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We propose a micromechanical computational framework for the high fidelity prediction of failure mechanisms in brittle polycrystalline materials. A three-dimensional direct numerical simulation of polycrystalline structures is constructed to explicitly account for the microstructural features, such as grain sizes, grain orientations, and grain boundary misorientations, by using the finite element method. In particular, grain boundaries are represented by a thin layer of elements with non-zero misorientation angles. The Eigen-fracture algorithm is employed to predict the crack propagation in the grain structure including intergranular and transgranular fractures. In the Eigen-fracture approach, an equivalent energy release rate is defined at the finite elements to evaluate the local failure state by comparing to the critical energy release rate, which varies at the grain boundaries and the interior of grains. Moreover, the constitutive model is considered as functions of the local microstructure features. As a result, the anisotropic response of brittle polycrystalline materials and the interaction between the fracture and topological defects in the microstructure under general loading conditions are explicitly modeled. Finally, the compressive dynamic response of hexagonal SiC with equiaxed grain structures is studied at different strain rates by using the proposed computational framework. The predicted compressive strength as well as the strain rate dependence of SiC agrees well with measurements in Split Hopkins Pressure Bar (SHPB) experiments.

brittle fracture; polycrystalline structure; eigen-fracture; dynamic compression strength; grain boundary