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Long-distance offshore pipelines always suffer large plastic deformation during installation and operation. Accompanied by high internal pressure, potential flaws are found to initiate from the girth welds, and this brings a significant challenge to the structural integrity of the pipelines. The currently used procedures for fracture assessment of pipelines are usually stress based, which are unsuitable for application to cracked pipeline subjected to large plastic deformation. Therefore, the aim of this paper is to investigate the fracture assessment of pipeline subjected to large plastic deformation and identify and understand the critical parameters influencing the fracture responses under actual loading conditions. The evolution of crack tip opening displacement (CTOD) of a pipeline segment with an embedded canoe shape crack located in the middle of the girth weld is investigated under pure bending and biaxial loading through 3D elastic–plastic finite-element simulations. The effects of crack width, crack length, pipeline thickness, material hardening, and internal pressure on fracture response are discussed. Finally, a strain-based failure assessment diagram (FAD) is developed, and comparison between fracture assessment by BS7910:2013 and finite-element simulations concludes that the former produces conservative predictions for deep crack.

The function of the third rail is to supply power in a mass rapid transit system through a semi-continuous rigid conductor placed alongside the rails of a railway track. Although it is fully segregated and fixed along the floating slab tracks (FSTs), which is used to insulate the surrounding buildings from vibration of the passing trains, the FSTs and the third rail are still prone to reverberation. Precisely because of this reason, many of the fasteners used to tighten the claw to the insulator eventually become loose, dislodging the claw holding the third rail and causing part of it to sag. This, in turn, can damage the collector shoes and causing the trains to lose power. Hence, the root of the problem is due to loose fastener in the third rail system. In this study, the dynamic response of a vehicle–rail interaction system is analysed, and the results show that the natural frequency of the interactive system decreases as a vehicle passes through a loose support. Based on this fact, a detection algorit...

This paper describes the determination of stress intensity factors (SIFs) of a 3D surface crack in acircular hollow section (CHS) T/Y-joint subjected to three basic loading. In order to achieve the main objective, anautomatic finite element (FE) mesh generator is designed whereby the mesh density and element type of the CrackTube zone can be controlled by the users. Extensive tests are carried out to check the accuracy and to test theconvergence of the mesh models. It is found that the generated mesh models are both accurate and robust.Subsequently, a total of 246 cracked CHS T/Y-joints subjected to axial loading; in-plane bending and out-of-planebending are analysed, and the influencing parameters β, γ, τ, θ, a/t0 and c/a on the SIFs of a 3D surface crack areinvestigated in this study. The SIFs at the deepest point of a 3D surface crack are also determined using an indirectmethod incorporated in BS7910. It is found that the later underestimates the SIFs by as much as -36.9% under axialload for crack located at the crown and -32.9% under out-of-plane bending for crack located at the saddle,respectively. Hence, the indirect method is found to be unsafe in estimating the SIFs of a 3D surface crack in CHST/Y-joints under certain loading conditions and crack location. Published version

For tubular T-joints subjected to axial load, the stress distribution along the weld toe can be predicted by some reported parametric equations in the literature. Conventional method indicates that the hot spot stress along the weld toe for tubular T-joints subjected to axial load is located at the saddle position. This conclusion is reliable when the thickness of the chord member of a tubular T-joint is relatively small. Alternatively, the hot spot stress is always fixed at the saddle position, when the geometrical parameter 7 (chord radius/chord thickness) is limited in a common range (12 ≤ γ ≤ 30) specified by CIDECT (2000). However, it is uncertain if this conclusion is still correct when the parameter γ is smaller than the above-specified range. In this study, the effect of geometrical parameters on the stress distribution for tubular T-joints subjected to axial load has been studied. First, a finite element method to model welded T-joints has been proposed, and the accuracy of this method to analyse the stress distribution along the weld toe of tubular T-joints has been verified by comparing numerical results with experimental results. Thereafter, 140 models of T-joints with different geometrical parameters have been analysed using finite element method. From the investigation on the numerical results, it has been found that the location of the hot spot stress along the weld toe is shifting between the crown and the saddle when the parameter γ varies. Thus, caution should be taken in practical engineering design when it is necessary to estimate the approximate position of the peak stress for tubular T-joints under axial load.

This paper summarizes the key steps involved in the construction of an accurate and consistent finite element model for general cracked tubular T, Y and K-joints. The joint under consideration contains a surface crack which can be of any length and located at any position along the brace–chord intersection. Welding details along the brace–chord intersection, compatible with the American Welding Society (AWS) specifications [American Welding Society. Structural welding code-steel, ANSI/AWS, 15th ed., Miami, 2000], are included in the geometrical model. In order to develop a systematic and consistent modelling procedure, the whole process is divided into four key steps. They are, namely, (1) construction of a consistent geometrical model of the joint with welding details, (2) determination of cracked surface to define the semi-elliptical surface crack profile, (3) generation of well-graded finite element meshes, and (4) stress intensity factor studies around the crack front. To produce a well-graded finite element mesh, a sub-zone technique is used in the mesh generation whereby the entire structure is divided into several sub-zones with each zone consisting of different types of elements and mesh densities. The stress intensity factors (SIFs) are evaluated using the standard J -integral method. Two full-scale T and K-joint specimens were tested to failure under axial load (AX), in-plane bending (IPB), and out-of-plane bending (OPB). In the tests, the rate of crack propagation was monitored carefully using the alternating current potential drop (ACPD) technique. Using the known material parameters C and m , the experimental SIFs were obtained, and they are found to be in complete agreement with the computed SIFs obtained from the generated models. Hence, the proposed finite element models are both efficient and reliable.

In the second part of this study, the reliability of the geometrical models and the mesh generation procedure developed in Part 1 are validated by comparing the modelling results with full scale tests results. Static tests were applied to study the stress concentration factors while fatigue tests were applied to study the stress intensity factor and the fatigue life of the joints. The results obtained indicated that the uncracked joint model could lead to reliable stress concentration factor estimations while the cracked joint models could lead to conservative stress intensity factor and residual fatigue life predictions close to experimental results. Accepted version

In order to understand the fatigue growth behaviors of tubular joints, large-scale tubular joint fatigue tests had been performed for a number of decades. But most of them were tested under basic loading, i.e. axial load (AX), in-plane-bending (IPB) and out-of-plane (OPB). In the current test program, full-scale circular hollow sections (CHS) and rectangular hollow sections (RHS) tubular joints were tested under the basic and combined loading so as to understand their fatigue crack growth behaviors as well as their fatigue strengths. The tests in this research project include experimental stress analyses under basic and combined loading and fatigue tests under basic and combined loading. The static tests were carried out first to determine the stress concentration factors (SCFs) of the joints, and the peak hot spot stress (HSS) locations where the cracks may initiate. The SCF results are also used to compare with some of the well-established existing SCF equations. In the past decades, many tests on tubular joints had been performed (van Delft et al., 1986; Ritchie et al., 1989; Myers, 1998 etc.), but the 3D crack shapes formed during propagation were scarcely captured in these fatigue tests. Therefore, it is difficult to model the accurate crack surface in finite element models which may produce inaccurate stress intensity factors solution. In order to validate the stress intensity factors along the crack front of the tubular joints for the next phase of the research project, fatigue tests were carried out whereby the 3D crack propagation and profiles were monitored using the Alternating Current Potential Drop (ACPD) technique, and hence the fatigue strengths of these specimens. RG 04/01

To study the feasibility of using the Alternating Current Potential Drop (ACPD) technique to measure the rate of fatigue crack propagation in a plate-to-plate welded joints. RG 32/95

The main objective of the Applied Research Project is to study the parameters influencing the fatigue strength of non-load carrying and load-carrying cruciform filter welded joints. Dual boundary element method has been used extensively for the analysis of these welded joints due to its ability to perform analysis of crack problems in a single-region formulation. RP 54/91