Airbus is replacing aluminium in a fitting in the aircraft door of the Airbus A350-900 with a high-modulus, carbon fibre-reinforced high-performance polymer. The bracket, now manufactured from VICTREX PEEK 90HMF40, have been developed by Airbus and are in serial production for commercial use after receiving the relevant component qualification. The successful substitution of metal has resulted in a 40 percent reduction in weight and costs. The injection-moulded polymer solution replaces the higher cost manufacture of the bracket machined from an aluminium block.

The fibre-reinforced polymer (FRP) structure of the A350XWB's aircraft door uses an outer skin coupled with a bracing structure on the inside. A fitting, now manufactured from VICTREX PEEK 90HMF40 thermoplastic, connects the outer skin to points on the internal bracing structure. The two components form a box-type structure to exploit the maximum geometrical moment of inertia.

Christian Wolf, Head of Airplane Doors Research and Technology, Airbus Helicopters, explains the operation and significance of the PEEK component: “In terms of the standard load case, i.e. the internal cabin pressure, this point-type joint reduces the deformation on the outer skin, thereby maintaining the aerodynamic quality of the aircraft door. All components in the aircraft door are of a singly-redundant design. If a component near the bracket fails, the bracket will provide an alternative path for transferring structural loads and is therefore part of the aircraft's primary structure.”

Metal replacement: New bracket reduces costs and improves quality

By using the carbon fibre-reinforced high-performance VICTREX PEEK 90HMF40 polymer instead of the aluminium previously used, Airbus has successfully manufactured an equivalent component that provides a range of benefits. Weight and production costs have each been reduced by 40%. Joining the PEEK component, instead of an aluminium component, to a thermoset makes drilling much easier. Optimised carbon-fibre-reinforced plastic (CFRP) drills improve the quality of the holes compared with the previous solution.

VICTREX PEEK 90HMF40 is a material specified by Airbus. The thermoplastic easily withstands the moisture that continuously accumulates inside aircraft doors, whereas aluminium, which is prone to corrosion, needed a special surface coating to prevent corrosion. “The suitable material, supplied by Victrex, as well as their expertise and collaboration with their materials experts have contributed to the successful development and component qualification. The expertise gained from the initial use of fibre-reinforced PEEK can be transferred to other components and to other areas of application with similar requirements”, says Wolf.

New developments and investments help maintain the lead

In the aerospace business the “design and build” process, e.g. development in accordance with a given specification, is a possible option for producing structural components. In this process, the developer has additional freedom in matters such as the selection of materials. “90HMF40 is a special high-performance thermoplastic which is also suitable for load-bearing structural components as now used for the first time in the Airbus A350-900 and therefore in regular airline operations. This first application is certain to be quickly followed by others”, explains Uwe Marburger, Aerospace Business Development Manager at Victrex. Operating worldwide, the UK-based company has over 35 years' experience and offers not only solutions based on polyaryletherketones (PAEK), but also consistent product quality, as well as security of supply.

In April 2015, Victrex put its third production plant into operation, further extending its lead as the leading supplier of PAEK, including VICTREX PEEK. “We are also ready to meet new challenges in the future, for example those involving cooperation with partners in “design and build” applications where a new design is needed as well as the selection of materials in order to achieve the specified function”, says Marburger confidently. Victrex only recently announced the successful launch of its advanced hybrid moulding process. This provides an excellent combination of strength and design freedom, especially in the development of very lightweight structures.

Aerospace designers and manufacturers benefit from the use of VICTREX PEEK 90HMF40. This high-performance polymer with high-modulus fibres (HMF) is based on the Victrex 90-Series polyaryletherketone, which is primarily used in very thin-walled injection-moulded components. High-strength components can be manufactured from this free-flowing, easily processed material. Its properties cannot be matched by those of the standard grades. For example, 90HMF40 has up to 100 times longer fatigue life and up to 20% greater specific strength and stiffness than aluminium 7075-T6 under the same conditions.