Assessment of semi-impregnated fabrics in honeycomb sandwich structures

Semi-impregnated fabrics, or semipregs, are fabrics alternating dry and resin impregnated areas along the fibre bed surface. Due to their increased initial through thickness permeability to gas flow, these could constitute an alternative to prepreg in the skins of vacuum-bagged honeycomb sandwich structures, reducing the pressure in the honeycomb. The semipreg through thickness air permeability before cure is measured and is approximately three orders of magnitude higher than that of a unidirectional prepreg impregnated with the same resin. A model is proposed for the air permeability change during cure, as dry areas get infiltrated. Due to resin pouring inside the honeycomb cells, this type of semipreg is viable as a skin only if combined with a material that has low permeability to resin, e.g., a prepreg.