Nature and distribution of corrosion fatigue damage in the wing-skin fastener holes of a Boeing 707

摘要

A more comprehensive metallographic examination and statistical analysis of damage in the fastener holes of the lower-wing-skin panels from a B707-321B aircraft that had undergone 24 years of commercial service was conducted. The aircraft had accumulated 57,382 flight hours and 22,533 flight cycles before being disassembled for a teardown inspection as a part of the J-STARS (Joint Surveillance, Target and Attack Radar Systems) program of the United States Air Force. The metallographic examinations included optical microscopy of the fastener holes at magnifications up to 300X, and serial sectioning and scanning electron microscopy of selected areas of two fastener holes. The extent and size of damage were found to be much more extensive than that indicated by the original J-STARS analyses, with some holes showing up to 68 cracks. Damage had resulted from localized corrosion (pitting) and subsequent corrosion fatigue cracking, and conformed to a distribution estimated from a mechanistically based probability model. The serial sectioning results and the need for further improvements of the model are discussed in relation to the development of quantitative methodologies for life-cycle design and management of aircraft.