Numerical investigation of the temperature dependence of dynamic yield stress of typical BCC metals under shock loading with a dislocation-based constitutive model

Abstract

Interpretation of the temperature dependence of the dynamic yield stress of shock-loaded metals has recently become a critical problem in shock wave physics. However, the temperature dependence of the dynamic yield stress of BCC metals is rarely investigated owing to the lack of an accurate description of the constitutive behavior of BCC metals subjected to high strain rate and high temperature. To unravel the underlying mechanism of the dynamic yield stress of BCC metals under such extreme conditions, we established a dislocation-based constitutive model in which the dislocation generation equation is proposed from the viewpoint of dissipation energy. When applied to shock-loaded BCC metals, this model reproduced the elastic–plastic wave characteristics observed in preheated plate-impact experiments quantitatively even at temperatures of >1000 K. It was found that forest hardening induced by thermally activated homogeneous nucleation (TA-HN) serves as the primary contributing factor to the thermal hardening behavior of vanadium at elevated temperature, while Peierls stress serves as the primary contributing factor to the thermal softening behaviors of other BCC metals. The novelty of this work lies in that the forest hardening mechanism, as a plastic hardening mechanism and usually regarded as temperature insensitive for BCC metals, has been proved to be temperature sensitive and influence dislocation motion significantly owing to TA-HN at high strain rate and high temperature. Based on this mechanism, we also predicted that the thermal hardening behavior would also occur in other BCC metals, e.g., molybdenum and tungsten, at temperature ranges beyond the limit of existing experiments.