The Influence of Finite Three-Dimensional Multiple Axial Erosions on the Fatigue Life of Partially Autofrettaged Pressurized Cylinders

Abstract

Erosion geometry effects on the mode I stress intensity factor (SIF) for a crack emanating from the farthest erosion’s deepest point in a multiply, finite-length or full-length eroded, partially autofrettaged, pressurized, thick-walled cylinder is investigated. The problem is solved via the FEM method. Autofrettage, based on von Mises’ yield criterion, is simulated by thermal loading and SIFs are determined by the nodal displacement method. SIFs were evaluated for a variety of relative crack depths, a/t=0.01-0.30 and crack ellipticities, a/c=0.5-1.5 emanating from the tip of the erosion of various geometries, namely, (a) semi-circular erosions of relative depths of 1–10% of the cylinder’s wall thickness, t; (b) arc erosions for several dimensionless radii of curvature, r′/t=0.05-0.3; and (c) semi-elliptical erosions with ellipticities of d/h=0.5-1.5. In the cases of finite erosions, the semi-erosion length to the semi-crack length, Le/c, was between two and ten, erosion angular spacing, α, was between 7 and 120 degrees, whereas percent autofrettage investigated included 30%, 60%, and 100%. The normalized SIFs and the normalized effective SIFs of a crack emanating from the farthest finite erosion are found to rise sharply for values of Le/c<3. Both the normalized SIF and normalized effective SIF values are mitigated as the amount of partial autofrettage increases with the most rapid decrease occurring between 0–60% autofrettage. The purpose of this study is to detail these findings.