Crack deflection in functionally graded materials

crack d~ection in brittle functionally graded materials (FGMs) is studied. The FGMs are modeled as simply nonhomogeneous materials, i,e., the effect of microstructur¢ 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; ther¢fore, the crack propagates along the direction of maximum energy release rate, 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. © 1997 Elsevier Science Ltd