Advanced high fidelity modelling of woven composites

In the last decades, advanced composite laminates have represented one of the most used material technologies able to ensure unparalleled performance in terms of strength to weight ratio and range of applicability. However, the newest aerospace engineering challenges has led to ever increasing demand for better mechanical properties and higher reliability. Traditionally, the composites laminate exhibit poor through-thickness strength and impact toughness. Therefore, the need arises to use more reliable materials in some specific applications such as fan blades or impact resistance structural parts, which in turn led to the development of more complex fibre interweaving architectures such as the 3D woven composites. The introduction of the binder yarns aim to interlace multiple fabric planes, providing a three dimensional reinforcement. However, associated with the outstanding properties exhibited by the 3D Woven composites the exponential growth in architecture complexity poses new challenges, in terms of manufacturing and virtual modelling.

This research aims to develop state-of-the-art modelling capabilities for meso-scale damage modelling in woven textile composites. In particular, 3D woven composites debonding is one of the key damage mechanisms that have been extensively observed via experimental test studies. In the absence of debonding models, Matrix cracks can progress directly from matrix to yarn materials, resulting in a premature prediction of failure. Consequently, it is essential to include this damage mode in simulation for accurate predictions of the ultimate failure strength. Here, a novel modelling technique is proposed to include reliable debonding failure detection in the meso-scale model of textile composites. As a first step, the more traditional Voxel meshes needs to be improved due to the lack of a distinct representation of the yarn surface. So, the research starts by developing a dedicated mesh technique i.e. an original Hybrid Mesh that aims to represent the contact surfaces between matrix and yarns with a high fidelity. Finite Element Analysis models will be compared, in terms of mechanical characterisation, with experimental results. Finally, a dedicated mechanical damage models will be investigated, including the non-linear matrix behaviour under shear loading. The validation of the results will be carried out against X-ray CT scans experimental tests to capture damage morphology as well as failure strengths.

This project's outcome will provide an important virtual modelling technique to enable the better design of structural components using woven composites. The proposed meso-scale model will be integrated in a multi-scale analysis framework, standing as cutting-edge software able to investigate the mechanical behaviour from the fibre/matrix constituents up to the components level made of woven composite materials.

Key aspects that will be covered to achieve a state-of-the-art 3D woven modelling capability include:

- Dedicated matrix modelling including shearing non-linearity.
- Yarn matrix debonding damage.
- Enhanced damage progression algorithms for Voxel meshes.
- 3D Woven dedicated conformal meshing methods.
- Computational enhancements to achieve a stable implementation of damage models in an implicit integration framework.
- Enhanced damage morphology experimental verification against CT-scans.

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.