Meso-scopic analysis of fracture process of concrete beam under bending

Concrete is regarded as a three-phase composite consisting of aggregate, mortar matrix and interfacial transition zone. Combining some experiments of mechanical properties for each constituents of concrete, numerical calculations for the concrete beam under bending were performed by nonlinear finite element method. According to the real mixture ratio, the two-dimensional equivalent area for various size distribution range can be calculated by the Walraven formula. Then, numerical concrete specimens are generated by the random aggregate model. The tensile strength failure criterion is used, and stress-displacement model is adopted to alleviate the sensitivity on mesh size in the softening region. Numerical results show that the thickness of the interface between 0.02 mm and 0.08 mm has little influence on the load-displacement curves, and the results from specimens with circular and random polygonal aggregate are approximately the same, the fracture energy of the interface has remarkable influence on the shape of macro-scopic load-displacement curves.