Study of onset of thermoplastic instability by modeling shear band formation in torsion of thin-walled steel tube

We modeled the formation and development of shear bands in metals on the mesoscale at a micrometer-scale resolution. We used the overstress approach to dynamic elasto-viscoplasticity rather than the flow stress (radial return) approach, which helped us to avoid noise upon partial unloading. To verify our model, we focused on the torsion of a thin-walled tube and assumed axial symmetry, so that our simulations were of simple shear in one dimension. We applied our modeling approach to four types of steel and compared the results to torsional Hopkinson testing data reported in the literature. We obtained good agreement with the experimental data in terms of the localization threshold strain, perturbation influence, shear band width, temperature and plastic strain evolution in the shear band. We were also able to relate the localization onset to the elastic unloading.