Aspects of the compaction of composite angle laminates: An experimental investigation

To date, a fundamental knowledge of flow and compaction mechanisms has been gained by the study of laminates with simple geometries. Since most of the applications of composites involve complex shapes, it is necessary to study their compaction behaviour to develop more accurate theories. In this paper, the flow and compaction of angle laminates, manufactured with the autoclave process, was studied for two carbon-epoxy composites (AS4/3501-6 and AS4/8552) under a wide range of bagging and moulding conditions. The variation of the laminate thickness, mass and local fibre volume fraction was investigated. The final thickness of the laminate was uniform in the flat section. It was found that laminate defects (voids, wrinkles, etc.) are localized at the corner. The low resin viscosity AS4/3501-6 laminates exhibit more resin loss than the high resin viscosity AS4/8552 laminates. In the flat section, the total compaction strain under bleed conditions is principally caused by percolation flow for AS4/3501-6. For AS3/8552 the total compaction strain is a combination of percolation and compaction strain caused by the collapse of voids introduced during lay-up. At the corner, high strains due to sheer flow are observed for a [90 degrees] lay-up, creating corner thinning for a convex tool and corner thickening for a concave tool. Finally, the fibre volume fraction gradient measured through the thickness and in the longitudinal direction confirms that under bleed conditions, net percolation of the resin occurs from the tool to the bleeder. Under no-bleed conditions, a small amount of internal percolation can be observed from the corner to the flat section of the angle.