The interaction of a crack front with a second-phase dispersion

Observations are presented showing that a crack front increases its length by changing its shape when it interacts with two or more inhomogeneities in a brittle material. These observations are presented for both cleavage and conchoidal types of fracture. Based on these observations and the concept that a crack front possesses a line energy, an expression for the fracture energy is obtained. This expression shows that the fracture energy should increase as the distance between the dispersed inhomogeneities is decreased. Using the Griffith fracture criterion, this result is discussed for the case of strengthening a brittle material.