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

Several material systems exhibit temperature and/or stress induced phase tr ansformations 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 sub jected to a stress induced martensitic transformation in a Tensile Split Ho pkinson Pressure Bar. This loading device allows for investigation of the m artensitic transformation under strain rates ranging from 500-4000 epsilon- 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 ident ified. The specimens failed in a mixed mode, ductile void growth followed b y transgranular failure. The void growth in incipient failure specimens sho wed ductile void growth throughout the specimen cross-section.