Prediction of crack motion from detonation in brittle materials

Abstract

A numerical model was formulated to predict propagation of a crack that is initiated and driven by an explosive. The model joins an energy release rate vs crack velocity fracture criteria with a two-dimensional finite difference computer program. The energy release rate for the material being fractured is computed with the J-Integral method. Crack velocity is determined from the energy release rate vs crack velocity curve of the fracturing material. Both the fracture criteria and the J-Integral computation were coded and adapted for use with an elastic-plastic hydrodynamic Lagrangian computer program. The accuracy of the code was verified by comparison of computed results with those obtained either theoretically or experimentally for three problems. In the first problem the stress intensity factor for a static edge crack in an infinite strip subjected to a uniform tensile stress perpendicular to the crack was calculated. The value computed with the model agreed to within 2% of the exact value. The second problem involved the computation of the stress intensity factor for a constant velocity central crack in a thick (plane strain) infinite plate. The computer generated values were found to converge to the theoretical ones as the finite difference mesh size was decreased. The final validation of the computer code model utilized results from dynamic photoelastic experiments involving an explosively loaded grooved borehole in a large plate. Comparison of crack length vs time data computed by the code with the experimental values showed good agreement.