Effect of residual stresses and their redistribution on the fatigue crack growth in cold-worked holes

The cold-expansion process is widely used to enhance the fatigue life of structures with fastener holes. Various studies assert that the cold-expansion improves the fatigue strength of fastener holes; however, the improvement of fatigue life is difficult to quantify. The influence on fatigue life of cold-worked hole in a 6061-T6 alluminum allosy was studied by numerical and experimental tests. Fatigue crack growth tests were carried out to find the crack length and growth rates of crack propagating from hole edge. Thus, the cold-expansion process was modeled with a Lagrangian implicit code for metal forming to obtain the residual stress field. Progressive crack growth along the observed fatigue path was simulated as part of the analysis to observe the residual stress redistribution due to the crack propagation. The behavior of a fatigue crack in the presence of the hoop residual stress is discussed.