Experimental and theoretical investigation of R-curve behaviour in AL/AL2O3 functionally graded materials

The effects of composition gradients on the crack propagation in metal/ceramic composites are investigated. It is demonstrated that crack propagation is affected in three different ways by the gradient: (1) The gradient in elastic properties modifies the driving force for crack propagation. (2) The gradient in thermal expansion behaviour leads to residual stresses which change the effective stress intensity factor acting on the crack tip. (3) The composition gradient leads to a position dependent crack tip fracture toughness and bridging stress relation.