  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.
