Apports des mesures d'auto-échauffement pour l'étude de la fatigue des aciers : effets d'histoire et cisaillement pur

Abstract : In the automotive industry, rolled steels are widely used to produce constituent parts of a car. The high cycles fatigue properties of these flat steel are usually determined in a virgin state of the material (i.e., without preliminary loading) under uniaxial cyclic loading with a constant stress amplitude. However, production of structural parts mostly involves some forming processes that have for consequence to modify the material state and thus to impact the fatigue properties. Furthermore, operational loads condition actually incurred by such a part is often multiaxial and with variable amplitude. The aim of this study is to take into account multiaxial and load history aspects in the fatigue characterization by means of self-heating measurements under cyclic loading. Multiaxial fatigue characterization usually involves a fatigue criterion that required the endurance limit of the material under a shear loading. But this limit is difficult to obtain for flat steel. That why a new shear test and two new disk-shaped specimens were proposed, permitting the use of self-heating measurements. Thus, the endurance limit of the material under a shear loading was determined. In order to study the impact of load history effects on fatigue properties, various self-heating tests were performed considering several initial pre-straining levels, several cyclic pre-loading and several load ratios. From these results, a new probabilistic two-scale model was proposed capable of describes self-heating curves with any load history considered and provides a reliable estimation of these load history effects on S-N-P curves.
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Julien Louge. Apports des mesures d'auto-échauffement pour l'étude de la fatigue des aciers : effets d'histoire et cisaillement pur. Mécanique des matériaux [physics.class-ph]. École Nationale Supérieure de Techniques Avancées Bretagne, 2019. Français. ⟨tel-02271001⟩

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