The Finite Element Analysis Of Welding Residual Stress And Static Strength For Lift Arm Structure Of Loader

1. IntroductionToday loader is used widely, but its work condition is relatively bad and workprocess is not presupposed, so the strength of lift arm assembly should be enoughto meet them. The lift arm assembly consists of lift arms,cross member and thesupport of the bell crank , all of these are connected by welding. After the effectingof welding and the welding temperature, the physical properties and mechanicalproperties of the metal around the weld seam have changed, meanwhile somewelding residual stress and welding crack arose in the welding position. Undercyclic loading and impact loading, the welding position will be damaged easily.Therefore, it is necessary to analyze the welding residual stress of some keyregion under typical case in the construction machine's design. We can obtain thestress variation regular and the stress curve by using the finite element methodcombined with relating software. All these will be helpful for us.2. Introduction for welding residual stress of lift armassemblyThe produce of welding residual stress has closed relation with weldingtemperature, so we can obtain the value and variation regular of welding residualstress by analyzing the welding temperature field in the ANSYS. Weldingtemperature field analysis is thermal analysis virtually.Thermal analysis consist of steady thermal analysis,transient thermal analysisand some coupling analysis just like thermal-struc coupling analysis,thermal-fluidcoupling analysis,thermal-magnetc coupling analysis and thermal-elect-struccoupling analysis. This paper imitate the welding process between lift arms andcross member by ANSYS, as the welding temperature and the thermal load isvaried with time ,so it is transient thermal analysis.This paper calculates the welding residual stress between lift arms and crossmember by the ANSYS thermal-struc coupling analysis block in order.Firstly, this paper imitate the welding process between through the finiteelement model of lift arm assembly by ANSYS, by doing this we can get thetemperature field of last time. Secondly, the thermal analysis should be transformedto structure analysis, and the temperature field should be put on the nodes of finiteelement model as thermal load, meanwhile boundary condition and displacementconstraint also should be put on the finite element model. Finally, we obtain thevalue and variation regular of welding residual stress.By calculating the welding residual stress, this paper gains the conclusions asfollowing:(1) welding residual stress near welded seam belongs to tensile stress, andwelding residual stress far from welded seam belongs to compression stress, andwelding residual stress more far from welded seam belongs to tensile stress also.The maximum value of welding residual stress is about 120MPa.(2) There is large residual stress and displacement in the welded seam andadjacent heat affected zone of lift arm assembly.(3)The finite element model established in this paper is correct generally.3. Introduction for static strength of lift arm assemblyThe finite element method is used more and more in the field of structuralanalysis. There are 7 kinds of structural analysis in the ANSYS. The displacementcan be calculated directly, but strain and stress need to be deduced.The static strength analysis block of ANSYS can calculate the displacement,strength and strain under the fixed load.The stress on the parts of working equipment varies with the operating mode,and this paper carries out the static strength analysis under the operating mode (3),namely the symmetry horizontal force and vertical force are put on the workingequipment synchronously.Under the symmetry horizontal force and vertical force combined operatingmode, the forces of each hinge joint can be calculated. According with the resultsthe boundary condition and displacement constraint should be put on the finiteelement model. Finally, we obtain the value and variation regular of weldingresidual stress.After finishing analyze, this paper samples out 8 nodes from the finite elementmodel. By adding the value of welding residual stress to the strength value underthe operating model an another value data will be gotten. Comparing the resultsfrom the finite element analysis and experiment, the rationalities of this model andthe dealing methods were testified. Meanwhile this paper obtains some conclusionsas following:(1) The numeral values of the finite element analysis are larger than those ofexperiments, but the stress variation regular and the stress curve are same generally,all this show that the model established in this paper is rational.(2) It is feasible to analyze the static strength of lift arm assembly by usingANSYS .(3) The static analysis obtains the stress and distortion of one operation model,and it can not analysis the continuous work model, while dynamic analysis candeal with the problem.(4) The analysis and experimental results show us the following: there areinequality stress at different area. It shows that this structure need to be improvedafter studying.