Inerter is a mechanical device capable of exhibiting an inertial effect that is orders-of-magnitude larger than its physical mass. By coupling linear motion with rotational motion of a built-in flywheel, the inerter generates a response force proportional to the relative acceleration between its two independent terminals. Here, we experimentally fabricate and characterize vibro-elastic metamaterial designs with embedded interters. Aided by computational simulations, our design aims to demonstrate a unique and fundamental advantage in forming a bandgap at extremely low frequencies. After fabrication, we perform wave-propagation testing on samples with both longitudinal (pressure) and transverse (shear) waves. The results show that our design can be made tunable by changing either the effective rotational inertia or the effective connection stiffness. This significantly enhances the metamaterial’s applicability in mitigating real-world structural vibration with at ultra-low frequency and very long wavelength. Our data indicate that inerter-based design may outperform traditional locally resonant metamaterials and could be more suitable for broader application scenarios, such as seismic events.
Networks of interconnected materials permeate throughout nature, biology, and technology due to exceptional mechanical performance. Despite the importance of failure resistance in network design and utility, no existing physical model effectively links strand mechanics and connectivity to predict bulk fracture. Here, we reveal a universal scaling law that bridges these levels to predict the intrinsic fracture energy of diverse networks. Simulations and experiments demonstrate its remarkable applicability to a breadth of strand constitutive behaviors, topologies, dimensionalities, and length scales. We show that local strand rupture and nonlocal energy release contribute synergistically to the measured intrinsic fracture energy in networks. These effects coordinate such that the intrinsic fracture energy scales independent of the energy to rupture a strand; it instead depends on the strand rupture force, breaking length, and connectivity. Our scaling law establishes a physical basis for understanding network fracture and a framework for fabricating tough materials from networks across multiple length scales.
Mechanical Metamaterials In article number 2206238, Bolei Deng, Katia Bertoldi, and co-workers present a neural accelerated evolution strategy to inverse design mechanical metamaterials with targeted nonlinear responses. The proposed platform could support the design of innovative footwear.
In this letter we investigate the propagation of nonlinear pulses along the free surface of flexible metamaterials based on the rotating squares mechanism. While these metamaterials have previously been shown to support the propagation of elastic vector solitons through their bulk, here we demonstrate that they can also support the stable propagation of nonlinear pulses along their free surface. Further, we show that the stability of these surface pulses is higher when they minimally interact with the linear dispersive surface modes. Finally, we provide guidelines to select geometries that minimize such interactions.
In article number 2001863, Katia Bertoldi and co-workers fabricate the first programmable kirigami balloons: soft devices that can be automatically designed to morph into a target shape upon inflation. This work provides a new platform for shape-morphing devices that could support the design of innovative medical tools, actuators, and reconfigurable structures. Cover art: Antonio Elia Forte.
Kirigami-inspired metamaterials are attracting increasing interest because of their ability to achieve extremely large strains and shape changes via out-of-plane buckling. While in flat kirigami sheets, the ligaments buckle simultaneously as Euler columns, leading to a continuous phase transition; here, we demonstrate that kirigami shells can also support discontinuous phase transitions. Specifically, we show via a combination of experiments, numerical simulations, and theoretical analysis that, in cylindrical kirigami shells, the snapping-induced curvature inversion of the initially bent ligaments results in a pop-up process that first localizes near an imperfection and then, as the deformation is increased, progressively spreads through the structure. Notably, we find that the width of the transition zone as well as the stress at which propagation of the instability is triggered can be controlled by carefully selecting the geometry of the cuts and the curvature of the shell. Our study significantly expands the ability of existing kirigami metamaterials and opens avenues for the design of the next generation of responsive surfaces as demonstrated by the design of a smart skin that significantly enhances the crawling efficiency of a simple linear actuator.
The advancement of Large Language Models (LLMs), including GPT-4, provides exciting new opportunities for generative design. We investigate the application of this tool through sequential steps of the computational design and manufacturing workflow. In particular, we examine how LLMs can aid in tasks including: converting a text-based prompt into a quantitative design specification, transforming a design into manufacturing instructions, producing a design space and variations within that space, computing the performance of a given design, and optimizing for designs predicated on performance goals. Through a series of examples, we highlight overarching capabilities and limitations of the current LLMs. By exposing these aspects, we aspire to catalyze the continued improvement and progression of these models, providing a roadmap to build on their strengths and reduce their weaknesses."How Can Large Language Models Help Humans in Design And Manufacturing?" is a two-part article. Part 2, "Synthesizing an End-To-End LLM-Enabled Design and Manufacturing Workflow" can be read here .
Phononic crystals and vibro-elastic metamaterials are characterized by their dispersion relations—how frequency depends on wave number/vector. While there are many existing methods to solve the forward problem of obtaining the dispersion relation from any arbitrarily given design. The inverse problem of obtaining a design for any arbitrarily given dispersion bands have only had very limited success so far. Here, we report a new design scheme capable of leading to arbitrary dispersion relations by incorporating non-local interactions between unit cells. Considering discrete models of one-dimensional mass-spring chain, we investigate the effects of both local (i.e., springs between the nearest neighbors) and non-local (i.e., springs between the next nearest neighbors and other longer range springs) interactions. First, we derive the general governing equations of non-local phononic chains. Next, we examine all design constraints for a linear, periodic, passive, statically stable, non-gyroscopic, and free-standing system. Finally, we perform analytical calculations and numerical simulations to solve the inverse problems. The results illuminate a new path toward novel wave manipulation functionalities, such as sophisticated combinations of roton-like, maxon-like, undulation-point and other zero-group-velocity (ZGV) modes, as well as multi-wavelength and multi-speed propagations of the same mode at the same frequency.
Dispersion relations govern wave behaviors, and tailoring them is a grand challenge in wave manipulation. We demonstrate the inverse design of phononic dispersion using nonlocal interactions on one-dimensional spring-mass chains. For both single-band and double-band cases, we can achieve any valid dispersion curves with analytical precision. We further employ our method to design phononic crystals with multiple ordinary (roton or maxon) and higher-order (undulation) critical points and investigate their wave packet dynamics.
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