Analysis Of Surface Crack Fatigue Growth On High Strength Steel Welded T-joint Based On Weight Function Method

With the development of steel research and production technology,high-strength steel has been increasingly applied to civil engineering structures.Because it has higher strength than ordinary steel,the use of high-strength steel can effectively reduce the size of components,the weight of the structure,and the amount of welding operations.It has high economic benefits,and the engineering application prospect is very broad,which is helpful for the development of circular economy Green Building.Welded connection is the main connection form of steel structure,and the strength,toughness and fatigue of welded joints are related to the safety reliability and service life of steel structure.However,the fatigue performance of the welded structure is not directly proportional to the yield strength of the steel.The fatigue performance of the high-strength steel welded joint is not as obvious as the static strength in comparison with the ordinary steel joint,which is mainly due to the little difference in the fatigue crack propagation ability between them.Therefore,the fatigue performance of high-strength steel welded structure has become one of the important factors restricting its engineering application.It is important for the safety of welded structures to know the characteristics of fatigue strength and to predict the fatigue crack propagation life of welded joints effectively.In addition,as an important technical parameter during welding,the heat input determines the microstructure and comprehensive performance of the weld and the welding heat affected zone.It also affects the welding residual stress and finally affects the fatigue crack propagation of the welded joints.Based on the above aspects,experimental tests were carried out with Q690 CFD steel T plate weld joints to study the effects of heat input on the shape of weld toe,microstructure and welding residual stress.Secondly,combined with the test data,the finite element software ABAQUS was used to simulate the welding process to obtain the welding residual stress distribution,and the numerical analysis results were compared with the measured data to verify the rationality of the model establishment and calculation parameter selection.Finally,based on the two-dimensional weight function method,a set of calculation methods for fatigue crack growth on the surface crack of welded joints were proposed,and the effects of initial crack size and bidirectional residual stress field on the fatigue crack growth characteristics of surface cracks were studied.The results show that the residual stress was affected by the change of heat input.The peak residual stress near the weld toe increased with increasing heat input.The narrower and longer the crack,the faster the crack grew in the depth direction and the shorter the fatigue life.When there was residual stress,it may accelerate the crack growth process and shorten the fatigue life.Therefore,in order to improve the fatigue life of the structure,it is necessary to use a reasonable welding process to control the residual stress after welding.In addition,for evaluate the remaining life of structures with crack more accurately,it is important to improve the detection accuracy of crack size.