Abstract.An axi-symmetric problem for a penny-shaped crack bridged by fibres is considered. The study is reduced to the analysis of a hypersingular integral equation with respect to the relative crack-face separation over a circular domain occupied by the crack. The special case of a large crack subjected to Mode-I loading is examined. A matched asymptotic expansions technique is used in order to estimate the stress intensity factor at the crack edge and to evaluate the magnitude of the applied load which provides the critical opening for failure of fibres at the centre of the crack.
Introduction.The physical problem that motivated this study relates to a body composed of a brittle matrix (in practice, a ceramic) reinforced by parallel fibres. The matrix contains a circular crack, in a plane normal to the axes of the fibres. The fibres, however, remain intact. They "bridge" the crack and carry some load, thereby increasing the material's resistance to catastrophic failure. The simplest model for this system represents the intact composite as an elastic continuum and the effect of the bridging fibres is taken into account by a continuous distribution of (generally nonlinear) springs, joining opposite points on the crack faces. Application of the model requires two steps: the determination of an appropriate force-separation law that characterizes the restraining tractions provided by the fibres, and stress analysis performed for a crack in a body loaded in some prescribed way at points remote from the crack. In the present paper we deal only with the second step, namely we consider a penny-shaped bridged crack in an elastic infinite body and describe the effect of fibres by introducing restraining tractions that follow either a linear or a quadratic force-separation law.The problem is formulated in terms of a hypersingular integral equation over a domain occupied by the crack. In general, this can be solved numerically [1], [2], In the particular case of a long crack, the governing equation contains a small parameter that multiplies the hypersingular integral, leading to a singular perturbation problem. A method for