No abstract

No abstract

A finite strain deformation formalism developed in the literature can be used to calculate Hugoniot states for isotropic materials. In the present paper, terms in the free-energy function are retained to third order, enabling temperature-stress-strain relations to be determined for uniaxial shock loading for stresses up to 150 kbar in metals. Coefficients of these terms are expressed as functions of the elastic constants of the material. The theoretical Hugoniot stress-strain curve for copper and aluminum agrees satisfactorily with experiment when the elastic constants are sufficiently accurate.

Sheet samples of pure nickel and Inconel 600 alloy (76% Ni, 16% Cr, 7% Fe) containing a fine precipitate were simultaneously shock loaded in sandwich assemblies at pressures of 50, 100, 150, 200, and 370 kbar by a planar pulse of roughly 2-μsec duration explosively initiated by a flying plate. The residual microhardness of the nickel was observed to saturate above 300 kbar while that for Inconel continued to increase steadily. Examination of the nickel substructures by transmission electron microscopy revealed a steadily decreasing cell size with increasing shock pressure; with almost no evidence of deformation twins at 370 kbar. The Inconel substructure was characterized by planar dislocation arrays which included an increasing concentration of dipoles and elongated loops to 200 kbar; while at 370 kbar deformation twins having an average thickness of 150 Å and occupying 19% of the volume were observed. The coherent precipitates in the Inconel matrix were observed to become incoherent at pressures above 50 kbar, with the concomitant production of dislocation tangles and loops at the particle-matrix interface. The precipitates were observed to enhance shock hardening by acting as sources for dislocation dipoles and elongated loops.

No abstract