Design And Welding With Trailing Shape Modifying Of Under-matched Welded Joint Based On Principle Of The Equal Bending Load-carrying Capacity

Load-carrying capacity of under-matched joint is lower than that of the basemetal or equal-matched joint, and thereby its practical application is restricted.There are related research on equal load carrying capacity of under-matched jointbased on strength parameter or stress intensity factor, but there is not report onbending load-carrying capacity(BLCC) of under-matched joint. To improve theBLCC of under-matched joints and make under-matched welded joints reach thatof the base metal, the criterion and realization condition of equal bending loadcarrying capacity(EBLCC) is proposed in elastic stage and in plastic stagerespectively by combination of theoretical research, finite element method(FEM)and experimental verification without consideration of welding metallurgy,welding flaw and residual stress. Moreover, EBLCC design criteria ofunder-matched joints are presented in elastic stage and in plastic stage respectively.EBLCC of the designed under-matched welded joints can reach that of the basemetal.The critical condition satisfies EBLCC requirement is studied theoreticallybased upon the fundamental theory of material mechanic in the case welded metalhas different mechanical properties with base metal. The critical geometry curvefor under-matched joints that satisfies EBLCC is derived theoretically in elasticstage. Under the condition of given the same bending load when the base metalyield exerted, take the maximum normal stress of under-matched welded metalshould be lower than the yield strength of weld metal as constraint conditions,Design criteria of of the inhomogeneous variable cross-section under-matchedEBLLC joint are proposed in elastic stage through detailed geometrical designsuch as minimum reinforcement, minimum weld width and weld toe radius. Thecritical condition satisfies EBLCC requirement is studied theoretically based uponthe elasto-plastic bend theory. The critical geometry curve for under-matchedjoints that satisfies EBLCC is derived theoretically in plastic stage. Under thecondition of given the same bending load when the base metal reach tensilestrength, take the maximum normal stress of under-matched welded metal shouldbe lower than the tensile strength of weld metal in plastic stage as constraintconditions, Design criteria of of the inhomogeneous variable cross-sectionunder-matched EBLLC joint are proposed in plastic stage through detailedgeometrical design. The correctness of the EBLCC design criteria ofunder-matched butt joint has been has been verified by FEM in elastic stage and inplastic stage respectively.Theoretical studies show that mis-match ratio of tensile strength of fillermetal and base metal cannot be used for EBLCC design in plastic stage. Theconcept of equivalent evaluating stress is proposed. It characterizes therelationship between plastic limit load corresponding to the tensile strength of thematerial and the equivalent evaluating stress. Mis-match ratio of equivalentevaluating stress is defined as the ratio of the equivalent evaluating stress of weldmetal to that of base metal. It is reasonable to be used for EBLCC joints design inplastic stage.Theoretically obtained reinforcement critical curve according to EBLCCdemand is a parabolic shape. Considering the engineering application, thefeasibility analysis of circular arc instead of parabola shape has been carried outconsider the factor of engineering convenient application. Design method ofthree-circle tangential under-matched butt joint suitable for engineeringapplication are given in elastic stage and in plastic stage respectively base onEBLCC design criteria. The correctness of the EBLCC design method ofthree-circle tangential under-matched butt joint has been has been verifiedrespectively by FEM and experimental method. Results of the validation show thatdesigned EBLLC under-matched joints meet the requirement of the EBLCCdesign.To overcome the shortcomings of present methods that produce EBLCCwelded joints, three-circle tangential shaping wheel is designed in this paper. Therequired geometry shape of EBLCC joints can be obtained by welding withtrailing shape modifying(WTSM). Moreover, to resolve the limitations of theshaping wheels with fixed shape and size, the flat-reinforcement shaping wheelswith adjustable width have been designed, which can broaden the application ofwelding trailing shape modifying. Mechanical performance test on under-matchedEBLCC welded joints by weld shape modifying are performed. It is indicated thatunder-matched EBLCC welded joints by WTSM can meet EBLCC requirement.Vickers hardness on the weld surface by WTSM is significantly higher than that ofas-welded, which reveals that WTSM has work-hardening effect. Residual stressof the EBLCC joints by WTSM is remarkably lower than that of as-welded.Compressive residual stress which is preferable brought in the weld by WTSM.The EBLCC design can make under-matched joints reach BLCC of the basemetal. So the welded structure subjected to bending loads can be designed direct inaccordance with BLCC of base metal. The feasibility of WTSM has been exploredand the required geometry shape of EBLCC joints can be obtained.