Improved Bending Correction Factor for Fatigue Assessment of Welded Joints

摘要

It has long been recognized that the fatigue performance of welded jointssubjected to bending stress is significantly better than those testedactually under a pure membrane stress. Since published design curvesare based almost exclusively on test data obtained under membranestress, they are conservative with respect to joints in bending. Inpreparation for the revision of BS 7608:1993, a correction procedure toallow for this was developed using fracture mechanics methodsfollowing BS 7910:2015. Subsequent consideration of published fatiguetest data, however, indicated that the correction procedure overestimatedthe benefit. Consequently, a new correction, based directly onthe available fatigue test data, was produced and included in BS7608:2015. A conclusion to draw from the above is that the currentfracture mechanics solutions for bending underestimate the stressintensity factor and are therefore non-conservative. This has wideimplications for both industry and BS 7910. An alternative conclusion isthat the experimental data are the problem since the specimens testedaxially were not identical to those tested in bending. In view of theimportance of this issue in relation to both fatigue design using BS 7608and fatigue crack growth assessment using BS 7910, a parametric studybased on fracture mechanics with both the 2D and 3D Mk solutions wasconducted to review k_(b-revision) derived in the revision work for BS7608:1993. A new equation for the bending correction factor kb-new,including the plate geometry effect (W/t) was derived using the 3D Mksolution in accordance with BS 7910:2015. Fatigue tests were conductedusing identical specimens for a range of thicknesses (25mm, 12.5mm and6mm) under both purely axial and purely bending loading, to validate thenew proposed bending correction factor.