Drilling-induced defects and mechanical performance of open-hole structures in thermoplastic and thermoset polymer composites

Abstract

To support the performance-oriented manufacturing, a critical focus in composite production, we present the first comparative study of the drilling-induced defects and the associated static open-hole tensile performance of thermoplastic carbon fibre reinforced polyetherketoneketone (CF/PEKK) and thermoset carbon fibre reinforced epoxy (CF/epoxy) composites. The spatial distribution of drilling defects (delamination and hole microstructural damage) and strain concentration across the drilled area under loading are analysed and compared for the first time using Digital Image Correlation (DIC) technique. Results show that while drilling of CF/PEKK induced 20.4–45.6 N (18.5 %−49.7 %) higher thrust force and 21.3–87.6 °C (44.6%–98.9 %) higher drilling temperatures as compared to CF/epoxy, it displayed less severe delamination (up to 43.9 % lower) and surface cavity defects. Despite the difference in drilling-induced damages, no significant impact was found in the open-hole tensile strength and modulus of both composites. This is attributed to the delamination and surface cavity areas not coinciding with the strain concentration sites, as confirmed by the DIC results. These findings have important industrial implications, suggesting that certain hole defects may be tolerable without significantly compromising tensile performance. This could reduce the need for tight tolerances in less critical applications, leading to potential cost savings. • Drilling-induced defects in CF/PEKK and CF/epoxy are compared. • Open-hole tensile behaviour and strain distribution are compared through DIC. • Distribution of strain concentration area, delamination and surface cavity defects are elucidated.