RESIN INFUSION OF SANDWICH STRUCTURES - CORE/SKIN INTERACTIONS AND VOID FORMATION R K Cullen, S M Grove, J Summerscales Advanced Composites Manufacturing Centre, School of Engineering, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, UK. Corresponding author’s email: r.cullen@plymouth.ac.uk SUMMARY This paper presents results of experimental and modelling work exploring aspects of fibre, core and resin interaction during the infusion process. In particular we observe the nature of regions of flow front convergence in areas containing various types of core, such as wood, sealed wood and closed cell foam. Data on comparative resin absorption for the various cores are presented. It is found that sealing porous core materials such as balsa does not prevent the absorption of significant quantities of resin. More importantly, completely impervious cores are unable to absorb either air or resin. The result of this is that air trapped during flow front convergence causes a higher degree of void content in the skin laminate, compared to more porous core materials. These phenomena appear to have attracted little research attention to date, and provide significant challenges for both experimentation and process simulation. Keywords: resin infusion; core materials; sandwich structures; resin absorption; void formation. INTRODUCTION Sandwich construction (thin, stiff skins combined with relatively thick, low density cores) is ubiquitous in virtually all industry sectors. It has been recognised for several years that the core itself can also play an important role in enhancing and controlling the long-range flow of resin in liquid composite moulding (LCM) processes. Commercial forms of core material, such as foams and balsa, are commonly available with features such as holes drilled through-thickness, kerf cuts in one or both faces and separate blocks of rigid core held together with glass scrim. These features are all regarded as providing some degree of ‘flow enhancement’, allowing liquid resin to reach both faces of the sandwich laminate and to flow long distances within the part, sometimes eliminating the requirement (in resin infusion) for a surface distribution mesh. Flow within skin laminate and core is thus complex and three-dimensional, and involves different physical domains, such as porous media and relatively large channels. The likelihood of convergent flow fronts occurring on a variety of scales is much greater than in simple monolithic laminates, and may have important implications for part quality. In resin infusion, flow is further affected by local variations in fibre volume fraction resulting from skin compression, and consequent non-linear effects on permeability. The core material leads to several additional complications in the modelling and control