Macroscopic modeling of strain-rate dependent energy dissipation of superelastic SMAs considering destabilization of martensitic lattice

TL;DR

This paper develops a macroscopic model for superelastic SMAs that incorporates strain-rate dependent entropy changes, improving the accuracy of simulating energy dissipation and hysteresis behavior under dynamic loading conditions.

Contribution

The authors introduce a novel rate-dependent entropy term into a one-dimensional SMA model, capturing the effects of strain-rate on phase transformation and energy dissipation.

Findings

Model accurately predicts dynamic superelastic hysteresis.

Incorporating entropy change improves simulation of energy dissipation.

Model aligns well with experimental data.

Abstract

Superelastic shape-memory alloys (SMAs) are unique smart materials with a considerable energy dissipation potential for dynamic loadings with varying strain-rates. The energy dissipation depends on the latent heat generated by the austenitic-martensitic transformation and the convection of that heat. Due to the thermomechanical coupling, the martensitic nucleation stress level and thus the propagation of martensitic phase fronts strongly depends on the material temperature. High strain-rate interferes with the release of the latent heat to the environment and determines quantity, position and propagation of martensitic transformation bands. Lastly, high strain-rate reduces the hysteresis surface. The propagation velocity and quantity of martensitic bands have an impact on martensitic phase stability. The degree of atomic disorder and accordingly the change in entropy influences the reverse phase transformation from martensite to austenite. In other words, the stability of the martensitic state affects the stress level of the reverse transformation. However, in phenomenological superelastic SMA models, which are used to simulate energy dissipation behavior, the effects of the rate-dependent entropy change are not considered in particular. To incorporate the rate-dependent entropy change, we improved a one-dimensional numerical model by introducing an additional control variable in the free energy formulation for solid-solid phase transformation of superelastic SMAs. In this model, the observed effects of the strain-rate on the reverse transformation are taken into account by calculating the rate-dependent entropy change. A comparison of the numerical results with the experimental data shows that the model calculates the dynamic superelastic hysteresis of SMAs more accurately.