Improved tensile strength of carbon nanotube-grafted carbon fiber reinforced composites

Abstract

Increased tensile strength of carbon nanotube (CNT)-grafted carbon fiber (CF) composites has been reported, but the mechanism of this increase is not yet clear. In this study, CNT-grafted CF unidirectional (UD) and woven composites were fabricated using a low-temperature chemical vapor deposition (CVD) and resin transfer molding. Two types of CNTs (short and thin, long and thick) were successfully grown and grafted to CFs without degrading the CFs in the preforms. The CNT-grafted CFs exhibited increased interfacial shear strength (IFSS) similarly regardless of the CNT type. Interestingly, however, long and thick CNT-grafted CF UD and woven composites exhibited significant increases in tensile strength (about 20% and 30%), suggesting other mechanisms besides increased IFSS. The splitting crack initiation under the mixed mode condition was quantitatively characterized for the CNT-grafted CF UD composites, demonstrating that long and thick CNTs delayed the splitting crack initiation. Delayed fiber splitting and increased IFSS were concluded to be the main sources of increased tensile strength of CNT-grafted CF composites.