Modeling Nonlinear Electromechanical Behavior of Shocked Silicon Carbide

Report No. ARL-RP-288
Authors: John D. Clayton
Date/Pages: January 2010; 24 pages
Abstract: A model is developed for anisotropic ceramic crystals undergoing potentially large deformations that can occur under significant pressures or high temperatures. The model is applied to describe silicon carbide (SiC), with a focus on α-SiC, specifically hexagonal polytype 6H. Incorporated in the description are nonlinear anisotropic thermoelasticity, electrostriction, and piezoelectricity. The response of single crystals of α-SiC of various orientations subjected to one-dimensional shock loading is modeled for open- and short-circuit boundary conditions. The influences of elastic and electromechanical nonlinearity and anisotropy on the response to impact are quantified. For elastic axial compressive strains less than 0.1, piezoelectricity, electrostriction, and thermal expansion have a negligible influence on the mechanical (stress) response, but the influences of nonlinear elasticity (third-order elastic constants) and anisotropy are not insignificant. The model is extended to incorporate inelastic deformation and lattice defects. Addressed are Shockley partial dislocations on the basal plane and edge dislocation loops on the prism plane, dilatation from point defects and elastic fields of dislocation lines, and cleavage fracture. The results suggest that electric current generated in shock-loaded α-SiC crystals of certain orientations could affect the dislocation mobility and hence the yield strength at high pressure.
Distribution: Approved for public release
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Last Update / Reviewed: January 1, 2010