3D Fracture Analysis of Cold Lap WeldDefect in Welded Structures

Abstract: This thesis is concerned with the classification and effect of cold lap weld defect onthe fatigue strength of a welded structure. Cold lap is a type of weld defect whichoccurs when molten metal does not completely fuse with the cold plate surface. Thisproduces a crack like defect, often very small, which is parallel to the plate. The coldlap weld defect has been classified into three types namely spatter, overlap andspatter-overlap cold lap. Study showed that all three types of cold lap defects have thecorresponded lack of fusion in the interface, which could be considered as initialmacro cracks in different shapes where a possible fatigue crack growth could start.Fatigue life assessment of the above mentioned three types of cold lap defects wascarried out using finite element and crack growth analysis in 2D and 3D. In the 2Danalysis the cold lap defects were modeled as line crack (assuming a/c=0). Based onthe experiments the cold lap defects were visualized as having two probable crackshapes; penny shaped and part through, which required 3D crack growth analysis.Results showed that in 2D analysis the three types of cold lap defects have sameinfluence on fatigue life of the weld. In 3D analysis, the shape of the cold lap defectsdid not show any difference in fatigue life. Overall penny shaped and part throughcracks in 3D analysis predicted 1.75 times longer fatigue life as compared to line crackin 2D analysis.