SHAPE-MEMORY EFFECT OF CLAMPED NI-TI ALLOYS

Ni-Ti alloys which have large recovery strains and recovery stresses, are used as a functional material. In this study the shape memory effect of clamped Ni-Ti alloys (50.20 and 50.85 at%Ni) has been investigated by tensile tests with heating. Then simulation with a finite element method (FEM) have been carried out to estimate the behavior of the alloys. The results obtained are summarized as follows: (1) Dislocation would be generated by slip when a clamped specimen is heated, then it induces internal stress. As a result, on the first heating recovery stress appeared unstable, while on the second heating it became stable and could exceed the first one relatively. (2) The generation of recovery stress played an important role in obtaining a high apparent Young's modulus. (3) FEM analysis proved that the apparent Young's modulus and the stress generated inside the structure could be controlled by the recovery stress.