Redesigning composite repair process using induction heating

The application of advanced composite materials in the aerospace industry, utilised for their superior mechanical properties, has grown exponentially over the last few decades. The largest limitation of these materials from both an economic and sustainability viewpoint are the inability for time and energy efficient repair. Traditionally, damaged plies are replaced with laminate patches or wet lay ups followed by a long cure cycle over the entire component. Therefore, there is a requirement for a more localised curing method which can produce repair patches cured in-situ in a fast and energy efficient manner.
To achieve this, induction heating will be testing by volumetrically heating composite laminates to gain a better understanding of its effects before producing repair patches cured in-situ. Preliminary experiments have achieved rapid heating in carbon fibre based laminates as well as glass fibre laminates containing metallic tufts. These experiments show heating patterns to be highly dependent on the geometry of the induction coil used. There is also a significant non uniformity in the heating of a composite panel both in plane and through thickness which could be improved using novel induction coil geometries as well has highly conductive susceptors.
This research aims to optimise the process of induction curing both in terms of rate of cure and uniformity of heating profile. Numerical modelling using the electromagnetic capabilities of Finite Element software, Abaqus, will form the basis for understanding the effect of coil geometries and materials parameters on the heating profile. These models will be used to manufacture an induction coil followed by an optimisation process to cure laminates quickly with high uniformity. This optimised process will be used to manufacture repair patches which will be compared to conventional methods.
The key objectives of this project are:
-Perform an optimisation of design variables to maximise the efficiency and uniformity of inductive heating using Finite Element modelling.
-Manufacture composite laminates using optimised process based on modelling.
-Apply experimental methods to produce repair patches cured in-situ.
The results of this work should allow manufacture of composite repair patches which can be cured in situ which will allow for repair of large laminate components significantly more time and energy efficient manner

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.