Creep relaxation of residual stresses around cold expanded holes

The cold expansion of fastener holes in aircraft components is a standard t echnique to improve fatigue life. There is concern that the beneficial resi dual stresses arising from cold expansion may relax due to creep. This pape r describes experimental measurement and finite element prediction of cold expansion residual stresses and their redistribution after creep, with and without additional mechanical load. Experimental measurements of near-surfa ce stresses used an X-ray diffraction technique while average through-the-t hickness stresses were measured using a new method based on Sachs' boring. This new method allowed non-axisymmetric residual stresses to be measured, as was the case when creep relaxation occurred with mechanical load. Axisym metric and three dimensional finite element analyses were used to predict t he stress distribution through the thickness of the component showing good agreement with measurement. Creep relaxation of residual stress does indeed occur, but some benefit of the cold expansion remains, particularly when c reep relaxation is combined with the application of mechanical load.