The effect of high compressive loading on residual stresses and fatigue crack growth at cold expanded holes

Abstract

The effect of monotonic compressive loading on the residual stresses developed at cold expanded fastener holes has been investigated using the neutron and X-ray diffraction techniques. Monotonic loading models the effect of the peak of a fatigue loading sequence experienced before a crack is initiated. It was found that the compressive loading significantly affected the residual stress distribution. A low load relaxed only the stresses near to the bore of the hole, whereas a larger load affected the stress distribution over a greater area. Residual stresses measured at the mandrel entrance face were more affected by the compressive loading than the residual stresses measured at the other segments of thickness. The comparison between the X-ray and neutron diffraction results showed that the techniques complemented each other well, enabling a three-dimensional residual stress distribution to be derived. This distribution was used for modelling the effect of compressive loading on fatigue crack growth, using a linear elastic fracture mechanics approach and assuming a stabilized residual stress field.