Dynamic thermo-mechanical behaviors of SME TiNi alloys subjected to shock loading

Abstract

Dynamic thermo-mechanical coupling behaviors of shape memory TiNi alloy in the strain rate ranging from 300 s−1 to 2000 s−1 are investigated by the split Hopkinson pressure bar (SHPB) device with an infrared (IR) detection system. In stress–strain space, dynamic response shows a strong strain hardening property, however, in stress–temperature space, transformation path is particularly sensitive to the strain rate. The corresponding temperature evolution measured synchronously shows that local temperature increased associated with the forward phase transition, and it would keep the loading maximum value unchanged or decreased for unloading, depending on the strain rate. Besides, local temperature evolution was consistent with the transformation stress and its values at different points are the same. Temperature evolution and transformation deformation mechanism is then analyzed by a simple one-dimensional model. The results show that latent heat and dissipated energy are responsible for temperature variation. Furthermore, the temperature evolution with strain rate reveals that with the increase of strain rate, the phase transformation deformation mechanism undergoes a transformation from phase transition fronts propagation during lower strain rates to combination of local nucleation and front propagation during middle strain rate and to uniform nucleations during higher strain rates. The results are helpful for a passive shape memory alloy (SMA) micro-valve design.