Study On The Nonlinear Fracture And Damage Characteristics Of Crack In Concrete

The problems of nonlinear fracture of concrete crack and the crack tip damage characteristics have always been concerned by civil engineering,water conservancy science and engineering.Due to the relatively large damage area in front of the concrete crack tip and the interaction between damage and crack propagation in the fracture process,the nonlinear fracture mechanism of concrete is complex.Thus the research on concrete nonlinear fracture and crack tip damage characteristics are of great scientific valuable.Combined the National Natural Science Fund project "nonlinear coupling mechanism of fracture and random damage of concrete" and based on theoretical analysis,numerical simulations and experimental means,the issues of concrete crack nonlinear fracture and crack tip damage characteristics were deeply analyzed this paper.The following researches were carried out:1.Based on the concept of permissible damage scale,the strain expressions of three-point bending beam and wedge splitting specimen in the first three classes were obtained by the application of William series expansions of the crack tip stress field.Considering the impact of stress relaxation,the analytical solution of permissible damage scale was derived.This paper combined the results of the existing three-point bending beam and wedge splitting tests to validate the theoretical solution,and the nonlinear fracture permissible damage scale of concrete crack was analyzed quantitatively from the perspective of the theory.2.The concrete crack fracture finite element numerical analysis method was studied by the use of nonlocal damage model.The propagation process of concrete crack was simulated combined with the numerical simulation software.By the comparison between the simulation results and the existing crack mouth crack extension test load-displacement curve,the reasonableness of numerical methods was verified.Then through the analysis of cracking damage scales at different time of crack propagation,the crack tip damage of nonlinear fracture throughout the process was analyzed quantitatively.3.Combined with white light digital speckle correlation method,wedge splitting tensile test of concrete crack fracture was carried out.The test curves of nonlinear fracture process were obtained and the numerical method was used for verification.By means of digital speckle correlation method,concrete crack fracture process were analyzed,the deformation and the damage evolution rule of corresponding material of crack tip at different times were studied.