Multiscales analysis of stress induced martensitic transformation in the shape memory alloys: microstructure-stresses correlation

In order to understand the microstructure-properties relationship and describe the principal mechanisms at the origin of the various classes of materials behavior, several multi-scales models have been proposed. These approaches establish the generation of a very strong heterogeneity of the stress field on the material during the mechanical loading. On the polycrystals materials this heterogeneity exists even in the case of the uniaxial loading. This work contributed to develop an original experimental protocol making it possible to achieve internal stresses analyzes on the grain scale in the polycrystal. Suggested approach combines various analyzes techniques: microstructural observations, in situ mechanical characterization, stresses analyzes by x-rays diffraction (XRD). This work has been applied on the Cu-Al-Be superelastic Shape Memory Alloy (SMA). Several original results were obtained. Some allowed refining the stresses analysis techniques in two-phase materials and to propose classifications of the transformation modes in the Cu-Al-Be SMA, but the majority contributed to better understand the variants martensite selection mechanisms in the shape memory alloys or to highlight the role of some parameters as grain size, elastic anisotropy or the effect of a mechanical cycling.