Corrosion enhanced fatigue and MSD

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Corrosion enhanced fatigue and MSD

Wei, R.P. / Harlow, D.G.

Multiple site (fatigue) damage (MSD) and its impact on the structural integrity (or safety of flight) of aging aircraft has been well recognized. Research to date has focused upon fracture mechanics based analysis and experimentation for the consequences of MSD. The impact of corrosion on the early onset of MSD, and the need for quantitative methodologies to predict the evolution and distribution of damage and MSD, on the other hand, are not fully appreciated. In this paper, the mechanism for pitting corrosion in airframe aluminum alloys and the influence of pitting on the onset of fatigue cracking are briefly reviewed, and the influence of localized corrosion on the evolution of MSD is discussed. A mechanistically based probability model for corrosion and corrosion enhanced fatigue crack growth and its application in predicting the probability of occurrence (PoO) of damage are summarized. The use of the PoO in a methodology to assess the onset and severity of MSD is demonstrated using teardown data from a Boeing 707 and two AT-38B aircraft.