Theoretical Predictions Of Welding Residual Stress And Deformation In High Strength Steel Thick-plate Welded Structures

Because of high strength,good comprehensive mechanical properties and processing performance,low-alloy high-strength steel has been widely used in many fields such as bridge engineering,architectural construction,transmission tower,offshore platform,ship building and so on.As an efficient and reliable metal joining process,fusion welding technology has been widely used to assemble steel structures.However,owing to the non-uniformity of the welding temperature field and the highly non-linearity of the material properties during welding,residuals stress and deformation are inevitably generated in and around the weld region.Moreover,steel structures are generally used multi-layer and multi-pass welding due the large size and thickness.In the process of multi-pass welding,the thermal cycles are more complex than that of single-pass welding process,so the residual stress distribution and deformation in such joint are more complicated than those in single-pass welded joint.The exaggerated welding residual stress in the weld zone and its vicinity seriously affect ultimate strength,fatigue strength,and structural stability.In addition,excessive deformation in welded structures significantly degrades manufacturing accuracy,increases schedule delays and additional costs.Therefore,investigating welding residual stress and deformation of thick high strength steel is of importance for safety assessment of the steel structure.As a fundamental research,based on MSC.Marc software,firstly,a thermo-elastic-plastic finite element method was developed to simulate welding temperature field,residual stress distribution and deformation in a single-pass surfacing joint.The influence of welding heat input and heat source model on welding residual stress and deformation in a single-pass surfacing joint was studied.Then,the welding residual stress distribution and deformation of the K-joint and T-joint were studied in detail by numerical and experimental methods.The formation mechanisms of residual stress and deformation were clarified.Meanwhile,the influence of heat source model on the residual stress and deformation in a K-joint was investigated.In addition,the influence of welding sequence on the residual stress distribution and deformation in an H-section steel butt-welded joint was studied by means of numerical simulation and experiment.The results show that the calculated results of welding residual stress by moving heat source and instantaneous heat source are very similar,but the instantaneous heat source fail to predict welding deformation while it can save computing time.Besides,with the increase of heat input,the peak and distribution trend of residual stress are roughly the same,but the region of tensile stress is increased.In addition,both the transverse shrinkage and angular deformation increase as the heat input increases.The numerical results of the K-joint show that the residual stress present longitudinal-transverse two-dimensional high tensile stress state at the weld zone and its vicinity,but the value of the residual stress in the thickness direction is relatively small.Moreover,the angular deformation increases as the number of weld passes increases,but when welding the after side,the angular deformation is partially offset due to the geometric characteristics of the weld arrangement.The numerical results of the T-joint show that the residual stress present three-dimensional stress state at the weld zone and its vicinity,and the residual stress presents tensile-compressive-tensile distribution in the central region of the web and the flange plate.Furthermore,the welding deformation increases and the increasing range decreases on the first welding side,but on the after welding side,the welding deformation reduces and the reducing range is much smaller than the first welding side.The numerical results of the H-section steel butt-welded joint show that the residual stress distribution of the web is significantly affected by welding sequence.The welding sequence not only can change the distribution of residual stress but also alter the magnitude of residual stress.However,the welding sequence has an insignificant influence on residual stress of the flanges and welding deformation.The computational approach developed in the current work is helpful to predict and control the residual stress and deformation in welded structure.The main conclusions obtained by the current study not only provide a reference for making the welding process parameters,but also provide important basis for designers to reduce and control residual stress and deformation and improve the quality of structures.