X-ray computed tomography observation of multiple fiber fracture in unidirectional CFRP under tensile loading

We investigated the initiation and propagation of fiber fracture in unidirectional (UD) carbon fiber-reinforced composites (CFRPs). The statistical fiber breakage of CFRPs and multiple fiber fracture (the propagation of fiber breakage near the broken fiber) have been studied and observed in specimens after fracture. To date, however, this propagation phenomenon has been rarely observed directly, and investigations have depended mainly on prediction. This direct non-destructive evaluation of fiber fracture phenomenon was performed via X-ray computed tomography of UD CFRPs. Specimens were loaded under various stress levels and imaged at low voltage (20 keV). The fiber breakages were analyzed from these images, which revealed multiple fractures leading to large clusters of broken fibers. Quantitative analyses after image processing revealed a marked increase in the number of multiple fractures, meaning the number of broken fibers in a broken fiber cluster, near the final fracture. Finally, the trend in multiple fractures was compared with the predicted results, showing reasonable agreement.