Stress Field Distribution At The Three-dimensional Crack Tip

In response to a large number of damage phenomena in pressure vessels and pipelines caused by crack,based on fracture theory,the problem of crack propagation is studied in this paper to master the change of stress field distribution in crack propagation.The main work of this paper is as following:(1)The fractal method in crack problem is studied.(2)The finite element method is used to model the elliptical surface crack in the plate.The simulation results are compared with the theoretical results to prove the applicability of finite element software ANSYS Workbench17.0 in this problem.(3)After trying different grid cell partition methods,an appropriate approach is found to ensure the accuracy of the results and reduce the amount of computation.The tetrahedral element is used for the mesh of the whole object,and the hexahedron element is used near the crack tip in this approach.(4)The results of the cylinder with surface crack are studied.It is found that the distribution of stress and strain in the vicinity of the crack is symmetrical,but the gradient of stress and strain is very large.It also can be seen that the deformation nephogram near the crack region presents a concentric circular distribution,and the shape variables gradually decrease from the center to the outside(5)The distribution of stress field at crack tip is analyzed.It is found that the equivalent stress increases slowly along the wall thickness direction,and then a sharp increase occurs,and after that the change will remain stable.The stress mutation occurs near the end of the short axis of the crack tip,indicating that the stress concentration is severe here.(6)The variation of the stress field under different conditions was analyzed by changing the internal pressure load P,crack length a and wall thickness ratio K.The stress intensity factors and the J integral value are analyzed under different conditions,and their influence factors are analyzed and discussed.The data and conclusions obtained in this paper can provide reference for the following research and engineering practice,and lay the foundation for the research on the prevention and control of fracture behavior in the future.