Thermomechanically Tunable Elastic Metamaterials With Compliant Porous Structures

Abstract

Adding programmable function to elastic metamaterials makes them versatile and intelligent. The objective of this study is to design and demonstrate thermomechanically tunable metamaterials with a compliant porous structure (CPS) and to analyze their thermomechanical behaviors. CPS, the unit cell of the metamaterial, is composed of rectangular holes, slits, and bimaterial hinges. By decomposing kinematic rotation of a linked arm and elastic deformation of a bimaterial hinge, a thermomechanical constitutive model of CPS is constructed, and the constitutive model is extended to a threedimensional (3D) polyhedron structure for securing isotropic thermal properties. Temperature-dependent properties of base materials are implemented to the analytical model. The analytical model is verified with finite element (FE) based numerical simulations. A controllable range of temperature and strain is identified that is associated with a thermal deformation of the bimaterial hinge and contact on the slit surfaces of CPS. We also investigate the effect of geometry of CPS on the thermal expansion and effective stiffness of the metamaterial. The metamaterial with CPS has multiple transformation modes in response to temperature while keeping the same mechanical properties at room temperature, such as effective moduli and Poisson's ratios. This work will pave the road toward the design of programmable metamaterials with both mechanically and thermally tunable capability, providing unique thermomechanical properties with a programmable function.

Temperature-induced shape morphing of bi-metallic structures

“…Twodimensional zero-CTE architected structures were then realized at the macroscale [17][18][19][20], and at the microscale [21], to create thin thermally-stable films that are potentially applicable as space telescope mirrors. Recently, others have extended this paradigm to hierarchical arrangements with theoretically unbounded thermal expansion [22] and three-dimensional structures with tailorable CTE, including zero or negative [23][24][25][26][27] values.…”

A Passive Thermal Switch with Kirigami‐Inspired Mesostructures

“…Initially, compliant porous structure (CPS) was conceived with compliant mechanisms with cutting slits and holes, but it turns out to be a Kirigami structure having horizontal and vertical cuts as illustrated in Figure a . Our previous works demonstrated unique properties of the Kirigami structures ‐ for example, negative Poisson's ratio (NPR), negative thermal expansion (NTE), and switchable bi‐stiffness together with a reconfigurable capability triggered by heat . Motivated by the versatile thermomechanical properties, we propose a design of thermal switch with CPS for a fixed heat source and heat sink as illustrated in Figure b and c. Here, we label the upper Kirigami unit A, while the lower Kirigami unit B for simplification as shown in Figure b.…”

“…However, they have a relatively small coefficient of thermal expansion (CTE), being difficult for engineering an ON/OFF switching ratio, which is not favorable for the design of thermal switches. Furthermore, regarding manufacturability, a gap of thermal switches for an OFF state is on the order of several microns, which makes the fabrication and reliability being challenged.…”

“…Recently, mechanical metamaterials have received considerable attention due to their potential capability to break the barriers of physical properties of materials in nature by rational design. Most work of mechanical metamaterials has been explored in the design of elasto‐static and elasto‐dynamic properties − design of zero or negative values for mechanical parameters − Poisson's ratio, thermal expansion, dynamic mass density, and stiffness, etc .…”

“…The available literature on the metamaterials for thermal management can be classified into two fields: i) synthesis of materials with desired thermomechanical properties and ii) control of the direction of heat flow through media. The former category is related to the design of material properties − thermal expansion even beyond the natural limits; for example, negative thermal expansion with an extremely high value . The latter has focused on thermal engineering − directional control of thermal energy by rationally arranged microstructures or temperature‐responsive materials to provide thermal functions such as thermal cloaking, focusing, and reversal .…”