A three-parameter model for fatigue behaviour of circumferential surface flaws in pipes

A three-parameter model, recently proposed by the authors for part-through-cracked round bars, is employed herein to examine the shape evolution of a circumferential external surface defect in a metallic round pipe under fatigue loading. The elliptical-are flaw presents an aspect ratio alpha = a(e1)/b(e1) (a(e1), b(e1) = ellipse semi-axes) and a relative crack depth xi = a/t, where a and t are the depth of the deepest point on the crack front and the pipe wall thickness, respectively. The third parameter of the model is the ellipse shifting s = a(e1)/a, which defines the distance of the ellipse centre from the external boundary of the pipe cross-section. Thick- and thin-walled pipes are considered. Fatigue crack propagation paths in the diagram of alpha against s and xi are numerically obtained for different initial flaw configurations under cyclic bending loading. (C) 2000 Elsevier Science Ltd. All rights reserved.