A cycle-dependent phase diagram to investigate the thermomechanical behavior of shape memory alloy wires under cyclic loadings

Abstract

Thermomechanical coupling in shape memory alloys causes temperature variations during cyclic loading, especially at high strain rates. This leads to dependence of response in each cycle to those in the previous ones until the stabilized response is attained. In this article, a fully coupled thermomechanical model is used to study either stress- or strain-controlled cyclic loadings on shape memory alloy wires. Experiments are carried out to verify the numerical results of this model. Instead of considering temperature changes, the material’s temperature is taken to be constant, but parameters in the shape memory alloy phase diagram are assumed to vary cycle by cycle. By introducing a cycle-dependent phase diagram, any specified cycle can be deemed as a quasi-static loading–unloading whose response is achieved independently from the previous cycles. Moreover, the number of cycles to reach stabilized hysteresis loops is achieved with no need to solve the transient cycles. Variations in the phase diagram parameters and the number of cycles to reach stabilization are studied at different conditions for two types of stress- and strain-controlled cyclic loadings.