Cyclic Deformation of a Bias-Type Two-Way Shape Memory Component using TiNi Alloy

Abstract

In order to investigate the basic mechanical properties of a bias-type two-way shape memory component, thermal cyclic experiments were carried out on a TiNi shape memory alloy wire under a constant spring constant of a bias spring. The cyclic characteristics of recovery stress and recovery strain and the conditions for application of cyclic recovery stress and recovery strain were discussed. The main results can be summarized as follows. (1) The recovery stress and recovery strain induced in the two-way component take the maximum values at the initial strain near the completing point of the stress-induced martensitic transformation. (2) The recovery stress and the recovery strain decrease significantly in the early cycles, but take almost constant values after these cycles. (3) In order to obtain large recovery stress, it is necessary to make the spring constant of the bias spring high and to make the initial strain small. In order to get large recovery strain, it is necessary to make the spring constant low and the initial strain large. (4) The transformation temperatures of the stress-induced martensitic transformation and the reverse transformation rise with the number of thermal cycles. (5) In progress of thermal cycles, the stress-induced martensitic transformation and the reverse transformation occur gradually with variation in temperature, and the starting and completion temperatures of each transformation become unclear.