Transformation induced plasticity revised an updated formulation

An externally stressed specimen in the process of a phase transformation may show a significant nonlinear behavior which is known as transformation-induced plasticity (TRIP). The TRIP-strain can be irreversible as in the case of steels, or reversible with a certain hysteresis as in the case of shape memory alloys. The basic mechanisms contributing to this nonlinear phenomena are the accommodation process of the transformation strain and the orientation process of the transforming microregions. TRIP strain formulations carried out so far do not meet both effects. A thermodynamical concept is presented in this paper to find a TRIP strain rate which takes into account the coupling of phase transformation and microplasticity. The start and progress of the transformation condition, during which the plastic behavior governs the transformation/plastic processes, are derived by solving a conditional extremum problem, composed of the dissipation inequality and the constraint conditions: the transformation condition and the yield condition. The thermomechanical and calorimetric constitutive equations are derived in rate form when the transformation and the plastic processes are fully coupled. Some illustrative examples are discussed by assuming a concrete form of the Gibbs free energy and the transformation/yield conditions. The cross-coupling effect of the transformation and plasticity is well understood in the TRIP strain rate and the transformation kinetics. (C) 1998 Elsevier Science Ltd. All rights reserved.