Characterization of tensile damage evolution in carbon nanotube-reinforced carbon fiber/epoxy composites using in situ X-ray CT

The addition of carbon nanotubes (CNTs) effectively enhances the matrix and regulates the interface in composite materials. However, the damage evolution and the reinforcement mechanisms of CNT-enhanced composites remain unclear. In situ CT experiments can monitor internal microstructural changes in real-time and non-destructively. They offer a direct view of the entire process of crack initiation, propagation, and final failure. This makes them a crucial and indispensable method for gaining insights into the damage mechanisms and studying the mechanical behavior of composite materials. In this study, CNT-enhanced carbon fiber/epoxy composites were fabricated using VARTM (Vacuum Assisted Resin Transfer Molding) technique. In situ tensile tests were conducted using X-ray CT to precisely reveal the actual microstructure and damage evolution under continuous loading conditions, comparing the failure process with that of CFRP (Carbon Fiber Reinforced Polymer) without CNTs. The results demonstrate that CNT-enhanced carbon fiber composites exhibit the same failure mechanisms as CFRP, with significantly improved elastic modulus and tensile strength. This enhancement is attributed to their large specific surface area and bridging effects, which effectively restrict crack propagation. The appearance and slow propagation rate of cracks in carbon nanotube-enhanced carbon fiber composites indicate superior toughness compared to traditional CFRP materials.