Bioinspired composites for the future: sustainable hybrid composites for compression

In recent decades, continuous synthetic fibre-reinforced polymers have become increasingly popular for advanced structural applications. This is largely due to their superior specific properties, corrosion resistance and potential for enhanced fatigue performance when compared to their metallic counterparts. However, with the sustainability of engineering materials becoming an increasingly important consideration amid growing environmental concerns, interest in natural fibre composites (NFCs) is growing due to their potential to replace synthetic fibre-reinforced polymers with improved sustainability and at a lower cost. NFCs can also offer specific properties comparable to E-glass fibre, which is one of the most common reinforcing fibres for polymer composites. Despite this, the uptake of NFCs for structural and load-bearing applications is limited. One key reason for this is the current gap in knowledge regarding their mechanical behaviour. In particular, very few reports in open literature discuss the compressive performance of NFCs, and the resulting scarcity of data severely degrades confidence in the use of NFCs for load-bearing applications. The longitudinal compressive performance is design-limiting for continuous fibre-reinforced polymers. The compressive loads that arise in structures are typically accounted for at the design stage with higher safety factors. This often results in overdesigned and inefficient structures, further solidifying the need for investigating the compressive performance of NFCs.
The aim of the project is to characterise the compressive failure of NFCs and develop an understanding of principles that govern the failure of NFCs in compression. Hybridisation will be investigated as a means to improve mechanical performance. The application of hierarchical and functional grading will also be considered since there is undoubted potential for bioinspired hierarchical architectures to help resolve the challenges that arise from intrinsically conflicting property demands. The end goal of the PhD is to produce and conduct macro-scale testing to assess the structurally representative performance of an NFC component. The design of this component will utilise the new understanding of sustainable hybrid composites developed throughout the project. Given the importance of future-proofing composites, the findings of this work could help industries working towards sustainable material solutions. The development of novel material systems with improved compressive performance may encourage new industries, which currently do not routinely use composites, to use higher-performance materials. They may be enabled to do so by the resulting less stringent design limits. Industries of interest include but are not limited to, the marine, wind energy and automotive sectors.

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.