An investigation into the performance of aligned discontinuous carbon fibre composites produced using the HiPerDiF technology

Abstract

Discontinuous fibre composites are well established in many industrial applications due to their fine handling and forming capabilities. However, they are mostly limited to low value parts because of low tensile performance caused by the discontinuity and misalignment of the fibres. To increase their mechanical performance, it is necessary to highly align the fibres highly as well as ensure they are longer than critical length. This research is focused on one such reprocessing method, with the aim to understand the tensile performance of the composite when the processing parameters are optimised. The overall goal is to characterise aligned discontinuous fibre composites (ADFRC) made from an up scaled and high-volume producing technology. The testing campaign utilised in this research will offer a comprehensive analysis of mechanical performance, failure properties, and fibre physical properties. ADFRC prepreg material was made using virgin discontinuous fibres (3 mm – 6 mm in length) and a high-performance resin system (CYCOM ® 977-2) provided by Syensqo. This material was made using a new, third-generation machine, HiPerDiF 3G, capable of producing up to 80 linear metres per day quantities. Machine parameters were optimised to increase the quality and alignment of the resulting prepreg material. Standard industry techniques were then used to manufacture ADFRC panels, which were analysed using a wide variety of mechanical tests in accordance with ASTM test methods. Optimised machine parameters showed improved mechanical properties in terms of tensile performance and the quality of the microstructure. There was an increase in stiffness by 3%, strength by 28% and failure strain by 26% compared with samples produced with the initial machine parameters. Samples manufactured from preform produced at the optimised setting had 73% of fibres spatially aligned within 10 ◦ and 62% of fibres aligned in plane within ± 10°. There was also a visual indication of fewer voids and a higher volume of fibres perpendicularly orientated to the fracture surface after testing. In comparison with similarly tested unidirectional continuous composite specimens, the ADFRC tensile specimens at 23% fibre volume fraction achieved 32% of the tensile modulus, 30% of the tensile strength and 57% of the failure strain. This work has demonstrated the viability of producing aligned discontinuous fibre preform in high volume has the capability of producing composites with improved tensile performance. With the upscaled HiPerDiF machine, high mechanical performance can be achieved as long as the machine parameters and fibre properties are optimised to maintain a high alignment and consistent areal weight. The next step will be to understand how fibre volume fraction can be optimised with the HiPerDiF 3G technology to achieve further gains in mechanical performance. This research will give a deeper understanding of the process parameters, fibre, and matrix interactions necessary to produce quality material reliably and effectively at high volume.

Date of Award	9 Dec 2025
Original language	English
Awarding Institution	University of Bristol
Sponsors	Syensqo
Supervisor	Ian Hamerton (Supervisor), Marco Longana (Supervisor), Carwyn Ward (Supervisor), Ram Ramakrishnan (Supervisor) & Jonothan Meegan (Supervisor)