Thermo-Electro-Mechanical Shakedown Response of Conditioned Shape Memory Alloy Wires Available to Purchase

The shakedown response of conditioned shape memory alloy wires (Flexinol^®) is examined experimentally during constant tension thermal cycles, at several load levels. Strain, temperature, and electrical resistivity are measured simultaneously using a specialized experimental setup that enables a relatively rapid temperature rate (1 °C/s) while preserving the temperature uniformity along the gauge length to less than 1.5 °C. Both elongation and electrical resistance are measured from the same local gauge length, allowing strain-corrected electrical resistivity to be inferred. The most repeatable behavior (least shakedown) occurs at the intermediate load of 191 MPa (consistent with the supplier’s maximum stress recommendation), with a small amount of shakedown (and some loss of two-way shape memory) at lower loads and progressively larger shakedown (strain ratcheting and reduction in hysteresis) at higher loads.