Bidirectional Non‐Newtonian Mechanical Metamaterials

ABSTRACT Mechanical metamaterials have garnered significant attention due to their rich, counterintuitive, and programmable mechanical properties, which are enabled by their structural design. To date, most studies have focused on quasi‐static responses, primarily involving deformation modes such as tension, compression, and torsion. However, many practical scenarios involve dynamic and impact loading conditions, where loading velocity becomes a critical factor governing mechanical response. Recently, velocity‐triggered mechanical metamaterials have emerged, with certain designs exhibiting non‐Newtonian characteristics. Nevertheless, these designs remain at an early stage and are largely restricted to unidirectional loading conditions. This work proposes an inertia‐based velocity‐dependent stiffness modulation mechanism that enables distinct stiffness states under different loading velocities. Based on this mechanism, a non‐Newtonian metamaterial is designed to extend velocity‐dependent mechanical behavior from unidirectional to bidirectional loading conditions. The proposed structures are fabricated via 3D printing and experimentally characterized using a velocity‐controlled testing platform. This work provides a new design strategy for achieving multidirectional, velocity‐dependent mechanical responses in impact‐regulating metamaterials.