TOTAL ELONGATION AT FRACTURE AT ULTRAHIGH STRAIN RATES

In our study of spall strength and spall development, we have developed a novel method which allows us to measure the total elongation at fracture for strain rates as high as 10**7 sec** minus **1. A 3 multiplied by 10** minus **9 sec long laser pulse is used to induce a shock wave in 0. 2 to 0. 5 mm thick metal foils. Spallation is produced by the compressive shock wave, reflected from the free surface of the foil in the form of a tensile wave with an amplitude that may exceed the spall strength of the material. For pure iron the total elongation at fraction was found to be 7. 8 percent at a strain rate of 10**7 sec** minus **1 as compared to an elongation of 18. 5 percent in quasistatic conditions. This is in good agreement with the lower ductility associated with increasing strain rate for body centred cubic structured materials. 8 Refs.