Flexural failure mechanisms in injection-moulded carbon fibre/PEEK composites

Two kinds of short-carbon-fibre-reinforced poly(ether ether ketone) composites were prepared with and without a transcrystalline interphase. The fibre-length distribution, fibre orientation and crystallinity were all characterized. These composites, with a thickness of 3 mm and a span-to-thickness ratio of 32, were subjected to three-point-bending tests at cross-head speeds of 0.5, 5, and 50 mm/min. Fractography was carried out by means of scanning electron microscope. Multiple shallow and deep shear cracks were observed in the compression side of the damaged specimen. The appearance of the load/deflection curves and the fractography suggest that compressive cracks occurred first; the stress concentration under the loading nose and the shear stress maximum induced the upper shear cracks which blunted the propagation of the compressive crack. The tension crack then initiated from the tension side, met with the lower shear crack near the core region, and resulted in catastrophic failure.