Experimental Investigation And Numerical Simulation On Mixed Mode Fracture For Initial Turning Angle Crack In Concrete

Concrete is a kind of synthetic multi-phase composite material, and the mechanical properties of concrete are closely related to the crack propagation. Owing to the random distribution of defects and micro cracks caused in the process of casting and curing and the influence of external load, the fracture mechanism of concrete is very complex.In recent years, researchers have paid more attentions on concrete fracture and get some achievements. However, researches in this field are still in primary stage. Compared with I mode crack, the ?-? mixed mode crack occurs more frequently during the service life of structures, and the fracture Therefore the process of crack initiation, stable propagation and unstable propagation of the ?-? mixed mode crack has been widely concerned. In order to further research the process of crack development, the paper carries out the research as follows:1. Experimental investigation on initial cracking criterion for concrete ?-? mixed mode crackThree point bending concrete beam specimens with four different crack-depth ratios (0.2,0.3,0.4,0.5) and four different turning angle (22.5°,45°,67.5°,90°) were used to study the curves of ?-? mixed mode fracture in concrete. And the complete P-CMOD curves and P-8 curves have been obtained. Based on the initial loads measured by the means of resistance strain gauges, the corresponding K? and K? can be calculated using finite element analysis software ANSYS. After that, a crack initial cracking criterion for ?-? mode crack is proposed.2. Numerical simulation of crack propagation for ?-? mixed mode in concreteBased on the criterion when the difference between the stress intensity factor caused by the applied load and the one caused by the cohesive force is greater than the initial fracture toughness of the ?-? mixed mode crack in concrete, the crack begins to propagate, the finite element analysis software ANSYS has been used to simulate the process of crack development in the three-point bending beam with initial turning angle crack. Only if the material parameter and the initial fracture criterion of concrete are given, the initial load, the maximum load, the complete P-CMOD curve and the complete P-CMSD curve can be obtained and compared with the experimental resules. The influence of the different crack-depth ratios and the different initial turning angles to the stress intensity factor of the ?-? mixed mode fracture in concrete are also analyzed.