Programmed bioinspired interfaces towards synergic impact and fire protection in composites

Interfaces in structural composites have long been treated as passive links and weak points to be strengthened. Here, the interface is designed as a programmed layer that directs mechanical and thermal loads into distinct damage pathways. A three-dimensional aramid fiber network is embedded within carbon fiber/polyphenylene sulfide (CF/PPS) laminates, designed to mimic the crack deflection capability of nacre and the heat-induced delamination behavior of Banksia seed pods. The bioinspired composite exhibits a penetration depth 60% lower than that of aluminum under 60 J impact and arrests projectiles at 212 m s⁻¹ through multiscale toughening (crack deflection, fiber bridging, and hierarchical fibrillation). Under flame exposure, in situ thermography and X-ray tomography show that heat becomes localized at the designed interface due to thermal conductivity mismatch, and this localized heating leads to delamination, forming an insulating air gap that acts as a self-sacrificing thermal barrier. This design yields an ultralight (1.62 g cm⁻³) composite with V-0 flammability and LOI >50%, which maintains a backside temperature of ∼252 °C under a 1300 °C flame while preserving structural integrity. As a honeycomb sandwich panel, it withstands 150 J impacts, providing excellent impact protection, which highlights its potential as a lightweight material candidate for protective structures such as electric vehicle battery enclosures.