Strain Rate Dependence of Hardness for PE and SME TiNi Alloys

Abstract

In this paper, the strain rate dependence of hardening behavior of polycrystalline pseudoelastic (PE) and shape memory effect (SME) TiNi alloy under impact loading was investigated by experiments. Measurements of stress–strain curves, hardening modulus, hysteresis loop area, and temperature variation are synchronized using in situ infrared detector system at the strain rate range from 300/s to 2000/s. It is shown that with the strain rate increasing, for PE specimens, strain rate hardening is observed, while SME specimens perform a strong nonlinear strain hardening. The results of synchronous temperature measurement show that in stress-temperature space, for PE samples, the dynamic transformation path is strain rate independent, but for the SME samples, the opposite is true. Thermal-mechanical coupling does not seem to explain this difference, and hardening from microstructure variation should be considered for such difference.

Synchronized Full-Field Strain and Temperature Measurements of Commercially Pure Titanium under Tension at Elevated Temperatures and High Strain Rates

“…The low emissivity of the investigated alloys, of approximately 0.15, allowed them to make measurements up to such temperatures without the use of any attenuation filters. Shen et al [30] and Liu et al [31] used a HgCdTe infrared detector to monitor the temperature of shape memory and pseudoelastic NiTi alloys under high strain rate compression and reported different maximum temperatures and temperature variations during loading and unloading. To the best of the authors' knowledge, there has not been any full-field temperature measurements of materials tested at very high temperatures, especially at high strain rate tensions.…”