ABSTRACT Bioinspired composite designs provide unique possibilities to enhance impact resistance, toughness, and energy absorption in structural materials. To accomplish this, unidirectional (UD), single (SHL), and double helicoidal laminates (DHL) were developed using alkali treated and untreated flax fibers reinforced with epoxy resin, mimicking the bouligand microarchitecture of beetle exoskeletons. The present research provides the first comprehensive comparison of single and double helicoidal flax fiber laminates fabricated by vacuum‐assisted resin transfer molding (VARTM) with optimized pitch architecture (having a pitch angle of 15°), showing synergistic toughening effects that clearly outperform traditional UD and single helicoidal natural fiber composites in out‐of‐plane and impact resistive properties. XRD and FTIR analyses confirmed that alkaline treatment effectively removed amorphous components, improving flax fiber crystallinity from 58.45% to 74.44% and enhancing fiber–matrix interfacial bonding. Mechanical tests indicated that treated DHL composites had the highest energy absorption and deformation capacity, with a 32% improvement in flexural energy absorption over SHL composites and 65% over UD composites. Fracture tests showed an increase in fracture toughness ( K IC ) of 9.14 MPa m 0.5 and energy release rate ( G IC ) of 21.18 kJ/m 2 , approximately 5 and 13 times greater than UD laminates, respectively. These improvements are attributed to synergetic mechanisms such as crack deflection, fiber bridging, interlaminar shear, and progressive delamination. The combination of natural fiber reinforcement and beetle‐inspired double helicoidal stacking provides a lightweight, sustainable, and mechanically robust bio‐composite system. Overall, the study's results suggest that flax fiber helicoidal laminates may be viable materials for next‐generation engineering applications, emphasizing design with energy dissipation, impact resistance, and sustainable design.
Saha et al. (2026) studied this question.