Abstract: As a low-cost renewable resource, cellulose nanofibers (CNF) have shown unique advantages in the reinforcement and modification of composite materials. In this paper, cellulose nanofibers were used to reinforce carbon fiber composites. Bending test was carried out, and acoustic emission technology was used for damage assessment. Based on k-means method, the characteristic frequency range and cumulative acoustic emission energy of different damage modes were determined, and the interface strength of reinforced composites was characterized by scanning electron microscope. Results show that the damage initiation of cellulose nanofibers reinforced composites was delayed, and less acoustic emission signals appear in damage evolution. The energy of acoustic emission signals decrease during damage, and the cumulative acoustic emission energy of matrix cracking and fiber/matrix debonding decrease by 78.1% and 87.6%, respectively. Scanning electron microscope results show that cellulose nanofibers improve the interfacial properties of fiber/matrix, consequently improving the bending strength.

Key words: cellulose nanofibers, carbon fiber reinforced polymer, acoustic emission monitoring, fiber/matrix interface, damage evolution