Flexural Properties and Low-Cycle Bending Fatigue of Anisotropic Carbon Fiber Mat Reinforced Composites

Abstract

The carbon fiber/polypropylene (CF/PP) nonwoven fabrics were manufactured by carding process, lay-up process and needle punched process. After hot pressing the nonwoven fabrics, the CF/PP composites were mold. CF/PP composites with carbon fiber lengths of 50 mm and 70 mm was prepared respectively. The 3-point bending test and the low-cycle bending fatigue test (LCBF) at constant stress of 55%, 70% and 85% of original flexural strength were performed. The results showed that the ratio of transverse direction (TD)/machine direction (MD) flexural modulus of CF50 and CF70 was 1.55 and 2.35, which indicated the composites exhibited anisotropic property. The longer the fibers were, the easier they were to be oriented. The effect of low cycle bending fatigue (LCBF) with 55% and 70% stress level on flexural properties was not obvious. The LCBF of 85% stress level has an obvious influence, and some samples have broken before reaching 30 times of fatigue. Optical observation shows that with the increase of fatigue stress level, the crack becomes deeper, and the bending modulus and strength decrease obviously.