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High -pressure deformation and failure of polycrystalline ceramics

Dongmei Zhang, University of Nebraska - Lincoln

Abstract

High-strength polycrystalline ceramics are increasingly being used for armor applications because of their light weight and superior ballistic performance over conventional armor steels. However, accurate material modeling needed in ceramic armor design remains a challenge because of their complex behavior under impact loading. A ceramic may display extremely high strength during rapid compression but lose tensile strength when the load reverses from compression to tension. A good understanding of the mechanisms governing the deformation and failure of ceramics under high-stress impact and a capability to accurately predict the resulting effective strengths of both intact and damaged ceramics are critically needed. To this end, a computational methodology for micromechanical analysis of polycrystalline materials has been developed. It combines finite element analysis with microstructural modeling based on the Voronoi polycrystals, and material modeling that considers nonlinear elasticity, crystal plasticity, intergranular shear damage during compression and intergranular Mode-I cracking during tension. ^ Using this method, simulations have been carried out on polycrystalline α-6H silicon carbide and α-phase aluminum oxide to determine if microplasticity is a viable mechanism of inelastic deformation in ceramics undergoing high-pressure uniaxial-strain compression. Further, the competing roles of in-grain microplasticity and intergranular microdamage during a sequence of dynamic compression and tension have been studied. The results show that microplasticity is a more plausible mechanism than microcracking under uniaxial-strain compression. The deformation by limited slip systems can be highly heterogeneous so that a significant amount of grains may remain elastic and thus result in high macroscopic compressive strength. On the other hand, the failure evolution during dynamic load reversal from compression to tension can be well predicted by intergranular Mode-I microcracking. It is found that microplasticity-induced heterogeneity may cause extremely heterogeneous local release process as the confining pressure decreases during unloading giving rise to local tensile stress or even cracking before the completion of macroscopic unloading. The result is a significant reduction in the material's effective tensile strength. It is also found that the effective tensile strength decreases with the rate of unloading. ^

Subject Area

Applied Mechanics|Engineering, Mechanical|Engineering, Materials Science

Recommended Citation

Zhang, Dongmei, "High -pressure deformation and failure of polycrystalline ceramics" (2005). ETD collection for University of Nebraska - Lincoln. AAI3194130.
http://digitalcommons.unl.edu/dissertations/AAI3194130

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