INTERNATIONAL JOURNAL OF FATIGUE, vol.17, no.8, pp.587-595, 1995 (Journal Indexed in SCI Expanded)
Cold expansion of holes in aircraft structures to combat fatigue is now common practice. The most effective and widely used method in the aircraft industry is the split-sleeve process. Expansion is achieved using commercially available equipment, which includes a lubricated sleeve and prescribed levels of mandrel interference. The optimum degree of mandrel interference for a particular application will however depend on the local geometry of the component, and fatigue life predictions of structures containing such expanded holes rely critically on estimates of the residual stress distribution surrounding the hole. The residual stress distributions of approx 9.52 mm (3 in) holes in high-strength Al alloy (7050) specimens that have been expanded using a commercial split sleeve method have been measured using X-ray diffraction and a modified Sachs method that has been validated using neutron diffraction. These techniques have enabled the three-dimensional stress distribution through the thickness of the plate to be determined. A substantial through-thickness effect has been established and is shown to affect the fatigue performance of the expanded holes. 13 ref.