A Continuum Framework for Finite Viscoplasticity and Classes of Flow Rules for Finite Viscoplasticity

Report No. ARL-RP-68
Authors: Mike Scheidler and T. W. Wright
Date/Pages: September 2003; 16 pages
Abstract: A continuum framework for finite viscoplasticity is developed based on Lee?s multiplicative decomposition with internal variables. Noteworthy features include a thermodynamically consistent treatment of the storage of cold work and plastic volume change and a careful examination of the restrictions imposed by the entropy inequality and the property of instantaneous thermoelastic response. Classes of flow rules for finite viscoplasticity are defined by assuming that certain measures for plastic strain rate and plastic spin depend on the state variables but not on the plastic deformation. It is shown that three of these classes are mutually exclusive for finite elastic strains. For small elastic shear strains, two of the three classes are approximately equivalent. A number of exact and approximate kinematic relations between the various measures for plastic strain rate and plastic spin are derived. Some inconsistent flow rules encountered in the literature are also discussed. Throughout the paper, arbitrarily anisotropic materials are considered, and some of the simplifications resulting from the assumption of isotropy are noted.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2003