Simulation Study On Fatigue Behavior Of Welded Joints Of Dual-phase Large Strain Pipeline Steel

The crack initiation and propagation of pipeline under overload and cyclic stress is one of the most dangerous forms of pipeline damage.Fatigue crack initiat ion,propagation and fatigue life of steel pipe are important parameters for the evaluation of pipeline safety design and operation integrity.In this paper,the fatigue behavior on welded joints of large strain pipeline steel is studied using ANSYS Workbench finite element analysis software combined with fatigue test data.Based on the above content,a fatigue analysis model of pipeline steel pipe is established,and the influences of weld geometry size on fatigue crack initiation position and fatigue life are systematically analyzed.The fatigue simulation results on welded joints of pipeline steel show that the position of minimum fatigue life occurs at the inside weld toe,and the cycles of fatigue fracture are 1.1302×10~5 N.This is consistent with the test results of the fatigue specimen,namely the crack initiation position of the fatigue specimen is also at the inside weld toe,and the cycles of fatigue fracture are 1.1×10~5 N.The equivalent alternating stress analysis shows that the point of maximum equivalent alternating stress occurs at the inside weld toe.In addition,the position of fatigue crack initiation coincides with that of the maximum equivalent alternating stress.The simulation results on the fatigue crack initiation position of the welded joints of the pipeline steel pipe are consistent with the simulation results on the welded joints of the pipeline steel.The fatigue crack initiation position is still at the inside weld toe,and the fatigue life is 1.0497×10~5 N.Compared with pipeline steel welded joints,the fatigue life is slightly reduced,which is related to the three-dimensional stress state of the steel pipe.The results of equivalent alternating stress analysis show that the point of the maximum equivalent alternating stress occurs at the weld metal,which is slightly larger than the stress at the inside weld toe.The simulation results of the steel pipe weld geometry size on the fatigue properties show that the lowest point of the fatigue life occurs at the weld toe where the weld penetration is smaller.With the increase of melt width and penetration depth,the equivalent alternating stress at the weld toe decreases and the fatigue life increases.