This study investigates the mechanical properties of novel, biodegradable polylactic acid (PLA) and short flax fiber composite sandwich structures with chiral architected cores, fabricated via additive manufacturing. Three core geometries were designed and tested: tetrachiral, anti-tetrachiral, and a novel anti-tetrachiral arrowhead configuration, each with one- and two-unit cells in width. Experimental results from tensile, compression, and three-point bending tests revealed that these lattices exhibit auxetic behavior (negative Poisson’s ratio), driven by the rotation of cylindrical nodes and the flexure of connecting ligaments. The mechanical performance was highly dependent on the core geometry and relative density. The anti-tetrachiral arrowhead core, in its two-cell configuration (AT4CA2), demonstrated superior tensile stiffness (Young’s Modulus of 423 MPa). In compression, anti-tetrachiral cores (AT4C2, AT4CA2) showed exceptional energy absorption capacity (93 J and 90 J, respectively), significantly outperforming their tetrachiral counterparts despite similar relative densities. Flexural tests confirmed that the sandwich structures provide a high stiffness-to-weight ratio, with the arrowhead geometry (AT4CA1) achieving the highest peak load, underscoring the critical role of microstructural engineering over mere material quantity. This work establishes that these bio-composite metamaterials, particularly the innovative anti-tetrachiral arrowhead design, offer a promising and environmentally friendly alternative for lightweight, high-performance structural applications.
Hamrouni et al. (Fri,) studied this question.