EFFECT OF FIBRE ORIENTATION ON COMPRESSION MICROMECHANICS IN CFRP INVESTIGATED BY COMPUTED TOMOGRAPHY

Kink band formation is the primary failure mode of unidirectional carbon fibre reinforced polymer composites (CFRP) loaded under compression, and the kinking stress is highly dependent on defects and fibre misorientation. However, the micromechanics of how defects and fibre misorientation impact kink initiation and propagation is not well understood. In this study, X-ray imaging is used to explore different methods of quantifying fibre misalignment/waviness, manufacturing defects, and their relation to kink band formation. Four samples are characterized; one sample with slightly misoriented fibres is used as a baseline alongside three samples manufactured to have fibres with more sinusoidal (wavy) trajectories. The direction and severity of misalignment is quantified for each fibre, tortuosity is determined and used as a metric for waviness, and voids and resin rich regions are identified. Postmortem computed tomography is then used to determine the kink plane orientation. The baseline sample kinked in the expected plane, predicted from the sample geometry and notch placement. One sample kinked in a plane parallel to the mean fibre misorientation direction, while kink failure in the final two samples was affected by a combination of voids, resin rich areas, and fibre misalignment.