Simultaneously reducing the modulus difference and smoothing the modulus transition through bi-directional structural design for enhancing interfacial properties of carbon fiber/epoxy composites

The modulus mismatch between CF and resin and the weak interfacial bonding strength result in poor interfacial properties, limiting its application in the field of structural materials. In this study, the modulus difference reduction and the gentle modulus transition would be achieved by simultaneously designing structures of the carbon fiber (CF) and resin to enhance the interfacial properties of the composite. The modulus difference was narrowed by improving resin modulus. Meanwhile, the multi-scale structural design on CF surface smoothed the transition modulus from fibers to resin. In brief, under the above combined effects, a multi-stage modulus gradient decreasing structure was constructed, which could make the external stress more effectively dispersed for excellent interface properties. The bi-directional structural design increased the ILSS of CF/EP composites to 82.6 MPa, which was 17.7% and 8.0% higher than that of CF surface modification only and EP modification only, respectively. This work was expected to provide new ideas for improving the mechanical properties of CF composite through multi-scale structural design to meet the needs of different fields.