Dynamic tensile plasticity and damage evolution in shape-memory Ni-Ti

Several material systems exhibit temperature and/or stress induced phase transformations over the temperature and loading range which they may likely experience in service. The most notable example is the near stoichiometric system NiTi. In this research, NiTi specimens of various geometries are subjected to a stress induced martensitic transformation in a Tensile Split Hopkinson Pressure Bar. This loading device allows for investigation of the martensitic transformation under strain rates ranging from 500-4000 ε-sec-1. In addition to the large strain rates, the specimens are tested to large strain levels such that void growth and failure mechanisms are identified. The 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