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Abstract Inspired by the protective armors in nature, composites with asymmetric 3D articulated tiles attached to a soft layer are designed and fabricated via a multi-material 3D printer. The bending resistance of the new designs are characterized via three-point bending experiments. Bending rigidity, strength, and final deflection of the designs are quantified and compared when loaded in two different in-plane and two different out-of-plane directions. It is found that in general, the designs with articulated tiles show direction-dependent bending behaviors with significantly increased bending rigidity, strength, and deflection to final failure in certain loading directions, as is attributed to the asymmetric tile articulation (asymmetric about the mid-plane of tiles) and an interesting sliding-induced auxetic effect. Analytical, numerical, and experimental analyses are conducted to unveil the underlying mechanisms. 

Abstract For artificial materials, desired properties often conflict. For example, engineering materials often achieve high energy dissipation by sacrificing resilience and vice versa, or desired auxeticity by losing their isotropy, which limits their performance and applications. To solve these conflicts, a strategy is proposed to create novel mechanical metamaterial via 3D space filling tiles with engaging key‐channel pairs, exemplified via auxetic 3D keyed‐octahedron–cuboctahedron metamaterials. This metamaterial shows high resilience while achieving large mechanical hysteresis synergistically under large compressive strain. Especially, this metamaterial exhibits ideal isotropy approaching the theoretical limit of isotropic Poisson's ratio, ‐1, as rarely seen in existing 3D mechanical metamaterials. In addition, the new class of metamaterials provides wide tunability on mechanical properties and behaviors, including an unusual coupled auxeticity and twisting behavior under normal compression. The designing methodology is illustrated by the integral of numerical modeling, theoretical analysis, and experimental characterization. The new mechanical metamaterials have broad applications in actuators and dampers, soft robotics, biomedical materials, and engineering materials/systems for energy dissipation. 

This investigation explores novel two‐phase chevron mechanical metamaterials that exhibit auxetic properties. Unlike traditional foam‐like cellular or porous auxetic materials, these designs are composed of chevron patterned layers embedded in anisotropic matrix. This innovation design allows for auxeticity in two orthogonal in‐plane directions (bi‐auxeticity) or in all in‐plane directions (complete auxeticity), providing not only a general strategy but also detailed guidelines for designing non‐porous auxetic mechanical metamaterials with tunable auxetic behaviors. One goal of this work is to explore the mechanical behavior, specifically effective stiffness and Poisson's ratio, of these new designs and to identify the design space for auxetic behavior using numerical and experimental methods. Systematic finite element (FE) simulations are conducted using ABAQUS and Python scripts to quantify effective stiffness and Poisson's ratio within a small strain range. To validate the numerical predictions, three representative designs are selected and fabricated via multi‐material polymer jetting. Uniaxial tension experiments are conducted on these specimens. Design spaces for non‐auxeticity, partial‐auxeticity, and complete auxeticity are identified through an integrated numerical approach. Theoretical criteria for determining the completeness of auxeticity are proposed and verified via FE simulations.