| Scissors elevating platform is a welding high altitude manned equipment.Its fatigue reliability is related to the personal safety of the operator so the fatigue strength design and fatigue life check are required at the design stage.However,the load environment of the components of the elevating platform is very complicated,and traditional methods are difficult to obtain its fatigue life.Given this situation,based on the theory of weld fatigue simulation,multi-body dynamics simulation,FEM modeling in the component coordinate system and modal superposition,a new efficient numerical analysis algorithm for fatigue life prediction of welded components with a large range of rigid body motion was formed in this paper.The contents are as follows:(1)Aiming at the problem of fatigue failure of engineering welded structures,the different characteristics of fatigue strength of base metal and welded joints were systematically summarized.And the random fatigue load spectrum conversion processing method in the fatigue simulation process was systematically summarized too.At the same time,the similarities and differences between fatigue problems of welded structures and metal,and fatigue research theories of welded structures were introduced.(2)In order to obtain the fatigue load spectrum required for the fatigue analysis of the elevating platform,a multi-body dynamic model of the scissors elevating platform was established.Extract the hinge reaction force of the scissors rod and map the hinge reaction force to the coordinate system of the scissors rod part to form the fatigue load spectrum of fatigue analysis.This is done to eliminate the adverse effects of rigid body motion on FEM modeling of fatigue analysis.(3)A typical component FEM model based on the component coordinate system is established,and the quasi-static method is used to analyze the fatigue life of the FEM model with welds.By applying a unit load and calculating its stress distribution,the stress distribution and the corresponding fatigue load spectrum are imported into the fatigue analysis software,and the fatigue life simulation analysis is performed according to the British Standard 7608 to obtain the fatigue life value and the fatigue life distribution.Carry out the fatigue test of the same type of elevating platform under the same working conditions to obtain its test fatigue life.The comparison and analysis of simulation results and test results verify the correctness and effectiveness of the fatigue life simulation method proposed in this paper.Because the algorithm avoids the solution of transient dynamics and belongs to quasi-static analysis,the calculation is very efficient.(4)MSC’s three software(Patran,Adams,Fatigue)joint simulation analysis method can further analyze the fatigue life of moving parts.This method is based on the modal superposition method and uses MSC.Patran to form a modal neutral file of a typical flexible member.Using MSC.ADAMS,a rigid-flexible coupling multi-body dynamics model is established,and dynamic simulation is performed to obtain the time history of the stress of the flexible body.Based on British Standard 7608,the fatigue life distribution of the scissors rod is calculated by MSC.Fatigue.By comparing the fatigue simulation life and test life results of the scissors rod,it is verified that the joint simulation method can accurately predict the fatigue crack initiation position and fatigue life of the welded member of the scissors lift platform. |
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