ABSTRACT
The work described in this paper, concerns the assessment of the effects of cracks on the ultimate load carrying capacity and fracture behaviour of tubular joints. The key aim is to provide guidance on the plastic collapse load of cracked tubular joints to be used in the assessment of defects according to PD 6493/CEGB R6 type failure assessment procedures.
The results of ultimate strength investigations on cracked tubular K joints subject to balanced axial loading, are reported. These studies involve using both the non linear finite element technique and a series of small scale experimental tests at room and low temperatures on joints in both the uncracked and through thickness cracked conditions.
Data on crack driving force parameters, obtained from the FE analyses of the cracked joints, have indicated significant mixed mode I & mode III crack displacements. Level 2 Failure Assessment Diagrams, constructed from the FE J-integral predictions, have confirmed that the standard PD 6493 Level 2 FAD is appropriate for defining limits for safe loading of cracked tubular joints if used with suitable safety factors.
Recommendations to estimate the plastic collapse strength of through thickness cracked K joints, based on the FE and experimental data, are outlined and supplemented by data on stress intensity factors.
Practical implications of the present and previous data with regard to application of the failure assessment diagram approach and effects of mixed mode crack loading are discussed.
