Abstract:In shape memory materials,that have been trained to have a two way shape memory effect(TWSM),the martensitic variants are classified into two groups,i.e.,preferentially oriented variants and self-accommodating variants.Applied stress may promote or constrain the transition of preferentially oriented variants and so change transformation temperatures but has no essential effect on self-accommodating variants.According to the point of view mentioned above,some experimental phenomena during thermocycling of a TWSM device may be ex- plained,such as the absence of synchronization between the plot of resistance change.temperature and the plot of memory strain vs.temperature.

Key words: shape memory alloy; martensitic variant; transformation; constraint heating; phase interface