Stress-Induced Martensitic Phase Transformations in NiTi Shape Memory Alloys During Dynamic Loading

This research explores the near-adiabatic, high strain rate stress-induced martensitic phase transformation in NiTi shape memory alloys using both a compressive and tensile Split Hopkinson Pressure Bar (SHPB). The results of the dynamic loading tests are presented with emphasis on the loading rate, stress-strain response, specimen temperature and post-test microstructural evaluation. In addition to the large strain rates, tensile specimens of various geometries are tested to large strain levels such that void growth and failure mechanisms are identified. The dynamically loaded specimens failed in a mixed mode, ductile void growth followed by transgranular failure. The void growth in incipient failure specimens showed ductile void growth throughout the specimen cross-section.