Strain Rate Sensitivity of Dynamic Flow Stress of FCC Metals at Very High Strain Rates.

Abstract

The strain rate sensitivity in FCC metals is known to increase dramatically when the strain rate exceeds about 3×103/s. Previous studies indicate that the flow stress above the critical strain rate depends strongly on instantaneous strain rate. It seems that this behavior is caused by a transition in a rate controlling mechanism of dislocation motion. A simplified model for the kinetics of dislocasione is used to consider the transition mechanism. The flow stress calculated using the expression derived from the model shows fairly good agreement with the directly measured flow stress over a wide strain rate range. It is concluded that the steep increase in the strain rate sensitivity of the flow stress is due to the transition in the rate controlling mechanism of the dislocation motion from a thermally activated process to phonon viscosity drag.