Crack deflection in functionally graded materials

Small crack deflection in brittle functionally graded materials (FGMs) is studied. The FGMs ate modeled as simply nonhomogeneous materials, i.e., the effect of microstructure is neglected and the material property variation is considered to be continuous. Considering local homogeneity and the small scale inelasticity of brittle materials, the toughness is taken to be independent of direction; therefore, the crack propagates along the direction of maximum energy release tate, or the direction which gives a vanished mode II stress intensity factor. Kink directions for several specimens which may be used to experimentally study fracture behavior of FGMs are calculated. It is shown that material gradients have a strong effect on the kink direction when the crack is at the central region of a FGM, whereas they have little effect when the crack is close to the boundaries of the FGM. (C) 1997 Elsevier Science Ltd.