Scientific advances enabling next generation management of corrosion induced fatigue

Recent work on microstructure-scale crack propagation from corrosion damage on a 7000-series alloy in realistic airframe environments is reviewed and its pertinence to airframe prognosis established. The impact of corrosion damage can be accurately modeled by assuming formation life fraction is nil, long crack growth rates, and linear elastic fracture mechanics. An empirically validated corrosion modified-equivalent initial flaw size distribution was established by “back calculation” from measured-total fatigue life; serving as a quantitative descriptor of the deleterious effect of corrosion on fatigue and an initial flaw size input to fracture mechanics modeling. High fidelity characterization of the corrosion pit and fracture surface, coupled with finite element analysis, validated the crack formation and micro-structurally small crack propagation assumptions inherent to fracture mechanics modeling. A large-beneficial effect of low-temperature loading environment was observed; incorporation of this behavior into airframe prognosis could substantially reduce the inspection burden.