Shear Stress-Strain Behavior of Ni-rich and Ti-rich Shape Memory Alloys at High Strain Rates

摘要

High strain rate shear tests are carried out on two types of shape memory alloys. One is Ni-rich 50.75Ni-49.25Ti (at%) alloy and the other is Ti-rich 49.5Ni-50.5Ti (at%). The former is austenite phase at room temperature before the test, and the latter alloy is initially martensite. Simple shear dynamic loading is applied using the split Hopkinson pressure bar apparatus with a specially designed jig to hold the shear specimen. Shear stress versus strain curves are obtained for a strain rate order of 2000 (1/s) and the results are compared with those of the quasi-static test. It is observed that the Ni-rich alloy requires a much higher stress level to induce martensite in the dynamic test than in the static loading. Meanwhile a significant difference is not observed for the Ti-rich specimen between the dynamic and static tests.