The mechanical performance of carbon fibres-addressing the role of microstructure

Copyright 2019. Used by the Society of the Advancement of Material and Process Engineering with permission. A new SAXS-WAXS method has been developed at the Australian synchrotron for the structural analysis of carbon fibres. The new technique, referred to as serial SAXS-WAXS fibre scattering is used to map the microstructural properties of single carbon fibres, ranging in diameter from 5 to 8 µm. Based on an automated scanning protocol, a single carbon fibre is mounted in vacuum and aligned relative to the incident X-ray beam. After (automated) alignment points on each monofilament are acquired. In the forward scattering direction both the SAXS and WAXS signal are recorded as a single image to ensure that the fibre scattering cross-section is known precisely. Under these conditions both the size and alignment of the microstructural features from fibre-to-fibre are quantified. Importantly, the graphitic alignment, spacing and apparent crystallite size can be directly related to the macroscopic fibre modulus. In addition, quantitative analysis of the SAXS scattering signal from pores trapped within the fibre provides an indication of macroscopic strength. The utility of these techniques are demonstrated for carbon fibres prepared on the Carbon Nexus single tow line at 3 different carbonization tensions.