Research On Fatigue Life Assessment Method For Welded Structure Of Loader Working Device

The working device is one of the important components of the loader for shoveling,loading,unloading and transporting materials.The working performance and working efficiency of the working device will directly affect working performance of the loader.As a weak link of fatigue strength in the working device,the welded structure is prone to fatigue damage during daily work.Therefore,the study of fatigue life assessment method for the welded structure is a great significance thing to improve loader's performance and reliability.In this thesis,taking the working device of ZL50 G loader as the research object,the fatigue life evaluation method of welded structure based on equivalent structural stress method is studied.The three-dimensional modeling and assembly of the working device under the fatigue test attitude was completed by Pro/E software.The simulation method of weld and pin connection in HyperMesh software was studied,and a complete finite element model of working device was established.According to the fatigue test requirements of the working device,the boundary conditions is applied and calculated,stress contour of the working device is obtained.And provide a basis for the fatigue life analysis of the welding structure of the working device.According to the results of finite element analysis,the load-stress conversion coefficient of fatigue attention point is determined,and the nominal stress variation range spectrum is obtained.The influence of average stress on the welded structural damage calculation is analyzed.The difference between the fatigue life evaluation of the welding structure of the working device is studied by the IIW standard and the BS standard.And a fatigue life evaluation model for welded structures of the working devices based on nominal stress method was established.The definition and calculation steps of structural stress are analyzed,and the structural stress at the weld toe of T-weld joint is calculated by different grid sizes.The structural stress grid size insensitivity is verified.The difference between nominal stress method S-N curve and mast S-N curve is studied,and a fatigue life evaluation model of the welded structure of the working device based on the equivalent structural stress method is established.The fatigue life prediction software of the welded structure of the loader working device was developed based on the nominal stress method and the equivalent structural stress' s fatigue life evaluation model for welded structures of the working devices.The example calculation proves that the software realizes the function of fatigue life prediction.The error between the fatigue life result obtained by different theoretical methods and the fatigue test result of the working device is analyzed.The error of the equivalent structural stress method and the fatigue test is the smallest.Therefore,it is recommended to use the equivalent structural stress method to evaluate the fatigue life of the welded structure.