Strain Rate Dependence of Dynamic Flow Stress of 1070 Aluminum at High Strain Rates

Abstract

In order to evaluate the strain rate dependence of the dynamic flow stress of 1070 Aluminum, high strain rate tests are performed at strain rates ranging from about 4.4×10³/sec to 2.2×10⁴/sec and strain rate reduction tests are also conducted at the strain rates of about 1×10⁴/sec and 2×10⁴/sec, respectively. A gradual increase in the flow stress is observed in the high strain rate. A simplified model for dislocation kinetics under a dynamic plastic deformation is used to consider the deformation mechanism in the above strain rate range. An equation derived from the model can describe the both at lower strain rates where the motion of dislocation is controlled by a thermally activated process and at higher strain rates where the effect of a phonon viscosity drag against the dislocation motion becomes explicit. However, the results of the reduction tests detect that the increase in the flow stress observed in this experiment is not attributed to the rate dependence of the viscous drag against the dislocation motion. The strain rate region conducted on high strain rate tests is still controlled by the thermally activated process and the gradual increase in the flow stress can be expressed by the stress dependence of the activation volume. The transition in the rate controlling mechanism seems to be in the higher strain rate side.