A micro-mechanical study of dynamic failure in a polycrystalline ceramic

Materials scientists and engineers have long recognized the fundamental importance of understanding the relationship between distribution of flaws and material failure. Rapid progress in simulation technology enables building increasingly closer and robust bridges between continuum mechanics, micromechanics, and materials science-based models. In this presentation, we have recourse to finite-element modeling to analyze the micromechanics of cracking in a brittle ceramic. Whereas defects may take various forms (including inclusions, pores, and grain boundaries), we limit the scope of the analysis to understanding how statistical variations in grain boundaries properties affect macroscopic mechanical properties. A two-dimensional finite-element model is build to investigate compressive[1] and tensile loading[2]. Intergranular and transgranular cracking in the microstructure are captured explicitly by using cohesive interfaces and adaptive meshing. We discuss the choice of the representative volume element and mesh size for the microstructure. We then study the influence of structural confinement pressure on macroscopic strength and apparent ductility. We also analyze the effects of friction at the damaged boundaries, and of the applied strain rate on resulting fragment sizes. Finally, we consider spatial and statistical variations of grain boundary properties. Our results indicate possible design directions for Grain Boundary Engineering. In particular, we quantify the influence of grain elongation on macroscopic strength and toughness.