A simple micromechanical model for thermoelastic martensitic phase transitions (PT) is developed. It is deduced from the local description of PT in transforming particles with subsequent usage of average procedure, based on a model for elastic three-phase materials (austenite, martensite and new infinitesimal nucleus) under assumption of homogeneity of stresses in each phase. In contrast to known approaches, a new local PT criterion and a corresponding extremum principle for PT with dissipation are used. The macroscopic PT criterion obtained is split into two different equations for description of temperature-induced PT and stress-induced PT. To identify the material parameters of the model and to check its validity, simple one-dimensional experiments were carried out for CuZnAl alloy. The experimental values of martensite start and finish temperatures and austenite finish temperature for temperature-induced PT and the stress-strain diagram for stress-induced direct PT at any fixed temperature have allowed to determine six material parameters of the model for the simplest one-dimensional case. Then model prediction is compared with other independent tests. A good agreement is obtained of the calculated stress-strain curves for reverse PT (martensite-austenite) at θ,1 = 20°C and for direct PT at temperature range of 30-80°C with experimental data. Finally, the formula for determination of the transformation heat during temperature-induced PT for the given model is derived. It is shown that the predicted transformation heat is close to the experimental one. © 1999 Technomic Publishing: Co., Inc.