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.

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