver superior process performance, which was so far achieved through the application of Lean Manufacturing techniques. The following case study built around the assembly process of a pneumatic cylinder, tends to analyse not only the actual benefits of cobot implementation, but also the success factors, in conjunction with Lean Manufacturing usage. Finally, this paper suggests a draft method towards the successful integration of cobot.

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International audience; Blood is a complex fluid in which the presence of the various constituents leads to significant changes in its rheological properties. Thus, an appropriate non-Newtonian model is advisable; and we choose a Modified version of the rheological model of Phan-Thien and Tanner (MPTT). The different parameters of this model, derived from the rheology of polymers, allow characterization of the non-Newtonian nature of blood, taking into account the behavior of red blood cells in plasma. Using the MPTT model that we implemented in the open access software OpenFOAM, numerical simulations have been performed on blood flow in the thoracic aorta for a healthy patient. We started from a patient-specific model which was constructed from medical images. Exiting flow boundary conditions have been developped, based on a 3-element Windkessel model to approximate physiological conditions. The parameters of the Windkessel model were calibrated with in vivo measurements of flow rate and pressure. The influence of the selected viscosity of red blood cells on the flow and wall shear stress (WSS) was investigated. Results obtained from this model were compared to those of the Newtonian model, and to those of a generalized Newtonian model, as well as to in vivo dynamic data from 4D MRI during a cardiac cycle. Upon evaluating the results, the MPTT model shows better agreement with the MRI data during the systolic and diastolic phases than the Newtonian or generalized Newtonian model, which confirms our interest in using a complex viscoelastic model.

International audience; In this work the results related to the influence of selected electrical parameters of the abrasive electrodischarge grinding process on the surface layer temperature and morphology of machined samples in comparison to the conventional grinding method are presented. The basis of this work has been investigations of the deep grinding of surfaces of the samples made of titanium 5553 β, Inconel 617, Hastelloy X and magnesium AZ31 using a cubic boron nitride (CBN) grinding wheel with metallic binding agent. For the comparative evaluation of the conventional grinding and abrasive electrodischarge grinding, measurements of the specific grinding energy, temperature on the surface layer (at the contact of the grinding wheel‐workpiece) and geometric structure of the surface layer have been used.

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International audience; This paper investigates the windage power losses generated by helical gears rotating in pure air based on experimental results and a computational fluid dynamic code. It is found that the simulated flow patterns are totally different from those calculated for spur gears and that both tooth face width and helix angle are influential. The windage losses derived from Dawson’s and Townsend’s formulae are critically assessed using computational fluid dynamic results thus highlighting the limits of a unique formulation for accurate windage loss prediction. Finally, an analytical approach is suggested which gives good results providing that the flow rates at the boundaries of the inter-tooth domains can be estimated.

International audience; This brief presents an unknown input observer design method for a class of nonlinear systems in the presence of disturbances in both the system dynamics and the output. The theoretical result proposed can be considered as an extension of those established in [1] and [2], which are dedicated to observer design for estimating both the state of the system and an unknown input. By means of regular transformations, the robust observer design problem is turned into a linear matrix inequality feasibility problem. One of the main motivations of this brief is to develop a state estimator for proton exchange membrane fuel cell stack systems. More precisely, this brief addresses the problem of observer design for estimating the main variables of the fuel cell systems. Simulation results are presented to highlight the good convergence properties of the observers proposed.

In this work the results related to the influence of selected electrical parameters of the abrasive electrodischarge grinding process on the surface layer temperature and morphology of machined samples in comparison to the conventional grinding method are presented. The basis of this work has been investigations of the deep grinding of surfaces of the samples made of titanium 5553 β, Inconel 617, Hastelloy X and magnesium AZ31 using a cubic boron nitride (CBN) grinding wheel with metallic binding agent. For the comparative evaluation of the conventional grinding and abrasive electrodischarge grinding, measurements of the specific grinding energy, temperature on the surface layer (at the contact of the grinding wheel‐workpiece) and geometric structure of the surface layer have been used.

International audience; — Companies have evolved over time and this includes their efforts to overcome obstacles. In this article, we discuss sustainability as synonymous with success, and evaluate the sustainability of Continuous Improvement Programs (CIP) and the elements that affect it. The objective of this article is to highlight and analyse the results from a self-assessment investigation. We appraise the impact of a set of elements over sustainability and their maturity (absence or their degree of presence) while being deployed within the organization. This appraisal is done by assigning different weights and scores to the answers of the self-assessment investigation. We were able to observe that those elements with a higher impact score are heavily linked with management approaches. On the other hand, those same elements are not necessarily the more mature or appropriately displayed, and by the use of the maturity scoring system, we investigate the different stages of each element. This opens a pathway for further research into the behaviour of particular elements with the potential of enhancing or diminishing the sustainability of Continuous Improvement Programs.

The objective of this work is to study the improvement of the tribological properties of low alloy steel using a duplex treatment of low pressure carburizing and the deposition of a Cr–(WC–Co) coating by dual RF magnetron sputtering. The treatments result in a 500 μm thick carburized layer and a sputtered coating thickness of ~ 2 μm. Tribological tests were made with a ball-on-disk tribometer under dry conditions with low load and low speed. The worn surfaces of the disk, the wear counterpart, and resulting debris were analyzed by X-ray diffraction, optical microscopy, optical profilometry, and a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer. The wear performance of the samples was evaluated in terms of wear rates and friction coefficients during the sliding processes against two different counterparts. Experimental results have shown that sliding wear, of the investigated duplex treated low alloy steels, is strongly dependent on the counterface materials. Under testing conditions, the overall wear performance of a Cr–WC coating (Cr/W ratio of 1.12:1) deposited onto the surface of a carburized low alloy steel (0.61 wt.% C; HV = 654 ± 5) can be recommended as the best. The duplex-treated samples suffered severe, concentrated wear when against alumina. This wear is characterized by a combination of delamination, mild abrasion and oxidative wear. However, the wear mechanism seems to be oxidative and adhesive when against WC balls.

The sustainability of Continuous Improvement Programs (CIP) is characterized by a set of elements that originate from internal or external factors. They can be found in different levels of an organization; either strategic, tactical or operational. We have studied the literature regarding Continuous Improvement (CI) and then selected a total of fifteen elements. One of their characteristics is the closeness they have with the changing spirit of CIP, but also the fact that they can be studied as potential stability triggers. The purpose of this paper is to corroborate the existence of these elements within a real business environment and evaluate their impact on CIP sustainability. In order to achieve that, we have designed a self-assessment survey targeted to manufacturers and CI leaders. The results were related not only to actual element impact, but also to the different visions of sustainability. Based on these results, further research is suggested, for example study of the relationship between key elements and how their impact can be a reflection of CIP knowledge. This research will allow us to deepen our knowledge on key elements that characterize the sustainability of CIP and to anticipate possible risks to the weakening of dynamics of CIP., La pérennisation des démarches d'amélioration continue (DAC) est caractérisée par un ensemble d'éléments qui peuvent se trouver à différents niveaux de l'organisation (stratégique, tactique ou opérationnel) et qui peuvent être influencés par des facteurs internes ou externes à l'entreprise. Nous avons analysé la littérature concernant l'Amélioration Continue (AC) et nous avons sélectionné quinze de ces éléments. Une de leurs caractéristiques est la proximité avec la nature changeante des processus d'AC, mais aussi le fait qu'ils peuvent être considérés comme de possibles facilitateurs de stabilité. L'objectif de cet article est de montrer comment nous avons été en mesure de corroborer leur existence dans un contexte industriel et d'évaluer leur impact sur la pérennisation des DAC. A cette fin, nous avons élaboré un questionnaire d'autoévaluation, destiné aux industriels et responsables d'AC. Les résultats obtenus prennent en considération l'impact tangible des éléments clefs et les différentes visions de la pérennisation. En se basant sur ces résultats, d'autres recherches seront proposées, comme par exemple, la relation entre les éléments et leur impact sur la pérennisation des DAC. Ces recherches permettront d'approfondir nos connaissances sur les éléments clefs du processus de pérennisation des DAC et d'anticiper d'éventuels risques à l'essoufflement de la dynamique des DAC.

International audience; In a rapidly changing business environment, the implementation and sustainability of effective continuous improvement programs are synonymous with success. Maintaining an expected performance level over time is seen as the ultimate goal for any company. However, it becomes a complicated issue when there is little consensus for sustainability. The purpose of this paper is to study the definition of sustainability within the existing literature from different authors, dividing their work into five major subjects: semantics, financial, environmental, health and industrial. Keywords are highlighted in order to achieve a single definition, developed upon a continuous improvement setting. This definition will help companies to understand by a richer meaning the concept of sustainability. This leaves the door open for indepth studies, especially when facing sustainability of continuous improvement approaches. Based on this definition, further works could look at the incongruities innate to its definition and the elements influencing sustainability that are spread throughout the organization. The ultimately goal is to support continuous improvement sustainability.

Deoxidation is an unavoidable step in the elaboration of steel. The study of its influence could improve the quality of low-carbon steel (0.20–0.25 wt.% of carbon). There are many deoxidation methods, and the most-common one consists of adding aluminum. Although it is a classic method, determining the optimal process parameters (quantity, yield, etc.…) could be very sensitive. Deoxidation plays a determining role on inclusion cleanliness, especially on sulfide morphology. In order to control the efficiency of deoxidation, different techniques can be used. In this paper, an automated counting procedure on a scanning electron microscope with a field emission gun (FEG-SEM) is presented. This method was applied on samples cast in our laboratory under different deoxidation conditions. According to this, the resulting inclusion population is correlated with the aluminum content to find the optimal process parameters.

22d congress of the European Society of Biomechanics, LYON, FRANCE, 10-/07/2016 - 13/07/2016; Cardiovascular diseases are the leading cause of death worldwide. Their analysis leads to multidisciplinary problems that require diversity, transversal and complementary approaches. This contribution is part of a research project in Computer Aided Surgeryand intends to contribute to the improvement of TEVAR procedures in terms of accuracy and optimization of the operating strategy. The aim is first to identify the aortic arch mechanical behaviourusinga stereo-correlation technique. AFluid-Structure Interaction computation will be then made including non-Newtonian blood behaviour validated with4DCardiovascular Magnetic Resonance Imaging. This wouldprovide a diagnostic tool and support for clinical planning.

International audience; In rolling contact fatigue (RCF), failure mechanisms are known to be very sensitive to material microstructure. Yet, among the different numerical models developed to predict the RCF life, few models use a microstructure representation. A granular cohesive finite element model has been developed to simulate progressive damage of a structure subject to RCF and to investigate failure initiation mechanisms. This paper focuses on the implementation of crystal elasticity in the model. The numerical analysis of a representative volume element (RVE) validates the use of cubic elasticity to represent crystal behavior. The influence of the RVE size and the influence of boundary conditions applied on the RVE are evaluated in the finite element approximation framework. As regards the implementation of cubic elasticity in the RCF model, the generation of stress singularities at triple junctions is first highlighted. Then the average value of the intergranular shear stress is proved to be mesh size independent and therefore can be used as damage criterion. Finally, the influence of crystal elasticity on micro-cracks distribution is presented.

International audience; A thermal model of a back-to-back gear test rig relying on a network approach is presented in which the predictions of temperatures and power losses are coupled. The numerical findings are in good agreement with the measurements for transient regimes on a FZG test rig and it is demonstrated that the proposed simulation is reliable. A number of results are presented which illustrate the influence of the pinion and gear immersion depths. It is found that, in certain conditions, the classic isothermal method for estimating integral temperatures is highly questionable because the actual bulk temperature can substantially deviate from that of the oil sump. The practical consequences in terms of scuffing capacity are emphasised.

International audience; L’étude porte sur les aciers bas carbone (0,2 %) faiblement alliés bruts de fonderie. Les différentes opérations effectuées dans le bain liquide de l’acier influent sur la population inclusionnaire ; ces inclusions sont elles-mêmes responsables d’une partie des propriétés mécaniques de l’acier. Leur contrôle et leur étude revêtent donc une grande importance. L’objet de ce travail est de mettre au point une méthode de comptage, d’en évaluer la fiabilité et la reproductibilité ainsi que d’en montrer la limite. D’ordinaire, cette opération est réalisée par microscopie optique, méthode longue à mettre en œuvre et ne couvrant qu’une surface d’échantillon très limitée. La méthode présentée ici requiert un microscope électronique à balayage (MEB) doté d’une forte stabilité du faisceau d’où l’utilisation d’un canon à émission de champs (FEG). Cette méthode est plus rapide et couvre une surface plus large. Elle est déjà utilisée en sidérurgie pour des aciers laminés mais est beaucoup moins courante pour des contrôles métallurgiques sur des aciers moulés. Pour transposer cette méthode à ce type d’acier il est donc nécessaire de confirmer sa fiabilité et sa répétabilité. Dans un premier temps, un opérateur définit des critères morphologiques et chimiques sur les inclusions rencontrées dans une zone représentative très réduite. Dans un second temps, un logiciel scanne automatiquement une zone beaucoup plus large et classe les inclusions détectées selon les critères pré-définis (taille, forme, nature). Afin de statuer sur la répétabilité et la reproductibilité de cette méthode, une étude statistique est réalisée sur une surface test ; cette zone est analysée plusieurs fois dans le but de définir des intervalles de tolérances. Si les résultats obtenus en termes de population inclusionnaire sont significatifs, il sera alors possible de statuer sur la pertinence des différentes opérations effectuées dans les bains d’acier liquide.

Different economical configurations, due for instance to the relative cost of the fuel it consumes, can push a heat engine into operating whether at maximum efficiency or at maximum power produced. Any relevant design of such system hence needs to be based, at least partly, on the knowledge of its specific "power vs. efficiency" characteristic curve. However, even when a simple model is used to describe the engine, obtained for example thanks to Finite Dimensions Thermodynamics, such characteristic curve is often difficult to obtain and takes an explicit form only for the simplest of these models. When more realistic models are considered, including complex internal subsystems or processes, an explicit expression for this curve is practically impossible to obtain. In this paper, we propose to use the called Graham's scan algorithm in order to directly obtain the power vs. efficiency curve of a realistic Stirling engine model, which includes heat leakage, regenerator effectiveness, as well as internal and external irreversibilities. Coupled with an adapted optimization routine, this approach allows to design and optimize the same way simple or complex heat engine models. Such method can then be useful during the practical design task of any thermal power converter, almost regardless to its own internal complexity., Comment: 17 pages, 10 figures

Colloque avec actes et comité de lecture. Internationale.; International audience; Un modèle thermo mécanique d'un banc FZG est développé. Le modèle numérique se base sur la méthode des réseaux thermiques et prend en compte les pertes de puissance dues aux dentures, aux roulements et au brassage du bain d'huile. Des mesures soulignent que les bagues des roulements présentent un gradient de température significatif. Pour expliquer ce gradient, deux modèles de roulement sont proposés et comparés aux mesures. Leur influence sur le comportement thermique global de la transmission mécanique est discutée et analysée.

Colloque avec actes et comité de lecture. Internationale.; International audience; Les mécanismes d'initiation de fissures en fatigue de contact sont fortement liés à la microstructrure du matériau. Cependant, la plupart des modèles utilisés pour prédire la durée de vie en fatigue de contact se situent à l'échelle macroscopique. Un modèle basé sur une représentation de type Voronoi des grains (échelle mésoscopique) est développé afin d'analyser les mécanismes d'initiation. Le concept d'endommagement est appliqué aux joints de grain modélisés par la méthode des zones cohésives (CZM). La représentativité du modèle a été améliorée par la modélisation de l'anisotropie cristalline. Enfin, une nouvelle méthode d'application de l'endommagement aux joints de grain a permis de rendre les résultats plus cohérents en termes d'estimation de la durée de vie.

Colloque avec actes et comité de lecture. Internationale.; International audience; Le principal composant du pont est un couple conique, spiro-conique ou hypoïde, qui joue un rôle majeur en termes de pertes. Le frottement au niveau du contact est étudié, en s'intéressant d'une part aux paramètres de la denture, et d'autre part au comportement thermique général du pont qui peut influer sur les caractéristiques du film lubrifiant.

Colloque avec actes et comité de lecture. Internationale.; International audience; Dans cette étude, une méthode originale pour analyser la répartition des pertes de puissance dans un réducteur épicycloïdal est présentée. Elle est basée sur le couplage fort entre le rendement d'une transmission et son comportement thermique. Ce modèle est utilisé pour analyser les résultats expérimentaux obtenus à l'aide d'un banc d'essai. Dans le cas du réducteur épicycloïdal testé, les résultats montrent que les pertes de puissance indépendantes de la charge produites par la transmission sont majoritairement dues aux pertes hydrodynamiques générées dans les roulements des satellites et que les effets de ventilation sont négligeables.

International audience

This paper presents the principle and testing of a novel technique developed for carburizing processes monitoring. The technique relies upon an experimental device made of a thin iron foil with a carburizing atmosphere on one side and a decarburizing atmosphere on the other. The principle of carburizing control is based on the fact that when steady-state of carbon diffusion is reached across the thin iron foil, the measured mass flux of carbon on the decarburizing side is related to the inflow of carbon into the parts during the carburizing treatment. Hence, as a probe could be inserted directly into a given furnace, it would provide an in situ control facility. The proposed device could then be used for controlling atmospheric or low-pressure (vacuum) carburizing treatments. The results presented here are limited to atmospheric conditions. Nevertheless, they gave the incentive to the researchers to pursue the development of the device to allow for measurements in a low-pressure furnace and to refine the experimental bench to quantify thoroughly the phenomena involved within the foil.

International audience

International audience

International audience

International audience; The objective of this study is to determine the influence of duplex treatment (low pressure thermochemical treatment and PVD coating) on tribological properties. The carbide and carbonitride coatings are deposited by dual RF magnetron sputtering on the reference steel 18CrMo4 and the carburized and carbonitrided one (respectively).The low-pressure carburized and carbonitrided samples present 0.72 and 0.69 w. % carbon content at their surface respectively and a hardness of about 700 Hv0.1. The carburizing and carbonitriding layer are respectively 540 and 390 µm thick, while TiWC and TiWCN were 2.8 and 3.4 µm thick respectively. Tribological tests were performed by a Pin-on-Disk rotative tribometer with alumina and steel (100Cr6) balls. A comparison of the friction coefficient and the wear rate for each sample has been made. The adhesion of the coatings has been performed by analyzing the wear track using optical profilometry, optical microscopy and scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer. The best tribological performances were observed by combining carbides coatings and carburized 18CrMo4 or reference steel. In contrast, the TiWCN thin film completely delaminated.

The effect of the composition of two steels (B and 6MnCr5) on precipitation of undesirable phases (carbides, nitrides and carbonitrides) under thermochemical treatment (low-pressure or vacuum carbonitriding) is investigated. Metallographic and x-ray diffraction studies and thermodynamic computations are performed. BMI Fours Industriels, St. Quentin Fallavier, France