Research On Influence Factors Of Crack Tip Mechanical Field And Crack Propagation Path Of Dissimilar Metal Welded Joints

The dissimilar metal welded joints are widely used in harsh working conditions.The material mechanical properties,microstructure properties,and residual welding stresses around the weld seam and adjacent areas are inhomogeneous because of the heterogeneity of materials and different welding processes.The stress corrosion cracking(SCC)poses a substantial hidden danger to PWR nuclear power plants’ safe operation,which threatens the critical nuclear power structures of the primary circuit safety end of PWR,such as welded joints.There is uncertainty in the crack propagation behavior of the welded joints and nearby regions because of the heterogeneous mechanical properties of welded joints.The cladding layer of dissimilar metal welded joints at the safe end of the primary circuit of the pressurized water reactor is taken as the research object in this research.The crack propagation path and the distribution of mechanical field at the crack tip of the welded joint samples are analyzed,which provides a reference for the structural integrity evaluation of dissimilar metal welded joints.The main research content is shown as follows:Based on the theory of continuous ball penetration test,the mechanical properties of the fusion line and nearby region of the dissimilar metal welded joint was characterized by the continuous indentation test,such as the work hardening exponent,yield strength,and tensile strength.On this basis,the user-defined field subroutine(USDFLD)in ABAQUS was used to establish a heterogeneous finite element material model suitable for describing the continuous change of mechanical properties of welded joints.The heterogeneous and traditional sandwich finite element material models were used to describe the mechanical field around the crack tip of the welded joint specimen by mises stress field,strain field,and stress triaxiality.And then,the driving force of the crack tip propagation of the welded joint was solved.The accuracy of the heterogeneous finite element material model is verified by comparing and analyzing the difference between the simulation results of the two material models.The extended finite element method was used to analyze the interface crack propagation path of bi-material welded joints.The effects of yield strength,tensile strength,and combined strength mismatch on the crack propagation length and crack deflection angle were discussed,respectively.The research object was taken by the cladding layer of dissimilar metal welded joints(SA508-304SS).The established heterogeneous finite element material model was used to numerically simulate and analyze the propagation paths of vertical and parallel fusion line cracks,respectively.The change of mechanical field at the crack tip during crack propagation was studied.