Study On Helical Crack Propagation By Extended Finite Element Method

Spiral crack is a kind of widespread phenomenon in practical engineering and scientific experiments, the essence is how biaxial load affects the crack extended path. Extended finite element method (XFEM) is a fracture mechanics numerical method which do not need elements remesh. In this thesis extended finite element method was used to analyze the propagation process of three kinds of spiral crack.In order to analyze the crack propagation in thin wall barrel caused by thermal stresses, approximate expressions of stress intensity factor and crack extended angle were deduced and XFEM was used to simulate the propagation process of spiral crack. The results show that XFEM based on cohesive model can work out smooth spiral crack better, the average extended angle of spiral crack increases with the increase of the angle of initial crack but decreases with the increase of the linear expansion coefficient ratio. The less the mesh size was, the better the convergence was and the more coincident average crack extended angle can be got.In order to analyze the crack propagation in thin wall barrel cased by biaxial stresses, analytical solution was given by simplifying the problem as a plane crack problem. Finite element method and extended finite element method were used to calculate the initial crack extended angle and XFEM was used to simulate the formation of spiral crack. The results show that the average extended angle of spiral crack decreases with the increase of stress ratio, increases slightly with the increase of barrel thickness and decreases with the increase of material Poisson’s ratio. The results calculated by XFEM coincide with that by finite element method perfectly and coincide with theoretical solutions roughly.The formation of spiral crack in fiber-shell model was simulated in this thesis. The analysis results coincide with experiment approximately. The stiffness of cohesive layer decreased dramatically, both the longitudinal and tangential stresses are very large at the crack tip, material properties of two materials and cohesive zone model have significant effects on the crack shape.The significance of our research is as follows:on the one hand to simulate practical spiral crack phenomenon with numerical method, on the other hand to provide references for the deliberate induced failure of structures and special machining of material in some cases.