Elucidation of crystalline morphology, crystallinity and mechanical properties of carbon fibre/PEEK composites under different cooling rates

This study investigated the influence of the cooling rate on the crystallinity and mechanical properties of carbon fibre-reinforced polyether ether ketone (CF/PEEK) composites. Interlaminar shear and compressive performance of CF/PEEK composites were studied under different cooling rates ranging from 1.5°C/min to 300°C/min. The bond strength, crystallinity and crystalline morphologies were correlated. The crystallinity percentage was measured by differential scanning calorimetry, X-ray diffraction, and the crystalline morphology was revealed by focused ion beam etching. The study found a 14% decrease in crystallinity with an increase in cooling rate. The interlaminar shear strength (ILSS) and the compressive strength (CS) were assessed by short beam shear (SBS) and combined load compression (CLC) tests, respectively. The increase in cooling rate was observed to reduce the ILSS and CS by 6-11% and 1-30%, respectively. The reduction in ILSS and CS was attributed to the presence of void and the decrease in crystallinity. The failure modes for both tests were examined at macro and microscopic levels, providing practical insights into the behaviour of CF/PEEK composites under different cooling rates.