A finite-element investigation of the interlaminar shear behaviour of non-crimp-fabric-based composites

In this paper the interlaminar shear behaviour of non-crimped-fabric-based composites is investigated by using a finite-element approach. It is intended to provide an understanding of the basic mechanisms which control the NCF behaviour, together with manufacturing guidelines for the fabric structure to optimise the NCF properties. The present approach is based on a bi-dimensional mesoscopic model of a biaxial blanket developed in a previous study devoted to the compressive strength of NCF (Drapier, S, Winsom MR. Finite element investigation of the compressive strength of non-crimp fabric based composites. Composites Science and Technology, 1999:59:1287-97). This through-thickness repeating cell is completed with the proper boundary conditions representative of interlaminar shear loading. It is established that the NCF ILS behaviour is controlled by the development of high shear-strain concentrations induced by the combination of mechanical and mesoscopic geometrical characteristics. These shear-strain concentrations are very likely to lead to local damage that could affect the NCF load-bearing capacity. II is mainly the resin shear behaviour, and to a lesser extent the tow size, which are shown to control the ILS behaviour. Also, the presence of resin layers which can form between the tows during the manufacturing process increases these strain concentrations. From a manufacturing point of view, it comes out from this study that the resin should have high shear stiffness and yield stress, and that tow bunching should be prevented by limiting both the stitching tension and the size of the lows used. Finally, the formation of resin layers should be limited as far as possible. (C) 1999 Elsevier Science Ltd. All rights reserved.