CIRCUMFERENTIAL SURFACE FLAWS IN PIPES UNDER CYCLIC AXIAL LOADING

The behaviour of a circumferential external surface flaw in a metallic round pipe under cyclic axial loading is examined. The defect is assu med to present an elliptical-are shape with aspect ratio alpha = a/b ( a, b are the ellipse semi-axes), whereas the relative depth xi of the deepest point on the front is equal to the ratio between the maximum c rack depth, a, and the pipe wall thickness, t. Thick- and thin-walled pipes are considered. The propagation path of the surface flaw is obta ined in the diagram of cc against xi through a two-parameter theoretic al model. A simplified model (iso-K criterion) is also applied to pred ict the stable crack growth. Finally the unstable crack growth process is analysed. (C) 1998 Published by Elsevier Science Ltd. All rights r eserved.