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 brittl e layer impinging on the interface with the neighbouring brittle layer and either branching, if the interface is weak, or inducing plastic y ielding, if a ductile bonding agent is present. For the case of a weak interface, the effect of debonding along the interface is analyzed an d results for the stress redistribution in the uncracked layer directl y ahead of the crack tip are presented. Debonding lowers the high stre ss concentration just across the interface, but causes a small increas e in the tensile stresses further ahead of the tip in the uncracked la yer. 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 o f the interface in three-dimensional tunnel cracking through an indivi dual layer is also discussed and analyzed. Residual stress in the laye rs is included in the analysis.