Shear instability and considerably localized melting in quasi-static compression

Abstract

It is a big challenge to identify whether or not a high temperature rise at high strain rate is a prerequisite for shear instability in crystalline materials. In contrast to the prevailing report of shear instability at high strain rate loading, the shear band (SB) was generated at quasi-static loading in a martensite steel. This gives strong evidence that the high temperature rise is not essential as the quasi-static loading is not able to generate enough heat to initiate the shear instability. Different from the conventional narrow SB at high strain rate loading, a large patch of SB was firstly observed. Considerably localized melting occurred due to the abrupt fracture of SB. SB displays different TEM microstructures at melting and no-melting places. This indicates the significance of distinguishing the microstructure formed during shear instability from the one affected by the fracture of SB. The result suggests that the strain localization mechanism in this material is attributed to the microstructural change instead of the thermal softening. The findings provide a new insight into understanding the formation mechanism of SB from the perspective of microstructural evolution in crystalline materials.