Thermo-Mechanical and Functional Properties of NiTi Shape Memory Alloy at High Strain Rate Loading

The results of experimental studies performed during the past decade at Saint-Petersburg State University in collaboration with the Mechanics and Materials Science Research Centre at Ningbo University (China) and Lobachevsky State University of Nizhny Novgorod (Russia) with the aim of investigating the basic regularities of the high rate straining of NiTi shape memory alloys are reviewed. The studies were concerned with the mechanical behaviour of these materials at high rate compression and tension, and the effect of high rate straining on the basic functional properties (shape memory effect and two-way shape memory). Special attention was given to the application of dynamic fracture theory to NiTi shock loading and to methods for obtaining experimental findings concerning the theoretical parameters involved in the criteria for determining the transition of these materials from an elastic to an inelastic state while high rate straining was applied. The effect of the quasi-equilibrium structure of NiTi on martensitic transformations and the role of this structure in the formation of more complicated effects than shape memory and superelasticity were studied. The results obtained are used to elaborate a method for the improvement of the functional properties of NiTi and a procedure for reversing two-way shape memory induction.