Innovative Approaches for Future Polymer Composites

Taking place on 8th March 2023, this seminar was SUKIC’s first venture outside the UK mainland, and was planned with some trepidation in relation to whether the greater cost and time for air travel would restrict the number of delegates. In fact the seminar was probably our greatest success to date, with almost 100 delegates, 5 table top exhibitors and 11 presentations.  Financial support from sponsors was the highest received for this event, and special thanks go to: Artemis Technologies, Toray Advanced Composites, Royal Academy of Engineering, Surface Generation, Spirit Aerosystems, and to NIACE for the free-of-charge provision of excellent conference facilities and administration. The University of Edinburgh supplied the very efficient registration process. We also acknowledge the important contribution from our exhibitors, the names of which are listed at the end of this report. Finally our thanks go to the SAMPE Events Team Sub-Committee, headed by Conchúr O  Brádaigh (University of Edinburgh) supported by Alasdair Ryder, Alistair Mcllhagger and a team of committee members dedicated exclusively to this event.

1. Keynote: Optimised Composite Wings and Aerosystems. Mark Braniff. Spirit Aerosystems.

  • Mark is head of R&T at Spirit Aerosystems. The objectives of the 8 work packages of the “OPTICOM” project were described. Spirit works in cooperation with NIACE and AMIC (Advanced Manufacturing Innovation Centre, Ulster University), the latter engaged in developing  novel technologies  for “The Factory of the Future.”  
  •  The objective is to optimise both the production process and performance of spars, stringers and wing skins, utilising a maximum of automation for fabrication, assembly and manufacture. Spirit has developed RTI (Resin Transfer Infusion) over a period of 25 years, and the latest iteration involves introducing resin at 5 ports in order to maximise uniformity.  RTI is used in combination with autoclave moulding, and selects the best practices of both processes. Skin thickness can therefore be controlled to a tolerance of +/- 15 thou (0.015”) in order to minimise shimming. NDT data are carefully analysed to help control skin thickness and minimise variation.
  • A special peel ply, which does not cause contamination from adhesive, is used to optimise the cosmetics of the surface after painting.  A video was shown of a robotic “snake arm” used to apply sealant accurately to internal joints. If carbon fibres are packed too tightly at the edge of the wing it is possible to cause “edge glow” at the fibre ends, and this is a possible ignition source. This is eliminated by a controlled reduction in the Vf of the edge plies in order to reduce the electrical conductivity, whilst still achieving the required level of lightning strike protection. Finally, the fatigue testing of the finished wing assembly was described involving 120,000 tilt cycles.

The following two presentations are by the winners of our Student Seminar which was held the previous day, 07/03/23, at Ulster University.  

2. A Novel Profiling Concept to Increase the Mechanical Performance of Metal to Composite Joints. Adam Whitehouse. Imperial College London.

  •  Important examples of metal-composite joints include helicopter composite rotor blades joined to a metal hub, and metallic erosion shields joined to long wind energy blades involving very high tip speeds. Adhesive-bonded joints often cause the delamination of surface layers when under flexural load.
  •  Instead of a planar interface, a novel ”tortuous” (zigzag) profile is introduced. This gives a larger load transfer region to better distribute stresses. This increases the mechanical performance of the joint and deflects fracture compared with an adhesive joint.

3. A Route to Certification of bonded Thermoset Composite Structures via Resistance Welding. Thomas Maierhofer. University of Bath.

  • Joining composites can be a challenging process. The traditional methods of mechanical fastening and adhesive bonding both have their deficiencies. Hence a novel fusion bonding technique has been investigated (welding).
  •  A thin layer of thermoplastic PEI is applied to the CF/epoxy joining surfaces. A DC electrical supply is routed to the carbon fibres, and pressure is applied. This produces a resin interphase with high joint integrity.
  • This is a fast process – 0.5 minutes at 350°C / cycle time less than 5 minutes – and no surface preparation is required. Qualification is based on the specification and control of process parameters, and on the mechanical performance window of the joint, as measured by fracture toughness, GIC.  Results showedresistance bondinggives 360%-520% higher toughness than co-bonded joints.  
  • PEEK and other thermoplastics were examined but bond less well to thermosets and require extensive surface preparation.

4. Innovating Towards Large Scale Implementation of Thermoplastics in Aerospace. Guillaume Ratouit. Toray Advanced Composites

  • Over the past 30 years there has been a steady growth in the use of thermoplastics in terms of both the volume and the size of the parts manufactured. Toray has used their CETEX 1225 thermoplastic in a demonstrator programme involving several partners, including  Airbus. The programme specifies a functional aircraft fuselage demonstrator, 8m x 0.4m, and a technical target of 1T weight saving, and a production build of 100 aircraft.
  •  PAEK, PEEK, PEKK, PEI and CETEX 1225 were evaluated in the programme. CETEX 1225 has been designed to combine the processing ease of PPS with the mechanical performance of PAEK, and it has been selected to go forward.
  • The thermoplastic offers (i) high level of automated lay-up (ii) out of autoclave fabrication via vacuum bag  followed by oven consolidation or hydrostatic consolidation at 30 Bar (iii) ultrasonic welding stringer to skin (iv) laser welding of longitudinal fuselage struts (v) integrated design, for example for lightning strike protection using UD or cross-ply CF / thermoplastic mesh.
  • CETEX 1225 thin UD tape has also been selected for use in filament wound liquid H2 tanks for aerospace.

5. Testing Interfaces of Lattice Spacecraft Structures. Brendan Murray. ATG Galway.

  • The work is focused on weight saving for the PLATO satellite programme. A variety of open-cell lattice structures (i.e.criss-cross pattern) was demonstrated comprising thin CF unidirectional ribs joined at the nodes, at which points, and crucially, the fibres continue in an uninterrupted pathway. Patches, comprising CF laminate of various thicknesses, are then bonded onto some of the apertures. The pattern and amount of patching is varied. Also the patches can be applied to fill only certain single cells, or can fill adjoining cells in a 3-way triangular pattern. In this way a whole family of structures can be produced with different ratios of weight to mechanical performance. In total 5 different patterns were evaluated.
  • Reductions in mass of 20%-60% were achieved with no failure of the lattice. FEA forecasts agreed well with practical mechanical test results. A lattice cylinder based on the actual PLATO satellite gave just over a 30% weight saving with the required mechanical performance.

6. Induction Melt Thermoforming of Advanced Thermoplastic Composites. Phil Harrison. University of Glasgow.

  • An EPSRC programme was described to reduce wrinkling when stamp-forming a 3-D shape from a flat composite layup. A simple 0 /90 layup usually produces satisfactory results but quasi-isotropic structures often lead to wrinkling. The defect occurs between the 0/90 and the +/- 45 layers and can be ameliorated using a thermoplastic film to act as a lubricant layer between these layers, but this leads to a reduction in Vf  due to the addition of matrix.The current novel technique involves the use of a molten metal lubricant layer.  
  • Tin is selected because it does not stick or wet-out (like mercury) and has a favourable melting point similar to the nylon matrix, tin 232°C / nylon 223°C. A contactless induction  coil was used to heat the sandwich layup and a special tiered compression head (like a wedding cake shape) was used for the “sequential” thermoforming of the 3-D shaped dome. In this manner the tin is completely pushed out of the structure on a layer-by-layer basis. Photographs of wrinkle-free 3-D shapes were shown, and stereoscan images to demonstrate the absence of tin in the finished composite   

7. Development of a Lightweight Multi-Role Missile Canister. Tony Millar. CCP Gransden.

  • CPP is partnered with Thales and Ulster University in DTEP – Defence Technology Exploitation Programme. Work began in 2018 to find a composite solution to the Starstreak missile canister (launch tube) with lower cost and weight than the metal standard item.  
  • The composite canister must pass all the current specified requirements including the critical burst pressure, drop / topple test, electromagnetic shielding and lightning strike protection.
  •  The canister is filament wound and the work has identified the optimum fibre layup for both mechanical and electrical performance, and the relationship between these two properties has been quantified.  Enhanced EM and lightning strike protection has been achieved by using graphene and a copper / aluminium mesh. The special assembly jig was explained.
  • A mass reduction of around 20% was achieved.
  • CPP’s filament winding expertise has been extended to the fabrication of H2 pressure vessels. 100% carbon fibre and 100% Aramid winds have been evaluated together with various hybrid winds. Thermoplastics offer several advantages over thermosets: reduced or no cure, recycled canisters can be used, structures can be dried in a vertical orientation without sagging or “ovalisation”, structures are less brittle with higher impact resistance, and a lower cost set-up to evaluate  viability.

8. Composite Materials for Aircraft Interiors. Richard McBride. Collins Aerospace.

  • Richard is Associate Director of Collins Aerospace which in turn is part of the giant Raytheon Technologies  group. Raytheon has 70k employees, 16k of which are engineers, positioned in over 300 sites globally. The markets divide 62% commercial, 38% military. Collins Aerospace’s interests are focused on aircraft interiors including:  galley, seating, waste and water systems, and veneers including exotic woods.
  • CA has 2.5m seats in service. First class seats are highly engineered for maximum comfort and involve much manual fabrication. Economy seats have a challenging budget ceiling and require a high use of automation. Materials and process selection is complex and needs to satisfy (i) a viable and accepted route to certification (ii) structural and flammability specifications (iii) availability and cost in relation to market size (iv) production rate requirements (v) cosmetic appearance.
  • With the primary drivers of cost, quality, performance, lead time and increased functionality, the current trends for aircraft interiors were given as: (i) increased composite content (ii) thermosets replaced with thermoplastics (iii) bio-composites (iv) new structures (vi) a move from subtractive to additive manufacture (vii) scrap reduction (viii) circular economy (ix) Industry 5.0 (humans increasingly working with robots and AI)

9. High Rate Thermoplastic Composites Technology. Gareth Deering. Denroy Aerospace.

  • Denroy’s speciality is in the high rate thermoplastic injection moulding of composites for aerospace and defence. Their expertise is in the production of complex parts with bespoke properties including EMI shielding, thermal and chemical resistance. Technology extends to the over-moulding of plastics with metals, and over-moulding of plastic directly onto fibre structures for anisotropic structures.
  • There is a large choice of thermoplastics. PEEK is often the best choice which offers very high strength and stiffness approaching that of metals, excellent heat and chemical resistance, and tailored electrical properties – conductive  /  insulating, and a suitable optimum minimum level for electrostatic dissipation.  40% glass fibre / PPS is the best choice for low cost and insulating properties, whereas polypropylene is the choice for good flame resistance, low cost and high aesthetic finish.
  • Overall, the growth rate for thermoplastics is good due to favourable production rate, low cost, sustainability and circularity.

10. Lghtweight Foiling Vessel. Emer McAleavy. Artemis Technologies.

  • Artemis was founded in 2017, has 100 staff and has expertise in maritime, aerospace, automotive road cars, and F1 racing. Artemis has invested £250m in the past few years, solely in maritime R&T. They are lead partner, with 12 other organisations from industry and academia, in the Belfast Maritime Consortium comprising a £53m programme to produce zero-emissions commercial vessels.
  • A video was shown of trials with a demonstrator racing boat, “The Pioneer of Belfast,” (also known as EF12), which, as the boat accelerates, lifts out of the water suspended on four thin hydrofoils. This produces 80% less drag and almost 90% total energy savings by using a bespoke battery power pack. Extensive use of composites is required to achieve the light weight needed to facilitate levitation. Other advantages are, a quiet and comfortable ride, no wake and hence no bank erosion of the water medium , near zero emissions. EF12 has a range of 60 nautical miles and a cruising speed of 34 knots.
  •  Following on from EF12, the focus of the Consortium is now on EF24, a passenger ferry, to be launched in 2024. This is near to the maximum possible size of vessel using this technology, due to the constraints of the “design envelope” in which a maximum use of lightweight composites defines the maximum weight (and power) of the battery.                                                                 
  • Work is underway to study and improve the impact damage tolerance of the foils, with computer modelling by Queens University, Belfast. There is also a team working on bio-fouling which increases both weight and frictional drag. Traditional anti-fouling marine paints based on organometallic compounds of copper and tin are not attractive, particularly in environments relatively close to shore.

11. Optimisation of Compression Moulding for Enhanced Composite Assemblies. Luke Gardner. Creative  Composites.

  • Creative Composites was formed in Year 2000 in a management buyout of a springboard company and acquired purpose built plant with compression moulding facilities. In this respect CC and its forerunner is over 40 years old.  In the early days there was a focus on boat building with much hand layup.
  • CC has grown significantly over recent years and has a whole division focused on RTM, and a major expansion in SMC compression moulding, with one of the largest presses in UK which enables their expertise in the manufacture of large composite parts. CC has had an active programme in the development of SMC’s with longer fibre lengths, 25 – 50 cm, giving enhanced mechanical performance together with design flexibility and parts reduction compared with metals. Composites based on SMC can approach the performance of UD carbon fibre structures, and are significantly superior to injection moulded parts.
  • Markets include automotive – including cars, buses and off-highway vehicles – leisure and medical.    

Table Top Exhibitors

Airborne
SHD Composites Materials
Airtech
Surface Generation
Toray Advanced Composites