In-situ Observation of Fracture Mechanism of Unidirectional CNT Yarn/Epoxy Matrix Composites by Synchrotron Radiation X-ray Imaging

抄録

Carbon nanotubes (CNTs) have excellent mechanical properties and are expected to be used in various applications, especially in composite materials. Since CNTs are nanoscale dimensions and difficult to handle individually, composite materials using CNT yarns, in which multiple CNTs are twisted together, as a reinforcing element of plastics, are currently studied. However, the tensile strength and Young's modulus of CNT yarn composites are much lower and far from practical application. To enhance the mechanical properties of CNT yarn composites, it is crucial to understand the tensile fracture mechanism of CNT yarn in a matrix environment. Since CNT yarn/epoxy matrix composites and carbon fiber reinforced plastics (CFRPs) have similar structures, we hypothesized that the failure mechanism of unidirectional CNT yarn/epoxy matrix composites could be understood from the aspect of unidirectional CFRPs. In this research, double-fiber specimens with two CNT yarns embedded in parallel in an epoxy matrix were prepared and the interaction of the distance between the yarns was evaluated. We conducted synchrotron radiation X-ray computed tomography and double fiber fragmentation tests to examine the fracture behavior of an adjacent CNT yarn in the epoxy matrix. This study showed that the CNT yarn in the epoxy matrix fractured in a brittle manner and that adjacent fractures occurred due to stress concentration, similar to the fracture behavior observed in unidirectional CFRPs. Additionally, we observed that matrix cracks occurred in a helical shape, and internal cracks within the CNT yarn propagated longitudinally, differing from the fracture morphology of carbon fibers in a matrix environment. Clarification of the fracture mechanism of the unidirectional CNT yarn/epoxy matrix composites will lead to improvement of the tensile strength and development of strength prediction models of CNT yarn/epoxy matrix composites, which will lead to the practical application of CNT yarn composites.