Study On Strength Mismatching Welded Joints Based On Geometry Constraint And Its Application

A lot of inhomogeneity factors universally exist in welded joints and are very complicate,among them,the material strength mismatching of weld and base metal had a great influence on crack tip fields and fracture toughness.Owing to the reasons of welded joints methods that appear welding defects in it very easily,which lead welded joints to be the weak link of the welded structure,and many of the fracture of welded structures are derived from here.Consequently,the study on the effect of material strength mismatching to the fracture of welded structure has important practical significance.Based on the geometry constraint,this paper analyzes the effect of material strength mismatching deeply,and obtains the formula J-A₂-A_2m which is based on the J-A₂ three-term solution of homogeneous material to predict crack tip fields of welded joints,and apples it to the modified of J - R resistance curves of welded joints.Firstly,the applicability and scope of application of J-A₂ three-term solution is anaylsised and the crack tip stress fields predicted by J-A₂ three-term solution is compared with the finite element solution.Afterwards,by using the finite element method and binding J-A₂ three-term solution,the overmatched no geometry constraint welded joints,undermatched no geometry constraint welded joints and all weld geometry constraint welded joints modified boundary layer models are performed.After researching the relationship of developing diagram of these two cases,a new constraint parameter A_2m has been established for overmatched welded joints,allowing the material mismatching effect on the crack tip stress to be quantified,for the full field geometries,both geometry and material mismatching effects are present,after analysis the relationship of A_2m and A₂, the formula J-A₂-A_2m which can predict crack tip fields of welded joints is educed.Then,in order to verify the formula J-A₂-A_2m,a three-point bend specimen finite model is constructed,meanwhile,the predictive result of J-A₂-A_2m is compared with the finite element result to analyze the application scope and error limitation.In the end,on account of the difference of geometry and mismatching constraint, the J-R resistance curves of standard welded component can't take place the practical welded specimen's.For the sake of obtaining the J-R resistance curves approaching to the practical component,meanwhile,using experimental results to verified the formula J-A₂-A_2m,this paper uses the formula J-A₂-A_2m to modify the J -R resistance curves to eliminate the influence of constraint effectively.Then,the predictive result is compared with the experiment data of this material to validate the effectiveness of modified J - R resistance curves.Compared with the former predictive methods,the formula J-A₂-A_2m proposed in this paper is more accurate in describing the crack tip stress fields,the application scope is larger,which is yielding in both small and large scale,and the results of welded joint J -R resistance curves modified by J-A₂-A_2m also proves that the formula J-A₂-A_2m is a effective method which can be used in practical engineering.