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 assumed 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 crack depth, a, and the pipe wall thickness, t. Thick- and thin-walled pipes are considered. The propagation path of the surface flaw is obtained in the diagram of cc against xi through a two-parameter theoretical model. A simplified model (iso-K criterion) is also applied to predict the stable crack growth. Finally the unstable crack growth process is analysed. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.