In order to obtain experimental knowledge on the behaviour of dislocations at high rates of strain, time-resolved measurements of the ultrasonic attenuation and velocity in specimens undergoing dynamic plastic deformation have been tried. In this paper, some analyses of the ultrasonic data for polycrystalline aluminium are made by using a kinetic model for the motion of dislocations cutting through the forest dislocations. The model given its quantitative basis by the ultrasonic data can

more »

... e fairly well the strain rate dependency of the flow stress over a wide range of strain rate.