Delamination Control of Composite Rotor Hubs

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Abstract
Methods for controlling free‐edge delamination considered in this study include changing the ply stacking sequence, minimizing Poisson's ratio mismatch, and adding an adhesive layer to the laminates. S2 glass‐laminates were used to investigate the effect of these parameters on delamination strength. The finite‐element method was employed to evaluate the interlaminar stress and strain energy release rate. From analytical and experimental results, it is concluded that with a reduction in the Poisson's ratio mismatch between plies, the interlaminar stress can be reduced and the delamination strength can be significantly increased. Also, proper placement of an adhesive layer in glass laminates, as in graphite/epoxy laminates, can significantly increase the delamination strength. However, unlike graphite laminates, glass laminates with an adhesive layer delaminate before final failure. Finally, a method to predict the onset of free‐edge delamination strain, which accounts for the ratio G II /G I on interlaminar fracture toughness Gc , is proposed.