IR thermography and resistivity investigations on Ni-Ti shape memory alloy

The shape recovery efficiency of Ni-Ti shape memory springs has been investigated upon the application up to 6 × 105 thermo-activation cycles. The hysteretic behaviour of the Martensitic - Austenitic phase transition has been characterized by resistivity measurements and infrared thermography. A loss in the recovery efficiency of the original shape has been observed and has been ascribed to functional fatigue leading to the formation of the R phase upon sample heating. Nevertheless, one way shape memory effect was found to exhibit an asymptotic stable behaviour which makes possible the realization of Ni-Ti actuators able to operate for a relative large number of activation cycles.