The influence of preform joints on the processing of RTM composites

In order to develop preforms for large complex parts capable of meeting the demands of global and local loading conditions, resin transfer moulded parts are typically broken down into multiple elements. A separate preform is developed for each of these sub-sections, which are then assembled in the mould cavity and combined by the moulding process. While the decomposition of a structure into sub-sections eases the burden on the preforming operation(s) to form the desired shape with the appropriate microstructure, it also raises the issue of joining these multi-element preform sections. In previous composites applications, the presence of a joint was traditionally considered only in terms of its influence on the performance of the part, since the fibre and resin were already combined into pre-impregnated tape. However, resin transfer moulding (RTM) is a two-step process: fibre preforming followed by resin impregnation and cure. Since the resin must flow through the preform and wet-out the individual fibre bundles, the inclusion of a preform joint in the design of an RTM part's microstructure must be considered in terms of processing (resin flow and wet-out) as well as performance. In this paper we examine the influence of preform joint on resin flow through both computational and experimental approaches. The implications of such joints on the design and processing of RTM parts is discussed.