Evaluation of the Fracture Toughness of Short Carbon Fiber Reinforced Thermoplastic Composites

Abstract Short carbon fiber (SCF) reinforced thermoplastic composites (SCFRTCs) are attracting broad attention in various fields for their excellent mechanical properties. The fracture toughness, an essential characteristic of the resistance of materials to crack propagation, is considered a critical aspect of the long-term performance of SCFRTCs structures. The fracture toughness of SCFRTCs depends on two competing mechanisms: the interface between SCFs and polymer matrix may promote crack initiation, while the SCFs hinder the crack propagation. In this study, the fracture toughness of SCFRTCs with varying SCFs fractions is first measured by a three-point bending test. The results show that adding SCFs effectively improves the fracture toughness of SCFRTCs, and an increase of up to 73.7% is observed at the SCFs fraction of 9.80 wt%. In addition, it is found that the fracture toughness decreases slightly but is more stable after heat treatment. Subsequently, the full field strain around the crack tip is analyzed by Digital Image Correlation (DIC), and the strain level significantly decreases after adding SCFs. Moreover, the dynamic crack propagation is observed by DIC, and the crack initiation load is obtained successfully to verify the large deformation during crack initiation. Compared with the smooth fracture surface of the HDPE specimen, the fracture surface of the SCFRTCs specimen is much rougher, and obvious bridging SCFs are observed. The larger specific surface area and bridging SCFs of fracture surface absorb more energy during the fracture of SCFRTCs specimen, thus explaining the improved fracture toughness of SCFRTCs.