Flow stress of V, Mo, Ta, and W on nanosecond time scales*

The mechanisms and kinetics of plastic flow in body-centered cubic materials are of current interest in the development of fundamental theories of dynamic strength, applicable at high strain rates such as are found in high explosive and laser loading. We have performed dynamic loading experiments with the Janus and Trident lasers, using tailored pulse shapes to induce shock or ramp loading. The response of the sample was investigated through the surface velocity history, and in some cases with in-situ x-ray diffraction. The velocity histories exhibited clear elastic waves, from which the flow stress was deduced and compared with the elastic strain as determined by diffraction. We compare the deduced flow stress with models calibrated to samples millimeters thick, and to theoretical studies.