Rock fracture via strain-softening finite elements

The fracture of rock is assumed to arise from propagation of a blunt crack band with continuously distributed (smeared) microcracks or continuous cracks. This approach, justified by material heterogeneity, is convenient for finite element analysis, and allows analyzing fracture on the basis of triaxial stressstrain relations which cover the strain-softening behavior. A simple compliance formulation is derived for this purpose. The practical form of the theory involves two independent material parameters, the fracture energy and the tensile strength. The width of the crack band front is considered as a fixed material property and can be taken as roughly five-times the grain size of rock. The theory is shown to be capable of satisfactorily representing the test data available in the literature. In particular, good fits are demonstrated for the measured maximum loads, as well as for the measured resistance curves (R-curves). Statistical analysis of the deviations from the test data is also presented.