Recreation of Gap Test with Damaged Plasticity Model

A gap test is a relatively new experimental and numerical test proposed by Bažant and co-workers. The test is designed to show that the effective mode I (opening mode) fracture energy depends strongly on the crack-parallel normal stress. Other typical tests (for instance three-point bending) are not able to capture this influence. The gap test is therefore considered as a breakthrough in fracture mechanics. The authors of this paper tried to recreate numerically the gap test in a concrete specimen using a plasticity-based damage model for concrete, the so-called concrete damaged plasticity in Abaqus software. A specimen in the gap test is in the form of a concrete beam with a notch. At the first stage of the test the specimen is supported with poly-propylene pads. A static scheme of the specimen changes when the gap between the specimen and roller supports vanishes, exactly when the full yield of pads occurs. The gap test revealed the fact that the initial fracture energy varies its value depending on normal stress parallel to a crack propagating from the notch. To calculate the initial fracture energy, the authors of this paper used the size effect law. The results obtained by the authors are comparable with the laboratory and numerical results presented by Nguyen and co-workers.