Thermal-Viscous Model for Heterogeneous Yielding in Aluminum

摘要

The finite rise times of high intensity shock waves in metals are commonly interpreted in terms of a bulk viscosity which is observed to vary inversely as the square root of the strain rate. To interpret this result, a two-temperature thermal model of a heterogeneously-yielding metal has been constructed. The model assumes that the body is composed of thin shear bands in which irreversible energy is dissipated as heat and which are separated by the bulk of the material which undergoes isentropic compressive heating only. A condition of wave steadiness quantifies the irreversible energy dissipated during the passage of the shock. Two important results follow: first, the dependence of the apparent viscosity on the inverse square root of the strain rate stems from the microstructural, heterogeneous nature of the process, and is only expected for steady waves; second, when the model is used to interpret recent experiments, the viscosity calculated in the shear band itself is seen to be temperature independent. (ERA citation 81:025915)