Fracture behavior of 2D Disordered Network Mechanical Metamaterials

Disordered network mechanical metamaterials (DNMM), comprised of random arrangements of bonds and nodes, have emerged from theoretical and experimental studies as promising candidates for metamaterials with highly tunable elastic constants. This tunability is achieved through a computational approach called pruning that systematically removes bonds while optimizing for either the bulk or shear modulus. We take advantage of the pruning approach to study fracture behavior in 2D DNMMs. We perform quasi-static tensile testing to study the role of network architecture in controlling crack propagation. Unpruned and pruned networks with systematically varying bond thickness and materials (Silicone elastomer, Nylon 6 and Acrylic) are studied. We elucidate the impact of network architecture in strain localization during crack propagation and how it relates to the overall toughness of the networks. Our experiments demonstrate that it is crucial to finely control the bulk to shear modulus ratio of the DNMM to control toughness. This ratio describes the ability to change shape over its ability to change volume. The principles learned from the study of DNMMs with finely tuned local elastic properties might provide an effective route for materials with improved tear-resistant properties.