Design and fabrication of 3D isotropic chiral lattice metamaterials inspired by Kong-Ming locks

Structural materials for engineering applications often operate under forces from multiple directions, demanding isotropic mechanical performance. Mechanical metamaterials (MMs) exhibit high designability in mechanical properties, and their topology-based designs have enabled the realization of nearly isotropic mechanical responses in theory. However, most MMs are fabricated via additive manufacturing processes, where the layer-by-layer deposition introduces materials anisotropy that limits the actual performance obtained. Inspired by Kong-Ming Locks, this work proposes an orientation-controlled assembly strategy that transforms anisotropic 3D-printed modules into mechanically-enhanced isotropic metamaterials. The MM architecture is decomposed into modular planar components (printed with filaments aligned to its principal load-bearing direction); the components are then mechanically assembled to a macroscopic MM, thereby altering the deposition orientation along critical loading paths and enhancing isotropy. Experiments and finite element simulations are conducted to evaluate the mechanical performance under quasi-static, dynamic impact, and cyclic fatigue loads. The near-isotropic mechanical responses are achieved in assembled MMs: compared with integrated MMs, their anisotropy level is reduced by 94.3%, while stiffness, strength, failure strain, and energy absorption increase by 9.3%, 50.0%, 59.1%, and 155.5%, respectively. The proposed strategy provides a route to overcome AM-induced anisotropy and enables scalable manufacturing of high-performance, isotropic metamaterials for complex service environments.