Penny-shaped equilibrium cracks in aligned composites

A model is suggested for a partially bridged penny-shaped crack (axisymmetric problem) in a brittle aligned material like for a composite ceramic. Two different fracture criteria for its components (matrix and fiber) are accepted. On the basis of an analytical solution for a homogeneous anisotropic body, a force-separation law, and Novozhilov's brittle fracture criterion, the variation intervals of a diameter of an equilibrium crack and the width of a bridged crack part are estimated. It is shown that, like a fracture toughness, the critical width of the bridged crack part can be accepted as a constant parameter for a composite material reinforced by fibers. The value of this parameter for a penny-shaped crack is the same as for a crack under plane deformation. For two types of ceramics the variation intervals of a bridged part of a critical crack are found, and a dependence of an ultimate load upon the size of the crack in 2-D and axisymmetric problems is presented.