Plastic Flow and Shear Banding in Refractory Metals and Martensitic Steels at Very High Shearing Rates

Abstract

Abstract : Research is reported on the dynamic shearing response of three metals: OFHC copper, tantalum, and 4340 VAR steel. For OFHC copper the important new result is that the flow stress has been measured at strain rates up to 1,000,000/sec at temperatures up to 700 deg C. At the elevated temperatures the dynamic plastic response is remarkably stable and the flow stress is considerably higher than predicted by commonly used constitutive models. For tantalum foils the behavior at strain rates greater than 100,000/sec appears to be described quite well by a smooth extension of the previously measured response at lower strain rates. Again, the plastic flow at high strain rates appears to be remarkably stable. For 4340 VAR steel, a new pressure-shear plate impact experiment has been developed to impose Mode II or Node III loading. Pilot experiments have shown a shear-like, relatively flat failure surface. Further interpretation of the latter experiments must be deferred until the effects of a reflected tensile wave are eliminated.