A ready-to-manufacture optimization design of 3D chiral auxetics for additive manufacturing

The 3D chiral-type auxetic metamaterials have attracted massive attention in both academia and engineering. However, the complex deformation mechanism makes this kind of metamaterial hard to be topologically devised, especially in the 3D scenario. Most of existed studies only dealt with the re-entrant auxetics, and the optimized results are not able to be fabricated directly. This paper proposes a topology optimization design method for the 3D chiral-type auxetic metamaterial with ready-to-manufacture features. In this method, the matrix-compressed parametric level set is used to implicitly describe the high-resolution design boundary for the auxetic. In particular, the Gaussian radial basis function with global support is employed to parameterize the level set, and a discrete wavelet transform scheme is incorporated into the parametrization framework to effectively compress the full interpolation matrix. In this way, the optimization cost in 3D is noticeably reduced under a high numerical accuracy. To induce rotational deformation, rotation symmetry is applied to the micro-structured unit cell. The optimized microstructures possess explicit and smooth boundaries, and thus they can be 3D printed without tedious post-processing. Several 3D metallic microstructures with different Poisson’s ratios are numerically optimized and then fabricated using selective laser sintering. Practical Poisson's ratios of the samples are evaluated by conducting simulation and compression experiments. The tested Poisson's ratios by the compression experiment match the numerical estimation of the proposed method in a high consistency, which demonstrates the advances of our design method for creating reliable auxetic microstructures for 3D printing. The failure test is also implemented on different microstructures. It is concluded that the devised chiral metamaterial exhibits a great ability to absorb external deformation energy.