Research On Fatigue Life Of Main Beam Based On Equivalent Structural Stress Method

The main beam of the gantry crane is mainly welded by the box structure.Welding defects inevitably appear during the welding process,which is the weak link in the fatigue life of the main beam.Under long-term variable amplitude load,the welded structure is most prone to fatigue damage,which leads to fatigue failure of the main load-bearing parts.This article addresses the limitations of the nominal stress method,local stress strain method and hot spot stress method when describing the fatigue behavior of welded structures,and uses the equivalent structural stress method to study the weld fatigue life of 580 t × 102 m shipbuilding gantry cranes.The main research contents are as follows:1)The static model of crane girder is established with ANSYS.Based on the actual lifting situation,the stress distribution of the main beam and the dangerous part of fatigue under the crane’s dangerous working conditions are calculated.Through the stress test,the test results are coMPared with the simulation results to verify the rationality of the model.2)The sub-model technology is used to establish a solid model of the dangerous part of the main beam,and the sub-model is subjected to finite element analysis.By coMParing the stress at the boundary of the sub-model with the corresponding position of the cutting boundary of the overall model,the accuracy of the sub-model is verified.3)The VERITY module was used to coMPare and analyze the equivalent structural stress of the sub-models with different mesh sizes,and the mesh insensitivity of the equivalent structural stress method was verified.The fatigue test of a group of I-beam test specimens verifies the applicability of the equivalent structural stress method to the life evaluation of welded structures.Then,through the VERITY module combined with the compiled load spectrum,the fatigue life of the main beam weld is calculated.The results show that the fatigue life cycle number of the main beam of the gantry crane meets the requirements of the crane design specifications,and the equivalent structural stress method is also applicable to other metal welded structures that bear variable amplitude loads.Finally,through the research and analysis of the three factors that affect the fatigue life of the weld(foot size,groove angle and weld surface shape),the results can be used to guide the fatigue design of the main beam weld.