Lattice cores for high performance sandwich composite structures

Sandwich panels are employed in a wide range of engineering applications, especially in the aerospace and automotive sectors, to replace traditional bulk materials whenever structural mass is a critical performance metric. Notably, cellular cores provide a unique combination of properties to sandwich panels, including high specific stiffness and high specific strength, as well as low thermal conductivity, which makes them ideal for load-bearing, thermal insulation and energy-absorbing functions.

The mechanical performance of the core strongly depends on the deformation "mode", i.e. bending versus stretching, of the cell walls. Cores with cell walls undergoing axial stretching can be ten times stiffer than those deforming primarily through wall bending or buckling for the same relative density.

The aim of this PhD project is to investigate the feasibility of inducing stretch-dominated behaviour in lattices via the introduction of multi-material joints and flexural hinges in the core unit cell. This project will provide a novel and flexible method for tailoring specific stiffness, strength and thermal properties beyond what can be achieved by acting upon the topology of the unit cell alone. The properties of these novel cores will be explored both numerically, via high-fidelity finite element analysis, and experimentally, employing additive manufacturing methods to build prototypes.

The key objectives of this project are:

- Development of high-fidelity finite element models to understand the elastic, inelastic and thermal response of lattice cores at the unit cell and assembly levels.
- Optimisation of topology and multi-material hinged configurations to maximise the performance through parametric modelling.
- Additive manufacturing initial prototypes of the optimised lattice cores.
- Assessing the manufacturability in an efficient and robust fashion.
- Testing the prototype structures and evaluate the results against the finite element analysis simulations.

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.