Mechanical unfeelability concentrator through topology optimization

Abstract

Mechanical cloaks made from elastic metamaterials that make objects unfeelable have been developed, but usually each cloaking device performs only a single function. In this Letter, we present our computational attempts at instilling two different functionalities, cloaking and stress concentration, in a metastructure designed through topology optimizing a mechanical cloak-concentrator for linear elasticity. Solving this optimization problem involved improving two different objective functions, one for cloaking and the other for stress concentration. As an optimizer, the covariance matrix adaptation evolution strategy was adopted to find the optimal level set functions, which express the design configurations with clearly delineated boundaries. Optimized cloak-concentrators reproduce outer displacements as if nothing is present despite the presence of a system concentrating stress on an interior domain. We also present demonstrations of topology optimized configurations for mechanical unfeelability concentrators that perform robustly under loads at any location around the system and under the cloaked region of arbitrary Young's modulus. Our design scheme paves the way for designing metastructures that accommodate various multiple functions via the means of elastostatics.