Finite-element simulations were used to model crack propagation across twist-misoriented grain boundaries, which were an important source of toughness in lamellar microstructures such as TiAl. A twist grain boundary between two adjacent grains was considered, and it was assumed that each grain had a single cleavage orientation. The cleavage planes and were modeled as a set of cohesive surfaces, and the crack path and effective toughness of the system were simulated using a dynamic finite-element method. As the crack approached the grain boundary under remote mode-I loading, it was allowed either to deflect along the grain boundary and/or induce the nucleation of a periodic array of cracks in the adjacent grain. The simulations predict (i) a critical toughness ratio between the grain boundary and the cleavage planes for the crack to propagate into the adjacent grain; (ii) an array of cracks in the grain boundary and the twisted grain; (iii) the macroscopic mode I toughness of the solid as a function of a generalized measure of crack length; and (iv) the influence of grain boundary toughness and twist misorientation on the effective toughness of the solid.

Numerical Simulations of Crack Deflection at a Twist-Misoriented Grain Boundary between Two Ideally Brittle Crystals. Y.Wei, H.Gao, A.F.Bower: Journal of the Mechanics and Physics of Solids, 2009, 57[11], 1865-79