Constitutive equations for polycrystalline thermoelastic shape memory alloys. Part I. Intragranular interactions and behavior of the grain

A micromacro thermomechanical modelization of grain behavior of a polycrystalline shape memory alloy is presented. This model, based on thermodynamical approach and identification of stress sources, takes into account experimental observations of the transformation microstructure. Because plates of martensite are usually observed to appear in domains, similar to subgrains, we show that determination of average global fraction of martensite is not sufficient to describe grain behavior. A better approximation is done by taking an average fraction of martensite in each domain as internal variables. With these parameters a full description of evolution of material can be made. We point out that free energy of the material depends on an interaction matrix between martensites. Moreover the calculation of this matrix for CuAlBe alloys allows one to determine the interface between domains. The results of this study are used to model the whole behavior of the polycrystalline material with a self-consistent method. (C) 1999 Elsevier Science Ltd. All rights reserved.