Abstract:

Significance Carbon fiber-reinforced polymer composites (CFRP) are indispensable lightweight structural materials for aerospace, new energy vehicles, and wind power, offering exceptional specific strength and stiffness that enable significant mass savings and reductions in carbon emissions. However, their laminated architecture and the inherent brittleness of thermosetting matrices lead to poor interlaminar toughness, making CFRP vulnerable to barely visible delamination under impact or out-of-plane loads. This delamination severely compromises structural integrity, damage tolerance, and service safety, fundamentally limiting broader adoption in primary structures. Consequently, developing efficient toughening strategies that overcome the conventional imbalance between strength and toughness is crucial for both high-performance equipment and achieving carbon neutrality goals through extended component lifetimes. Robust interlaminar toughness is therefore a prerequisite for realizing the full lightweighting potential of CFRP in sustainable technologies.

Progress Recent progress in CFRP toughening has witnessed a shift from single-mechanism approaches to multi-scale synergistic strategies. Matrix modification incorporates elastomers, thermoplastics, or nanoparticles such as carbon nanotubes and polyimide microspheres that trigger crack pinning, deflection, and interfacial debonding, substantially raising mode I fracture toughness while preserving thermal stability. Z-direction reinforcement, through 3D weaving, stitching, or Z-pin insertion, creates through-thickness bridging ligaments that resist delamination propagation; surface-structured Z-pins further enhance interlocking and energy dissipation. Interlaminar toughening introduces thermoplastic films, nanofiber veils, or discrete particles between plies, establishing tough interlayers. Films like PEK-C/PES form multiphase morphologies that promote crack branching, while electrospun nanofiber mats, such as PAN with ZnO nanorods, induce hierarchical crack bridging and interfacial mechanical interlocking. Particle interlayers dissipate energy through plastic deformation and crack pinning. Importantly, the combination of these methods into multi-scale, multi-component systems, such as nano-modified fibers and hybrid interlayers integrating nanoparticles with nanofibers, achieves synergistic toughness enhancements that far exceed the sum of individual effects. Bio-inspired designs, mimicking nacre's brick-and-mortar structure or helicoidal architectures, utilize controlled crack deflection and extrinsic toughening to realize exceptional damage tolerance. Furthermore, a transformative shift is underway from passive toughening to active material resilience: self-healing microcapsules and dynamic covalent networks enable autonomous repair of microcracks, restoring mechanical integrity and prolonging service life. Despite these advances, challenges persist in balancing strength and toughness, ensuring uniform dispersion of nano-additives, and simplifying manufacturing for industrial scalability.

Conclusion and Prospect In order to propel CFRP toughening from laboratory innovation to widespread industrial adoption, future research must embrace multi-scale computational design, bio-inspired architectures, and circular life-cycle concepts. Key priorities include: 1) creating integrated computational frameworks that fuse molecular dynamics, finite-element micromechanics, and machine learning to predict the synergistic performance of hybrid nanoparticle/nanofiber interlayers and optimize processing; 2) establishing quantitative structure-property-processing-environment relationships for selecting toughening agents that remain robust under hygrothermal aging, cryogenic conditions, and fatigue; 3) advancing additive manufacturing of bio-inspired hierarchical composites, such as Bouligand and nacre-like structures, with controlled crack-deflection pathways that decouple strength and toughness; and 4) realizing closed-loop recyclability via dynamic covalent networks that enable repeated repair, reshaping, and recycling without compromising mechanical properties. Moreover, by bridging the scales from molecular engineering to structural integration, these strategies will deliver next-generation CFRPs that combine exceptional toughness, lightweight performance, and environmental sustainability, accelerating the transition toward a carbon-neutral economy.

Key words: carbon fiber, composites, interlaminar toughening, toughening mechanism, toughened resin