Finite element analysis of the residual stress by cold expansion method under the influence of adjacent holes

The body of aerospaceship has a lot of fastener holes. Under various situations these holes go through external forces which cause a tensile stress on the surface which leads to the failure of a material in the end. In this respect, the cold expansion method is one of the widely used methods with the shot peening method to improve the fatigue behavior of materials used in aerospace industry, and such improvement is due to the compressive residual stress developed when a tapered mandrel goes through the fastener hole a little smaller than the mandrel. Despite its great importance in the aerospace industry, little attention has been devoted to the accurate modeling of the cold expansion process. The residual stress distribution by cold expansion is varied from such parameters as the expansion rate, the direction of inserting mandrel, material properties, and so on. This study is devoted to the modeling and the simulation of the residual stress resulting from the cold expansion of two adjacent holes in these two cases: the simultaneous cold expansion and the sequential cold expansion. From the comparison of these two cases, it has been found that the simultaneous cold expansion of two adjacent holes lead to much higher compressive residual stress than the sequential cold expansion.