A finite element simulation of the cold working process for fastener holes

Two-dimensional axisymmetric finite element simulations have been conducted for the cold working of a fastener hole in an aluminium plate. The simulation models the actual cold working process where an oversize mandrel is pulled through the fastener hole. The results of the simulation are compared with a simplified finite element model where the cold working process is reduced to applying a uniform radial expansion to the hole edge. It is shown that substantial differences exist between the finite element simulations; specifically, the simulation of the actual process shows tensile residual radial stresses on the surface of the plate after cold working whereas the simplified simulation shows only compressive ones. Further comparisons are made for the axial deformation of the plate by using the results of an experimental measurement of the surface profile around a cold worked hole. There is good agreement between the finite element and experimental results. The results of this work show that accurate simulations of cold working are necessary if predicted residual stresses are to be used to assess fatigue life.