Environment Spectra and CPC Effects on Corrosion/Fatigue

Fatigue crack propagation (FCP) can be affected by environment in a variety of ways, each of which may compromise the aircraft’s structural integrity.[1] Corrosion occurring during ground basing can alter the initial discontinuity state (IDS) and create a modified damage state (MDS), which may promote fatigue crack formation and growth during flight. This corrosion may also cause stress enhancement due to material thinning, or even retardation of fatigue crack growth if sufficiently rigid corrosion product forms in a crack. Also, atomic hydrogen produced on the alloy surface during localized corrosion may enter the metal and contribute to damage on subsequent mechanical loading. This corrosion fatigue (or environmental fatigue) problem has been the objective of considerable scientific study over the past 30 years, but important uncertainties hinder accurate rate and life prediction of operating airframe components. These uncertainties are the motivators behind this project whose goals are to improve the laboratory characterization, mitigation methods, basic understanding, and modeling of FCP laws necessary to manage fatigue in aerospace aluminum alloy structures. The work focuses on environment-fatigue interactions and deals with major issues associated with the effect of unique environments and corrosion prevention compounds (CPCs) on FCP rates in aluminum alloys