Effect of stress on the thermal hysteresis of martensitic transformations - A continuum based particle dynamics model

The hysteretic behavior of shape memory alloys (SMA) is technologically important and advantageous in some applications but detrimental in others. In this paper, the effect of stress on the thermal hysteresis of SMA during the martensite transformation is studied. A recently developed discrete particle approach referred to as the continuum based particle dynamics (CPD) is used for this study. The CPD model uses a multibody interactions among the discrete particles which is directly derived from poly-convex free energy pertinent to such material behaviors. In the analysis, temperature of the domain is considered as the control parameter and is varied uniformly through out the domain above and below the transformation temperature. The hysteresis response resulting from this thermal cycle is observed in specific heat-temperature plot (DSC curve) and strain-temperature plot. The effect of prestress on thermal hysteresis along with the corresponding martensite microstructure is modeled. The results show a decrease in hysteresis with increased stress. This effect is attributed to the force required to propagate the ledges along the twin or phase boundary, which is smaller for the stressed material as compared to the stress–free material.