Leaf-vein-inspired fiber-matrix composites with graded chevron architectures

Inspired by the vein structures of leaves in nature, fiber-matrix composites with chevron architecture and functionally graded fiber orientations are designed and evaluated via systematic FE simulations and experiments on 3D printed specimens. This study aims to engineer the bio-inspired composites with enhanced mechanical characteristics under both mechanical and thermal loads. To investigate the effective mechanical properties of these novel composites, finite element (FE) models of representative volume elements (RVEs) are developed, and an extensive parametric study is conducted. The design space for auxeticity in two orthogonal directions is identified. It is found that by varying the fiber orientation at different levels, the effective stiffness and the effective Poisson's ratio can be tuned across a broad range. To further assess the mechanical performance of the designs, specimens with positive and negative Poisson's ratios are selected and fabricated via a multi-material 3D printer. Uniaxial tension and three-point bending experiments are then conducted. Additionally, the thermal stress generated by temperature changes is evaluated via both FE simulations and experiments on 3D printed specimens in a thermal chamber. The results demonstrate that auxetic designs exhibit higher ductility and reduced thermal stress.