JEC COMPOSITES MAGAZINE - Issue #39 - March/April 2008 - 55

Infusion respective X - Y planes, are separated by a plurality of fibres (3) generally lying in a “Z” direction. The overall thickness dimension (d) of the fabric may most usefully be between about 1 or 2 mm up to about 25 or 30 mm, and in some cases even thicker. Frequently, the fibre density for the “Z” fibres may be only a minor fraction of the fibre density of the outer layers (1, 2), but this may also vary according to the architecture and fibre population of the outer layers. The outer layers may range from an open honeycomb structure to a more tightly woven or knitted structure. The IFR™ spacer fabrics for infusion are generally designed to collapse under vacuum pressure, as illustrated in Figure 2, where d is reduced to d’. However, even though collapsed, they are designed such that there remains sufficient mean free path within the collapsed cross-section to facilitate the rapid distribution of resin throughout the structure, including the surrounding and adjacent plies of the entire laminae. The spacer fabric is in the collapsed state at the end of the infusion process and remains collapsed in the final part. Developed in collaboration with World and National Disabled Water Ski Champion, Ann O’Brine-Satterfield, the company’s Sit-Skis enable men and women with a variety of disabilities to pursue the full sport of water skiing from beginner through jump and competition slalom. To date, several hundred skis have been produced and successfully fielded using this technology. In manufacturing the Sit-Skis, the gelcoat is first sprayed into a standard female mould with a 5-cm flange. As shown in Figure 4, unidirectional carbon fibre is laid into the mould, followed by the Polybeam® IFR™. Fig.4: Sit-ski laminate schedule Fig.2: Vacuum collapsed spacer fabric When an IFR™ spacer fabric having a tightly woven or knitted X,Y fascia and resilient Z-direction fibres is used as a lamina between the skin and the core, the resilient nature of the Z-fibres enables “spring back” that enhances the interfacial planarity of the bond line between the core and adjacent laminae, as illustrated in Figure 3. A plain sheet of 1.3-cm foam core precut to fit the mould is then laid in, followed by another ply of the Polybeam® IFR™. Next, the biaxial fibreglass lamina and a semi-rigid gelcoated floating counter tool (float tool) are placed over the ply stack. The term “floating” refers to the free position of the counter tool within the vacuum envelope. The IFR™ extends beyond the float tool to accommodate the resin feed and vacuum port lines. The resin feed and vacuum ports are then appropriately placed and the infusion proceeds. The ski is released at the end of the cycle and trimmed for delivery. Enveloping the core with the spacer fabric lends numerous benefits to the sandwich composite beyond enabling the infusion process. The use of the spacer fabric between the core and adjacent lamina enhances the bond strength at this critical interface by rendering the two surfaces planar while accommodating interfacial inconsistencies and allowing efficient energy transfer through the Z fibres. Fig.3: “Spring-back” enhances interfacial planarity Water ski application By way of example, Liquid Access of Melbourne, Florida, USA, a leader in adaptive water ski design, manu-facturing, and instruction, turned to Polybeam® IFR™ enabled sandwich construction to meet the demands of a unique water ski in a cost-effective manner. The spacer fabric also assures resin flow on both sides of the laminae. A key benefit derived from the use of the IFR™ spacer fabric in this application is that it allows the use of a plain core over an infusion (grooved, perforated, scored) core. This not only eliminates the weight gain and cost associated with an infusion core, but also assures the core properties are maintained. Derived from a recent study using Airex C70.75 core and Ashland AME6000 INF vinyl ester No39 March - April 2008 / JEC Composites Magazine

JEC COMPOSITES MAGAZINE - Issue #39 - March/April 2008

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #39 - March/April 2008