Plasticity and Spall in High Density Polycrystals:Modeling and Simulation

Report No. ARL-RP-153
Authors: John D. Clayton
Date/Pages: September 2006; 10 pages
Abstract: The high strain rate behavior of multiphase, high density metallic polycrystals is studied via constitutive modeling and numerical simulation. Crystalline elasto-plasticity models are developed to account for the thermomechanical response of each bulk phase, and a cohesive zone approach is invoked to model the response of grain and phase boundaries. The following physical phenomena are captured by the bulk constitutive models: finite deformations, temperature- and pressure-dependent elasticity, nonlinear thermal expansion, slip-system level viscoplasticity with thermal softening due to increasing dislocation mobility, and dislocation accumulation in conjunction with strain hardening and the stored energy of cold working. The cohesive laws account for stress-state and temperature effects on interfacial strengths and correlate with the spall strength of the multiphase material. Numerical results are obtained from a 2D finite element implementation of the model under impact loading, in which individual phases, grains, and interfaces within a two-phase tungsten alloy are fully resolved. Effects of lattice orientations, grain morphology, and cohesive model parameters are reflected in the spall behavior and statistics associated with predicted free surface velocity profiles.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2006