Elastic fracture mechanics analysis of thick-walled curved tubing with a semi-elliptical surface crack by the boundary element method

In this paper, the boundary element method is used to obtain the mode I stress intensity factors (SIFs) for a semi-elliptical crack in thick-walled curved tubing or elbow under internal pressure. A relatively wide range of geometric parameters for the tubing – the bend radius ratio, the cross-sectional radius ratio, and the angular extent of the circular bend – is considered. For each case of the curved tube geometry, a crack of semi-minor to semi-major axis ratio of 0.8, with depth varying from 20 per cent to 80 per cent of the wall thickness at the intrados is analysed. The computed values of the normalized SIFs are shown to be higher than those corresponding to a straight cylinder for the same relative crack depth and cross-sectional radius ratio. They are also found not to vary significantly along much of the crack periphery in the cases considered, increasing rapidly only as the free surface is approached. Furthermore, for a given relative crack size and location, they increase with decreasing bend radius ratio and decreasing cross-sectional radius ratio, but are, however, less sensitive to the angular extent of the elbow.