WrapToR hierarchical space frames made from natural material composites

Trusses and space frames are some of the most efficient structural configurations developed to date. They achieve very high levels of performance through taking advantage of highly non-linear structural scaling laws by putting small amounts of material into localised members which are spaced far away from each other, allowing them to balance large forces and bending moments with minimal stress. Such structures are typically made from metals, which provide very good performance, but require large amounts of energy and resources to extract, smelt, and form. If such structures could instead be made from natural materials then their environmental impact could be significantly lowered and they could be adopted to a much wider range of applications. However, natural materials tend to have lower mechanical performance than metallic or traditional composite solutions. One potential way of mitigating the lower mechanical properties is to further exploit geometry by creating truss structures made from members which are themselves trusses. These Hierarchical Space Frames have been shown to be very promising in previous initial work with carbon fibre composite materials, and applying them to natural materials is made tenable through adoption of a patented truss beam manufacturing method being developed at Bristol, the Wrapped Tow Reinforced (WrapToR) truss manufacturing approach.

WrapToR trusses are made by using a simple adaptation of filament winding that wraps pre-made longitudinal members in a wetted composite tow to produce a rigid web of shear members when cured. These truss beams can then be made into Hierarchical Space Frames by assembling them with joint structures. This, alongside the innate hierarchical makeup of natural materials, would create a synergistic order of hierarchy from the global structure down to the material level.

WrapToR trusses and spaceframes made from natural materials are currently a promising but unexplored area of research, and practical, cost effective methods for joining WrapToR beams need to be developed. This work aims to develop the WrapToR method to devise a sustainable and low cost process for producing trusses and spaceframes from natural materials. To fulfil this aim the following objectives are set:

- Develop the WrapToR method to maximise structural performance of natural material truss structures, aiming to account for and exploit the unique features of natural materials.
- Experimental testing of natural material WrapToR trusses to characterise unique behaviour that is produced as a result of natural materials being used, that may differ from previously tested WrapToR trusses. Determining key relationships between structural performance, structural failure, material properties and truss geometry. Then using computational modelling and optimisation to design both individual trusses and Hierarchical Space Frames.
- Investigate relevant, existing contemporary and traditional methods for joining trusses and beams in order to develop a practical and cost-effective process for joining individual WrapToR trusses into hierarchical space frames.

These objectives will culminate with the manufacture of a full-scale natural material WrapToR Hierarchical Space Frame demonstrator for a relevant, real world application that can be tested under realistic loading conditions.

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.