Honeycombs aramid

The prices of sandwich composite cores (Figure 2.15) range from 1 (reference) for balsa to 5 for the aramid honeycombs. 

The aramid honeycombs, for example Nomex, generally have ... 

Oriented CF/epoxy composite chassis—improved energy absorption Epoxy/glass faced aramid honeycomb for monorail Improved strength and dielectric properties over GFRP Epoxy/CF sound boards as facings for violins... 

Figure 8.44. Evolution of reflection coefficient (dB) vs frequency for a polj yrrole impregnated aramid honeycomb. The curve (a) is related to basic material and the curve (b) is related to the same one impregnated with an epoxy resin.

Aramid honeycombs find use in the fields of aerospace, transport equipment, etc. Aramid honeycomb sheets comprising a nylon-type resin, particularly a p-aramid honeycomb resin, have flame retardant, tough and other excellent properties required for a honeycomb core structure. However, the method of fabrication of aramid honeycombs is a rather complicated process. The process is described in detail in the literature. ... 

P.-Y. Lin. High shear modulus aramid honeycomb. US Patent 5 137 768, assigned to E. I. Du Pont de Nemours and Company (Wilmington, DE), August 11, 1992. 

K. Nomoto. Aramid honeycombs and a method for producing the same. US Patent 6 544 622, assigned to Showa Aircraft Industry Co., Ltd. (Tokyo, JP), April 8, 2003. 

Apart from the normally accepted textile products, heat and fire resistant textiles find use in engine insulation (e.g. ceramic stractures around combustion chambers), fuselage acoustic iusulatiou (e.g. glass fibre-based battiugs iu FR polymeric film containers), reinforcements for composites (e.g. carbon fibre reinforcements for major stmctural elanents), aramid honeycomb reinforcanent for wall and floor stractures. 

Aramid honeycombs are normally formed into hexagonal shaped cells for optimum mechanical properties. It is also possible to over expand the material so that the cells become rectangular in shape. Over-expanded honeycomb has improved drapability for use in production of curved sandwich structures. 

Woven carbon fiber reinforced phenolic skins bonded to an aramid honeycomb are made by Hexcel for the flooring in the cabin and flight areas of Airbus aircraft (Aerospatiale has a 37.9% stake in the Airbus consortium). 

Using factorial analysis, samples of the mohair/silk (MS) fabric were variously treated with a selection of flame retardants, back-coating formulations and adhesive, mounted on a typical aramid honeycomb board specimen, and each composite was tested using cone calorimetry at the preferred heat flux of 50 kW (shown to be equivalent to the 35 kW m flux used in the OSU calorimeter). 1 An optimum combination of flame retardant, back-coating and adhesive at specific application levels was found to yield the lowest heat release values, and this system was applied to each of the above six fabrics. Testing in both the OSU at 35 kW m heat flux and at 50 kW m" in the cone calorimeter gave the results for peak heat release in Table 4.5 below. From this it is seen that all fabrics have PHRR values < 65 kW m" and that OSU and cone calorimeter results are equivalent. 

As a family of resins originally developed in the early twentieth century, the nature and potential of phenolic resins have been explored thoroughly to produce an extensive body of technical literature (1-9). A symposium sponsored by the American Chemical Society commemorated 75 years of phenolic resin chemistry in 1983 (10), and in 1987 the Phenolic Molding Division of the Society of the Plastics Industry (SPI) sponsored a conference on phenolics in the twenty-first century (1). Exciting new developments continue as new systems are developed for carbon-carbon composites, aramid honeycombs, and new derivative chemistries such as cyanate esters and benzoxazines. New U.S. patents with phenolic resins in the claims are growing at about 150 patents per year. 

Other microwave-active CP-textiles described include a P(Py)/aramid honeycomb [885], and materials for use in naval aviation applications [886]. 

Epoxide resin laminates are of particular importance in the aircraft industry. It has been stated that the Boeing 757 and 767 aircraft use 1800 kg of carbon fibre/ epoxide resin composites for structural purposes per aeroplane. The resin has also been used with Aramid fibres for filament-wound rocket motors and pressure vessels. The AV-18 fighter aircraft is also said to be 18% epoxide resin/cc bon fibre composite. The resins are also widely used both with fibres and with honeycomb structures for such parts as helicopter blades. 

Honeycombs are structures with hexagonal or cylindrical cells made from thin sheets of aluminium, aramid (Nomex), paper or extruded polypropylene. The dimensions of the cells are generally in the range of 5 mm to 10 mm. The two faces are covered with a firmly adherent composite (or sometimes metal) skin. 

Aramid pulp is widely used as a substitute for asbestos. The aramid paper is used as insulating paper. In this case, mica, ground quartz, glass fibers, alumina, or talc, can be incorporated to improve the insulating properties. In contrast, if alumina laminae, carbon black, or stainless steel short fibers are incorporated, electrical conductive papers are obtained. Aramid paper is also used as a reinforcing agent in honeycombs. 

In the case of high loading rates an increase in material stiffness and strength compared to the static behavior may occur. This is addressed as strain rate effect. This effect is important in dynamic hnite element calculations. Actually, in taking account of this effect the material may be designed more lightly. A strain rate effect has been demonstrated for aramid paper honeycombs. ... 

Producing airplanes at lower costs is another aspect of advanced RP structural applications. In many cases, the carbon and aramid fiber RP components compare fevorably with the cost of conventional component structures, in spite of the rather high material costs. An important aspect here is the possible simplification of the design. For example, the complicated leg fairing of the Airbus was replaced by a simple all-RP sandwich (honeycomb core) panel reinforced by two RP beams. Besides a weight savings of about 30%, the production hours were reduced by 27%. 

Aramid cores are made from paper (typically 1.5 mil in thickness) comprising w-aramid floe and fibrids, similar to the papers used in electrical applications discussed in the previous section. Adhesive node lines are printed on paper sheets that are then stacked, pressed, and heated to cure the adhesive. The resulting block is expanded. The adhesive-free areas form the hexagonal cells of the honeycomb configuration. The core is dipped several times in an epoxy or phenolic resin solution until the desired density and mechanical property levels are reached. The core is then cut into slices of the desired thickness. Face sheets are glued to each side of the core. The most common face sheet today is a composite of carbon fiber and epoxy resin. 

PinzeUi, R. and Loken, H., Honeycomb cores from NOMEX to KEVLAR aramid papers, JEC Composites, 2004, 8, 133. 

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