Constitutive modeling for the training process of two-way shape memory effect under thermal cyclic loading

Abstract

Shape memory alloys (SMAs)—if trained properly—can induce two-way shape memory effect which is applicable in actuator design using SMAs. In this study, a three-dimensional phenomenological model is proposed for SMAs within the framework of irreversible thermodynamics in order to predict the training process under cyclic loading and the induced two-way shape memory effect. In this regard, transformation and permanent strains are considered as internal variables and Helmholtz free energy function is introduced using several material parameters accounting for elastic, transformation and permanent deformation mechanisms. In order to demonstrate the capabilities of the proposed model, we first compare the model results with several experimental results and prove that the current model fits well with various experiments under cyclic loading as well as two-way shape memory effect. In addition, the capabilities of the present model in predicting the two-way shape memory effect, degradation effects, evolution rate, stabilization of permanent strain as well as multiaxial loading have been carefully examined through parametric studies. It is concluded that the present model is able to predict the training process from the initial cycles to stabilization and two-way effect for different materials and conditions.