An investigation into the performance of aligned, discontinuous carbon fibre produced with the scaled-up HiPerDiF process

Fibre reinforced polymer composites provide the opportunity to produce lighter, cheaper and, durable products with increased mechanical performance compared with metallics. However, this creates challenges related to the complex manufacturing processes, and composite waste. Waste fibres are in a discontinuous and randomly oriented form and to create a valuable product it is necessary to realign them to achieve high volume fractions. The HiPerDiF technology, invented at the University of Bristol, can process a variety of fibre types to produce a highly aligned discontinuous fibre preforms. The advantages of using discontinuous fibres are that they provide better handling and forming capabilities with the potential to reduce defects. The cured composite material can also achieve mechanical properties comparable to that of its continuous counterparts.

While significant progress has been made to optimize the mechanical performance of aligned discontinuous fibre prepregs produced using HiPerDiF technology, it has mostly been lab-based with a low throughput. As a result, this has allowed a limited characterisation of the produced material. A new generation machine, HiPerDiF 3G, capable of producing kg/hr quantities of aligned discontinuous fibre prepregs has been recently installed. This will industrialise the HiPerDiF technology, making it suitable to a wide range of composite applications. With the increased production rate, enough material can be produced to allow a full characterisation of the produced material both in terms of quality control and its mechanical performance under various loading conditions. The project will concentrate on virgin discontinuous fibres sourced from production waste.

The scale-up of any new technology brings with it new challenges. Therefore, this project will aim to identify risks associated with transforming the process into a larger scale and investigating the effects on the performance and quality of the produced material. To achieve this, the project will:

- Produce panels using material from HiPerDiF 3G to compare with panels produced with continuous fibre prepreg of the same constituent materials.
- Design and conduct a testing campaign that will analyse mechanical performance, failure properties, and fibre physical properties to determine the material's limits.
- Experimentally determine the feasibility of optimising the process to maximise performance by varying the key process parameters.
- Explore suitable measurement techniques which can be used to implement quality control into the HiPerDiF 3G manufacturing process.

Based on the results of this project, further research can be conducted to establish an efficient control strategy with a better understanding of the process parameters interactions and their effects.

This project will be supported by Solvay.

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.