Mechanical characterization of auxetic chiral-reentrant cellular metamaterials: A finite element study

This study investigates the mechanical behavior of a novel tubular auxetic metamaterial combining chiral (rotation-dominated) and reentrant (hinging) mechanisms in a hybrid “Circle-I” design. The sole design variable was the internal extrusion thickness (the difference between external and internal diameters), varied across five configurations from 1 mm to 9 mm in odd increments. Finite element simulations under quasi-static axial compression were used to evaluate load-displacement response, stiffness, energy absorption (EA), specific energy absorption (SEA), and structural negative Poisson's ratio (NPR). Results showed strong thickness dependence: increasing internal thickness significantly enhanced conventional mechanical properties, with peak force reaching 917 N in the 9 mm configuration at smaller displacements, stiffness rising from 18 N/mm to 598 N/mm, and energy absorption increasing from 50 J for the thinnest configuration to 1496 J for the thickest. In contrast, NPR exhibited a non-monotonic trend, becoming more negative (from −1.5 to a peak of −1.8) as thickness increased from 1 mm to 5 mm, before dropping to −1.0 at 9 mm. This non-monotonic behavior highlights an optimal intermediate thickness for maximum auxeticity via efficient chiral-reentrant coupling. Experimental validation confirmed the numerical predictions. The findings demonstrate that internal thickness is an effective single-parameter control for tailoring multifunctional performance in tubular chiral-reentrant metamaterials, with potential applications in impact protection, biomedical devices, and lightweight structures.