Size-Effect Stiffening and Densification Strain Regulation Shape Micro Metamaterials for Ultra-High, Cycle-Stable Energy Absorption.

Abstract

Thin-walled metamaterials hold great promise for energy absorption, yet a fundamental conflict persists between high energy absorption and cycle stability in most existing designs, which is the key challenge for applications of these materials. Here, a new kind of energy-absorbing and cycle-stable integrated (ECI) microscale metamaterials are presented that overcome this limitation, surpassing conventional thin-walled metamaterials in compression strength and energy absorption by 1-4 orders of magnitude. Cyclic loading experiments show that the programmable ECI micro metamaterials retain 87% of their energy absorption capacity after multiple cycles. These breakthroughs stem from a novel design methodology that harnesses size-effect-induced bending stiffness enhancement together with densification strain regulation. Guided by this approach, the rotatable frames with tunable densification strain and curvature-optimized micro shells with enhanced bending stiffness were innovatively coupled, leading to a 630% improvement in compressive strength and energy absorption over macroscale equivalents. Dynamic characterization reveals that the optimal ECI micro-metamaterial significantly outperforms conventional energy-absorbing materials and lattice structures, specifically exceeding them by an average of 124% in rebound attenuation. This work redefines the performance envelope of thin-walled metamaterials and provides a new paradigm for designing ultra-robust protective systems through geometric-stiffness hybridization.