Threshold strength prediction for laminar ceramics from bifurcated crack path simulation

Thin compressive layers sandwiched between thicker tensile layers in laminar ceramics can stop unstable cracks. As shown by Lange and co-workers, the arrested crack propagates stably through the compressive layer under increasing load until a critical load or threshold strength is reached. In 4-point flexural loading tests, cracks can bifurcate after entering into the compressive layer. This paper presents finite element simulations of bifurcated crack paths and threshold strength prediction in two-dimensional approximation. In rather good agreement with experiments the calculated threshold strength increases with compression and is higher with bifurcated cracks than with straight cracks, and higher with loading axis parallel to the laminar plane than normal to it.