The Influence of Matrix Resin Toughening on the Compressive Properties of Carbon Fiber Composites

The poor impact resistance of carbon fiber reinforced composites limits their application in broader fields. In this study, a toughened epoxy resin (E2) modified with toughening agents and a micron-sized toughening particle (TP) were developed. Standard epoxy resin (E1), toughened epoxy resin (E2), and TP-toughened E2 resin (E3) were prepared into prepregs with SYT55-12K carbon fiber and ultimately fabricated into carbon fiber reinforced composites. The mechanical properties of the resins and the composites, particularly the compression properties, were characterized. The failure morphology of the composites and the distribution of toughening particles were observed using scanning electron microscopy (SEM), ultrasonic C-scan testing, and metallographic microscopy. It was found that the toughening agents improved the bending strength of the resin by approximately 12%, while the incorporation of TP enhanced the impact performance of the resin by 122%. Further characterization of the mechanical properties of the carbon fiber reinforced composites revealed that, with the addition of toughening agents, the resin increased the 0° bending strength of the composites by 29.9% and the 0° compressive strength by 34.3%. Additionally, significant enhancements were observed in interlaminar shear strength and open-hole compressive strength. After the addition of TP, the compressive strength of EC3 compared to EC2 increased by 74.3% after impact, while the mode I interlaminar fracture toughness increased by 34.8% and the mode II interlaminar fracture toughness improved by 67.9%. C-scan analysis indicated that the damage area of EC3 decreased by 60.7% compared to EC2, demonstrating that the particle toughening significantly enhanced the impact resistance of the composites. The compression failure of the TP-toughened EC3 exhibited typical characteristics of kink band failure, and the micron-sized particles were able to significantly balance and absorb loads. The findings of this study indicate that resin toughening can significantly improve the 0° compressive strength of carbon fiber reinforced composites, and that the use of micron-sized toughening particles can markedly enhance the post-impact compressive strength of the composites through interlaminar toughening. This research provides insights for improving the compressive and impact resistance performance of carbon fiber reinforced composites, with implications for industrial application and guidance for further industrialization trials.