Anisotropy in vascular bundle-inspired structures during in-plane compression

Purpose The purpose of this study was to investigate the anisotropic axial loading behaviour of three distinct vascular bundle-inspired structures, envisioned as unit cells for the fabrication of high-performance bio-inspired metamaterials. Design/methodology/approach Three geometric variations of the structure were designed (with different relative densities of 0.50, 0.34 and 0.29) and fabricated via the fused filament fabrication technique using commercial polylactic acid filaments. The compression tests were undertaken in the two perpendicular planes of each structure, and their load–displacement behaviours were reported. A finite element model based on Ansys Explicit Dynamics Module was used to explain the deformation and failure mechanisms of the structures under uniaxial compression. Findings It was shown that the symmetric vascular bundle structure (the samples with relative density of 0.34) had the highest peak force, and it did not exhibit anisotropic behaviour. The failure mechanisms were dependent on the relationship among the geometry, loading direction and stress concentration: either along internal vertical struts that led to the collapsing of the central hole (brittle for 0.5 Direction 1, 0.29 Direction 1), or at outer corners/connecting points causing outer wall fracture while preserving the central hole (0.5 Direction 2, 0.29 Direction 2), with the 0.34 density sample demonstrating a more uniform, less catastrophically localised stress pattern. Originality/value To the best of the authors’ knowledge, for the first time, the paper demonstrates the anisotropic axial compression behaviour of novel vascular bundle-inspired structures. These designs have potential as unit cells in bio-inspired metamaterials, given their inherent ability to closely pack, interlock or connect, thereby enabling the creation of large and flexible assemblies for diverse applications.