Unravelling the role of inter CNT yarn–yarn interactions in governing the failure behavior in a unidirectional CNT yarn-reinforced plastic composite

Recent rapid advancements related to enhancing the material properties of carbon nanotube (CNT) yarns, which are composed of twisted nanoscale CNTs, have opened new possibilities for their application as reinforcing agents in composite materials. In this study, the failure behaviors of CNT yarns were examined in a polymer matrix environment under tensile loading using synchrotron radiation X-ray computed tomography (CT) and polarized light microscopy. Double-yarn fragmentation specimens, composed of two closely positioned CNT yarns embedded in parallel, were employed to examine the failure interactions between the CNT yarns. X-ray CT observations revealed that the fracture surfaces of the CNT yarns exhibited a high degree of irregularity, with cracks propagating into the surrounding matrix and some extending into the yarn bodies, thereby suggesting that the failure of CNT yarns involves both breakage and slippage of the CNTs. The investigation of yarn–yarn failure interactions revealed that ∼70 % of the fractures observed in the CNT yarns occurred as coordinated fractures, which was clearly higher than the ∼20 % observed without such interactions. This finding demonstrates that the failure behaviors of CNT yarns in the polymer matrix environment are governed by yarn–yarn interactions rather than by the statistical strength distributions of the yarns. These results provide valuable insights for researchers in the field of composite materials, ultimately promoting further advancements in the development of strength prediction models based on the actual failure behaviors of CNT yarns in the polymer matrix environment.