Background

The Automotive Composites Research Centre (ACRC) is a dedicated facility within WMG's Materials Engineering Centre, where the research team develop high-volume composites manufacturing processes for automotive components. Their specialist structural composites group links technology with applied research to address the challenges the automotive industry faces in providing lighter vehicles with lower emissions and reduced environmental impact.

WMG's Centre for Imaging, Metrology and Additive Technologies (CIMAT) provides a hub for innovation and research that, for the first time, brings together state of the art technologies for the enhancement and understanding of product and process performance

Fibre architecture dictates the mechanical properties of fibre reinforced composites. Therefore, determining the fibre architecture is the key to design and manufacture of high-performance automotive composite structures.

Compression moulding of high fibre content, long discontinuous carbon fibre Sheet Moulding Compound (CF-SMC) is an attractive solution for high-rate manufacturing of automotive composite structures. SMC flows under compression force to fill the mould cavity, allowing complicated geometry (e.g. ribs and bosses) to be manufactured. One of the main design challenges with SMC is that in-cavity flow during compression moulding increases the level of heterogeneity of the material, particularly in terms of fibre content and fibre orientation.

Understanding the fibre behaviour during the manufacturing process is the key to improve part quality, and to better predict the structural performance of the part. The level of heterogeneity and complicated fibre architecture in SMC requires 3D analysis of the material’s internal structure. Radiologic techniques such as ultrasound and CT scan can be useful for such purpose. However, due to the low contrast between the densities of carbon fibre and resin, applications of radiologic techniques could only be achieved at the micro-scale for carbon fibre composites.

In order to address the challenges and gaps identified, the Automotive Composites Research Centre (ACRC) teamed up with the Centre for Imaging, Metrology and Additive Manufacturing (CiMAT), seeking novel and robust experimental solutions for characterising fibre architecture, particularly fibre orientation distribution in CF-SMC.

This research was funded by the EPSRC Future Metrology Hub as a feasibility to deliver a step-changing technology in metrology for composites. The ACRC is internationally leading in applied research for high-volume composites manufacturing of automotive structures, and have successfully collaborated with industrial partners on a number of CF-SMC focused projects, notably the APC 6 funded CHAMELEON project and the APC 10 funded TUCANA projects. The CiMAT is equipped with top class CT scanning facilities and high-powered workstations with proprietary software for robust fibre composite material analysis. The collaboration between the two research teams provides an ideal opportunity to achieve this significant advancement in technology.

The study consisted of a series of systematically designed experiments in which the following solutions were delivered:

• New CT scanning methodologies were established to enable clear identification of fibre tows with CF-SMC components
• Commercial fibre analysis package VGStudio was successfully employed to quantify the fibre orientation tensor distributions from the CT scans
• The robustness of the new method was demonstrated through case studies and comparison with other methods such as eddy current and process simulation

This project has successfully enabled robust and reliable fibre architecture characterisation for CF-SMC for the first time, which represents a significant advancement in relation to the current state-of-the-art. High-quality imaging of the internal architecture of the material also allows the researchers from the ACRC to gain better understanding of the processing behaviour of the material, which could not be investigated previously due to the lack of methodology.

A number of journal publications and conference proceedings are currently being prepared to disseminate this work. A webinar titled ‘Understanding fibre architecture: Challenges and novel solutions for carbon fibre SMC’ was produced in June 2021 by Prof Ken Kendall, Dr Connie Qian, Dr Danielle Norman, Dr Nessa Fereshteh Saniee and Dr Jai Gupta to showcase the outputs from this feasibility study. The webinar received over 100 registrations and over 50 external participants joined the live webinar. The webinar also highlighted WMG’s great commitments to EDI and one of the audience commented: “Great example of women in Engineering, well done WMG!”