DESIGN OF 2D AND 3D METAMATERIALS WITH TAILORED THERMOMECHANICAL PROPERTIES

• Autor(a) principal: Cardoso, João Oliveira
• Data de Publicação: 2024
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/175607
• topic: Metamaterials; Auxetic; Anepectic; Negative Poisson’s ratio; Negative thermal expansion; Additive manufacturing; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia dos Materiais

Metamaterials are a method of organizing materials according to different architectures to obtain properties not usually found in nature. These materials have the potential of addressing complex and nuanced engineering problems. Although originally metamaterials were confined to electro-optical properties, the scope has broadened to encompass all fields including structural metamaterials, which are the subject of this work. Herein, several 2D and 3D architectures were studied via modelling, simulation, and experimental characterization, comparing results to obtain insights regarding the achievement of negative/null values for the Poisson's ratio (NPR), resulting in the so-called auxetic behavior; and the obtention of similarly negative/null values for the thermal expansion coefficient (NTE), which when coupled with NPR corresponds to a behavior dubbed anepectic. Ultimately, the objective was to find means to tailor both parameters' values to specific targets by modifying the metamaterial's architecture. All the structures were produced via additive manufacturing, and can be resumed as: ● A 2D re-entrant metallic auxetic mesh. This didn't result in success, but several milestones were reached, and possible strategies were laid out for future work. ● A 2D polymeric auxetic mesh obtained via topology optimization. In the case of these 2D structures, a valid design and validation methodology has been established, to be adopted in subsequent research. ● A 3D re-entrant polymeric anepectic lattice. As a follow-up from previous results obtained with 2D re-entrant meshes, their 3D counterparts represented the most immediate approach to achieve the desired NPR and NTE behavior. ● 3D polymeric lattices based on the double-elliptic ring unit cell. With this architecture, an auxetic structure, ultimately intent on mimicking the behavior of inter-vertebral disks, was designed, and tested. Also, by adequate partial substitution of the constituting material, a functional anepectic prototype was designed and its behavior validated experimentally. ● 3D auxetic architectures based on triple periodic minimal surface (TPMS) geometries, ultimately chosen as a way to match the properties of femoral bone. Among these TPMS architectures, the gyroid geometry was the object of extensive studies, which apart from the determination of its properties led to the development of different metamaterial design methodologies. As a complement, a different TPMS, the Schwarz P geometry, served as a means to explore the viability of additively manufactured auxetic metallic structures.