Mechanical response of near-equiatomic NiTi alloy at dynamic high pressure and strain rate

Understanding the behavior of near equi-atomic NiTi alloys under high strain rates and high pressures is important for the development of shock mitigating structures, particularly those that protect satellite and space vehicles from the impact of hyper velocity space debris. In this paper, the equation of state and constitutive relationships of NiTi alloy at pressures of 20-50 GPa and strain rates from 104s(-1) to 107s(-1) were investigated by means of magnetically driven quasi-isentropic compression and by shock compression from the impact of magnetically launched flyer plates. An inflection point at a pressure of 2 -3 GPa was found on plots of Lagrangian sound speed versus particle velocity in both quasi-isentropic and shock compression experiments, and it shows the elastic-plastic transition of austenitic NiTi alloy. The effect of the strain rate on the elastic limit of NiTi alloy was clearly seen between strain rates of 104s(-1) and 107s(-1). We also found that the bulk sound speed calculated from the shock data was lower than that deduced from the ultrasonic measurements. Finally, a rate dependent Johnson-Cook model was modified to describe the dynamic responses of NiTi. With this modified model, hydrodynamic simulations agreed well with our observations. (C) 2017 Elsevier B.V. All rights reserved.