Research On Multi-axial Fatigue Life Of Welded Structure Of Shipbuilding Gantry Crane

hipbuilding gantry crane is welded by all kinds of steel structures.Under long-term variable amplitude load,the connection of main girder and rigid leg bears complex bending composite load both bending and compression,which results in stress concentration effect,So it may lead to multi-axial fatigue damage.At present,the life analysis of crane weld at home and abroad is mainly based on uni-axial fatigue theory or multi-axial proportional prediction method,while the life prediction of welding parts under non-proportional loading is still in the stage of data accumulation.If the uni-axial or multi-axial proportional method is used,there will be some errors.Therefore,it is necessary to study the prediction method of multi-axial non-proportional fatigue life.In view of the limitations of energy method,critical surface method and critical surface energy method in multi-axial fatigue analysis,this article takes the welding seam between the main beam and the rigid leg of 580 t gantry crane as an example to study the multi-axial fatigue life by using structural stress method.The main contents are as follows:(1)The three-dimensional stress history of the measuring points near the connection between the main beam and the rigid leg is analyzed,and the multi axis non-proportional characteristics of the crane are determined.The stress history curve of real vehicle test is studied,and the typical operation cycle of crane is analyzed.(2)The finite element model of the whole machine is established to analyze the stress distribution under typical working conditions and obtain the location of dangerous points.According to the structural stress method,the solid element with weld details in the dangerous position is established and the mesh is subdivided.Then the MPC technology is used to connect the solid element with other shell elements to obtain the stress distribution of the solid element,which lays the foundation for extracting the structural stress at the weld toe.The reliability of the model is verified by comparing the real vehicle test results with the finite element calculation results.(3)With the help of verity module of ANSYS and FE-SAFE software,combined with the load spectrum,the multi-directional structural stress at the welding toe of the dangerous part is extracted,the structural stress time curve is drawn,and the cyclic counting is carried out by PDMR method.A non-proportional damage factor is introduced to quantify the non-proportionality of the loading path,and,realizes the transformation from non-proportional loading path to proportional loading path.Under the same loading conditions,according to the master S-N curve,the life calculation of multi-axial non-proportional,multi-axial proportional and uni-axial fatigue methods shows that the non-proportional loading process will cause greater damage,and the multi-axial non-proportional fatigue analysis method has higher reliability and applicability.Finally,the influence of horizontal load on weld life is discussed,and the influence law is obtained.The research results can be used to guide the use and design of crane.