Hybrid processing of thick skins for honeycomb sandwich structures

Carbon–epoxy prepregs are generally used to form the skins of honeycomb sandwich structures used in aerospace or racing yachts. For some applications, it is desirable to increase the thickness of the skins. In order to achieve an ideal core pressure level during cure for maximal skin–core bonding, the issue of air extraction from the honeycomb cells through the skin during processing thus becomes critical, in particular if vacuum only processing is used. In the present work, partially impregnated prepregs, called semipregs, having high initial transverse permeability to air, are combined with traditional prepregs to form a hybrid skin. Results are presented on the pressure change inside the honeycomb cells and the skin permeability to air during cure, as well as on skin–core adhesion. The final sandwich quality is assessed and found to be comparable to that obtained with prepreg skins.