Twinning-Induced Stress Concentrations in Polycrystalline Solids

Polycrystalline ceramics and metals can undergo induced cracking under external loading programs or spontaneous cracking when cooled from high processing temperatures. The formation of these microcracks is often attributable to internal stresses. This analysis shows that interaction of mechanical twins with grain boundaries can result in concentrations of stress fields whose asymptotic behavior, near intersections of twinning planes with grain boundaries, corresponds to a power-law singularity. Considering that microcracks are often generated at various stages of a manufacturing process, such as annealing or quenching, the authors have studied the interaction of mechanical twinning with pre-existing microcracks, both intergranular and transgranular. Their numerical results obtained by using the material properties of α-iron and copper zirconium show that the stress field near the crack tip intersected by twinning planes exhibits a singularity of higher order than the usual -singularity. This indicates that the interaction magnifies the stress concentration and hence promotes the crack growth.