MICROMECHANICS OF TRANSFORMATION-INDUCED PLASTICITY AND VARIANT COALESCENCE

Quantitative micromechanics descriptions of both transformation-induce d plasticity (TRIP) associated with the martensitic transformation in an Fe-Ni alloy and of variant coalescence in a Cu-Al-Ni shape memory a lloy are presented. The macroscopic deformation behavior of a polycrys talline aggregate as a result of the rearrangements within the crystal lites is modelled with the help of a finite element based periodic mic rofield approach. In the case of TRIP the parent --> martensite transf ormation is described by microscale thermodynamic and kinetic equation s taking into account internal stress states. The simulation of a clas sical experiment on TRIP allows to quantify the Magee-effect and the G reenwood-Johnson effect. Furthermore, the development of the martensit ic microstructure is studied with respect to the stress-assisted trans formation of preferred variants. In the case of variant coalescence th e strain energy due to internal stress states has an important influen ce on the mechanical behavior. Formulating the reorientation process o n the size scale of self-accommodating plate groups in terms of the mo bility of the boundaries between martensitic variants the macroscopic behavior in uniaxial tension is predicted by an incremental modelling procedure. Furthermore, influence of energy dissipation on the overall behavior is quantified.