Projected Area Approach For Pitting Corrosion Fatigue Life Prediction

The aluminium alloy widely used in the aircraft structures was sensitive to the corrosive environment and the synergetic effect of corrosion with fatigue loads has a direct influence on the aircraft structural integrality and safety. There were various types of corrosion damage and pitting corrosion is one of the main corrosion models on the aircraft structures in servicing. The study on the torn-down aircraft structures and pre-corroded fatigue experiments show that fatigue cracks were initiated from the pitting and there was a significant relation between the appearance of pitting and the reduction of fatigue life, so there is important research value in the pitting corrosion fatigue.In this thesis, the fatigue life models in existence was reviewed and summarized in briefly. The data of material corrosion experiments and torn-down aircraft structures were analyzed and the geometrical characteristics of pitting corrosion of aluminum alloy parts of aircraft were studied. The projected area approach for pitting corrosion fatigue life prediction was put forward. In this approach, the projected area of the corrosion pit was used as the metric for corrosion damage and one model for calculating fatigue notch factor was put forward based on the Murakami's theory and then the pitting corrosion fatigue life of structures can be predicted with the nominal stress approach and based on S-N curve in the dry environment. The model was verified by the experimental results of 2024-T3 and 7075-T6 Al alloy pre-corroded specimens. It shows that the fatigue notch factor and fatigue life predicted by the presented model are good agreement with the experimental results.