Modelling Crack Propagation in Compression

ABSTRACT: Fairhurst and Cook's (F-C) 2-D model of extensively growing crack in uniaxial compression, consisting of a straight crack wedged at the center by a couple of concentrated forces is investigated, both experimentally and theoretically. Such a crack alone grows in a stable manner. The presence of a free surface parallel to the crack amplifies its growth such that the crack becomes unstable after reaching a certain critical length. Although compression parallel to a straight crack does not normally make the crack open, the presence of the free surface is found to provide a case when the crack can grow. This happens if the compression on the sample top concentrates between the crack and the free surface, whereas the balancing compression at the bottom is distributed over the whole sample width. The crack propagates mostly parallel to the free surface as a mode I crack until the separated layer becomes slender and buckles. This may be a mechanism of rock chipping. In the 3-D case when a single inclined initial crack cannot grow extensively, the F-C crack is shown to be a reasonable model of growth of large tensile cracks driven towards the compression direction by certain combinations of interacting initial cracks.