The introduction of a “weak” interface in a bimaterial is used to increase its resistance to cracking when this interface encourages the deviation of a crack. Figure 6.1 shows the crack deviation mechanism observed within a ceramic matrix composite [DUG 93]. A matrix crack has deviated at the fiber-matrix interface. The mechanical response of the ceramic composite is not brittle, but presents a nonlinear portion corresponding to the development of a network of matrix cracks deviated at the interfaces [CAM 00].
A similar mechanism has been observed inside layered ceramics [CHA 95, MOY 99]. Control of interfacial zones is achieved by introducing interphases of various compositions and low thickness compared to that of the films [LIU 96, HAT 01]. The deviation mechanism at the interfaces reduces the concentration of stresses induced by the main crack and encourages additional energetic dissipation during interfacial propagation.
Chapter written by Eric Martin.
More generally, Figure 6.2 shows a schema of the various interaction mechanisms between a main crack and an interface that have been observed inside lamellar ceramics: a) penetration of the interface; b) deviation at the interface; c) interfacial propagation; and d) branching of an interfacial crack into an adjacent film. Each mechanism will be analyzed below.