Micro-structured medium with large isotropic negative thermal expansion

Abstract

A challenge in nano- and micro-mechanics is the realization of innovative materials exploiting auxetic behaviour to tailor thermal expansion properties. For this purpose, a new class of micro-structured media possessing an extremely wide range of tunable (positive, negative or even zero) thermal expansion is proposed and analytically and experimentally assessed. For this class of isotropic Mechanical-Auxetic Thermal-Shrinking media, the effective coefficient of thermal expansion is explicitly linked to two microstructural variables via a simple relation, allowing the design with desired values. The theoretical predictions for the negative thermal properties are fully validated by the experimental and numerical outcomes. The simplicity of the proposed structure makes the design useful for the production of a new generation of advanced media, with applications ranging from micromechanical devices to large civil and space structures.

Hierarchical auxetic and isotropic porous medium with extremely negative Poisson’s ratio

“…Alternative approaches to design auxetic media are presented in the reviews [28][29][30][31][32]. Some auxetic systems are also characterised by a negative value of the coefficient of thermal expansion, implying that they shrink when subjected to an increase in temperature [33][34][35]. Additionally, it has been shown that it is also possible to achieve a smooth transition through a wide range of negative and positive Poisson's ratios by using an origami cell that morphs continuously between a Miura mode and an eggbox mode [36][37][38].…”

Buckling vs unilateral constraint for a multistable metamaterial element

“…However, meta-materials exhibit extraordinary mechanical properties even when subject to quasi-static loading, particularly when large deformations are involved [19,20,21,22,23,24,25,26]. Examples are numerous, including cloaking [27], extreme stiffness [28], shape morphing [29], auxeticity [30,31], negative thermal expansion [32], and multistable architectures [33,34,35,36,37]. A flow in this research stream is the exploitation of structures beyond buckling and instability loads [38], in a range of extreme deformations [39].…”

Buckling versus unilateral constraint for a multistable metamaterial element

“…However, metamaterials exhibit extraordinary mechanical properties even when subject to quasi-static loading, particularly when large deformations are involved [19][20][21][22][23][24][25][26]. Examples are numerous, including cloaking [27], extreme stiffness [28], shape morphing [29], auxeticity [30,31], negative thermal expansion [32] and multistable architectures [33][34][35][36][37]. A flow in this research stream is the exploitation of structures beyond buckling and instability loads [38], in a range of extreme deformations [39].…”