Computing the Effect of Environmental Damage on Aircraft Structural Integrity

Abstract

This paper studies the combined effect of corrosion and fatigue on the growth of cracks in aircraft and on the effect of skin corrosion and stress corrosion cracking on the load bearing capacity of rib stiffened aircraft wings. In this context it is shown that the growth of cracks from surface pitting, and also from intergranular cracking at a fastener hole, can be accurately computed using the Hartman-Schijve variant of the NASGRO crack growth equation. The examples studied support the lead crack approach, that has been independently developed by the USAF and the Australian Defence Science Technology Group, in which the growth of lead cracks is often exponential. In the case of skin corrosion it is shown that to be consistent with the US Joint Service Structural Guidelines (JSSG2006) assessment of its effect on the load bearing capacity of the wing should involve an assessment of whether at 115% DLL the remaining material exceeds the yield stress of the material.

Management of Airframe In-Service Pitting Corrosion by Decoupling Fatigue and Environment

“…Management of aircraft fatigue and environmental degradation is generally well understood when these aspects are viewed as distinct and separate tasks, e.g., in typical Aircraft Structural Integrity Management Plans (ASIMP) [1]. For example, this is the case for fatigue nucleating from unintentional manufacturing discontinuities, often surface connected, that occur in typical production-quality metallic airframes; and also for assessing the effect of corrosion (material loss) on static strength and stiffness and hence the structural integrity [2].…”