Healing of fatigue damage in NiTi shape memory alloys

Progressive accumulation of stress-induced martensite during cyclic loading of NiTi shape memory alloys results in both structural and functional fatigue. We present experimental data demonstrating that periodic annealing of the fatigued samples above the austenite finish temperature ('healing') retransforms the residual martensite back into the parent phase, and therefore enhances the fatigue life (stress-controlled testing, structural fatigue) or partly reverses the changes in the pseudo-elastic hysteresis (strain-controlled testing, functional fatigue).