Hydrothermal Aging Behavior and Mechanical Properties Degradation of Flax/Basalt Fiber Hybrid Composites

ABSTRACT To enhance the durability of flax fiber reinforced composites and promote their broader industrial applications, hydrophobic basalt fiber was incorporated to prepare flax/basalt fiber hybrid reinforced composites (HFRP). Tensile, three‐point bending, low‐velocity impact, and post‐impact bending tests were performed on HFRP laminates with different stacking sequences after different aging cycles. Combined with Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR) characterization, the failure mechanism of HFRP in a hydrothermal aging environment was analyzed. The results indicate that the moisture absorption behavior of HFRP at different temperatures follows Fickian law. When basalt fiber is positioned in the outer layer, the material's moisture absorption rate and saturated moisture absorption rate are effectively reduced (the maximum decline was approximately 66%). Tensile and there‐point bending strength of composites decrease with higher hydrothermal aging temperatures across all layups. Among them, the performance of [B 2 F 2 ] S and [F 2 B 2 ] S deteriorated more significantly. The tensile strength decreased by 67.44% and 54.7% compared to the initial strength, while the bending strength decreased by 46.13% and 49.78%. The impact resistance and there‐point bending properties after impact of hybrid composites before and after aging are improved compared with single fiber composites. The there‐point bending strength retention rate (63% ~ 82%) of [F 4 B 4 ] S under different aging conditions is higher than that of [F 16 ] (57% ~ 77%), and the there‐point bending strength retention rate (51% ~ 74%) of [B 4 F 4 ] S is higher than that of [B 16 ] (48% ~ 72%). This study reveals the performance degradation mechanism of HFRP in extreme environments and provides a theoretical basis for optimizing material design and improving its application performance in complex environments.