Predicting the performance of sustainable composite materials in a range of manufacturing techniques

Recycled carbon fibre (rCF) composites are a valuable solution for industries such as aerospace to move towards a more closed-loop manufacturing model. Reclaiming fibres from manufacturing waste or end-of-life (EoL) components increases the material efficiency of composite materials and decreases their environmental impact of subsequent laminates due to their lower embodied energies from cradle to gate. Recyclates are also cheaper to manufacture than their virgin counterparts. RCF does have its own drawbacks. Depending on the recycling process used, the fibre's modulus, strength and surface energy can be diminished. In addition to this, the majority of economically viable recycling processes chop the fibre into lengths typically between 3-25mm. The result of this is that rCF materials are often downcycled into components that do not require the same load-bearing capabilities as virgin carbon fibre (vCF) components. This is because most recycled materials are in the form of randomly oriented discontinuous fibre mats and therefore do not possess the anisotropic mechanical properties or high fibre volume fractions required for more structural applications. This is not the best use of this valuable material. This is where fibre realignment techniques, such as High-Performance Discontinuous Fibre (HiPerDiF), are closing the discrepancy between vCF and rCF composite fabrics by transforming waste fibres between the lengths of 1 and 12mm into realigned tapes. Laminates made from these tapes have been manufactured using a range of methods such as autoclave, hot press and 3D printing, yet there has not yet been a characterisation of the ability to manufacture these aligned discontinuous materials using liquid composite moulding (LcM) techniques.

This PhD will aim to characterise the ability to manufacture aligned discontinuous fabrics using a selected range of LcM techniques for structural aerospace components. In particular, there is interest in whether the discontinuous aligned fabrics will be displaced by the resin front, known as fibre washout. The degree of alignment of the laminates' fibres, fibre overlap, and fibre volume fraction will be measured and compared to the mechanical properties. The mechanical characterisation methods used will include a range of quasi-static, high-rate and hot/wet tests to understand the full scope of both the simple static response and durability of these laminates. After both proof of concept and bench scale specimens have been created, the materials will then be applied to a demonstrator case study. Mechanical testing of this component will then take place as a way of comparing the current materials and manufacturing methods. A finite element analysis (FEA) modelled will be created to validate the load distribution on the materials compared with the structure. Finally, a life cycle assessment (LCA) can be made to show the impact of using reclaimed materials instead of virgin. This will help to strengthen the case for using recyclates in more challenging structural applications.

This project is supported by GKN Aerospace.

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.