Mechanical metamaterial
[1][2][3][4][5][6][7][8][9][10][11][12][13] 3D printing, or additive manufacturing, has revolutionized the field in the past decade by enabling the fabrication of intricate mechanical metamaterial structures.
Some of the unprecedented and unusual properties of classical mechanical metamaterials include: Poisson's ratio defines how a material expands (or contracts) transversely when being compressed longitudinally.
It has been shown, however, that metamaterials can be designed to exhibit negative compressibility transitions, during which the material undergoes contraction when tensioned (or expansion when pressured).
This anomalous behavior stems from their carefully engineered microstructure, which allows for internal deformation mechanisms that counteract the applied stress.
[32][33][34][35][36][37][38][39][40] Furthermore, their unique elastic properties may find utility in creating novel structural components with enhanced resilience and adaptability to dynamic loads.
When the unit cells of typical metamaterials are not centrosymmetric it has been shown that an effective description using chiral micropolar elasticity (or Cosserat [43]) was required.
[44] Micropolar elasticity combines the coupling of translational and rotational degrees of freedom in the static case and shows an equivalent behavior to the optical activity.
[45][46][47] While theoretical composites that achieve the same upper bound have existed for some time,[48] they have been impractical to fabricate as they require features on multiple length scales.
[49] Single length scale designs are amenable to additive manufacturing, where they can enable engineered systems that maximize lightweight stiffness, strength and energy absorption.
To date, most mainstream studies on mechanical metamaterials have focused on passive structures with fixed properties, lacking active sensing or feedback capabilities.
Similar to complex living organisms, intelligent mechanical metamaterials can potentially deploy their cognitive abilities for sensing, self-powering, and information processing to interact with the surrounding environments, optimizing their response, and creating a sense–decide–respond loop.
[50] Recent studies explore new classes of mechanical metamaterials that can response to different excitation types such acoustic,[62] thermophotovoltaic[63] and magnetic.
Meta-tribomaterials[65] [66] proposed in 2021 are a new class of multifunctional composite mechanical metamaterials with intrinsic sensing and energy harvesting functionalities.
[67] These material systems are created via integrating mechanical metamaterials, digital electronics and nano energy harvesting (e.g. triboelectric, piezoelectric, pyroelectric) technologies.
[67] Such computing metamaterial systems can be particularly useful under extreme loads and harsh environments (e.g. high pressure, high/low temperature and radiation exposure) where traditional semiconductor electronics cannot maintain their designed logical functions.
