Material strength and inelastic deformation of silicon carbide under shock wave compression

In-material, lateral, manganin foil gauge measurements were obtained in dense polycrystalline silicon carbide (SiC) shocked to peak longitudinal stresses ranging from 10-24 GPa. The lateral gauge data were analyzed to determine the lateral stresses in the shocked SiC and the results were checked for self-consistency through dynamic two-dimensional computations. Over the stress range examined, the shocked SIC has an extremely high strength: the maximum shear stress supported by the material in the shocked state increases from 4.5 GPa at the Hugoniot elastic limit (HEL) of the material (11.5 GPa) to 7.0 GPa at stresses approximately twice the HEL. The latter value is 3.7% of the shear modulus of the material. The elastic-inelastic transition in the shocked SIC is nearly indistinctive. At stresses beyond twice the HEL, the data suggest a gradual softening with increasing shock compression. The post-HEL material strength evolution resembles neither catastrophic failure due to massive cracking nor classical plasticity response. Stress confinement, inherent in plane shock wave compression, contributes significantly to the observed material response. The results obtained are interpreted qualitatively in terms of an inhomogeneous deformation mechanism involving both in-grain microplasticity and highly confined microfissures. (C) 1998 American Institute of Physics.