Abstract:
This report investigates a new fatigue life enhancement process called Stress Wave Cold Working (SWCW) and compares it to the conventional split sleeve method for fastener holes in high-strength aluminum aerospace alloys, with a primary goal of using post-yield Finite Element Analysis to understand the resulting residual stress states and to optimize process parameters. The study relied on extensive nonlinear FEA using the LS-DYNA software suite, including LS-PrePost for modeling and LS-OPT for design optimization. The Finite Element models simulated the distinct phases of the SWCW process: indentation, material relaxation (springback), and final hole trimming followed by another relaxation. Both 2D axisymmetric and full 3D Finite Element models were created, incorporating nonlinear material behavior with true stress-true strain data and isotropic hardening assumptions. The FEA methodology was first validated by comparing simulation results of residual hoop stresses with experimental X-ray and neutron diffraction data, which confirmed that 3D models provided the best correlation. The validated FEA approach was then used to optimize the SWCW indenter shapes and process parameters to maximize the resulting deep compressive residual stresses, confirming the new method's superior and more uniform through-thickness stress distribution compared to the split sleeve method.
