The mean dynamic yield strength of copper and low carbon steel at elevated temperatures from measurements of the “mushrooming” of flat-ended projectiles

Mean dynamic yield strengths for copper and mild steel are deduced from strain measurements on the “mushroomed” ends of flat-ended projectiles, after impact on a flat, nominally rigid anvil. The kinetic energy at impact is equated with plastic work, to give a mean dynamic yield strength averaged over the deformed specimen. Experiments are carried out over the temperature range 20–700°C, with impact velocities in the region of 600 ft/sec, giving a mean strain rate estimated at 5 × 103/sec. The yield stress-temperature results obtained show an abrupt increase in dynamic/static mean yield stress ratio at homologous temperatures, TTM, of 0·4 for steel and 0·5 for copper. These results agree generally with the findings from other investigations into high-speed blanking5 and indentation.7 Existing theories for the mushrooming of flat-ended projectiles1, 3 do not predict the profiles actually obtained in the present experiments.