Weld magnification factors for semi-elliptical surface cracks in fillet welded T-butt joint models

Abstract

The weld magnification factor method has been widely used in the determination of the stress intensity factor (SIF) for weld-toe cracks in welded structural components. Weld magnification factors Mk are normally derived from two-dimensional crack models with fillet weld profiles to take account of the effect of weld-notch stress concentration at the deepest point of the crack front. This paper presents a detailed three-dimensional analysis of weld-toe surface cracks in fillet welded T-butt joint models using the finite element method. Effects of the weld notch and the welded attachment stiffness on the SIFs of the weld-toe surface cracks have been studied quantitatively. Weld magnification factors applying to the whole surface crack fronts have been estimated. Numerical results show two contradictory effects; that the effect of weld notch increases S1F values throughout the shallow surface crack fronts which are in the region of notch stress concentration, while the effect of local structural constraint reduces the SIF values. The increase in the SIF values mainly depends upon the relative crack front depth and the decrease in the SIF values mainly depends upon the crack shape aspect ratio for a specific weld profile. Both effects on the weld magnification factors can be estimated separately. A simple approach for deriving the weld magnification factors for various weld-toe surface crack problems is proposed for engineering applications.

The development of an accurate model for the fatigue assessment of doubly curved cracks in tubular joints

“…Nevertheless, the assumption is made that, if the nodes used are very close to the crack tip, the curvature of the path is negligible. It is necessary to use nodes close to the crack tip anyway, since (1)- (9) are only valid in this area. Consequently, results from the first three brick elements were used for the extrapolation back to the crack tip.…”

“…For plain plate cracks, it is generally accepted that plane strain conditions exist everywhere along the crack front apart from where the crack meets the free surface. Fu [8,9], in his work on 3-D T-butts, assumed plane strain everywhere whereas Kristiansen and Fu [19], having examined the area where the crack meets the weld toe in detail, concluded, not surprisingly, that the condition was somewhere between plane stress and plane strain. Results from the current work were calculated assuming plane strain everywhere.…”

“…lc) provides a very good approximation of the actual conditions in a tubular joint, although the different overall geometry means that the loading across the crack and the crack plane restraint are still not properly accounted for. Furthermore, data for 3-D T-butts remains limited [7,8,9], probably due to the difficulties in generating adequate meshes. Line-spring finite elements in shell meshes (Fig.…”

“…For validation of the 3-D T-butt, the work of Fu et al [8,9] was chosen. Fu et al concentrated on shallow cracks with a/Tup to 0.4 and did not model the weld toe radius.…”

Weight Functions and Stress Intensity Factors for Semi‐elliptical Cracks in T‐plate Welded Joints

“…The calculation of stress intensity factors for surface cracks at the welded toe of these joints is very difficult due to the complex geometry. Several authors (most recently [1–3]) have conducted detailed 3‐D finite element calculations for simple loading conditions, i.e. far‐field tension and bending.…”