Morphology-induced fatigue crack arresting in carbon fibre sheet moulding compounds

Carbon Fibre Sheet Moulding Compounds (CF-SMCs) are tow-based composite materials. Interrupted fatigue tests, combined with computed tomography, were performed here to investigate the damage mechanisms in high in-mould flow CF-SMC. The tow-based microstructure created obstacles for fatigue damage propagation, increasing the CF-SMC's resistance against cyclic loading. Failure is shown to nucleate inside the tows, but inter-tow crack propagation tends to be hindered by the presence of the other tows. Tows oriented perpendicularly to the initial fatigue crack stop the crack itself, showing an intrinsic crack arrest mechanism. Additionally, pre-existing manufacturing cracks or voids do not propagate at all. As a result, flatter slopes of the SN diagrams were observed for CF-SMC than for other carbon or glass fibre composites with short, long and even continuous fibres