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International audience; A novel single shear specimen (SSS) together with a correction coefficient method is used to study the deformation behavior of a 304 stainless steel under shear loadings. Shear stress-shear strain relations over a wide range of shear strain rates (0.001 to 39000 s−1) at three initial temperatures (77 to 473 K) are obtained experimentally. The effects of strain rate and temperature on the flow stress curves are determined. With increasing strain rate or temperature, the strain hardening rate decreases continuously. At the maximum strain rate of 39000 s−1, negative strain hardening rates are observed. At very high strain rates above 13000 s−1, a sharp increase in flow stress is observed, indicating a rapid rise in strain rate sensitivity. The fracture morphology of post-mortem specimens is analyzed and no well-developed adiabatic shear bands are observed. This may be due to the shear-tension stress state without hydrostatic pressure in the fracture process. Based on the experimentally obtained shear stress-shear strain curves, parameters of a modified Johnson-Cook (MJC) model are determined. A good agreement between experiments and model predictions is found, with an average error of 3.9%. Using finite element analysis, distributions of stress and strain components in the specimen shear zone is analyzed. It is found that the shear stress and shear strain play dominant roles, and a simple shear stress state with low stress triaxiality (0.015) and Lode angle parameter (0.014) is obtained.

International audience; As an emerging technology to harness the marine current energy, tidal stream turbine (TST) systems have been developed due to high predictability and energy density in tidal current resources. However, considering that various challenges such as swell disturbances, unknown disturbances, or parameter uncertainties may deteriorate the system performance, it is interesting to investigate alternative control strategies to the conventional proportional-integral (PI) controls. In this paper, the active disturbance rejection control (ADRC) approach is proposed to replace PI controllers in the conventional generator-side control scheme. In this approach, two ADRC schemes (cascaded and second-order ADRC strategies) are respectively applied and compared to achieve MPPT under current velocity and turbine torque disturbances. Performances of the proposed ADRC approaches are compared to PI and sliding mode control strategies. Energy production during swell wave disturbance is also evaluated under these control strategies. The comparisons show that the cascaded ADRC has better performance than the second-order approach. Moreover, the cascaded ADRC is tested under parameter variations to evaluate its robustness. The carried out simulation-based comparative study shows the effectiveness and advantages of the cascaded ADRC strategy over conventional PI controller in terms of fast convergence, overshoots elimination, and improved robustness under disturbances and parameter uncertainties.

International audience; The 3D indoor deployment of sensor nodes is a complex real world problem, proven to be NP-hard and difficult to resolve using classical methods. In this context, we propose a hybrid approach relying on a novel bird's accent-based many objective particle swarm optimization algorithm (named acMaPSO) to resolve the problem of 3D indoor deployment on the Internet of Things collection networks. The new concept of bird's accent is presented to assess the search ability of particles in their local areas. To conserve the diversity of the population during searching, particles are separated into different accent groups by their regional habitation and are classified into different categories of birds/particles in each cluster according to their common manner of singing. A particle in an accent-group can select other particles as its neighbors from its group or from other groups (which sing differently) if the selected particles have the same expertise in singing or are less experienced compared to this particle. To allow the search escaping from local optima, the most expert particles (parents) ''die'' and are regularly replaced by a novice (newborn) randomly generated ones. Moreover, the hybridization of the proposed acMaPSO algorithm with multi-agent systems is suggested. The new variant (named acMaMaPSO) takes advantage of the distribution and interactivity of particle agents. Experimental, numerical and statistical found results show the effectiveness of the two proposed variants compared to different other recent state-of-the-art of many-objective evolutionary algorithms.

Mechanism and Machine Theory, 121, ISSN:0094-114X

International audience; In today’s business environment, the trend towards more product variety and customization is unbroken. Due to this development, the need of agile and reconfigurable production systems emerged to cope with various products and product families. To design and optimize production systems as well as to choose the optimal product matches, product analysis methods are needed. Indeed, most of the known methods aim to analyze a product or one product family on the physical level. Different product families, however, may differ largely in terms of the number and nature of components. This fact impedes an efficient comparison and choice of appropriate product family combinations for the production system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster these products in new assembly oriented product families for the optimization of existing assembly lines and the creation of future reconfigurable assembly systems. Based on Datum Flow Chain, the physical structure of the products is analyzed. Functional subassemblies are identified, and a functional analysis is performed. Moreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of thyssenkrupp Presta France is then carried out to give a first industrial evaluation of the proposed approach.

This paper is a contribution to the phenomenological modeling of damage evolution in DP steels in the framework of Gurson's approach. It is based on recent results of X-ray tomography in-situ tensile tests and subsequent one-dimensional metallurgical void nucleation models proposed in [C. Landron et al., Scripta Materialia 63 (2010) 973–976]. A macroscopic void nucleation law for DP steels is proposed, covering a wide range of stress triaxialities. The respective effects of nucleation, growth and coalescence are clearly separated. Validations with respect to experimental porosity measurements were performed for several monotonic loading cases and for two loading sequences involving large strains and strain-path changes. Keywords: GTN model, Phenomenological void nucleation law, DP steels, Finite element simulation, Damage evolution

International audience; Tolerance analysis aims on checking whether specified tolerances enable functional and assembly requirements. The tolerance analysis approaches discussed in literature are generally assumed without the consideration of parts’ form defects. This paper presents a new model to consider the form defects in an assembly simulation. A Metric Modal Decomposition (MMD) method is henceforth, developed to model the form defects of various parts in a mechanism. The assemblies including form defects are furtherassessed using mathematical optimization. The optimization involves two models of surfaces: real model and difference surface-base method, and introduces the concept of signed distance. The optimization algorithms are then compared in terms of time consumption and accuracy. To illustrate the methods and their respective applications, a simplified over-constrained industrial mechanism in three dimensions is also used as a case study.

During the last eighty years, new work philosophies has been introduced and technological advancement changed radically the way of work, making it more reactive, agile but complex as well. As a result, classical approaches for production system design may no longer be sufficient to ensure productivity and safety of industrial systems. In the domain of occupational diseases, adopting a pure biomechanical approach, consisting in ensuring the non-violation of workers’ biomechanical limits at each workstation is proved to be uncomplete. Beside biomechanical risk factors, psychosocial risk factors, which are strongly linked to the dynamic of the physical and informational flows, may contribute to the genesis of Musculoskeletal Disorders. By granting a certain workers’ margins of manoeuver, these risk factors can be limited. This article introduces AEN-PRO, a simulation tool for investigating the impact of physical flow on the production system and particularly workers, to assess their margins of manoeuver and to ensure safer and productive systems.

International audience; We present a novel solution algorithm for a specific set of linear equations arising in large scale sparse interconnections, such as the PageRank problem. The algorithm is distributed, exploiting the underlying graph structure, and completely asynchronous. The main feature of the proposed algorithm is that it ensures that the consistency constraint (the sum of the solution components summing to one) is satisfied at every step, and not only when convergence is reached, as in the case of the different algorithms available in the literature. This represents an important feature, since in practice this kind of algorithms are stopped after a fixed number of steps. The algorithm is based on two projection steps, and represents a variation of the classical Kaczmarz method. In this paper, we present a completely deterministic version, and prove its convergence under mild assumptions on the node selection rule. Numerical examples testify for the goodness of the proposed methodology.

In the expanding context of device miniaturization, forming processes of ultra thin sheet metals are gaining importance. Numerical simulation of these processes requires accurate material modeling. In this study, both the phenomenological modeling approach and the crystal plasticity finite element method (CPFEM) are considered. Theoretical definitions of both models, numerical implementation as well as their parameter identification procedures are outlined. Subsequently they are compared on a one to one basis, mainly with regards to their ability to predict mechanical responses for a variety of strain loading paths. Agence Nationale de la Recherche, ANR-12-RMNP-0009-02

International audience; This paper proposes a novel model of opinion dynamics with limited confidence. As opposed to other models, the onset of reciprocal influences between individuals is not defined by absolute thresholds, but by a notion of relative relevance for each link. The proposed dynamics takes the form of a hybrid dynamical system, where topology and opinions are coupled but as distinct variables. We prove converge to opinion distributions where disconnected clusters of individuals agree locally, while each cluster holds a different opinion. We also illustrate the dynamics via simulations.

International audience; Integrated product design and development in today’s highly competitive and economically challenging world is a complex process depending upon client requirements. One of the main factors contributing to the complexity of process is uncertainty due to lack of system knowledge, known as epistemic uncertainty. This paper proposes a systematic approach to reduce epistemic uncertainty in design process in early stages of design. The approach is based on “CTOC” and “CPM” to decompose the system behaviour and determine the relationships between function and structure of a system. An application of the approach is demonstrated through an industrial case study.

International audience; In tolerancing analysis area, the most various existing approaches do not take form defects of parts into consideration. As high precisions assemblies cannot be analyzed with the assumption that form defects are negligible, the paper focuses in particular on the study of the form defects impacts on the assembly simulation and that by comparing two optimization algorithms (iHLRF and Quapro). The study is limited firstly to the cylinders. For the optimization, two main types of surfaces modelling are considered: difference surface-based method and real model. The compared models allow assessing the non-interferences between cylinders with form defects, potentially in contact. This is in the main issue to validate a tolerance analysis approach.

International audience; This paper deals with the modeling of insulation material lifespan in a partial discharge regime under certain accelerated electrical stresses (voltage, frequency and temperature). An original model, relating the logarithm of the insulation lifespan, the logarithm of the electrical stress and an exponential form of the temperature, is considered. An estimation of the model parameters is performed using three methods: the design of experiments (DoE) method, the response surface method (RSM) and the multiple linear regression (MLR) method. The estimation is obtained on learning sets determined according to each method specification. The performance, in terms of estimation, of each of the three methods is evaluated on a test set composed of additional experiments. For economic reasons and flexibility, the learning and test sets are composed of experiments carried out on twisted pairs of wires covered by an insulator varnish. The ability of the DoE and the RSM methods to organize and to limit the number of experiments is confirmed. The MLR method, however, shows more flexibility with regard to the studied configurations. Thus, it offers an efficient solution when organization is not required or not possible. Moreover, the flexibility of MLR allows specific ranges for the factors to be explored. A local analysis of the estimation performance shows that very short and long lifespans cannot be simultaneously represented by the same model.

The microstructure investigation and flow behavior during thixoforging of M2 steel parts were investigated. Partial remelting was performed at processing temperatures ranging from 1290 ◦C to 1340 ◦C corresponding to a liquid fraction range between 10% and 30% (according to differential scanning calorimetry measurements and quantitative image analyses). A conventional microstructure for thixoforming process was obtained: spherical solid grains surrounded by liquid phase. The microstructure across the heated billets was relatively homogeneous with bigger grain size near the surface. Successful thixoextrusion for producing parts was finally achieved at processing temperatures. By investigating the microstructure and load-displacement curves, different mechanisms in various forming stages were proposed.; International audience; The microstructure investigation and flow behavior during thixoforging of M2 steel parts were investigated. Partial remelting was performed at processing temperatures ranging from 1290 ◦C to 1340 ◦C corresponding to a liquid fraction range between 10% and 30% (according to differential scanning calorimetry measurements and quantitative image analyses). A conventional microstructure for thixoforming process was obtained: spherical solid grains surrounded by liquid phase. The microstructure across the heated billets was relatively homogeneous with bigger grain size near the surface. Successful thixoextrusion for producing parts was finally achieved at processing temperatures. By investigating the microstructure and load-displacement curves, different mechanisms in various forming stages were proposed.

International audience; This study aims at evaluating the mechanisms of biofilm detachment with regard of the physical properties of the biofilm. Biofilms were developed in Couette-Taylor reactor under controlled hydrodynamic conditions and under different environmental growth conditions. Five different conditions were tested and lead to the formation of two aerobic heterotrophic biofilms (aeHB1 and aeHB2), a mixed autotrophic and heterotrophic biofilm (MAHB) and two anoxic heterotrophic biofilms (anHB1 and anHB2). Biofilm detachment was evaluated by monitoring the size of the detached particles (using light-scattering) as well as the biofilm physical properties (using CCD camera and image analysis). Results indicate that volume erosion of large biofilm particles with size ranging from 50 to 500 lm dominated the biomass loss for all biofilms. Surface erosion of small particles with size lower than 20 lm dominates biofilm detachment in number. The extent of the volume detachment events was governed by the size of the biofilm surface heterogeneities (i.e., the absolute biofilm roughness) but never impacted more than 80% of the mean biofilm thickness due to the highly cohesive basal layer. Anoxic biofilms were smoother and thinner than aerobic biofilms and thus associated with the detachment of smaller particles. Our results contradict the simplifying assumption of surface detachment that is considered in many biofilm models and suggest that discrete volume events should be considered.

International audience; Tolerance verification permits to check the product conformity and to verify assumptions made by the designer. For conformity assessment, the uncertainty associated with the values of the measurands must be known. In fact, to evaluate form characteristics of large aircraft structure workpieces, sampling is required, so a measurement error is present: exact estimation of form characteristics would require complete knowledge of the surface. To minimise this measurement error, this paper presents a Krigingbased procedure to identify the minimum of measured points to check the conformity with a given confidence level. The proposed method is validated on a simple example of orientation tolerance and then performed to inspect the form defect on three large aircraft workpieces.

The authors warmly thank Luc Morhain and Marc Wary (Arts et Métiers ParisTech CER Metz) for their technical support.; International audience; Thixoforming of steels poses challenges due to the high temperatures involved and the lack of understanding of thermomechanical behavior. The volume fractions of the liquid and solid phases in the semi-solid state are the most important parameters for such a form-ing process, as they affect the viscosity and hence the flow behavior of the material. Two-dimensional observations might not always be sufficient, as the size distribution and the connectivity of phases cannot be obtained from associated measurements, which can only be determined by three-dimensional (3-D) investigation. This paper presents the first application of high-energy X-ray microtomography to the microstructure of steel in the semi-solid state. The microstructure of M2 high-speed tool steel was studied in both as-received and heated-and-quenched states. From the reconstructed images, 3-D information could be obtained and was compared with scanning elec-tron microscopy and energy dispersive spectrometry observations. The volume fraction and the location of liquid phase in the semi-solid state were determined in particular, and the continuous solid skeleton was investigated.

Semi-solid forming is an effective near-net-shape forming process to produce components with complex geometry and in fewer forming steps. It benefits from the complex thixotropic behaviour of semi-solids. However, the consequences of such behaviour on the flow during thixoforming, is still neither completely characterized and nor fully understood, especially for high melting point alloys. The study described in this paper investigates thixoextrusion for C38 low carbon steel material using dies at temperatures much lower than the slug temperature. Four different process parameters were studied: the initial slug temperature, the die temperature, the ram speed and the presence of a ceramic layer at the tool/material interface. The extruded parts were found to have an exact shape and a good surface state only if the temperature was below a certain value. This critical temperature is not an intrinsic material property since its value depends on die temperature and the presence of the Ceraspray©layer. Two kinds of flow were highlighted: a homogeneous flow controlled by the behaviour of the solid skeleton characterized by a positive strain rate sensitivity, and a non homogeneous flow (macro liquid/solid phase separation) dominated by the flow of the free liquid. With decreasing ram speed, heat losses increase so that the overall consistency of the material improves, leading to apparent negative strain rate sensitivity. Finally, some ways to optimise thixoforming are proposed.; International audience; Semi-solid forming is an effective near-net-shape forming process to produce components with complex geometry and in fewer forming steps. It benefits from the complex thixotropic behaviour of semi-solids. However, the consequences of such behaviour on the flow during thixoforming, is still neither completely characterized and nor fully understood, especially for high melting point alloys. The study described in this paper investigates thixoextrusion for C38 low carbon steel material using dies at temperatures much lower than the slug temperature. Four different process parameters were studied: the initial slug temperature, the die temperature, the ram speed and the presence of a ceramic layer at the tool/material interface. The extruded parts were found to have an exact shape and a good surface state only if the temperature was below a certain value. This critical temperature is not an intrinsic material property since its value depends on die temperature and the presence of the Ceraspray©layer. Two kinds of flow were highlighted: a homogeneous flow controlled by the behaviour of the solid skeleton characterized by a positive strain rate sensitivity, and a non homogeneous flow (macro liquid/solid phase separation) dominated by the flow of the free liquid. With decreasing ram speed, heat losses increase so that the overall consistency of the material improves, leading to apparent negative strain rate sensitivity. Finally, some ways to optimise thixoforming are proposed.

International audience; This paper deals with mechanical fault diagnosis in three-phase induction machines from stator current measurements. According to machine models, mechanical faults lead to amplitude and/or phase modulations of the measured stator current with possibly time varying carrier frequency. The modulation diagnosis requires a univocal de¯nition of the instantaneous phase and amplitude. This is performed by associating a complex signal to the real measured one. For a convenient separate modulation diagnosis, the complex signal instantaneous phase and amplitude are expected to carry respectively information about the phase and amplitude modulations. The complex signal is classically obtained through the Hilbert transform. Under Bedrosian conditions, the so-called analytic signal allows a separate modulation diagnosis. However, mechanical faults may also produce fast modulations violating the Bedrosian conditions. This study proposes an alternative complex signal representation which takes advantage of the three stator current measurements available in a three phase machine. From two stator current measurements, the Concordia transform builds a complex vector, the so-called space vector, which unconditionally allows separate modulation diagnosis. This paper applies and compares the Hilbert and Concordia transforms, theoretically and in case of simulated and experimental signals with various modulation frequency ranges.

The authors are grateful for funding provided to this project by the French Ministry of Industry, Dassault Aviation, Dassault Systemes, and F. Vernadat for his review and recommendations.; International audience; The research concerns automated generation of process plans using knowledge formalization and capitalization. Tools allowing designers to deal with issues and specifications of the machining domain are taken into account. The main objective of the current work is to prevent designers from designing solutions that would be expensive and difficult to machine. Among all available solutions to achieve this goal, two are distinguished: the generative approach and the analogy approach. The generative approach is more adapted to generate the machining plans of parts composed of numerous boring operations in interaction. However, generative systems have two major problems: proposed solutions are often too numerous and are only geometrically but not technologically relevant. In order to overcome these drawbacks, two new concepts of feature and three control algorithms are developed. The paper presents the two new features: the Machining Enabled Geometrical Feature (MEGF) and the Machinable Features (MbF). This development is the result of the separation of the geometrical and the technological data contained in one machining feature. The second objective of the paper is to improve the current Process Ascending Generation (PAG) system with control algorithms in order to limit the combinatorial explosion and disable the generation of unusable or not machinable solutions.