Disorder Enhances the Fracture Toughness of Mechanical Metamaterials

TL;DR

Introducing disorder into mechanical metamaterials can significantly improve their fracture toughness by promoting distributed damage, with an optimal disorder level maximizing toughness without compromising strength.

Contribution

This work reveals that disorder, rather than specific geometry, enhances toughness and provides a mechanics model linking disorder to toughness, validated by simulations and experiments.

Findings

Toughness more than 2.6 times that of ordered lattices at optimal disorder

Disorder level controls toughness enhancement, not specific geometry

Model accurately predicts toughness based on disorder without crack path knowledge

Abstract

Mechanical metamaterials with engineered failure properties typically rely on periodic unit cell geometries or bespoke microstructures to achieve their unique properties. We demonstrate that intelligent use of disorder in metamaterials leads to distributed damage during failure, resulting in enhanced fracture toughness with minimal losses of strength. Toughness depends on the level of disorder, not a specific geometry, and the confined lattices studied exhibit a maximum toughness enhancement at an optimal level of disorder. A mechanics model that relates disorder to toughness without knowledge of the crack path is presented. The model is verified through finite element simulations and experiments utilizing photoelasticity to visualize damage during failure. At the optimal level of disorder, the toughness is more than 2.6x of an ordered lattice of equivalent density.