Effects of cellulose nanofibers on flexural behavior of carbon-fiber-reinforced polymer composites with delamination

Understanding the influence of delamination defects on the damage evolution behavior of carbon-fiber-reinforced polymers (CFRPs) is crucial to improve their engineering applications. This study examined the flexural damage behaviors of CFRP composites by using a combination of acoustic emission (AE) and X-ray micro-computed tomography (micro-CT). Four specimens with different delamination defects and 0.1 wt% cellulose nanofibers (CNFs) were subjected to three-point bending tests. AE was employed to monitor the loading process, and then, micro-CT was utilized to detect the internal damage. The results showed that for the specimens with preset delamination defects near the surface, CNF-reinforced specimen exhibited no obvious enhancement effect on bending strength, and its cumulative acoustic energy decreased by 28% compared with that of CFRP specimens. For the specimen with preset delamination damage in the middle position, CNFs had an obvious enhancement effect on mechanical behavior, and the cumulative acoustic energy decreased by 43%. No obvious kink band was observed in the CNF-reinforced specimens, and during crack propagation, causing cracking and delamination damage was difficult. The results of micro-CT are consistent with those of AE. The results combined the combination of AE and micro-CT reflect the superiority of the hybrid detection system.