Transition in rate controlling mechanism of FFC metals at very high strain rates and high temperatures

In order to clarify the rate controlling mechanism of FCC metals at the high strain rates, a,test is conducted for high-purity polycrystalline aluminium and copper in the strain rate range from about 1 X 10(3) similar to 2 X 10(4)/s at temperatures ranging up to 600K. A simplified model for a dislocation kinetics under a dynamic plastic deformation is used to consider the deformation mechanism in the above strain rate and temperature ranges. The increase in the mobile dislocation density with increasing temperature lowers the flow stress and shifts the transition range to the higher strain rate side. The results indicate also that a internal stress decreases slightly with increasing a temperature, which reflects the temperature dependency of cross-slip of a screw dislocation. It is confirmed that a steep increase of the flow stress observed at the high strain rates is attributed to the transition in a rate controlling mechanism of a dislocation motion from the thermal activation to the phonon drag.