Butterfly-shaped honeycomb structures with embedded elliptical units: Tunable Poisson’s ratio and energy absorption

Auxetic honeycomb structures are promising for lightweight energy-absorbing applications. However, achieving a wide tunable range of Poisson’s ratio while maintaining good energy-absorption performance remains challenging. This study proposes a honeycomb system with a butterfly-shaped outer contour and embedded circular/elliptical units, termed EBHs, including three configurations: vertical ellipse (VEBH), horizontal ellipse (HEBH), and circle (CEBH). Through combined 3D printing, finite element simulation, and parametric analysis, key geometric parameters, namely the major-to-minor axis ratio k of the embedded ellipse (generalized as the radius R for CEBH), defect line inclination θ , and wall thickness t , are systematically investigated. Results show that t mainly governs stiffness and load-carrying capacity, whereas k / R and θ regulate Poisson’s ratio and deformation mode. VEBH exhibits a stable negative Poisson’s ratio through ellipse rotation at small k and θ ; CEBH shows a non-monotonic evolution from positive to quasi-zero at R = 5 mm and then to negative; and HEBH enables a continuous transition from negative to positive through θ adjustment. In addition, compared with four representative auxetic honeycomb benchmarks, all three EBHs configurations exhibit higher specific energy absorption. These findings propose a parameterized design strategy for achieving programmable negative, quasi-zero, and positive Poisson’s ratios in lightweight energy-absorbing structures.