MICROMECHANICAL APPROACH OF THE FATIGUE BEHAVIOR IN A SUPERELASTIC SINGLE-CRYSTAL

Mechanical cycling of superelastic alloys leads to significant change in their observed behavior. Critical stress needed to induce the marte nsitic transformation is reduced while the tangent transformation modu lus is increased. Microstructural observations have shown that a mecha nical cycling produced a strongly oriented pattern of dislocations. Th is dislocation network is associated to an internal stress field. It s eems reasonable to relate this internal stress field to the observed e volution of the mechanical response. This is phenomenologically perfor med in this work considering the thermodynamical potential associated to the martensitic transformation of a single crystal of parent phase in presence of a microstructure of defects. Evolutions of the microstr uctural state are defined using the volume fraction associated to the variant of martensite and additional volume fractions of defects relat ed to the dislocation pattern. Results such obtained well-captured exp erimental observations.