Development of martensite transformation kinetics of NiTi shape memory alloys under compression

Abstract

Martensite transformation kinetics is the principal factor underlying the constitutive model of shape memory alloys (SMAs). Therefore, the transformation kinetics formulation is essential for predicting the thermo-mechanical behavior of SMAs. In this work, we show that previous models, including the Brinson model, which is the most widely used one-dimensional phenomenological model, cannot describe the compressive thermo-mechanical behavior of SMAs due to the tension-compression asymmetry. In addition, a new transformation kinetics is derived which precisely predicts the compressive behavior of SMAs based on the following experimental results: (1) drastic variation exists during transformation, and the plastic deformation is not ignored in compression; (2) the plastic deformation increases in proportion to the volume fraction of detwinned martensite; and (3) the critical stress-temperature slopes largely increase and the slopes of the start and finish temperatures of each phase are not identical to each other. Finally, numerical calculations using the suggested transformation equation are conducted to verify its capability through a comparison with the compressive experimental results. According to the results, the suggested transformation kinetics can predict the thermo-mechanical behavior of SMAs more precisely under compression.