THERMODYNAMICAL MODEL OF CYCLIC BEHAVIOR OF TI-NI AND CU-ZN-AL SHAPE-MEMORY ALLOYS UNDER ISOTHERMAL UNDULATED TENSILE TESTS

The thermodynamical description of observed evolution of mechanical pr operties of shape memory alloys during isothermal simple tension cycli c loading (in pseudoelastic temperature range) is presented. To define the new internal state parameter, the concept of instantaneous residu al martensite is introduced. The known form of the free energy functio n is suitably modified, and the appropriate kinetic equation for the n ew state variable is proposed. All constants occurring in constitutive equations are determined for special Ni-Ti and Cu-Zn-Al alloys, The s atisfactory agreement between predicted and experimental stress-strain hysteresis loops is shown.