| TC4 alloy has the advantages of cold and hot forming,easy welding,corrosion resistance and so on.It has been used in the field of ship and ocean engineering.In the welding process,welding stress and deformation are unavoidable,which affect the mechanical properties and dimensional accuracy of structural.And the problem of stress and deformation on titanium alloy plate are more serious.Compared with traditional arc welding,pulse MIG welding technology has low heat input and good heat controllability,which is conducive to reducing welding stress and deformation.Therefore,through the method of numerical simulation,the residual stress and deformation of TC4 welded complex structure are predicted.Understanding the evolution of residual stress and deformation is helpful to resist the welding stress and deformation of titanium alloy and optimize the process parameters,which has important theoretical and practical value.In this thesis,a three-dimensional finite element numerical analysis model for the residual stress and deformation of TC4 titanium alloy welded components is established based on the thermal elastic-plastic theory.In this model,the physical properties of materials,the geometric and the characteristics of heat source are considered.The stress and deformation distribution characteristics of welded joints are calculated by ANSYS software.At the same time,in order to improve the calculation efficiency,the inherent strain was obtained and corrected,based on the results of thermal-elastic-plastic method.And the effect of welding sequence on residual stress and deformation is considered by optimizing the loading of the inherent strain.Besides,Based on the modified inherent strain method,the residual stress and deformation of titanium alloy welded joint and complex structural are studied,and the effect of welding sequence and constraint on welding deformation of titanium alloy complex structural are discussed.The results show that the weld shape and longitudinal residual stress measured by experimental is in good agreement with the numerical simulation,which proves the validity and accuracy of the developed three-dimensional finite element model.For the T-joint,high tensile longitudinal stresses are in the region within 7mm from weld zone center,and the difference between peak stress and yield stress is much small.Under the conditions of 4mm,5mm and 6mm flange plate,with the increase of the flange thickness,the distribution characteristics of welding residual stress have little change.At the same time,the longitudinal shrinkage of the weld area decreases,while the angular deformation increases first and then decreases with the growth of flange thickness.Besides,the deformation of the flange on both sides of the web are asymmetrical distribution.The asymmetric deformation characteristics of T-joint can be discovered by the modeified inherent strain method in this thesis,which is100 times as efficient as that of thermal-elastic-plastic method.Residual stress of structural is mainly concentrated on the weld zone,and the influence of different welds is small.The maximum deformation of the bottom plate of structural is about 13.9mm,and that of side plate is about 28.4mm.The deformation distribution of TC4 structural calculated by modified inherent strain is similar to that of thermal-elastic-plastic method,and the difference of deformation is about 10% at most.In addition,the welding sequence has a significant effect on the deformation distribution.To reduce deformation of TC4 welded structural,the short weld bead should be finished first to get a certain stiffness,and then the long weld can be welded.The method of predeformation can effectively control the overall deformation of the TC4 welding structural.After the equal reverse deformation is applied to the maximum deformation position of the complex titanium alloy structural,the maximum deformation at the bottom plate is reduced by 55% and the maximum deformation of the side plate is reduced by 37%. |
PDF Full Text Request