Multiaxialité, hétérogénéités intrinsèques et structurales des essais d'auto-échauffement et de fatigue à grand nombre de cycles

Abstract : High Cycle Fatigue and self-heating tests are linked by the onset of microplasticity. For example an empirical law allows one to predict "the" fatigue limit with only one specimen and a short test for several materials. A unified framework based on the random onset of micoplasticity has been proposed, leading to estimation of the fatigue scatter. As the majority of these studies deals with uniaxial loadings, multiaxiality is first discussed. Tension-torsion self-heating tests are performed on tubular specimens to validate two versions of the former model from a thermal point of view. The heterogeneity of samples is taken into account. After a series of proportional loading paths, the role of mean shear stress is investigated. Two types of non-proportional loading paths are studied. Different fatigue tests are performed to find the validity domain of each version of the model. In a second part the case of surface effects on steel sheets are analysed. The mean temperature revealing the presence of a surface effect but not precisely enough, the temperature field in the transverse direction of the sheet is looked for by use of in situ IR microthermography. A specific protocol is designed to prevent - at least reduce - several artefacts due to thermoelasticity, rigid body motions, optical properties, convection. Finally amplitudes of heterogeneities as small as 10-3 K are measured in steady-state cases at submillimetric scales. This experimental protocol allows for the qualification of the studied surface effects.
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Submitted on : Thursday, December 20, 2007 - 11:21:17 PM
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  • HAL Id : tel-00200459, version 1

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Martin Poncelet. Multiaxialité, hétérogénéités intrinsèques et structurales des essais d'auto-échauffement et de fatigue à grand nombre de cycles. Mécanique [physics.med-ph]. École normale supérieure de Cachan - ENS Cachan, 2007. Français. ⟨tel-00200459⟩

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