Investigation of Crack Nucleation in the Vicinity of Cold-Worked Fastener Holes

摘要

During one of the scheduled inspections conducted within an aircraftrnfull scale testing, a single crack was inspected at the side windshieldrnretainer, between the window cutout and the nearby fastener hole. Thernfastener hole was cold-worked during the aircraft assembly process, tornenhance its expected fatigue lifetime. The crack was detected and verifiedrnby means of two different NDI methods, namely, High Frequency EddyrnCurrent (HFEC) and detailed visual inspection. As part of a root causernanalysis conducted, a detailed finite element model was constructed. Thisrnmodel simulates the cold-working procedure that was applied to thernretainer during assembly, as well as the applied loads during typical flight.rnThe finite element analysis implied that the cold-working process at thernfastener holes induced residual tensile stress in the nearby cutout radius.rnCombining this effect with the typical operating loads acting on thernwindshield retainer leads to crack nucleation at the window cutout. Thesernpreliminary conclusions were validated by means of fractographic analysis.rnHowever, the cold-working process has some beneficial effects. The crackrnpropagation was further monitored during test, and it was concluded thatrnthe cold-working process slowed the crack growth rate of the continuingrndamage from the fastener hole up to complete failure of the retainer, asrncompared to predictions.