Thermodynamics of isotropic pseudoelasticity in shape memory alloys

The thermodynamic theory of the pseudoelastic behaviour of SMA is generalized to include new observed effects in isotropic solids. It has been shown that macroscopic eigenstrain due to martensitic phase transitions (p.t.) is a homogeneous function of the stress of order zero, provided that partial thermodynamic equilibrium occurs. The specific form of the Gibbs potential is presented and new conditions for the initiation of p.t. are derived. They are expressed in terms of the temperature, second and third invariants of the stress deviator. The thermostatic properties and phenomenological constants are found for a NiTi alloy using experimental data reported in the literature. The theoretical and experimental results are compared for simple tension compression and pure shear.