Study On Concrete Fracture Process And Size Effects

Size effect is the inherent properties of quasi-brittle material and particularly evident in the concrete. By studying the fracture parameters of small size specimen, how to accurately and reasonably analyze large size concrete structure fracture failure is the problem needs to be resolved. Studying concrete fracture parameters and establishing concrete fracture failure criterion should firstly study the crack extension law in the process of concrete fracture. Currently, the research on concrete crack extension path involves little and mostly just observing crack extension from the surface of concrete specimen. Therefore, crack extension law in the process of concrete fracture and the size effect of fracture parameters still have important research value.The digital image correlation method is used to research the entire fracture process of concrete wedge splitting specimen. Based on the entire process of concrete crack extension and the fitting analysis of tail curve of P-CMOD, computing and analyzing the size effect of concrete fracture energy and fracture toughness. On the basis of comparison of physical tests do numerical simulation study on the further, random aggregate model is established by Matlab and grid cells are divided by Ansys, and finally numerical model import to FLAC3D for computing and analyzing. By comparing the physical experiment and numerical simulation to study the size effect of fracture parameters and crack extension law of concrete.Comparing the results of physical tests and numerical simulation:(1) The digital image correlation method can truly reflect the internal crack extension process of concrete fracture, strain localization band exists near the crack tip at the time of concrete failure, subcritical extension exists in crack extension process. Researching concrete cracks expansion by the digital image correlation method, which has guiding significance for evaluating the stability of concrete structures and the control of crack extension direction.(2) Fracture energy and fracture toughness exist size effect in the concrete fracture process, concrete fracture energy and fracture toughness increases with the increases of concrete specimen height. The specimen height is more than 500mm, concrete fracture toughness is unrelated to specimen size.(3) Numerical results are consistent with the physical tests results, numerical experiments provides an effective way for solving large size specimens-making and experimental difficulties.