Study on the Residual Stress Fields, Surface Quality, and Fatigue Performance of Cold Expansion Hole

Cold expansion is an efficient way to improve the fatigue life of an open hole. Knowing the stress fields of cold expansion hole and influencing factors is very important to key components designing, manufacturing, and fatigue properties assessment. In this article, four finite element models have been established to study the residual stress fields of cold expansion hole, experiments were carried out to measure the residual stress of cold expansion hole and verify simulation results. Four groups of specimens of different cold expansion level are examined by fatigue test. The fracture surfaces of specimens are observed by scanning electron microscope (SEM). The finite element method (FEM) results show, with interference values developing, the maximum values of circumferential residual compressive/tensile stresses increase in oinfiniteo and ofiniteo domain, and higher positive stress values are obtained at the boundary of ofiniteo domain. The effects of friction between mandrel and hole surface and two cold expansion techniques on the distribution of residual stress is local, which only affects the radial residual stress around the maximum value and the circumferential residual stress near hole edge. Residual stress fields varying with plate thickness and distributing along plate thickness are observed too. The compressive stresses on the mandrel entrance face are less than that on mid-thickness and mandrel exit faces. Cold expansion processing can decrease the surface roughness of the hole and improve surface quality. The crack always initiates near entrance face, and the propagation speed of crack along transverse direction is faster than speed along axial direction.