Microstructural model for shear strain localization and occurrence of adiabatic shear band at high strain rates

The occurrence of adiabatic shear bands during high strain rate deformation of metals has been analyzed using a finite element approach. It was found that these bands occur at inhomogeneities in the microstructure and result from the competing processes of strain hardening and adiabatic heating. In microstructures which are reinforced by the presence of hard precipitates or second phase particles, the adiabatic shear bands are confined to narrow spacings between such hard precipitates and thus are narrow in shape with very large strains within the bands leading to microcracks. In more homogeneous microstructures, the bands are wider, with lower total strains and less susceptibility to damage. This theory is verified by several experiments on metals and alloys including steels, titanium, and aluminum/alumina composites. In all these experiments, the occurrence of shear bands is associated with the precipitates' spacing in the microstructure where they can initiate and develop.