FRACTURE-BEHAVIOR OF CERAMIC LAMINATES IN BENDING .1. MODELING OF CRACK-PROPAGATION

These two papers concern the fracture behaviour of specimens made up of ceramic sheets, separated by thin interlayers, which act to deflect cracks and thus to prevent catastrophic failure of the specimen, The treatment is divided into two parts. In this first paper, the behaviour of this type of material during bending is quantitatively modelled, while the second paper compares predictions from the model with experimental data. The model is based on through-thickness cracks propagating when a critical stress is reached and interfacial cracks then advancing a distance dictated by the available energy. The variation in laminae strengths is modelled using a Monte Carlo method to determine the strength of successive laminae for a given Weibull modulus. The model is used to predict load/displacement plots and to explore the effects of changes in loading geometry and specimen variables, including Young's modulus, lamina strength, loading span, interfacial toughness, as well as lamina and sample thickness. A distinction is drawn between the energy actually absorbed in causing complete failure of the specimen as measured from the area under the load/displacement curve, and the amount of energy necessary to cause the crack propagation which occurred. These differ if the energy available to drive the interfacial cracks is more than sufficient for them to reach the ends of the specimen or if energy is dissipated elsewhere in the system. A criterion is derived by which specimens can be designed so as to minimise the difference between these two quantities. The significance of this concept in optimising the toughness of these laminated materials is briefly discussed.