Mechanical Properties of Cochiral and Contrachiral Mechanical Metamaterials Under Different Temperatures

Abstract

The concept of materials with negative Poisson's ratio, that is, auxetic materials, first appeared in 1944. [1] The term "auxetic" was first used in 1991. [2] The first artificial auxetic re-entrant structure was proposed in other studies. [3,4] Artificial auxetic materials include cellular foams, [5][6][7][8][9][10][11][12][13][14] two-phase composites, [15][16][17] and molecular structures. [18][19][20] Some auxetic structures were obtained via topology optimization [21,22] and periodic tessellation. [23] There are also a few auxetic natural materials [1,19,24,25] and biomaterials, such as cow teat skin [26] and cancellous bones. [27] Among all of them, auxetic cellular materials are one important category due to their lightweight, excellent energy absorption capability, and multifunctionality responding to external environment. Auxetic materials have many engineering advantages due to their superior properties. For example, compared with the conventional materials, auxetic materials have increased indentation resistance, [28][29][30] shear resistance, energy absorption capability, [31] and variable permeability. [32,33] They can be used as fasteners, [34,35] to achieve synclastic curvature [5,36] and to develop shape memory materials and smart materials. [9,37] In addition, auxetic materials have better acoustic and vibration properties over their conventional counterparts. [38][39][40][41] Extended reviews of auxetic materials can be found in other studies. [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] There are various deformation mechanisms to achieve auxeticity, including re-entrant cells, [8] rotating units, [54] sliding bars, [55] and chiral structures. [9] Due to unique chirality-induced cell rotation, chiral auxetic structures have been extensively explored in the past two decades. Compared with conventional symmetric cellular materials such as honeycomb and re-entrant honeycomb, chiral structures have more stable deformation under external loads. [10] Therefore, they can preserve auxetic effects under large deformation. Based on the number of ligaments and their connecting method, existing auxetic chiral structures include hexachiral, [56] trichiral, antitrichiral, tetrachiral, [57] and antitetrachiral [58,59] designs. Also, based on various 3D expansion strategies, there are cubic-symmetric, noncubic symmetric [60] chiral designs.Chiral mechanical metamaterials achieve auxeticity via chirality-induced cell rotation. It was found that for chiral mechanical metamaterial, increasing rotation efficiency is the key to amplify auxetic effects. [61] A rigid-rod-rotational-spring model was proposed, [9] which analytically demonstrated that the rotation efficiency can be significantly increased by increasing the stiffness ratio of the center springs and corner springs in a missing-rib type of chiral design.Recently, the effects of handedness distribution on the in-plane effective mechanical property in bichiral mechanical metamaterials were explored. [11] Handedness is also a ve...

Inverse design of Bézier curve-based mechanical metamaterials with programmable negative thermal expansion and negative Poisson's ratio via a data augmented deep autoencoder

“…23,24 To widen the range of NTE and NPR with increased design flexibility, more complex structures such as hybrid design of bending and stretching behaviors, and patterned bi-material strips have been introduced. [25][26][27] However, such structures were designed through a parametric study based on the iteration of numerical simulation, which roughly infers the design parameters within the range. Studies on utilizing topology optimization for the design of MMs exhibiting arbitrary NTE and NPR have also been proposed, but topology optimization requires an iterative optimization process for each inverse design of MM, which entails a large computational cost.…”