A Two Variant Thermomechanical Model for Shape Memory Alloys

Shape Memory Alloys (SMAs) undergo stress and temperature induced reversible diffusionless crystalline phase transformations between a high synmaetry phase (austenite) stable at high tenlperatures and low stresses, and a low symmetry phase (martensite) stable at low temperatures and high stresses. Unusual macroscopic effects arise from these crystallographic changes, chiefly shape memory and superelastic effects. Superelastic effect is the recovery, caused by stress induced formation of prefered variants of martensite, of large deformations in loading unloading cycles. Shape memory effect is realized when such stress induced transformations are thermally reversed.