Bio-inspired heterogeneous hard-soft architectures for carbon-aramid/epoxy hybrid composites with suppressed damage evolution under cryogenic conditions

In cryogenic environments, carbon fibre-reinforced polymer (CFRP) composites are prone to micro-void nucleation and interlaminar crack propagation, primarily arising from matrix embrittlement and thermal stress mismatch at the fibre-matrix interface, leading to a critical deterioration of structural integrity under extreme conditions. Inspiration from heterogeneous “hard-soft” architectures prevalent in biological materials, this study presents a carbon-aramid/epoxy (CAF/EP) hybrid composite, which features an alternating ply configuration and facilitates synergistic load-sharing between high-modulus carbon fibre (hard phase) and high-toughness aramid fibre (soft phase). By integrating in-situ X-ray micro-computed tomography (micro-CT) with Digital Volume Correlation (DVC), the three-dimensional damage evolution of the CAF/EP composite was characterised at both room temperature (293 K) and cryogenic temperature (183 K). Complementary Finite Element Analysis (FEA) was employed to elucidate the stress distribution and substantiate a fundamental transition in damage evolution between 293 K and 183 K. At 293 K, extensive micro-void accumulation was observed, with 534 micro-voids detected in the critical size range. The CAF/EP hybrid composite exhibited a marked suppression of void nucleation at 183 K, where the micro-void count drastically reduced to 107. Accordingly, the number of large interlaminar cracks (>1.5 mm) decreased from 10 to 6. Meanwhile, the tensile strength only slightly decreased from 524.4 MPa to 514.3 MPa, corresponding to a reduction of approximately 1.9%. DVC reconstruction confirmed that strain concentration is significantly alleviated, and the high-strain regions exhibit a strong spatial correlation with the final fracture location. This bio-inspired architecture offers a novel approach for cryogenic composite structures in practically extreme environments.