CHARACTERIZATION OF PRODUCTION-INDUCED DEFECTS IN CARBON FIBER REINFORCED THERMOPLASTIC TECHNOLOGY

Advanced thermoplastic composites such as carbon fibre reinforced polyetheretherketone (CF-PEEK) have a great potential for efficient processing. Along the production chain certain manufacturing steps may cause slight, superficial flaws or mere optical effects without greater impact on performance whereas others may lead to severe changes of the final part properties. These production–induced defects can arise already in the early stages of the production chain and may hence cause significant downstream effects. Ultrasonic spot welding is a well-established manufacturing step in aerospace industries. As such, it is applied in preforming to locally melt the matrix of advanced thermoplastic prepregs, to bond stacked layers to one another and later produce a tailored organic sheet or part, e.g. via vacuum consolidation. Depending on the process parameters ultrasonic spot welding may, however, cause detrimental overheating of the laminate, penetration of the horn into the part and disruption of fibres. In this work the influence of production-induced defects on the properties of fully consolidated specimen is investigated and correlated with methods of non-destructive testing. The experimental analysis focusses on the impact of the respective welding and processing parameters on the mechanical performance and the detectability by non-destructive testing, e.g. optical lock-in thermography. The aim is to improve the robustness of the process by detecting, defining and dimishing production-induced defects. In this context, non-destructive testing (NDT) is employed to detect quality issues in an early stage of production