Research On Fatigue Performance And Effect Of Welding Quality Of Weathering Steel Welded Joints

Good ship welding quality is the premise of long-term safe operation of ships.In ship construction,marine steel welded joints exist as basic components and are always under complex load conditions during service.There are usually various defects in the weld area of welded components,resulting in stress concentration,accelerated crack propagation,and reduced service life.Therefore,whether a welded structure with defects can operate safely is a hot spot that needs attention,and it is also a potential hidden danger involving the safety of life and property,and a scientific assessment must be carried out.This paper uses a combination of experimental and simulation methods to carry out research into the fatigue performance and welding quality of weathering steel butt joints and cruciform joints.The structural stress method was used to analyse the fatigue performance of weathering steel butt joints and cruciform joints,combined with fatigue test data to draw S-N curves,and fracture observation to analyse internal defects in the joints.The results show that:for butt joints,corner deformation reduces the fatigue performance of the joint;the residual height of the weld root causes local stress concentration,making it a budding area for fatigue cracking;for cruciform joints,corner deformation and misalignment reduce the fatigue life of the load bearing weld,and when corner deformation and misalignment are well controlled,the fatigue performance of load-carrying cruciform joint with the same failure mode is not significantly different from that of non-load-carrying cruciform joint;under the current process,The existence of root unfused defects in load carrying welds does not affect the failure mode of the joint,and when the weld foot size reaches the plate thickness(t=12mm),it is recommended that the root unfused size be controlled within 0.75t;the thinner the weld part,the smaller the stress concentration and the higher the fatigue strength of the cruciform joint.Based on the fatigue test data in this paper,the S-N curve applicable to the fatigue strength assessment of the joint type in this paper was constructed,and the median S-N curve parameters Cd’ and h’ were 4794.02 and 0.1807 respectively,with a standard deviation of 0.1568,which was 8%lower compared to the original S-N curve and improved the fatigue resistance design guidelines for welded joints.With the help of the strain energy density method to carry out research on the impact of different levels of bite edge defects,in the finite element simulation to select the appropriate mesh size to ensure the accuracy of the calculation,and combined with fatigue data to draw the W-N curve and the strain energy density change curve.The results found that:when the class undercut defects appear at the toe,the fatigue strength of the specimen is affected,and the gradient of strain energy density change of the specimen increases with the increase of undercut depth;for butt joints,when the class undercut defects appear at the remaining height of the weld front,there is almost no effect when the undercut depth is lower than 0.1mm,and when the class biting defects appear at the toe,the undercut defects are at the joint failure location.Plate thickness of 12mm,0.2mm,0.5mm and 1mm depth of the undercut edge defects to reduce the fatigue life of the joint by 17%,60%and 83%respectively;plate thickness of 10mm,0.2mm,0.5mm depth of the undercut edge defects to reduce fatigue life by 20%and 61%respectively;for cruciform joints,plate thickness of 12mm,0.2mm,0.5mm and 1mm depth For cruciform joints with a thickness of 12 mm,the fatigue life is reduced by 18%,47%and 71%for 0.2 mm,0.5 mm and 1 mm depths respectively.At the same thickness,the fatigue strength of butt joints is more affected by undercut defects than cruciform joints when the undercut depth is 0.5/1mm.