Three-dimensional numerical study on mode-I local crack propagation of concrete considering boundary effect

A three-dimensional numerical method considering the boundary effect on fracture energy and initial fracture toughness was proposed to simulate the whole propagation process of mode-I local crack in concrete. The initial fracture toughness-based criterion was employed to determine the propagation of local crack surface. The numerical analyses were carried out to obtain the initial cracking load, peak load and load-crack mouth opening displacement curves for a series of concrete beams with a local crack of different sizes. Comparing with the experimental results performed in this study, the numerical results showed good agreements and applicability of the proposed method was verified. After that, the numerical analyses were conducted on the whole fracture process of local crack in concrete. The results indicated the local crack of three-point bending beam always propagated along the thickness direction firstly on the bottom surface of the specimen. The crack front was basically parallel to the upper boundary of specimen after the load decreased to 40%Pmax. For beams with a local crack of different sizes, the variations of the ratio of crack propagation area to ligament area with the ratio of load to peak load were the same so that a function expression was given to predict the increment of crack surface area under different loads. In addition, the fracture process zone evolution during the local crack propagation was discussed.