Assessment of partly circumferential cracks in pipes

摘要

This paper presents a new method for predicting the stress intensity factors around a partly circumferential elliptical surface crack in a pipe. The solution is applicable to structures with both double and single curvature. The technique involves a conformal transform in conjunction with a semi-analytical approach that uses a finite element model to obtain the stress distribution in the undamaged structure. By using an indirect methodology, the model development is simplified and the analysis time is minimised. As such a coarse mesh can be used to obtain solutions for multiple crack geometries. Three examples are presented to verify this methodology. They include a partly circumferential elliptical crack under uniform tension, a pipe subject to a residual stress field, and a problem involving double curvature. For simple loading the solution compares with other published solutions to within 5 percent for an external crack, and to within 15 percent for an internal crack. For more complex loading conditions the majority of the solutions were within 5 percent of other published results at the deepest point, and most solutions at the surface agreed to within 15 percent. For the problem involving double curvature, the solutions agreed to within 4 percent for an internal crack, and 15 percent for an external crack.