Study On Prediction Of Welding Deformation In Thin-plate Q235 Steel Structure And Prevention Of Buckling Distortion

The ship is a large-scale waterborne mobile structure that can assume the tasks of transportation,production,and combat.For a country with a long river and a stretch of coastline,the development of the shipbuilding industry is extremely effective in improving people's lives and ensuring national security.During the period of shipbuilding,a large number of metal components are joined to form a structure.Fusion welding has been used as the most important join method in shipbuilding due to its high production efficiency,good joint performance,and easy operation.In the welding process,the material undergoes a thermal cycle of local heating and rapid cooling,and welding distortion is induced by uneven temperature distribution.Welding deformation has an adverse effect on the appearance and mechanical properties of the structure.Once excessive welding deformation occurs,additional corrections are required.When the welding deformation exceeds the correction range,the welded structure will be scrapped.Therefore,how to prevent and control welding deformation is an important research topic in shipbuilding community.As a fundamental research,based on ABAQUS software,a thermo-elastic-plastic finite element method considering material nonlinearity and geometric nonlinearity was developed to simulate welding temperature field,residual stress distribution and deformation of Q235 steel T-joint with the thickness of 3.5 mm.Meanwhile,experiments were carried out to measure welding residual stress and out-of-plane deformation.Through comparing the simulated results and measured data,it was found that both welding residual stress and deformation predicted by numerical simulation were in good agreement with experimental measurements,the effects of aspect ratio on residual stress and welding distortion were also discussed.The influences of three heat source models on the computational accuracy and computational efficiency of welding deformation of small-scale panel structure were investigated by the means of both numerical simulation and experimental methods.The welding deformation of a large-scale panel structure was calculated using a full-segmented transient heat source,the characteristics and causes of buckling deformation of the large-scale panel structure were analyzed,the influences of heat input,welding manner and outer constraint on the out-of-plane deformation of the large-scale panel structure were also investigated.The following results are important.(1)In case of T-joints of Q235 steel with the thickness of 3.5 mm,the aspect ratio has a significant effect on the transverse residual stress.With the increase of the aspect ratio,the transverse residual stress decreases significantly,while the influence of aspect ratio on longitudinal residual stress and out-of-plane deformation can be neglected.(2)In case of small-scale panel structures of Q235 steel with the thickness of 3.5 mm,the longitudinal residual tensile stress is mainly distributed near the weld,and the transverse residual tensile stress is mainly distributed near the transverse weld.Three different heat source models were adopted to calculate welding residual stress,respectively.The patterns of residual stress distribution are the same.(3)Three heat source models were also used to calculate the welding deformation of the small-scale panel structure,respectively.The patterns of deformation are the same.The simulated deformation using moving heat source is in good agreement with the measured deformation.However,the segmented transient heat source is more efficient than the enhanced moving heat source,and the full-segmented transient heat source is more efficient than the segmented transient heat source.(4)In case of large-scale thin plate panel structures of Q235 steel,the torsional buckling happened when the transverse web was welded,the main reason for structural buckling is that the compressive residual stress exceeds critical buckling stress.The heat input has a great influence on the out-of-plane deformation of thin sheet large-scale panel structure.When the excessive heat input was adopted,the torsional buckling of the structure occurred,and the buckling deformation and excessive out-of-plane deformation can be avoided through decreasing heat input.When wave buckling only occurred at the edge of flange,the decrease of the heat input has an insignificant effect on the decrease of the welding out-of-plane deformation.The welding manner has obvious influence on the out-of-plane deformation of the large-scale thin-plate structure,and the out-of-plane deformation caused by the double-side welding is always larger than that of the single-side welding.Although it is beneficial for reducing the amount of out-of-plane deformation to apply outer constraints,the buckling of the structure still occurred with various modes.The research results of this paper can provide reference for predicting the welding deformation of large structures,and also provide theoretical basis for preventing the structural buckling and reducing the welding distortion.