Fracture analysis of a single polyacrylonitrile-based carbon fiber in rigid-fixing and flexible-fixing chopping processes

Chopping is an efficient way to produce short carbon fiber (CF). Generally, there are two types of fixing constraints available in the chopping process: rigid-fixing and flexible-fixing. Simplified experiments were performed using glass and rubber as the fixing constraints in cutting a single polyacrylonitrile-based CF to reveal the influence of the fixing constraints in CF chopping. The cutting forces and the bending angles with different fixing constraints were analyzed. Furthermore, the failure surface of the CF was observed. Due to an additional bending effect in the flexible-fixing cutting, the failure surface of the CF was rough, and the cutting-off force was approximately 5% of the force in rigid-fixing cutting. Therefore, flexible-fixing cutting is a suitable way to decrease the cutting-off force in CF chopping. Moreover, it was concluded that the fiber fracture in rigid-fixing cutting is caused by compression, whereas in flexible-fixing cutting, it results from bending. We hope our work is beneficial to the design of the chopping procedure for short CF.