Predicting the orientation-dependent stress-induced transformation and detwinning response of shape memory alloy single crystals

The present investigation examines three models that predict the orientation dependence of the stress-induced transformation strain in shape memory alloys (SMAs). The merits of each model are considered in light of experimental results for three SMAs: NiTi, Cu-Ni-Al, and Ni-Al. Published experimental results fit model predictions well in most cases; the few exceptions can be accounted for by factors not included in the present models. As part of the comparison of model results with experimental observations, Ni-Al stress-strain curves generated by one of the models are found to closely match experimental stress-strain curves for the [001], [011], and [111] stress axis orientations. Finally, the predicted transformation stress anisotropy is analyzed in detail to examine the effect of detwinning of the stress-induced martensite.