Cyclic deformation of TiNi shape-memory alloy helical spring

The influence of training and shape-memory processing temperature on cyclic deformation of TiNi shapememory alloy helical springs is investigated. The results are summarized as follows. (1) For large strain, significant irrecoverable elongation appears in the early cycles. The appearance of the irrecoverable elongation can be avoided by the training. (2) The recovery force of the spring varies slightly during the thermal cycles, which shows the very stable cyclic characteristics of the force. (3) The cyclic characteristics of deformation in the helical springs depend on the size of the region accompanied by the stress-induced martensitic transformation in the cross section of the wire.