Abstract
The safety assessment procedure in the new BS 7910:2013+A1:2015 guide is based on the failure assessment diagram (FAD) method. This paper aims to validate the above procedure for complex geometries such as damaged multi-planar square hollow section (SHS) welded joints and to recommend optimal solutions if necessary. FAD curves are constructed for cracked multi-planar SHS TT-, YT- and KT-joints for the first time and are compared with the Option 1 curve of the BS guide. A robust novel automatic finite element (FE) mesh generator, which is validated using the full-scale experimental test results, is used in this study. The new FE mesh generator addresses the issue of non-convergence by using a key-hole for the modelling the crack tip in elastic-plastic analyses. The new FE mesh generator is capable to model cracks and geometries of arbitrary dimensions and is able to achieve convergence of solutions even at a high plastic deformation. It is shown to be aiding in speedy generation of cracked FE mesh models which is otherwise time consuming to generate using commercial software packages. The results show that the Option 1 curve does not always guarantee safe solutions for multi-planar SHS welded joints. Hence, a penalty factor of 1.1 is recommended to be used to calculate the plastic collapse load. The use of proposed penalty factor gives optimal solutions for cracked multi-planar SHS TT-, YT- and KT-joints.
Highlights
A common issue faced by designers of offshore structures concerns the joints between the tubular members which must be assessed for plastic collapse, fatigue and fracture
BS 7910:2013+A1:2015 [1], Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures specifies the guidance for assessing the acceptability of defects in welded structures based on failure assessment diagram (FAD) method
The J-integral is calculated using the virtual crack extension (VCE) technique which is built in ABAQUS software [17]
Summary
A common issue faced by designers of offshore structures concerns the joints between the tubular members which must be assessed for plastic collapse, fatigue and fracture. BS 7910:2013+A1:2015 [1], Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures (hereafter referred to as ‘The Guide’) specifies the guidance for assessing the acceptability of defects in welded structures based on failure assessment diagram (FAD) method In this method, a design curve named as failure assessment curve is used in interpolating between the two failure criterions namely brittle fracture and plastic collapse (Figure 1). The Option 1 curve in the ‘The Guide’ [1] is intended for general applications and is independent of the structural geometry and the material stress-strain curve of the specimen assessed It was developed from extensive experimental databases of laboratory specimens [4]. The meshing details, benefits of new automatic FE mesh generator and the validation of the results using the full-scale experimental test results are described in the following sub-sections
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