JEC COMPOSITES MAGAZINE - Issue #43 - September 2008 - 60

KNOW-HOW Materials g…/… Development of helicopter blade coatings polyurethane-butadiene and high-performance polyurethane resin matrices capable of generating mechanically robust and erosionresistant elastomer frameworks were used. Conductive resin formulation Basic erosion-resistant compositions using polybutadiene, polyurethane resins and polyester fibres were moulded and cured in 2.54 mm sheets. The initial aim was to establish how carbon filling (10-50%) affects the overall mechanical properties of elastomers and subsequently optimizes their electroconductive properties. Attaining high heat conductivity using randomly oriented conductive fillers is a very challenging task. So, the use of a small test panel made of elastomers incorporating oriented carbon rods was proposed. The use of ordered systems to achieve high conductive characteristics, for example, as a result of the orientation induced by the extrusion process has been reported in the literature [11]. This approach was extended to the aligned array of carbon nanotubes responsible for the preferential electrical and thermal gradients along orientation vectors. Layer 2 (thermal conductivity) A carefully chosen thermo-conductive filling component compatible with selected resin compositions was used. This component has optimal conductive properties and effectively promotes de-icing of the boot while helping maintain the material’s integrity. Layer 3 (electrical conductivity) An electrical grid/wire (loop) is inserted in the package to provide current throughout the length of the boot. It is possible to change current and voltage and simultaneously change thermal conductivity. Layer 4 (adhesion) Adhesive enhancement additives were used to secure tight binding of the boot elements to the reinforced-epoxy rotor blade. These elements also ensure cost-effective and prompt field replacement of the boot at the end of a service period. Optimized combinations of layers 1 through 3 were cured in moulded flat sheets of 1.27-2.54 mm thickness. The boot prototype was designed as a composite system with a steel shim (for better thermal conductivity and structural reinforcement) sandwiched between two prefabricated elastomer sheets. Test coupons of the boot were investigated at certified facilities (Wright-Patterson Air Base and Neutzch) for erosion resistance and thermal conductivity. NAT’s state-of-the-art boot material concept addresses all the critical technical and economical requirements set out by the Navy, namely: - erosion and wear resistance, - thermal conductivity and stability, - hydrolytic resistance along with hydrophobicity, - low weight, - cost-effective field replacement, - high adhesion to substrate, - low manufacturing cost, - based on commercially available components. Experimental conformation work An experimental conformation work was carried out to verify the model proposed in figure 5. To heat the top layer of the erosionresistant boot element, a galvanized steel grid was used as a built-in heating element residing on the inner surface interface of the heatconductive elastomer sheet. To optimize heat transfer, insulation was provided by wrapping a base layer of the non-conductive elastomer produced using the same basic formulation, in a 3-layer sandwich composite. The base layer also provided an optimum interface with the rotor blade substrate and met the adhesive requirements (see figure 6). Fig. 6: Rotor blade V 22 osprey Fig. 5: Boot design concept 1. Erosion-resistant, heatconductive elastomer layer 2. Heat-conductive reinforcing metal grid 3. Insulating elastomer layer 4. Adhesive 5. Rotor blade substrate The high-speed boot pultrusion process is described in figure 7. Practically speaking, a KaZaK Composites installation was used to manufacture a helicopter leading edge using the “TEM” development technology. In this installation, dry polyester fibre (2) is placed on the frame (1) and pulled out to two impregnation baths (3, 4, 5). The first bath (3) contains polybutadiene resin and the second bath (5) contains polyurethane resin. Carbon fibre is added in the second bath (5). The mass melts in an electrical heating chamber (6) and then passes through a die (7) to produce the boot. The boot is rapidly cooled in a cooling chamber (8) and then pressed by two hydraulic cylinders (9, 10). A mandrel (11) is installed JEC Composites Magazine / No43 September 2008

JEC COMPOSITES MAGAZINE - Issue #43 - September 2008

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #43 - September 2008