Microstructural and micromechanical property characterisation of CF/PEKK composites using nanoindentation

The present work seeks to characterise the micromechanical properties of carbon fibre/poly(etherketoneketone) (CF/PEKK) composites with different crystallinity levels and morphologies. CF/PEKK laminates were manufactured under various compression-moulding and automated tape placement (ATP) conditions. Nanoindentation experiments were performed at different locations across the thickness of the laminates to evaluate hardness and elastic modulus at the micron scale. The polymer matrix of compression-moulded laminates, which was found to be fully crystallised, performed significantly better than the matrix of the ATP laminates. The central region of the ATP laminates performed slightly better than regions close to the top and bottom surfaces, likely due to a higher crystallisation development in the central area. A transition in response from the fibre to the matrix bulk was observed across all samples via nanoindentation testing. Overall, the study of micromechanical properties can provide insight into the impact of manufacturing conditions on the composite's performance at the macro scale, ultimately contributing towards higher-quality end products. To the authors’ best knowledge, the in-depth work presented in this article is the first to use nanoindentation to characterise the effect of manufacturing processes on the micromechanical properties of CF/PEKK laminates.