Bioinspired 3D helical fibers toughened thermosetting composites. (1st July 2021) - Chang, Xinhao
Abstract: Thanks to the special helical structure, natural composites such as shell, wood, and bone have remarkable toughness, strength and damage tolerance. Herein, a bioinspired spiral nylon monofilament/epoxy composite is developed, which is a representative example of helical fiber/thermosetting composites. The relationship between toughness and strength of composites was studied by controlling parameters of the helical fibers. As a result, the impact resistance is regularly increased by the increase of pitch and the decrease of helix fiber angle. With a single-layer addition, the impact toughness of composites is increased by 150% without decreasing the mechanical strength and that is increased by 450% in the case of three-layer addition. The proposed toughening mechanism was verified by finite element analysis and dynamic mechanical analysis, which including 3D stress dispersion, the interlocking fibrous building interface, and energy absorption capacity of viscoelastic spring polymer. Furthermore, the toughness and strength of the composites is improved by 310% in single layer via surface modification of spiral fibers. The introduction of the three-dimensional spiral structure into the composite is demonstrated to be a unique strategy to overcome the trade-off between toughness and strength of high-performance composite materials. Graphical abstract: A spiral nylon monofilament/epoxy composite served as an example of helical fiber/thermosetting composites, which is inspired by the biological helical structure of natural composites, is manufactured. The novel change of fibers' structure can realize the three-dimensional dispersion of stress, which can greatly improve the impact strength of composites. Image 1 Highlights: A spiral nylon monofilament/epoxy composite served as an example of helical fiber/thermosetting composites is manufactured, inspired by the biological helical structure of natural composites. The composites with high impact resistance relies on changes in the physical structure of fibers. This toughening mechanism is proposed, including 3D stress dispersion, the interlocking fibrous building interface, and energy absorption capacity of viscoelastic spring polymer. Interface modification and multilayer design play a better role in toughening.