Shape-Memory Alloy-Based Auxetic Smart Metamaterials: Enabling Inherently Bidirectional Actuation

Auxetic metamaterials, characterized by their negative Poisson's ratio, have garnered significant interest in various fields due to their unique mechanical properties. This article presents a pioneering approach to the development of auxetic smart metamaterials using shape memory alloy (SMA) as the core material. As SMAs can be Joule heated to change between their low- and high-temperature phases to trigger the actuation of the structure, the auxetic smart metamaterial can actively modify its shape and stiffness to produce bidirectional actuation with a single power input and using a single bias mechanical element. The proposed active auxetic metamaterial consists of an SMA plate patterned with auxetic cuts, creating hinges that modulate the deformation of the structure to produce an auxetic behavior. This work looks at the impact of different geometric parameters on the behavior of the structure, including its generated force, its maximum strain, and its Poisson's ratio. The study also investigates the effect of the number of segmented units, revealing that designs with more segmented units suffer from stress concentrations near attachment points, limiting their advantages. This article shows that smart materials can help imbue metamaterials such as auxetic metamaterials with active properties to facilitate their implementation in future robotic applications. Shape-memory alloy-based auxetic smart metamaterials enable the active deformation of an auxetic structure such that the structure can produce inherently bidirectionally coupled deformations. The structure can be stretched or compressed and Joule heated to recover its initial shape, and can find use in applications such as four-jawed microgrippers to minimize the number of components.image (c) 2024 WILEY-VCH GmbH