FATIGUE PROPERTIES OF TI-NI SHAPE-MEMORY ALLOY SPRINGS

Fatigue properties of a Ti-Ni shape memory alloy coil spring are studi ed as a function of the amount of the B19' martensite generating in th ermal cycles. The recovery force decays more with the number of cycles with an increasing amount of the martensite. The temperature ranges o f the R-phase and R-->B19' martensitic transformations also widen with the increasing martensite. The shape memory characteristic change of the coil spring results from the reduction in its free length. It Is d educed from the change in the transformation temperatures that the fre e length reduction is caused by the introduction of dislocations durin g the thermal cycles.