Compressive Mechanical Behavior of Additively Manufactured 3D Auxetic Metamaterials with Enhanced Strength

Compared with 2D auxetic metamaterials, 3D auxetic metamaterials present better structural, mechanical, and functional properties, which are more applicable in many potential applications in engineering fields. Herein, three types of 3D star-shaped auxetic (SSA) structures, re-entrant and star-shaped composite auxetic (RSA) structures, and star-rhombic auxetic (SRA) structures with small unit cell are proposed and fabricated by selective laser melting method. The compressive behavior and energy absorption of the auxetic structures are explored and compared based on finite-element method (FEM) verified by the compression test results of the sample. Meanwhile, the numerical results present good agreements with the experimental results in terms of deformation mode, Poisson's ratio, and compression behavior. The results reveal that SRA structures exhibit superior elastic modulus, compressive strength, and energy absorption than SSA and RSA structures, which stems from the auxetic effect, obstruction of rhombic structures to the deformation of inclined struts and more plastic hinges. It is precisely because of the obstruction of rhombic structures that SRA structures exhibit weakening auxetic characteristic and even no auxetic behavior during the higher strain range. In addition, the length of the structural strut presents a significant impact on the energy absorption performance and compression strength of all the structures.