FATIGUE OF THICK-SECTION COLD-EXPANDED HOLES WITH AND WITHOUT CRACKS

— Fatigue tests under spectrum loading were conducted to evaluate hole cold‐expansion in thick‐section open‐hole aluminium alloy specimens, some of which contained residual fatigue cracks before cold expansion. Cold expansion resulted in an increase in life by a factor of about 7. Small residual fatigue cracks did not inhibit the effectiveness of the cold‐expansion process, indicating that it may not be essential to remove such cracks prior to hole cold‐expansion. The increase in life is primarily associated with a reduced crack propagation rate compared with that for cracks from non‐cold‐expanded holes. Cold‐expanded hole fractures displayed a marked disparity in crack depths adjacent to the two faces of the specimens. Considerable differences were evident in crack depths and fatigue crack areas at failure between cold‐expanded and non‐cold‐expanded hole specimens. These findings have ramifications in the damage tolerance assessment of aircraft structures.