Observations from the Inspection of an Aged Fuselage Panel

Abstract

An aged aluminum 7075-T6 fuselage panel was inspected for evidence of time-based degradation. Although corrosion pitting and intergranular attack (IGA) were the focus of the investigation, evidence of cracking and fretting wear were documented as well. The investigation was performed at several levels of magnification through the use of magnifying glasses and stereoscopic, metallurgical, and scanning electron microscopy. Comparisons were made for the various levels of investigation. Significant levels of corrosion or cracking damage were discovered in approximately 40% of the fastener holes during the initial low-magnification inspection. Several fastener holes were investigated via sectioning. These specimens were examined with metallurgical and scanning electron microscopes. This investigation revealed tunneling pits, pitting in the countersink region, IGA, cracking and pitting in and away from fastener holes, as well as fretting within the fastener holes and on the faying surface of the panel. This work is significant and applicable to the structural integrity of aging aircraft; it lends credence to the multitude of past and present efforts that focused on time-based degradation of aging aircraft. Teardown inspections emphasize the need for continued research and careful management of aging aircraft fleets.