Synergistic improvement of the compression-after-impact performance of composite laminates by multi-scale CNF/Z-pin reinforcement

This paper investigated the effects of carbon nanofibers (CNF), Z-pin, and multi-scale CNF/Z-pin on the compression-after-impact (CAI) properties and damage morphology of laminates after 10 J, 30 J, and 50 J impact. The deformation and strain field variations of the laminate during the CAI process were clearly characterized by 3D-Digital Image Correlation (DIC). The process from local buckling to the global failure of the laminate was clearly revealed. The mechanical response results showed that the CAI strength of unreinforced, CNF, Z-pin and CNF/Z-pin-reinforced laminates increased in order after impact with the same energy. After 50 J impact, the CAI strength of CNF, Z-pin and CNF/Z-pin-reinforced laminates was increased by 18.6%, 28.7% and 36.4 %, respectively, compared to unreinforced laminates. By constructing a simulation model to analyze damage and mechanical response, the model's effectiveness was verified. Additionally, the damage morphology, damage mechanism, and synergistic toughening mechanism between CNF and Z-pin in CAI specimens were revealed from optical photographs and scanning electron microscopy (SEM).