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

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 volume fractions is first determined 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% at the SCFs volume fraction of 5.45 vol%. In addition, it is found that heat treatment and its temperature have no effect on the fracture toughness of SCFRTCs. 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. The fracture surface of the SCFRTCs specimen is much rougher compared with HDPE, and obvious bridging SCFs are observed, which make it to absorb more energy for fracture, thus explaining the toughening mechanism of SCFs on SCFRTCs.