Effect of residual stress on fatigue life of cold expanded fastener holes L. Edwards, A.T. Ozdemir Fracture Research Group, Materials Discipline, Faculty of Technology, The Open University, Milton Keynes, UK ABSTRACT Cold expansion of holes in aircraft structures to combat fatigue is now common practice. Expansion is usually achieved by a commercial split sleeve process using prescribed levels of mandrel interference. A sleeveless method of cold expansion which allows the degree of cold expansion to be infinitely varied in a simple manner has been developed at the Open University, applied to 5mm thick 7050 plate and compared to the commercial split sleeve process. It is shown that whilst both techniques produce significant increases in fatigue life, the commercial process is more effective. Measurement of the residual stress profile produced in each case using a modified Sachs boring technique shows that this is due to the greater compressive residual stress produced.