Fracture Toughness of Si3N4/S45C Joint with an Interface Crack

by Liedong Fu, Yukio Miyasita, & Yoshiharu Mutoh AZojomo, September 2005 Fracture toughness tests were carried out for Si₃N₄/S45C specimens with interface cracks of different lengths. It was found that the specimen with a crack of 4 mm has higher apparent fracture toughness than those with cracks of 1 mm and 2 mm due to the reduction of the residual stress. Fracture propagated into Si₃N₄ from the crack tip in the direction of 40o for cracks of 1 mm and 2 mm while it propagated along the interface for crack of 4 mm. Elasto-plastic analysis was carried out considering S45C as the linear hardening material and Si₃N₄/S45C as the elastic material. It was found that the stress around the crack tip is dominated by an elasto-plastic singular stress field, which is substantially the same as the elastic singular stress field of an interface crack. Evaluation of the fracture path and toughness was carried out based on the stress intensity factors of the elasto-plastic singular stress field. Read more