Lightweight Self-Forming Super-Elastic Mechanical Metamaterials with Adaptive Stiffness

摘要

Scarcity of stiff, yet compliant, materials is a major obstacle toward biological-like mechanical systems that perform precise manipulations while being resilient under excessive load. A macroscopic cellular structure comprising two pre-stressed elastic "phases" is introduced, which displays a load-sensitive stiffness that drops by 30 times upon a "pseudoductile transformation" and accommodates a fully recoverable compression of over 60%. This provides an exceptional 20 times more deformability beyond the linear-elastic regime, doubling the capability of previously reported super-elastic materials. In virtue of the pre-stressing process based on thermal-shrinkage, it simultaneously enables a heat-activated self-formation that transforms a flat laminate into the metamaterial with 50 times volumetric growth. The metamaterial is thereby inherently lightweight with a bulk density in the order of 0.01 g cm(-3), which is one order of magnitude lower than existing super-elastic materials. Besides the highly programmable geometrical and mechanical characteristics, this paper is the first to present a method that generates single-crystal or poly-crystal-like 3D lattices with anisotropic or isotropic super-elasticity. This pre-stress-induced adaptive stiffness with high deformability could be a step toward in situ deployed ultra-lightweight mechanical systems with a diverse range of applications that benefit from being stiff and compliant.