Development of Hybrid Compounds for Compression Moulding for Structural Composites

Academic Institution: University of Edinburgh

Academic Supervisor: Dr Francisca Martinez-Hergueta

PhD Student: James Pheysey

Summary

The aim of this project was to develop novel hybrid composite materials to achieve improvements in mechanical performance and cost reductions. This work was sponsored by the Scottish Research Partnership in Engineering and Fortescue Zero with supervision from Francisca Martinez-Hergueta and Francesco De Cola.

Traditional continuous fibre composites are limited to high-cost applications due to their material cost and slow manual manufacturing processes. Discontinuous fibre composites have a much lower material cost, however, they also have a significantly lower mechanical performance. Hybridisation, through the combination of continuous and discontinuous fibres or different fibre materials, can improve composite performance whilst maintaining a competitive cost.

The first part of this work focused on the development of a low-cost composite suitable for automotive applications. The baseline low-cost composite consisted of a low-cost short fibre injection moulding compound, which contained short fibres with an approximate length of 0.15 mm and exhibited limited mechanical properties.

Hybridisation was proposed to develop a new structural material combining this short fibre compound with a high-performance unidirectional continuous fibre composite manufactured through compression moulding.

The hybrid composite exhibited significant improvements in tensile and flexural response with only a slight increase in cost. Failure was inspected through scanning electron microscopy with fibre failure in the UD fibres and fibre pull out in the short fibre core. Additionally, a finite element model was developed to analyse the variability in mechanical properties due to the stochastic nature of the randomly oriented fibres. The influence of temperature and strain rates in the mechanical properties was also analysed, revealing improved performance for impact applications.

Finally, vibrational performance was study, exhibiting a superior damping capacity comparable to the performance of natural fibres. There findings provide solid support for the future implementation of this hybrid composite in automotive applications.  

 

The second phase of this work looked at hybridisation of sheet moulding compounds for improved damage tolerance. This are discontinuous fibre composites with a fibre length of 25 mm. Hybridisation was achieved through the combination of glass and carbon fibres. This showed an improved tensile performance over the glass fibre composite whilst showing a significantly reduced crack density following low velocity impact compared to the carbon fibre composite. This makes the hybrid material suitable of structural applications subject to low-velocity impacts.

Publications

https://www.sciencedirect.com/science/article/pii/S1359835X24001180

https://www.sciencedirect.com/science/article/pii/S1359836823005838

https://www.sciencedirect.com/science/article/pii/S0263822324003921

Key Outcomes

  • Combination of short fibre carbon fibre/PEEK injection moulding compound and UD carbon fibre/PEEK composite through a compression moulding process increased tensile stiffness by 130.6% and flexural modulus by 330.4% for only a 21.5% increase in cost when compared to the short fibre material.

  • Decrease in operational temperature resulted in an increase in compression strength or short fibre and hybrid PEEK composites.

  • Increased strain rate resulted in an increase in tensile and compressive strength of a short fibre composite with the hybrid only showing this in compression due to the UD fibres dominating the response in tension.

  • Short fibre composite showed a much higher specific damping capacity than a quasi-isotropic laminate with a the high material showing an intermediate performance allowing for good damping and tensile properties.

  • Hybridization using glass and carbon fibres in an SMC improved the impact performance over a carbon fibre SMC, as the glass fibres have a higher elongation to break, allowing more compliance and resulting in a reduced crack density

Contact details

Dr Francisca Martinez-Hergueta:

francisca.mhergueta@ed.ac.uk

PhD Student:

james.Pheysey@ed.ac.uk