Drilling induced defects on carbon fiber-reinforced thermoplastic polyamide and their effect on mechanical properties

In this study, a carbon fiber-reinforced thermoplastic (CFRTP) laminate has been drilled and the drill-hole quality was evaluated. Drill-holes were introduced into the laminate by two 5.9 mm diameter step drills to simulate low and high quality machining processes. Defects from manufacturing of the laminate as well as resulting from the machining process were identified and classified by different imaging techniques on representative images. It became obvious, that burr formation is the dominant but not exclusive type of damage in drilled CFRTP in contrast to delamination in case of CFRP. Subsequently, 4-point-flexure and tensile tests have been performed with initial and differently drilled samples to characterize the starting material as well as to determine the influence of the different drill-hole qualities on the mechanical performance and failure behavior. These tests showed that there is no critical influence of the drill-hole quality on the open-hole tensile and flexure strength of the applied CFRTP.