A Demonstration using Low-kt Fatigue Specimens of a Method for Predicting the Fatigue Behaviour of Corroded Aircraft Components

Corrosion is well known to reduce the structural integrity of aluminium alloy aircraft components. In addition, it can cause early fatigue failures in components in which fatigue is not considered to be a life limiting factor. This is because corrosion damage, such as corrosion pits, is up to 100 times the size of the inclusions intrinsic in most aerospace aluminium alloys. The trailing edge flap lug of the F/A-18 Hornet aircraft is an example of an unexpected failure due to corrosion damage. In this report a Monte Carlo model is developed to simulate this phenomenon. This model predicts the fatigue lives of corroded and uncorroded specimens of the aluminium alloy 7010-T7651. It does this using high-quality fatigue crack growth data for this alloy from a previous research project (SICAS) combined with probability density functions for size of the corrosion pits and inclusions in this alloy. The distribution of the predicted fatigue lives is an excellent match for that observed in the SICAS project. The model was then extended to predict the location of fatigue failures. It showed that with good laboratory data the model could very accurately predict the location and life of pittinginduced fatigue failures. RELEASE LIMITATION Approved for public release