Maximising DLF technology potential

Over 30 years ago, Greene, Tweed became one of the first commercial adopters of PEEK high performance polymers within the aerospace industry. Both then and now, the material was used within the aerospace industry for, among other things, high performance sealing components in demanding applications such as landing gear and primary flight control systems.

Having developed that expertise in applying, processing and optimising the use of PEEK material, Greene, Tweed has developed a new composite format of the material for structural parts. Based upon well-established aerospace grades of Carbon/PAEK prepregs, Greene, Tweed's Xycomp DLF is a Discontinuous Long Fibre form of material that is helping to dispel the myth that high performance, high fibre volume thermoplastic materials are cost prohibitive to employ successfully within an aerospace environment where cost-effectiveness is a key driver in new technology adoption.

Tim Greene, global composite product manager for Greene, Tweed explains: “One of the challenges remaining for composites in commercial aerospace applications is the ability to produce highly-complex 3D-shaped components with an acceptable value proposition versus metals. Greene, Tweed's Xycomp DLF materials and proprietary processing capabilities were developed to address this need and have successfully demonstrated the ability to produce highly-complex parts for adoption in production applications. Our Xycomp components are flying in significant numbers within all three of the major new civil aerospace platforms, Boeing 787, Airbus A350 and Bombardier's CSeries.”

Complex-shape capability however, is only one of a number of elements that need to be considered.

“One of the challenges of a discontinuous fibre composite material is that it obviously behaves in a very different way mechanically to continuous fibre materials,” states Dr James Myers, European aerospace composites applications engineering supervisor (pictured right). “In order to fully prove the suitability of Xycomp DLF for our target applications, we have been working both internally and with key aerospace partners to prove the technical maturity of the technology and it's suitability for deployment within demanding aerospace environments. Process and performance repeatability, technical predictive capability and simulation have all been key to our development. To date we have successfully demonstrated DLF's suitability for productionised tertiary structural applications and are well progressed along our roadmap to demonstrate Xycomp DLF's suitability for secondary and ultimately primary structural components.”

“It is a very versatile material to design with,” continues Dr Myers. “Near-net complex shape moulding, the ability to incorporate integrated moulded-in inserts/components in a single shot moulding operation and potential for structural hybridisation with continuous fibre elements for tailored directional strength and stiffness to compliment the DLF complex shape capability, to name a few examples all provide the designer with a comprehensive design toolkit from which to choose.”

Environmental considerations

The current production application focal area for Xycomp DLF is tertiary/semi-structural components, but developments are progressing to be able to produce more critical structures. Greene, Tweed has already proven the technology's capability for such applications via multinational R&T projects. One such example led by Aerolia, a major aerostructures manufacturer and subsidiary of Airbus Group was supporting research and development efforts in the aviation sector focused on environmental preservation and sustainable development.

Gereon Schenk, senior business manager at Greene, Tweed further explains that weight reduction from Xycomp DLF supports goals of reducing the environmental footprint by reducing fuel use and associated emissions. Furthermore, with appropriate considerations, the thermoplastic matrix used for Xycomp DLF material permits recycling and remoulding of components at end-of-life.

Based upon Airbus A350 fuselage geometries, the work has included investigations into fuselage upper attachment fittings and a highly-loaded landing gear drag stay fitting where part performance and failure predictability was critical. The work has helped to validate Greene, Tweed's technology roadmap, and in particular efforts aimed towards achieving a future Certification by Analysis approach to working with discontinuous fibre structures.

The Aerolia work focused upon a primary structural part used to attach fuselage frames to cockpit structures. The programme included material characterisation of Xycomp DLF across an array of properties to supplement design allowable development over multiple environmental and coupon geometry configurations, part sizing and part testing by Aerolia to achieve the desired Airbus Technology Readiness Levels (TRL) for production applications.

DLF bridges the gap

Vincent Labatut, Aerolia R&T stress engineer states: “New composite-intensive aircraft continue to include a substantial number of machined metallic components due to a lack of cost-effective complex-shape composites solutions. Xycomp DLF is able to provide complex-shaped composite parts with both part count and weight reduction advantages over simple loaded metal parts, bridging the gap between complex machined metal components and cost-intensive continuous fibre composites layup technologies.”

Another component development under the same Aerolia-led programme was between Greene, Tweed and Latécoère. This was an example where Xycomp DLF was shown to provide significant benefits versus the incumbent metallic technology. With the application focused around a high load nose landing gear drag stay fitting, the methodologies employed for the DLF technology have allowed the collaboration on the successful design, manufacture, integration, test and accurate prediction of the behaviour on test assembly of a high load, safety critical structure.

“The component has allowed for DLF technology to be successfully demonstrated as potentially suitable for future use within such applications,” Philippe Gail, project manager for Latécoère explains. “The work done to TRL 5 has shown the possibility to employ DLF technology in larger assemblies to compliment the behaviour of traditional composite materials.

Dr Myers adds: “With the work to validate the predictive capability of part and process ongoing; high load, critical applications will ultimately be possible for production on new or revised or ‘re-engined' platforms and at future technology insertion points on existing aircraft programmes.”

Proven production pedigree

For now, with major platforms ramping up production rates, immediate term component production focus for Xycomp DLF technology remains around new and existing, less structurally-critical applications than those developed under the above research programmes. This is allowing the production pedigree to be proven and successfully deployed on major flying platforms to support the ongoing parallel development of the technology for future use in more safety critical and high load applications.

Dr Myers concludes: “The technical cornerstones are firmly in place with design and analysis; production capability is robust and has demonstrated the ability to produce high volume parts with predictable, repeatable behaviour and high quality. With that, we are well on the way ensuring that the capability of the material is fully utilised and we, our customers and our partners can take full advantage of the possibilities that Greene, Tweed's Xycomp DLF technology offers.”

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