Using optical coherence tomography to evaluate the optimal settings for inline detection of defects in glass-fiber-reinforced unidirectional thermoplastic tapes.

While for several decades composites have been manufactured mainly from thermosets, such as epoxy- or polyester-based resins, a clear trend towards using thermoplastic matrix systems has recently emerged. Their reversible melting behavior gives them several advantages, including better recyclability and faster and more easily automated production. Increasing the productivity of thermoplastic composite manufacturing processes requires appropriate, reliable inline quality assurance systems. Optical coherence tomography (OCT), originally developed for biomedical applications, has been proven to be a powerful tool for non-destructive testing and characterization of unidirectional (UD) fiber-reinforced thermoplastic tapes made from glass fibers. Previous offline OCT measurements on a test rig demonstrated the reliability and robustness of the method in detecting visually apparent tape defects, such as gaps and fiber breakages and – one of the most critical bulk defects – insufficiently impregnated fiber regions. In this work, inline OCT measurements were performed on stationary Polycarbonate (PC)/glass fibers (GF) UD tapes in an industrial-scale production line. Systematic experimental analyses were carried out in which the OCT sensor was moved across the tape width, and the influences of (i) single scan sampling rate, (ii) single scan averaging, and (iii) sensor travel speed on measurement accuracy and data size were evaluated. Measurement accuracy was validated using optical microscopy. Optimal sensor settings were derived to improve the inline capability of the measurement approach under real production conditions. [ABSTRACT FROM AUTHOR]