Behaviour of core materials during resin transfer moulding of sandwich structures

The use of sandwich structures is a well documented and accepted engineering approach. Composite sandwich structures, consisting of a fiber reinforcement impregnated with resin surrounding a foam core, can be used to improve bending stiffness, thermal insulation, and specific mechanical properties at relatively low cost. Such materials can be produced by the resin transfer moulding (RTM) process by incorporating the core within the fiber preform before resin injection. However, this process may result in a number of defects including core shifting, deformation, and delamination, which will have a detrimental effect on mechanical performance. The occurrences of these defects have been studied as a function of the fiber volume fraction, resin pressure, and skin thickness. Delamination between the skin and the core is also a major concern, although this can be controlled by abrading the core surface before moulding. The effect of process parameters on moulding quality and, in particular, the response of the core during moulding and the subsequent delamination resistance of the reuslting sandwich structure are presented. This is applied to a range of commercially available core materials. Core materials studied include PVC, polyurethane and balsa foams.