CRACKING AND STRESS REDISTRIBUTION IN CERAMIC LAYERED COMPOSITES

Problems are analyzed that have bearing on cracking and survivability in the presence of cracking of layered composite materials composed of brittle layers joined by either a weak interface or a thin layer of a well-bonded ductile metal. The problems concern a crack in one brittle layer impinging on the interface with the neighbouring brittle layer and either branching, if the interface is weak, or inducing plastic yielding, if a ductile bonding agent is present. For the case of a weak interface, the effect of debonding along the interface is analyzed and results for the stress redistribution in the uncracked layer directly ahead of the crack tip are presented. Debonding lowers the high stress concentration just across the interface, but causes a small increase in the tensile stresses further ahead of the tip in the uncracked layer. A similar stress redistribution occurs when the layers are joined by a very thin ductile layer that undergoes yielding above and below the crack tip, allowing the cracked layer to redistribute its load to the neighbouring uncracked layer. The role of debonding and yielding of the interface in three-dimensional tunnel cracking through an individual layer is also discussed and analyzed. Residual stress in the layers is included in the analysis.