EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Mechanical metamaterials with variable stiffness gained a lot of research interest, as they allow for structures with complex boundary and load conditions. Herein, we highlight the design, additive manufacturing and mechanical testing of a new kind of bending-dominated metamaterial. Advancing from well-established mechanical metamaterials concepts, the proposed geometry allows to vary the stiffness in the three spatial directions independently. Therefore, structures with different orientational properties can be designed, ranging from isotropic to anisotropic structures, including orthotropic structures. Gradual transitions from one unit cell to the next can be realized, enabling smooth transitions from soft to hard regions. Different additive manufacturing techniques have been employed to manufacture polymer-based specimens, namely Fused Filament Fabrication, Digital Light Processing and Selective Laser Sintering. The manufacturing of the structures is not limited to the presented techniques, but can be expanded to all available additive manufacturing techniques and their respective materials, including non-polymer-based ones. The properties of the structures were determined by mechanical tests in the form of compression tests. Two different numerical models have been employed using ABAQUS. First, simulations on the full-size structures were performed to verify the applicability of simulations to represent the compression tests. Second, a homogenization method was implemented to reduce the computational cost of the simulations. The material model for the simulations is based on three-point-bending tests.
The test results were in good agreement with the simulations and both showed a wide range of possible mechanical properties. In addition to isotropic structures, the possibility to create orthotropic and anisotropic variations was also investigated and affirmed via simulations. Thus, further highlighting the design-flexibility of the newly developed mechanical metamaterial.