The Effect of Misalignment on the Fatigue Strength of Welded Cruciform Joints

Abstract

The effect of axial misalignment on the fatigue strength of load-canying transverse cruciform welded joints was investigated using experimental and fracture mechanics methods. Where failure occurred by cracking from the weld toe, misalignment significantly reduced the fatigue strength. The reduction could be predicted using a nominal stress concentration factor (SCF). Misalignment had less effect where failure was due to cracking through the weld metal; an expression was deduced for the SCF in this case.For fracture mechanics assessments, an expression for an effective stress intensity factor using the SCF and stress intensity factors for aligned welds was shown to agree with the finite element (FE) results. Predictions of the effect of misalignment using the FE results agreed with experimental data. Misaligned transverse load-carrying cruciform joints should be assessed for fatigue failure from the toe using the same SCF as for a butt weld with the same misalignment. For failure through the throat, an alternative expression for the SCF is recommended. Fracture mechanics assessments of misaligned joints should be carried out using an effective stress intensity factor derived from the SCF and stress intensity factors for aligned joints. These recommendations are now incorporated in British Standard PD 6493: 1991. NOMENCLATURE a = crack length A = constant in crack growth law C = constant in S-N curve e = axial misalignment E = elastic modulus g = root gap in partial penetration joint h = fillet weld leg length K , = mode I stress intensity factor K,, K , = stress concentration factor for toe failure, and for weld metal failure I,, i2 = distances from end points to joint L =distance between end points rn = exponent in S-N curve and crack growth laws M = bending moment induced by misalignment N = cycles to failure P = axial load R = stress ratio (minimum stress/maximum stress) S = stress range in design S-N curve t = plate thickness S,, S, = nominal shear stress in weld metal due to axial load, and bending load w = weld throat thickness x, Yb = dimensionless stress intensity factor for axial loading, and bending loading Y,, = effective dimensionless stress intensity factor for misaligned joint tl = angular misalignment I = parameter oB, u, = axial stress, and bending stress ranges

Application of local approaches to the assessment of fatigue test results obtained for welded joints at sub-zero temperatures

“…This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ misalignment and residual stresses are well known to govern fatigue strength [49,50]. Comparing the axial misalignment of the test data, presented here, with data by Andrews [49], it becomes clear that the FAT class for weld root failure of cruciform joints is reached only in cases when the axial misalignment approaches the magnitude of plate thickness ( / = 1). For / = 1, the fatigue strength in Andrews [49] was about half the strength for / = 0.25.…”

Stress distribution and fatigue crack propagation analyses in welded joints

“…where σ 0 is the axially remote stress and σ b is the bending stress on the plate surface because of misalignment, as shown in Figure 9. In the present study, the k m because of axial misalignment is expressed as 56 :…”

Evaluation of Weld Root Failure Using Battelle Structural Stress Method

“…4 [11][12][13][14][15][16][17]. The joint plate thicknesses and the weld leg lengths evaluated are 10-4^0 mm and [11][12][13][14][15][16][17] 4-11 mm, respectively. 4, cyclic tension loading was applied for all joint types; load-carrying cruciform joints [11][12][13][14][15][16][17], doubler plate joints [15], and tube joints [16].…”

“…As indicated in Fig. About 300 fatigue testing data collected from [11][12][13][14][15][16][17] were employed for this evaluation of weld root failure. The joint plate thicknesses and the weld leg lengths evaluated are 10-4^0 mm and [11][12][13][14][15][16][17] 4-11 mm, respectively.…”

“…The weld root fatigue data in [11][12][13][14][15][16][17] plotted using the engineering shear stress range (Acr^,) are shown in Fig. 6.…”