Development and application of a crack tip opening displacement-based mixed mode fracture criterion

Consistent with experimental observations, a crack tip opening displacement (CTOD)-based, mixed mode fracture criterion is developed for predicting the onset and direction of crack growth. The criterion postulates that crack growth occurs in either Mode I or Mode II direction, depending upon whether the maximum in either the opening or the shear component of CTOD, measured at a speci®ed distance behind the crack tip, attains a critical value. The proposed CTOD-based fracture criterion is implemented in two ®nite element codes to predict the stable tearing behavior of (a) a modi®ed Arcan test specimen made of AL 2024-T3 and (b) a double cantilever beam (DCB) specimen made of AL 7050. Using the measured load-crack extension data as input, results from simulations of stable crack growth along experimentally measured crack paths for the Arcan specimen demonstrate that the CTOD values obtained in the simulations are in excellent agreement with the proposed criterion. Then, using the CTOD criterion as input, simulations of the Arcan and DCB specimens demonstrate that the CTOD fracture criterion successfully predicts (a) load-crack path data for both specimens, (b) load-crack extension behavior for the Arcan specimen and (c) load-load point displacement data for the DCB specimen.