Aeroelastic optimization of composite wings including fatigue loading requirements

An analytical model to predict the fatigue life of a composite laminate is formulated. The model calculates stresses in each ply using classical lamination theory, degrades the residual strength using the linear wear-out law and predicts failure based on Tsai Wu failure theory. The cycles to failure are predicted using the updated cycle-by-cycle probability of failure. The predictions are validated for both a constant amplitude and a variable amplitude loading on a Glass/Epoxy laminate. Additionally the analytical model is extended to work with laminates described using lamination parameters instead of ply angles and stacking sequence. The analytical fatigue model is then integrated in the TU Delft aeroelastic and structural optimization tool PROTEUS. A thickness and stiffness optimization of the NASA Common Research Model (CRM) wing has been carried out. Results show that fatigue, strength and stiffness are the design drivers in the aeroelastic optimization of a composite wing. Furthermore, by including the analytical fatigue model instead of using a traditional knockdown factor to account for fatigue, a lighter wing is obtained.