【Frontiers of HaiChuan Technology】Tianjin University develops 3D thermally expanding metamaterials

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Tianjin University develops 3D thermal expansion metamaterials 2024-12-24 14:04:25 Recently, a team led by Professor Chen Yan from the School of Mechanical Engineering at Tianjin University, in collaboration with Professor Wei Guowu from the University of Salford in the UK and Professor You Zhong from Oxford University in the UK, has designed a series of 3D thermal expansion metamaterials that enable extremely large-scale \"expansion when cold and contraction when hot\" on a 3D scale, or even \"no expansion or contraction at all\". This achievement was published in the journal Advanced Materials. 　　The research team designed a single-degree-of-freedom truncated octahedron paper-cut cell based on the principles of paper cutting. Dual-metal sheets were placed at the folding lines of the paper-cut polyhedron; when heated, these sheets would bend in either a forward or backward direction, thereby causing the deformation of the polyhedral cell structure. When the bimetallic strip bends in the forward direction, the metamaterial exhibits negative thermal expansion properties ； When the bimetallic strip bends in the opposite direction, the metamaterial exhibits positive thermal expansion properties ； When the cell structure is orthogonally symmetric, the thermal expansion of the metamaterial remains consistent and uniform in the three orthogonal directions. By adjusting design parameters such as the thickness of the bimetallic strip, a very wide range of control over the thermal expansion coefficient can be achieved. 　　Furthermore, the research team arranged alternating combinations of anisotropic unit cells with negative and positive thermal expansion, and through precise modeling, achieved negative/zero/positive thermal expansion responses in all three orthogonal directions of a single supermaterial, thereby meeting the directional requirements for a material’s response to heat in specific application scenarios. 　　It is said that mechanical metamaterials are a new type of artificial material that overcomes the limitations of natural laws through a special topological arrangement of the underlying materials, thereby achieving extraordinary physical properties that natural materials do not possess. Thermal expansion and contraction are common phenomena in natural materials, but thermal expansion can cause the materials to deform, leading to structural damage or a loss of precision. Existing mechanical metamaterials can only achieve negative thermal expansion over a limited range.