Fatigue modeling for aircraft structures containing natural exfoliation corrosion

This paper presents the results of testing and modeling studies on the remaining fatigue life of aircraft wing skins containing natural exfoliation corrosion. Dogbone specimens were manufactured from 7075-T6511 upper wing panels containing natural exfoliation. The maximum depth of the exfoliation damage was determined by an ultrasonic non-destructive inspection (NDI). Fatigue tests were carried out under fully reversed constant amplitude loading (R = −1.0), and fractographic analyses were performed to examine the cracking mechanisms in the exfoliation region. Based on the test findings, a simplified fatigue model was developed to estimate the remaining fatigue life of the corroded specimens. In this model, the exfoliation damage was assumed as a surface crack with a depth that was presumably available from an NDI or grindout database. The comparison indicates that the simplified model gave a good estimation for the remaining fatigue life of the naturally exfoliated specimens.