Bleeder Thickness Optimization for Controlling Resin Content in Thick Laminated Composites

Thick laminated composites are manufactured commonly by vacuum bagging of fiber-resin mix or prepregs on a suitable mould and, subsequently curing the lay-up at high temperature and pressure in an either autoclave or oven. At these pressures and temperatures, excess resin bleeds out of the lay-up during the initial stages of the curing. The amount of resin bleed is also a function of the bleeder parameters. Bleeder is a porous fibrous media that is laid around stacked lay-up to provide pathway for volatiles as well as absorb and hold the excess resin. Thicker or highly porous bleeders generally absorb higher amount of resin resulting in a resin starved laminate whereas very thin or denser bleeder leads to resin-rich areas within the laminate. It is thus important to select optimum bleeder parameters in order to achieve a desired resin volume fraction and its uniformity in a composite laminate upon curing. This paper details the simulation of the manufacturing of a thick laminated composite, where a significant amount resin is likely to flow out of a curing lay-up, leading to an optimization of bleeder parameters. A coupled, transient FE analysis is conducted that involves not only the heat transfer, resin flow and cure reaction kinetics simulation but also the simulation of the compaction of the wet laminate and the bleeder layers until the laminate is fully cured. Details of an experiment conducted to find compression characteristics of bleeder of varying thickness and the number of layers and related data that was used in the FE analysis are discussed in this paper. It is found that bleeder thickness significantly affects the amount of resin bleeding out from the curing laminate. As a result, the resin volume fraction of the laminate is affected. Case studies carried out to highlight the optimum bleeder thickness for a lay-up, and the method used to decide the thickness and the number of bleeder layers, are presented.