An analysis of microstructural and thermal softening effects in dynamic necking

• Stability analysis of dynamic tensile necking accounting for microstructure evolutions.
• Fully coupled thermomechanical analysis.
• Microstructural evolutions are dominant for neck formation in the lower strain rate regime.
• Inertia dominates neck formation in the higher strain rate regime.
• Thermal softening plays no dominant role in the range of investigated strain rates.

The competition between material and thermal induced destabilizing effects in dynamic shear loading has been previously addressed in detail using a fully numerical approach in Osovski et al. (2013). This paper presents an analytical solution to the related problem of dynamic tensile instability in a material that undergoes both twinning and dynamic recrystallization. A special prescription of the initial and loading conditions precludes wave propagation in the specimen which retains nevertheless its inertia. This allows for a clear separation of material versus structural effects on the investigated localization. The outcome of this analysis confirms the dominant role of microstructural softening in the lower strain-rate regime (of the order of 103s-1), irrespective of the extent of prescribed thermal softening. By contrast, the high strain-rate regime is found to be dominated by inertia as a stabilizing factor, irrespective of the material’s thermo-physical conditions, a result that goes along the predictions of Rodríguez-Martínez et al. (2013a) regarding dynamically expanding rings.