Life Prediction of Aircraft Aluminum Subjected to Pitting Corrosion Under Fatigue Conditions

Aircraft aluminum alloys suffer material degradation which affects structural integrity due to the complex pitting corrosion-fatigue process resulting from the operating environment. There is a need for developing simple models to predict the life of such materials in the preliminary design of aircraft. This paper briefly reviews major corrosion-fatigue models, and presents a simple deterministic model that considers the simultaneous existence of cyclic stressing and corrosive conditions. The model that takes into account the influence of cyclic stresses on pitting is based on the total-life approach, which considers all stages of the process, and is tested on aircraft aluminum alloy 2024-T3. The results indicate that the presence of a corrosive environment accelerates the fatigue damage even at nominal stresses. The crack initiation from pit sites is extremely fast at high stress levels and can occur even from relatively small pits. At lower stress levels, the crack initiation stage, in comparison with crack propagation, consumes a major part of the material's life. The life predictions obtained from the model are in reasonable agreement with the limited experimental data available from literature.