Transformation-induced creep and stress relaxation of TiNi shape memory alloy

Abstract

Abstract

The subloop deformation behaviour of a TiNi shape memory alloy (SMA) under various loading conditions was investigated. Creep and stress relaxation were induced for stress-controlled subloop loadings. The results obtained can be summarized as follows:

1. 1.

In the case of subloop loading under stress-controlled conditions, strain increases under constant stress in the loading process and decreases in the unloading process. Creep and creep recovery appear owing to martensitic transformation (MT).

2.

In the case of subloop loading under stress-controlled conditions, stress decreases under constant strain in the loading process and increases in the unloading process. Stress relaxation and stress recovery appear owing to martensitic transformation.

3.

In the case of subloop loading under strain controlled-conditions with a low strain rate, the reloading stress-strain curve passes through the unloading start point. In the case of stress-controlled conditions, return-point memory does not appear.

4.

The above behaviour of the return-point memory and pseudoviscoelastic behaviour of creep and stress relaxation appear according to the martensitic transformation and the reverse transformation, based on variations in stress and temperature.