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Vers une prise en compte du vieillissement thermique dans la filière de dimensionnement des structures pour la fatigue thermomécanique

Abstract : Cylinder heads of automotive engines are produced by casting of precipitation strengthened Al-Si alloys.The cylinder head quickly reaches a steady state temperature but the succession of starts and stops generates thermomechanical fatigue in the area between the valve seats. At service temperature, the precipitation microstructures evolve from their state after precipitation hardening heat treatment to an aged state, which results in the reduction of their mechanical properties. The increase of thermomechanical stresses in new engines requires taking thermal aging into account for sizing. To that end, the precipitation microstructures (precipitates crystal structures, composition, morphology, and distribution) have been analyzed by Transmission Electron Microscopy (TEM) for various aging conditions and the corresponding cyclic least-viscoplastic behavior has been determined. The effect of plastic deformation on the kinetics of precipitate growth has been studied throughout loadings representative of engine operation. The morphological characteristics of the precipitation microstructure resulting from the thermomechanical aging were determined by TEM for different numbers of cycles and compared with those resulting from the mere thermal aging in order to assess the effect of plastic deformation on the kinetics of precipitate growth. As micro hardness is a good indicator of the aging of precipitation strengthened aluminium alloys, micro hardness evolution models have been developed to calculate its decrease in the cylinder head during a test simulating in service conditions. The simulations give us a better understanding of the in-service aging of these alloys.
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Submitted on : Friday, June 25, 2021 - 10:47:56 AM
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  • HAL Id : tel-03270760, version 1

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François-Xavier Hoche. Vers une prise en compte du vieillissement thermique dans la filière de dimensionnement des structures pour la fatigue thermomécanique. Mécanique des matériaux [physics.class-ph]. Université Paris sciences et lettres, 2016. Français. ⟨NNT : 2016PSLEM051⟩. ⟨tel-03270760⟩

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