A MODEL OF CRACK-GROWTH IN MICROCRACKED ROCK

This paper considers microcrack-governed crack propagation and propose s a model for large-scale crack growth. The consecutive fracturing of volume elements at the crack front enables the crack to propagate and makes it effectively thick. The volume element size is determined from the competition between two effects: (a) reduction of the stress conc entration at the crack front due to increase of the crack thickness, a nd (b) reduction of the volume element strength due to increase of its size or, in other words, the internal scale effect governed by distri bution of the microcracks within the volume element. It is shown that the large-scale (macroscopic) fracture toughness may be assessed from laboratory measurements of the tensile strength scale effect.