Effect of Surface Roughness and Skin–Core Structure of Dry-Jet Wet-Spun T800G Carbon Fiber on the Impact Resistance of Carbon Fiber-Reinforced Composites

The mechanical properties of carbon fiber composites (CFRCs) are governed by the carbon fibers (CFs) themselves and the fiber–matrix interface (FMI), with the synergy between the two being crucial. This study focused on how microstructural heterogeneity affects the compression after impact (CAI) of the same epoxy resin (EP) composites. The research was conducted using two variants of dry-jet wet-spun T800G CFs, labeled CF-low and CF-high. The results indicated that while CF-low exhibited a higher number of deep axial grooves and a greater surface micro-zone compressive modulus, their pronounced skin–core structure and the excessively strong interfacial bonding formed by mechanical interlocking aggravated fiber core collapse and stress concentration under mechanical loading. In contrast, the homogeneous structure and moderate interfacial characteristics of CF-high facilitated efficient stress transfer between the CFs and EP. Compared with CF-low composites, CF-high composites exhibited a 9% increase in CAI strength and a 35% reduction in damage area, significantly improving the damage tolerance of the composites. This research underscores that optimizing the synergy between the fiber properties and the interfacial behavior is key to enhancing CFRC performance.