Numerical Study On Fatigue Crack Growth Of T-joints Based On XFEM

As a basic supporting structure applied to drilling platform,gymnasium and terminal,T-shaped tubular joints are likely to show the characteristics of fatigue damage after a certain period of service under the action of alternating cyclic loads such as tide,wave and wind for a long time.Therefore,it is necessary to study the fatigue crack propagation of the joints.In this paper,the fatigue crack of T-shaped circular steel tube is studied by means of Paris formula and extended finite element method.(1)On the basis of considering the geometric complexity of the intersection of welded pipes,the pre-processing interface(MDB related interface)developed by ABAQUS is used to write an efficient modeling program for automatically generating the finite element model of T-type welded joints,which provides a relatively labor-saving and efficient solution for similar welded pipe structure modeling;(2)The crack growth pattern and stress intensity factor of the tension plate with initial crack are calculated and analyzed.Under the influence of different initial crack size,loading conditions and geometrical parameters of the specimen,the error of XFEM calculation solution and analytical solution is within 3%,the accuracy meets the requirements,the stress state change of crack tip element is analyzed,and the accuracy and rationality of XFEM analysis of crack growth behavior are verified;(3)The influence of initial crack angle and mesh density on the calculation of stress intensity factor is analyzed.The results show that the distribution of stress intensity factors at the front of the crack is approximately the same with different initial crack angles at the saddle point,but the values are quite different.In the same initial crack state,the larger the mesh density is,the smaller the integral radius is when the stress intensity factor is stable;(4)In view of the possible position of fatigue failure of T-shaped circular steel tubular joints,the calculation and analysis of the stress intensity factor amplitude and the crack growth increment at the crack tip are carried out by XFEM combined with the fatigue crack growth formula(Paris formula)of fracture mechanics,and the fatigue crack growth life of the joints at the saddle point is obtained;(5)The propagation characteristics of the initial crack at the saddle point are as follows: before the crack penetrates the wall thickness of the main pipe,the crack propagates slowly in the radial direction and the circumferential direction.As the propagation proceeds,the radial crack propagation rate is lower than thecircumferential crack propagation rate,and the crack propagation life before the crack penetrates the wall thickness accounts for about 80% of the total fatigue propagation life of the joint;when the crack penetrates the wall thickness,the crack propagation life takes up about 80%?95% of the total fatigue propagation life of the joint After the crack runs through the whole main pipe wall thickness,the crack growth rate increases significantly until the crack growth behavior ends and the joint fails.The paper has 56 diagrams,14 tables and 82 references.