Simulations Of The Residual Stresses Around Split-sleeve Cold Expanded Holes In TC4 Titanium Alloy

As one of the most effective measures on improving fatigue life of fasteners with holes in aircraft structures, split-sleeve cold-expansion process is the most advanced cold expansion technique in international manufacturing industry of aeronautics and astronautics. In this paper, holes of TC4 titanium alloy were cold expanded at 2%, 3% and 4% nominal interferences respectively, and the photoelastic coating method was used to study the distributions of residual stresses around cold-expanded holes. Two-dimensional finite-element simulations were conducted for split-sleeve cold-expansion processes in order to determine the residual stress fields around expanded holes. The effects of nominal interferences, diameters of original holes, plate thicknesses, and edge distance ratios on the distribution of the residual stress fields were investigated as well.The main work and the achievements are as follows:1. The photoelastic coating method was used to study the distributions of residual stresses around cold-expanded holes at 2%, 3% and 4% nominal interferences respectively. The loads necessary to pull up the mandrel during the cold-expansion processes were recorded.2. Two-dimensional finite-element simulations were conducted to investigate the distributions of the residual stresses around the holes and the loads necessary to carry out the cold-expansion processes at different nominal interferences. The comparisons between the results of finite element simulations and the results of cold-expansion experiments revealed very good agreements.3. The effects of nominal interferences, diameters of original holes, plate thicknesses, and edge distance ratios on the residual stress fields were investigated using the two-dimensional finite-element simulations.