Symmetrical gradient design of helicoidal composite laminates for enhanced damage tolerance

Abstract

The Bouligand architecture found in various crustacean exoskeletons was an essential feature for organisms to resist external loads, and further microscopic observations indicate that the helicoidal pitches in the exoskeleton tend to be arranged in a gradient pattern to achieve excellent damage tolerance. Inspired by such structural gradient phenomenon, multiple helicoidal units with different rotation angles are introduced for regional configuration design of the composite laminates. By mimicking the gradient-helicoidal microstructures and conducting experimental characterization, this work demonstrates that the unidirectional gradient-helicoidal design schemes, including two mutually inverted structural configurations (denoted as GH-I and GH-II), exhibit a compromise in terms of bending force and energy dissipation compared to the traditional uniform-helicoidal controls. Notably, the symmetrical gradient-helicoidal configuration (denoted as GH-III) with the same structural parameters achieves superior mechanical properties, increasing load-bearing capacity by 6 %–64 % and energy dissipation by 37 %–59 % over benchmarks. The parametric analysis of biomimetic GH-III configurations further reveals that configuring larger rotation angles on the external sides and arranging a smaller rotation angle on the inner side is an effective optimization strategy. It successfully resists the damage initiation that usually occurs on the external sides and introduces matrix cracks into the internal side for stable twisting diffusion, fully exploiting the synergistic benefits of different structural parameters in terms of damage resistance and damage tolerance. Therefore, these findings have practical implications for bionic design and fabrication, providing inspiration for composite laminates with improved mechanical properties.