Comparative Study of Prediction Methods for Fatigue Life Evaluation of an Integral Skin-Stringer Panel under Variable Amplitude Loading

The study deals with an integral skin-stringer wing panel made of AA 7475-T7351. DT solutions for fatigue life prediction are based on computational methods. Crack growth is analysed under the flight by flight loading representative for a commuter aircraft. Crack growth predictions are performed by using both the linear damage accumulation principle and the FASTRAN retardation model. Different solutions of crack and structural geometry, which are expressed by the β correction factor related to stress intensity factor assessment, are compared. The predicted crack growth and original data for the integral wing panel are discussed. The influence of geometry correction factors, which are defined by considering different hypotheses of their determination, is not significant for the integrally stiffened panel. In contrast, the retardation effect for the flight by flight loading, investigated alloy and structural part is significant. The FASTRAN retardation model gives underestimated predictions of approximately 10% compared with the experimental data. The reason underlying the increasing difference between the experimental data and numerical predictions of longest crack length propagation is discussed.