Mechanical instabilities in periodic porous elastic structures may lead to the formation of homogeneous patterns, opening avenues for a wide range of applications that are related to the geometry of the system. This study focuses on an elastomeric porous structure comprising a triangular array of circular holes, and shows that by controlling the loading direction, multiple pattern transformations can be induced by buckling. Interestingly, these different pattern transformations can be exploited to design materials with highly tunable properties. In particular, these results indicate that they can be effectively used to tune the propagation of elastic waves in phononic crystals, enhancing the tunability of the dynamic response of the system. Using a combination of finite element simulations and experiments, a proof‐of‐concept of the novel material is demonstrated. Since the proposed mechanism is induced by elastic instability, it is reversible, repeatable, and scale‐independent, opening avenues for the design of highly tunable materials and devices over a wide range of length scales.

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The sliding friction of a graphene flake atop strained graphene substrates is studied using molecular dynamics simulation. We demonstrate that in this superlubric system, friction can be reduced nonmonotonically by applying strain, which differs from previously reported results on various 2D materials. The critical strain needed for significant reduction in friction decreases drastically when the flake size increases. For a 250 nm flake, a 0.1% biaxial strain could lead to a more than 2-order-of-magnitude reduction. The underlying mechanism is revealed to be the evolution of Moiré patterns. The area of the Moiré pattern relative to the flake size plays a central role in determining friction in strain engineering and other scenarios of superlubricity as well. This result suggests that strain engineering could be particularly efficient for friction modification with large contacts.

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Structural superlubricity, which promises an ultralow sliding friction due to the cancellation of the lateral force between two incommensurate interfaces, is a fundamental phenomenon in modern tribology. Achieving macroscale superlubricity is critical to its practical application, and the key is understanding how friction scales with real contact area, that is, the scaling law, especially for kinetic friction which accounts for most of the energy dissipation during sliding. Here, inspired by extensive molecular dynamics simulations we introduce an analytical general theory for the scaling law of structural superlubricity, which could well explain existing experimental measurements on the nanoscale. On the microscale, the scaling law is validated by measuring the friction of several microscale superlubric graphite/hexagonal boron nitride heterojunctions. The proposed theory predicts a characteristic size D = O(100 nm) above which the scaling transits from sublinear to linear. Our results provide insights in the origin of friction for structural superlubricity and benefit its application on macroscale.