Many manufacturing processes can induce residual stresses in components. These residual stresses influence the mean stress during cyclic loading and so can influence the fatigue life. However, the initial residual stresses induced during manufacturing may not remain stable during the fatigue life. This paper provides a broad and extensive literature survey addressing the stability of surface and near-surface residual stress fields during fatigue, including redistribution and relaxation due to static mechanical load, repeated cyclic loads, thermal exposure and crack extension. The implications of the initial and evolving residual stress state for fatigue behaviour and life prediction are addressed, with special attention to fatigue crack growth. This survey is not a critical analysis; no detailed attempt is made to evaluate the relative merits of the different explanations and models proposed, to propose new explanations or models or to provide quantitative conclusions. Primary attention is given to the residual stresses resulting from four major classes of manufacturing operations: shot peening and related surface treatments, cold expansion of holes, welding and machining.

A literature survey on the stability and significance of residual stresses during fatigue

The effect of cold expansion on improving the fatigue life of fastener holes

A series of experimental investigations concerning the residual stress fields at cold-expanded fastener holes and of the behavior of fatigue cracks at such holes has been conducted. These studies have included measurement of the initial, cold-work-induced residual stress fields at both uncracked and cracked holes and the performance of both constant amplitude and spectrum fatigue crack growth tests.

Experimental investigation on the effects of cold expansion of fastener holes

A closed form solution technique first presented by Hsu and Fonnan for the radial expansion of a fastener hole is extended to include elastic-plastic unloading and therefore the creation of a reverse yielded zone. In addition, the dependence of interface pressure upon interference with an elastic insert is established. Numerous parametric studies are presented to demonstrate the effect of significant model variables and selected example calculations are compared with experimental results.

Elastic‐plastic stress analysis of cold expanded fastener holes

In this article, the effect of interference fit on fatigue life of holed plate of mechanical joints was investigated both experimentally and numerically. In the experimental part, fatigue tests were carried out on the holed specimens of Al 7075-T6 alloy in which oversized steel pins were force fitted to them. These fatigue tests were conducted on open hole specimen and specimens with 1, 1.5, 2 and 4% nominal interference fit sizes at different cyclic longitudinal loads. From these tests the stress-life (S–N) data for different interference fit sizes were obtained. The results show that interference fit increases fatigue life compared to open hole specimens. In the numerical part of the investigation, 3D finite element simulations have been performed to obtain stress (or strain) histories and distributions around the hole due to interference fit and subsequent cyclic longitudinal loading using FEM package. The stress history from finite element (FE) simulation was used to explain the reason for fatigue life improvement in the interference fitted specimens.

An investigation about interference fit effect on improving fatigue life of a holed single plate in joints

An exact elastic-plastic solution for the stresses in an infinite sheet having a circular hole subject to pressure is obtained on the basis of J2 deformation theory together with a modified Ramberg-Osgood law. The sheet is orthotropic but isotropic in its plane. The results are assessed on the basis of Budiansky's criterion for the acceptability of J2 deformation theory. By using exact elastic-plastic stresses, the function connecting the pressure at the hole with the radial enlargement is obtained. Upon release of the pressure, residual stresses around the hole are produced.

Y. C. Hsu

Papers

Elastic-plastic analysis of an infinite sheet having a circular hole under pressure