Contributions à l'étude micromécanique des transformations martensitiques thermoélastiques

Abstract : This study carrying on the determination of the superelastic behaviour of the polycrystal memory shape alloys. This behaviour related the realisation under stress of thermoelastic martensite transformation modelled by E. Patoor, A. Eberhardt and M. Berveiller. We place in the limit of isotherm thermoelastic and describe thee physic transformation on the variables of martensite scale. The behaviour is determined from the definition of the transformation thermodynamique potential by adopting the volumics fractions of the variables. The physics stresses carrying on the variables are taking in to consideration by used the conditions of Kuhn and Tucker. Uniform stress assumption provide a lower boundary for the behaviour. This simple approach establish that if start of the transformation is related to the nature of this (relation of Clausius Clayperon) the end of the transformation depend strongly on the materials microstructure (crystallographic texture). This approach allowed too the determination of physical origin of the dissymmetry observed experimentally between the behaviour in traction and compression. To improve the results, we determined the interactions between the martensite variables from the computation micromechanic of the interaction energy related to the transformation. This work emerged on the definition of interaction matrix analogue to the work-hardening matrix in the classic plasticity. This results allowed to improve the results of first part by used of a computation code developed for the crystal plasticity by P. Lipinski and M. Berveiller and adopted to the superelastic behaviour by M. O. Bensalah and E. Patoor. This approach allow to obtain a good agreement with the experimental results and to determine without supplementary assumption the kinetic of the transformation and the evolution of the transformation and the evolution of the transformation average strain. The tridimensionelle exploitation of the model allowed the determination of the load surfaces and strain throw the transformation, it allowed to define a macroscopic criteria of the transformation non symmetric (modified equation of Hill-Prager). The last allowed to define a behaviour law, applicable to the computation in shape memory alloys
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Mohammed El Amrani Zirifi. Contributions à l'étude micromécanique des transformations martensitiques thermoélastiques. Autre. Université Paul Verlaine - Metz, 1994. Français. ⟨NNT : 1994METZ013S⟩. ⟨tel-01776051⟩

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