Dissertation•
Apports des mesures d’auto-échauffement pour l’étude de la fatigue des aciers : effets d’histoire et cisaillement pur
05 Apr 2019-
TL;DR: In this paper, a new notion of cisaillement and deux geometries d'eprouvette en forme de disque are proposed, permettant d'utiliser des mesures d'auto-echauffement.
Abstract: Dans l’industrie automobile, les aciers lamines sont largement utilises pour realiser les pieces constitutives d’un vehicule. Les proprietes en fatigue a grand nombre de cycles de ces produits plats sont generalement determinees sur le materiau dans son etat tel que sortie d’usine (i.e., vierge de toute sollicitation) sous chargements cycliques uniaxiaux a amplitude constante. Cependant, la fabrication de piece structurelle fait generalement intervenir des etapes de mise en forme qui ont pour consequence de modifier l’etat du materiau et donc d’impacter les proprietes en fatigue. D’autre part, les chargements en service reellement subi par une telle piece sont souvent multiaxiaux et d’amplitude variable dans le temps. Cette etude a pour but de prendre compte les notions de multiaxialite et d’effets d’histoire de chargement lors de la caracterisation en fatigue par le biais de mesures d’auto-echauffement sous chargements cycliques. La caracterisation en fatigue multiaxiale fait generalement intervenir un critere de fatigue necessitant la connaissance de la limite d’endurance du materiau sous sollicitation de cisaillement. Comme cette grandeur est difficile a obtenir pour le cas des produits plats, un nouvel essai de cisaillement et deux geometries d’eprouvette en forme de disque sont proposes, permettant d’utiliser des mesures d’auto-echauffement. Ainsi, la limite d’endurance sous sollicitation de cisaillement a pu etre determinee. Dans le but d’etudier l’impact des effets d’histoire sur les proprietes en fatigue, differents essais d’auto-echauffement ont ete realises en considerant differents niveaux de pre-deformation plastique initial, differents pre-chargements cycliques et differents rapports de charge. Les resultats obtenus ont permis de proposer un modele probabiliste a deux echelles permettant d’une part de decrire l’evolution des courbes d’auto-echauffement quel que soit l’effet d’histoire etudie et, d’autre part, de donner une bonne estimation de l’influence de ces effets sur les courbes S-N-P.
Citations
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TL;DR: In this article, the role of martensitic transformation in the self-heating behavior of 304L stainless steel was investigated under cyclic loading tests in different conditions and the effect of the testing temperature and a pre-strain at room temperature on the selfheating curves was investigated.
11 citations
TL;DR: In this article, two new specimen geometries are proposed to assess the fatigue limit under pure shear loading using self-heating measurements for isotropic material, and the thermal fields were imaged by an infrared camera, demonstrating the validity of using a 0D thermal approach.
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