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Open Access
L'université Paris Nanterre s'engage en faveur de l'Open Access
Par Open Access, on entend le libre accès aux résultats de la recherche, diffusés sous forme électronique et en ligne gratuitement. Ce mouvement existe au niveau mondial depuis la fin des années 90 et s'est concrétisé par des appels adressés à la communauté des chercheurs en faveur du partage des connaissances (Budapest, 2002 ; Berlin, 2003).
L'université Paris Nanterre favorise l'Open Access par le biais d'un portail HAL (Hyper Articles en Ligne), principale archive ouverte en France maintenue par le CNRS, qui rassemblent les publications des chercheurs affiliés à l'établissement.
D'autres initiatives de Paris Nanterre contribuent au développement du Libre Accès, comme la participation des Presses Universitaires au projet OpenEdition Books, la diffusion de plusieurs revues en Open Access sur Revues.org, l'ouverture de carnets de recherche sur la plateforme Hypothèses par des chercheurs ou encore le projet Open Data de l'université.
Les derniers dépôts de nos chercheurs !
- [hal-01305736] A posteriori global error estimator based on the error in the constitutive relation for reduced basis approximation of parametrized linear elastic problems22 janvier 2018In this paper we introduce a posteriori error estimator based on the concept of error in the constitutive relation to verify parametric models computed with a reduced basis approximation. We develop a global error estimator which leads to an upper bound for the exact error and takes into account all the error sources: the error due to the reduced basis approximation as well as the error due to the finite element approximation. We propose an error indicator to measure the quality of the reduced basis approximation and we deduce an error indicator on the finite element approximation.
- [hal-01421523] Features selection and classification to estimate elbow movements22 janvier 2018In this paper, we propose a novel method to estimate the elbow motion, through the features extracted from electromyography (EMG) signals. The features values are normalized and then compared to identify potential relationships between the EMG signal and the kinematic information as angle and angular velocity. We propose and implement a method to select the best set of features, maximizing the distance between the features that correspond to flexion and extension movements. Finally, we test the selected features as inputs to a non-linear support vector machine in the presence of non-idealistic conditions, obtaining an accuracy of 99.79% in the motion estimation results.
- [hal-01237733] Estimation of the validity domain of hyper-reduction approximations in generalized standard elastoviscoplasticity22 janvier 2018Background We propose an a posteriori estimator of the error of hyper-reduced predictions for elastoviscoplastic problems. For a given fixed mesh, this error estimator aims to forecast the validity domain in the parameter space, of hyper-reduction approximations. This error estimator evaluates if the simulation outputs generated by the hyper-reduced model represent a convenient approximation of the outputs that the finite element simulation would have predicted. We do not account for the approximation error related to the finite element approximation upon which the hyper-reduction approximation is introduced. Methods We restrict our attention to generalized standard materials. Upon use of incremental variational principles, we propose an error in constitutive relation. This error is split into three terms including a tailored norm of the hyper-reduction approximation error. This error norm is defined by using the convexity of an incremental potential introduced to state the constitutive equations. The second term of the a posteriori error is related to the stress recovery technique that generates stresses fulfilling the finite element equilibrium equations. The last term is a coupling term between the hyper-reduction approximation error at each time step and the errors committed before this time step. Unfortunately, this last term prevents error certification. In this paper, we restrict our attention to outputs extracted by a Lipschitz function of the displacements. Results In the proposed numerical examples, we show very good preliminary results in predicting the validity domain of hyper-reduction approximations. The average computational time of the predictions obtained by hyper reduction, is accelerated by a factor of 6 compared to that of finite element simulations. This speed-up incorporates the computational time devoted to the error estimation. Conclusions The numerical implementation of the proposed error estimator is straightforward. It does not require the computation of the incremental potential. In the numerical results, the estimated validity domain of hyper-reduced approximations is inside the reference validity domain. This paper is a first attempt for a posteriori error estimation of hyper-reduction approximations.
- [hal-01421500] Numerical simulation of the coupling between thermal dissipation and fish-eye crack growth in very high cycle fatigue regime22 janvier 2018In this paper, we study the temperature field associated with the propagation of a fatigue crack in a very high cycle fatigue regime during ultrasonic fatigue testing. We use a Paris\textendashHertzberg crack growth law to compute the evolution of the crack and a perfectly elastic\textendashplastic constitutive law to compute the plastic dissipation per cycle at the tip of the crack. A thermomechanical finite element model is proposed to estimate the evolution of the temperature field during the crack propagation. Numerical results obtained agree fairly well with experimental results.
- [hal-01421507] Error control in FORM reliability analysis22 janvier 2018This paper deals with the failure probability error induced by the coupling between the first-order reliability method (FORM) and the Finite Element Method (FEM). A FEM error estimator based on the concept of error in constitutive relation associated with goal-oriented error estimation is proposed. Furthermore an importance sampling technique is used to compute the error due to the FORM approximation. Both these errors are used to choose a finite element mesh adapted to the problem.
- [hal-01686407] A rapid scatter prediction method for very high cycle fatigue22 janvier 2018VHCF tests are often performed by a high frequency fatigue test system, such as ultrasonic fatigue test machine. In the article, simple VHCF tests and cumulative fatigue (LCF plus VHCF) tests are performed to investigate the fatigue behavior respectively for a low carbon manganese steel. The test results in Wöhler diagram show a large scatter in VHCF regime. Continuum Damage Mechanics model is extended to VHCF region to estimate the remaining fatigue life. A rapid fatigue failure probability prediction method is applied and extended to VHCF regime in order to evaluate the fatigue dispersion based on multi scales model and fatigue dissipation analysis.
- [hal-01688811] THE GENETIC BASIS OF ZEBRA FINCH VOCALIZATIONS20 janvier 2018Animal vocalizations play an important role in individual recognition, kin recognition, species recognition, and sexual selection. Despite much work in these fields done on birds virtually nothing is known about the heritability of vocal traits in birds. Here, we study a captive population of more than 800 zebra finches (Taeniopygia guttata) with regard to the quantitative genetics of call and song characteristics. We find very high heritabilities in nonlearned female call traits and considerably lower heritabilities in male call and song traits, which are learned from a tutor and hence show much greater environmental variance than innate vocalizations. In both sexes, we found significant heritabilities in several traits such as mean frequency and measures of timbre, which reflect morphological characteristics of the vocal tract. These traits also showed significant genetic correlations with body size, as well as positive genetic correlations between the sexes, supporting a scenario of honest signaling of body size through genetic pleiotropy (" index signal "). In contrast to such morphology-related voice characteristics, classical song features such as repertoire size or song length showed very low heritabilities. Hence, these traits that are often suspected to be sexually selected would hardly respond to current directional selection.
- [hal-01421699] Comparison of different techniques for the monitoring of the Lüders bands development22 janvier 2018In C-Mn and some low alloyed steels, the plastic deformation begins by a macroscopic heterogeneous strain which materializes into the propagation of a strain band along a tensile sample with a uniform cross-section. This band is named Lüders, or Piobert-Lüders, band and it is considered by some authors as a plastic wave. This particular strain localization, which goes through the length of the sample, is explained by an avalanche phenomenon which enables step by step to unfix the dislocations from their Cottrell’s atmosphere. However, although its effects are well enough known, one knows much less its causes. In this paper, the travel of the Lüders band is monitored thanks to several techniques based on different physical principles: optical (speckle interferometry), thermal (infrared pyrometry) and acoustic (acoustic emission). The position of the band, its inclination, its propagation speed and the strain rate inside the band are the main points of comparison between each technique. They allow verifying some features about the propagation of the bands and giving some new assumptions about their formation and their development.
- [hal-01687291] Analysis of the plastic zone of a circle crack under very high cycle fatigue19 janvier 2018Metals used in industry for structures and aero-engine components are sometimes subjected to very high cycle fatigue (VHCF) damage during their working service. In this paper, a novel method is presented to determine the size and location of a circular crack located within a metal specimen under 20 kHz VHCF loading conditions. The method is based on an analysis of the temperature rise on the surface of the spec-imen and correlation of this temperature rise to the energy dissipation in the plastic zone of the crack. The approach taken is to ﬁrst determine the heat source location and strength using an inverse heat transfer calculation based on the surface temperature measurements. Next, the relationship between the heat and the material hysteresis loop in the plastic zone, which is a function of stress intensity factor and vibration amplitude cyclic loading of the specimen, is found. The calculation of the stress intensity factor under vibrational loading is often an obstacle in VHCF research because there is currently no stan-dard or existing formula. In this paper a general polynomial formula for the stress intensity factory under 20 kHz loading conditions is obtained using a ﬁnite element modeling approach as a function of the spec-imen’s material properties and position and size of the internal crack.
- [hal-01687219] Surface crack initiation mechanism for body centered cubic materials in the gigacycle fatigue domain19 janvier 2018A BCC polycrystalline single phase Armco iron was tested in the Very High Cycle Fatigue (VHCF) régime using plate specimens and a load ratio of R = -1. Throughout testing until fracture, optical observations of the specimen surface (on one side) and temperature measurements and recordings (on the other speci-men side) were performed. After failure, the fracture surfaces were observed via SEM. The macroscopic observations showed an early occurrence of Persistent Slips Bands (PSBs). The observations of fracture surfaces clearly revealed an initiation and propagation stage. In the initiation stage, which ranges from about 200 to 550 lm, the grain traces are visible with intergranular, transgranular and mixed fracture. The comparison with the thermal recordings leads to the conclusion that the crack initiation stage is completed near the end of the fatigue life. Interrupted tests show damage in the bulk specimen before the crack initiation.
Mis à jour le 08 décembre 2017