Optical coherence tomography - A new method for evaluating the quality of thermoplastic glass-fiber-reinforced unidirectional tapes

Optical coherence tomography (OCT), originally developed for biomedical applications, has been found to be a powerful tool for the non-destructive testing and characterization of polymeric matrix composites. Increasingly, the thermosets, previously used as the only matrix material in these composites, are being replaced by thermoplastics. Thus, the issue of appropriate and reliable quality assessment has arisen. This study evaluated OCT as a technique for detecting common quality defects in the continuous production of thermoplastic glass-fiber-reinforced unidirectional (UD) tapes. Stationary offline measurements using a spectral domain OCT system were carried out to investigate typical defects, namely filled/unfilled gaps, fiber breakage, dry fiber regions, bubbles, and edge defects. While edge defects, dry regions, fiber breakage and empty gaps were successfully detected, polymer-filled gaps and small bubbles on the tape surface posed a greater challenge. We show that OCT is a powerful non-destructive high-resolution method for defect detection in glass-fiber-reinforced UD tapes that has great potential for inline quality assessment during continuous production.