Manufacture, characterisation, and optimisation of WrapToR stiffened skin panels for aerospace applications

This PhD will pioneer the use of highly efficient composite truss structures as reinforcement members for composite panels, with a particular focus on applications in the aerospace industries.

The patented wrapped tow reinforced (WrapToR) truss concept currently being researched at the University of Bristol has already been proven capable of producing low cost, consistent truss beam structures with a quick and simple fabrication process. An adapted filament winding technique allows continuous carbon fibre tow to be laid down as the shear elements, reducing the need for many individual members and automating much of the manufacturing. Previous work has already shown that these beams exhibit far superior stiffness and strength properties when compared to alternative structures of similar mass under a variety of loading conditions.

To date, research on this novel composite truss concept has focused on its use as beams and space frames, with the human powered helicopter Gamera II utilising the low mass and high stiffness properties of WrapToR trusses to break several FIA world records in human powered flight. The next step in developing this exciting technology is to integrate these naked beams and frames into closed panel structures to explore their use as reinforcement members. WrapToR reinforcement of skin panels has the potential to offer lower mass and higher stiffness and strength than alternative monolithic stiffening methods through exploitation of the excellent structural efficiency of trusses.

This project aims to use a multi-disciplinary approach to characterise and optimise the application of the WrapToR truss concept as a reinforcement member for structural panels, to demonstrate that WrapToR stiffened skin panels can improve the mechanical performance of aerospace vehicles such as rockets and reusable space planes, for a low mass budget. To achieve this aim, several objectives of increasing complexity have been planned out as shown below.

- Initially, a stiffened flat panel unit cell will be fabricated and tested to characterise its mechanical performance and validate models currently being developed.
- Secondly, validated models and optimisation algorithms will be used to design a larger, optimised flat panel structure to allow for comparative analysis of mechanical performance to alternative structures such as sandwich panels.
- Thirdly, the work will move from flat panel geometry to more complex curved geometry, with a curved stiffened panel demonstrator unit built and tested for stiffness and strength. Further development of models will be used for validation.
- Finally, a scaled down, curved stiffened structure will be designed, built, and tested for stiffness and strength to demonstrate the true potential of this novel technique. This scaled structure will replicate a relevant space or aerospace application to provide meaningful performance data that can be compared to current industry standards of panel stiffening.

Although this work will focus on aerospace vehicle structures, this concept would be suitable for a much wider range of industries and applications. From trains, planes, and rockets, to fuel tanks, ships, and wind turbine blades, where there is a need for mass efficiency in reinforcement, WrapToR stiffened skin panels can lead the way for the next generation of structural reinforcement.

There are seven principal groups of beneficiaries for our new EPSRC Centre for Doctoral Training in Composites Science, Engineering, and Manufacturing.

1. Collaborating companies and organisations, who will gain privileged access to the unique concentration of research training and skills available within the CDT, through active participation in doctoral research projects. In the Centre we will explore innovative ideas, in conjunction with industrial partners, international partners, and other associated groups (CLF, Catapults). Showcase events, such as our annual conference, will offer opportunities to a much broader spectrum of potentially collaborating companies and other organisations. The supporting companies will benefit from cross-sector learning opportunities and

- specific innovations within their sponsored project that make a significant impact on the company;
- increased collaboration with academia;
- the development of blue-skies and long-term research at a lowered risk.

2. Early-stage investors, who will gain access to commercial opportunities that have been validated through proof-of-concept, through our NCC-led technology pull-through programme.

3. Academics within Bristol, across a diverse range of disciplines, and at other universities associated with Bristol through the Manufacturing Hub, will benefit from collaborative research and exploitation opportunities in our CDT. International visits made possible by the Centre will undoubtedly lead to a wider spectrum of research training and exploitation collaborations.

4. Research students will establish their reputations as part of the CDT. Training and experiences within the Centre will increase their awareness of wider and contextually important issues, such as IP identification, commercialisation opportunities, and engagement with the public.

5. Students at the partner universities (SFI - Limerick) and other institutions, who will benefit from the collaborative training environment through the technologically relevant feedback from commercial stakeholder organisations.

6. The University of Bristol will enhance their international profile in composites. In addition to the immediate gains such as high quality academic publications and conference presentations during the course of the Centre, the University gains from the collaboration with industry that will continue long after the participants graduate. This is shown by the

a) Follow-on research activities in related areas.
b) Willingness of past graduates to:

i) Act as advocates for the CDT through our alumni association;
ii) Participate in the Advisory Board of our proposed CDT;
iii) Act as mentors to current doctoral students.

7. Citizens of the UK. We have identified key fields in composites science, engineering and manufacturing technology which are of current strategic importance to the country and will demonstrate the route by which these fields will impact our lives. Our current CDTs have shown considerable impact on industry (e.g. Rolls Royce). Our proposed centre will continue to give this benefit. We have built activities into the CDT programme to develop wider competences of the students in:

a) Communication - presentations, videos, journal paper, workshops;
b) Exploitation - business plans and exploitation routes for research;
c) Public Understanding - science ambassador, schools events, website.