Investigations into various methods of liquid injection to achieve mouldings with minimum void contents and full wet out

Much potential and interest exists for processing composite structures using liquid injection due to the lower cost possibilities when compared to that for wet hand lay-up autoclave techniques. The specification, however, for high-performance structures requires low void contents below 1% and high fibre volume fractions in excess of 50%, both of which are currently possible with existing autoclave technology. This investigation reports on various methods for resin transfer and eating to maximize fabric wet out and minimize void content. The initial tests were conducted using a volume fraction of 18% for plain weave glass fibre to identify any variations in processing through visual quality and mechanical properties. Composite plaques of 50% fibre volume were then manufactured using radial and peripheral gating from which the differences in wet out, void content, and process injection times are reported. This investigation concludes that peripheral gating using vacuum impregnation produced the optimum composite structure in terms of void content and visual transparency. This method of gating also achieved the lowest injection time during the impregnation stage of processing for fibre volumes of 18%. Radial gating failed to completely fill the reinforcement at 50% fibre volume using the same thermal and pressure conditions as peripheral gating. Thickness variation studies also revealed inadequate mould tool stiffness when subjected to pressure during resin injection. (C) 1998 Elsevier Science Limited. All rights reserved.