Zig-zag crack propagation in MgAl2O4 crystals

The zig-zag crack propagation associated with environmental effects observed in MgAl2O4 single crystals appears to have relevance to crack propagation in polycrystalline materials. The close parallel between intergranular (ie., microscopically rougher), rather than transgranular (ie., microscopically flatter), fracture and the zig-zag (rougher than normal) fracture as crack velocity increases indicates that such intergranular-transgranular changes could be a function of crack velocity. The observation that zig-zag crack propagation diminishes with increasing crack velocity also suggests that crack bridging in polycrystals, which requires similar zig-zag cracking, may also diminish with increasing crack velocity. 14 refs.