A MICROMECHANICAL APPROACH TO CONSTITUTIVE-EQUATIONS FOR PHASE CHANGING MATERIALS

When in a microregion the change of the Gibbs free energy (due to stre ss and temperature change) reaches a critical value, a so called thres hold value, then this microregion jumps from one into the other phase. Phase change in polycrystals can be described adequately using statis tical methods, e.g. by averaging over representative elementary volume s. Through this averaging one gets physical quantities in the mesodoma in, such as volume fractions, transformation strains, etc. Kinetic law s for these values follow from extremization of the energy dissipation rate under constraints, such as an averaged transformation condition. The present paper delivers kinetic laws for the martensitic volume fr action and the transformation strain as the constitutive equations for the phase changing materials. The results are in good qualitative agr eement with experiments. Quantitative agreement follows from matching of system parameters, which do not follow from the theory. (C) 1997 El sevier Science B.V.