Local Finite Element and Experimental Limit Loads of Cracked Piping Elbows Under Opening Bending

Abstract: Finite element (FE) and experimental data of cracked, 88.9 mm outside diameter, 5.49 mm thick, short radius, carbon steel piping elbows under displacement controlled, opening bending are reported. Short and long defects with depth-to-thickness ratios ranging from shallow to through-wall, axially or circumferentially centred about the bend crown centreline or intrados respectively, are considered.
The FE predicted general deformation mechanisms and overall strain distributions compare well with the experimental observations. Also, the strains agree well with the experimental values away from the defects. However, in the immediate vicinity of the defect, the FE strain data give much more detail about the initiation and spread of plasticity as the loading is increased towards plastic collapse of the component, but specific integration point strain data reveals that the variations are large and that steep strain gradients are evident even within individual elements. This explains the poor comparisons with experimental data in these regions. Using the above type of data, in conjunction with the twice-elastic slope (TES) method for the determination of plastic loads for the cases investigated, it has been shown that values lower than those obtained from similar global measurements (load-displacement plots) are consistently obtained.