The Influence of Multiple Axial Erosions on the Fatigue Life of Autofrettaged Pressurized Cylinders

Abstract

Erosion geometry effects on the mode I stress intensity factor (SIF) for a crack emanating from an erosion’s deepest point in a multiply eroded, autofrettaged, pressurized, thick-walled cylinder are investigated. The problem is simulated as a two-dimensional problem and is solved via the finite element method. Autofrettage, based on von Mises yield criterion, is simulated by thermal loading and SIFs are determined by the nodal displacement method. SIFs are evaluated for a variety of relative crack lengths, a0/t=0.01–0.45 emanating from the tip of erosions of different geometries, namely, (a) semi-circular erosions of relative depths of 1–10 percent of the cylinder’s wall thickness, t; (b) arc erosions for several dimensionless radii of curvature, r′/t=0.05–0.4; and (c) semi-elliptical erosions with ellipticities of d/h=0.5–1.5, and erosion span angle, α, from 6 deg to 360 deg. The effective SIF for relatively short cracks is found to be increased by the presence of the erosion, which in turn may result in a significant decrease in the vessel’s fatigue life of up to an order of magnitude. Deep cracks are found to be almost unaffected by the erosion.