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With operating costs continuing to rise and the perceived need to improve the revenue potential on each and every new aircraft being commissioned, both the OEM and supply sectors of the aerospace industry are evaluating all aspects of design and weight optimisation.
International airshows over the last few years have seen a ubiquitous emphasis on this issue, with an increasing focus on the role of advanced composites. Most recently the attention has shifted somewhat from the airframe to aircraft interiors in the continuous drive for weight reduction. For many commercial aircraft interior use of composites is just as crucial to the cost : revenue equation, as the weight of composite interiors actually exceeds that of the airframe. From overhead bins and ceiling panels to cabin dividers, galleys and bulkheads, the use of interior composites in the pursuit of weight reduction vies with lighter textiles and leathers on seating, lighter food carts, the elimination of in-flight magazines and thinner display screens to achieve the desired results. Huntsman Advanced Materials has launched an entirely high-performance and inherently flame resistant solution for RTM and infusion processing which offers greater strength whilst answering continued demand for weight reduction in interior aerospace designs. Araldite FST 40002 / 40003 is a different development that provides a unique combination of high mechanical, fire, smoke and toxicity (FST) performance alongside high quality, user-friendly composites processing conditions enabling efficient production of interior carbon and glass composites parts with maximised weight savings. The mixed two-component system exhibits a low viscosity at working temperatures above 50°C. The latency range from 50°C to 100°C provides the ability to produce complex parts in small and large dimensions. In addition, it has a low reaction energy of about 220 J/g which eliminates bulk exothermic safety issues and enables large thickness composite part production.In comparison to traditional RTM and infusion systems, its viscosity and reactivity profile shows snap-cure behaviour which allows fast Tg and interlaminar shear strength (ILSS) development. Also, after pre-cure conditions of approximately one hour at 100°C followed by one hour at 120°C, the system can be demolded, resulting in molding time and mold cost optimisation. Indeed after the latter pre-cure conditions, the system develops 85-90% of its ultimate ILSS – when measured on carbon fabric reinforcement. Pre-curing is followed by two-hour post-curing at 180°C, which can be done either in the mold or freestanding, to enable the ultimate performance development. It develops dry and wet Tg of 260°C and 185°C (measured by DMA) with very high ILSS performance of 97 MPa and 55 MPa at 23°C and 120°C respectively – when measured on unidirectional carbon reinforcement. Surprisingly for a system with such high Tg and high crosslinking density, it also exhibits high tensile elongation and appreciable toughness, enabling the substitution of metal in highly structural applications. The inherent FST properties of the system come from the chemical nature of the network and its high cross-link density. The new system meets the FAR 25.853 vertical burn, smoke and toxicity requirements with both carbon and glass fibre in all thickness configurations. The heat release of the system is highly dependent on composite thickness, making it ideally suited for non-visible parts in the interior that do not have direct contact with potential ignition sources as well as cockpit parts that currently do not need to pass heat release. Due to the filtration effect, filled systems are processed with open fabric where low fibre content sacrifices composites performance. With this system, the combination of good matrix mechanical properties and high fibre volume capabilities maximise performance, meeting industry demand for further weight savings. By comparison to phenolic resins which are subject to a polycondensation type reaction and are used for non and semi-structural applications, it undergoes a polyaddition reaction without gas release. This enables significant weight reduction, improved composites quality, elimination of intensive part production post-operations as well as a cleaner and healthier manufacturing solution for operators, supporting closed mold processes and VOC emissions free system exposure. The use of interior composites is expected to increase by some 50% over the period with the joint interests of operators and conservationists in the link between weight reduction and reduced carbon emissions. More information: www.huntsman.com