TRANSIENT HEAT-TRANSFER EFFECTS ON THE PSEUDOELASTIC BEHAVIOR OF SHAPE-MEMORY WIRES

Experimental results of a displacement-controlled elongation of a shape-memory wire of nickel-titanium are presented. It is observed that the hysteretic strain-stress curves depend strongly on the strain rates at which the wire is extended. A theoretical model is proposed to explain this phenomenon. This model couples the fully time-dependent heat transfer in the wire to its quasi-static mechanical behavior through the temperature dependence of the transformation stress of the alloy. It accounts quantitatively for experimentally observed changes in the pseudoelastic hysteresis. The model presented here is different from others proposed in the literature, as it does not make use of a kinetic relation and accounts for the observed changes in the pseudoelastic hysteresis without parameter fitting. The results show that a model consisting of a single moving austenite-martensite interface is sufficient to predict the response of the wire over several decades of strain rate.