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Published December 10, 1979 | Published
Journal Article Open

Release adiabat measurements on minerals: The effect of viscosity

Abstract

The current inversion of pressure-particle velocity data for release from a high-pressure shock state to a pressure-density path usually depends critically upon the assumption that the release process is isentropic. It has been shown by Kieffer and Delaney that for geological materials below stresses of ∼150 GPa, the effective viscosity must be ≲10^3kg m^(−1) s^(−1) (10^4 P) in order that the viscous (irreversible) work carried out on the material in the shock state remains small in comparison to the mechanical work recovered upon adiabatic rarefaction. The available data pertaining to the offset of the Rayleigh line from the Hugoniot curve for minerals, the magnitude of the shear stress in the high-pressure shock state for minerals, and the direct measurements of the viscosities of several engineering materials shocked to pressures below 150 GPa yield effective viscosities of ∼10^3kg m^(−1) s^(−1) or less. We infer that this indicates that the conditions for isentropic release of minerals from shock states are achieved, at least approximately, and we conclude that the application of the Riemann integral to obtain pressure-density states along the release adiabats of minerals in shock experiments is valid.

Additional Information

Copyright 1979 by the American Geophysical Union. (Received June 8, 1979; accepted August 27, 1979.) Paper number 9B1271. We appreciate having received a preprint of the Kieffer and Delany paper and are particularly indebted to D. E. Grady, D. L. Anderson, S. W. Kieffer, and a reviewer for their helpful comments. This work was supported by the National Aeronautics and Space Administration under grant NGL-05-002-105. Contribution 3226, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.

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August 19, 2023
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