Microcrack coalescence and macroscopic crack growth initiation in brittle solids

Abstract

The problem studied in this paper concerns the analytical estimation of the effect of microcracking on crack growth initiation in brittle solids. Particular attention is given to the counteracting effects of toughness degradation and shielding by macrocracking. with a view to determining the range of dominance of each mechanism. Crack growth initiation by coalescence with microcracks is studied with the aid of a cohesive zone model. The extent of shielding of the crack tip by the intervening microcracks is estimated under isotropic damage conditions. A comparison of these effects reveals that, were the crack capable of growing within its plane, the toughness enhancement derived from shielding would be almost exactly counterbalanced by the reduction of toughness in the microcracked material. However, if microcrack deflection is taken into account levels of toughening consistent with experimental data are computed.

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