Micromechanics Modeling of Skin Panel with Pitting Corrosion for Aircraft Structural Health Monitoring

Due to the increasing requirements from Aircraft Structural Health Monitoring, it is significantly meaningful to research the impact of pitting corrosion on the mechanical property of aircraft principle structural element. In this paper, micromechanics model of pitting corrosion based on Eshelby-Mori-Tanaka approach has been constructed to analyze the effect of pitting corrosion on structural stiffness. The main aims of this study are to determine the effective stiffness of aircraft skin panel structure under various degree and shape parameter of pitting corrosion. A simple accelerating experiment reveals that aircraft structural aluminum alloy materials are vulnerable to pitting corrosion in severe conditions. The Finite Element models are built to investigate the local stress-strain distribution with three different pits (hemi-spherical, cylinder and box). The effective stiffness of the skin panel with 2024 aluminum alloy or 7075 aluminum alloy has been discussed based on micromechanics model. The results show that structural effective stiffness could significantly decrease with gradual increment of degree of pitting. The variations of structural effective stiffness are relatively bigger for deep hemi-ellipsoidal etch pit (lambda > 1), yet their changes are comparatively smaller for flat hemi-ellipsoidal etch pit (lambda < 1). For the local strain around the corrosion pit, the strain around flat hemi-ellipsoidal etch pit (lambda < 1) is comparatively bigger than deep hemi-ellipsoidal etch pit (lambda > 1). Moreover when value of lambda is approximately 0.3726, the stiffness within etch pit is close to zero. The works presented in this paper can provide a preliminary corrosion prediction model for structural corrosion monitoring.