Comparison of different thermomechanical models for shape memory alloys

In the present work a thermodynamic model (Boyd and Lagoudas, 1994), and two earlier constitutive models (Tanaka, 1986, Liang and Rogers, 1990) describing the thermomechanical response of Shape Memory Alloys (SMA) are compared, and an extension to the thermodynamic model necessary to unify these apparently different approaches is introduced. In constructing the thermodynamic model, the first and second laws of thermodynamics apply general thermodynamic constraints, but some broad assumptions (the expression for free energy and dissipation potential) still need to be made to obtain complete constitutive equations. The specific selections for the form of mixing energy associated with the martensitic volume fraction are identified for the different approaches. To restore the experimentally observed linear dependence of effective stress and temperature in the transformation function, the thermodynamic model is modified by assuming that the transformation threshold value is a function of state variables.

Comparison of different thermomechanical models for shape memory alloys Conference Paper