Cyclic Deformation of TiNi Shape Memory Alloy

The cyclic deformation behavior of a TiNi shape memory alloy wire and of a helical spring for the martensitic transformation and the R-phase trasformation was investigated experimentally. The main results are summarized as follows. For cyclic deformation associated with the martensitic transformation, the transformation stress decreases and the trnasformation temperature rises. The amounts of variation in the stress and temperature are large in the early number of cycles and are small after about 20 cycles. For cyclic deformation associated with the R-phase transformation, the transformation stress and transformation temperature vary slightly. For cyclic deformation of a helical spring, the recoverable elongation is very large in the region of the R-phase transformation. The recovery deformation and recovery force of the helical spring under cyclic deformation vary slightly even in the region of the martensitic transformation.