Experimental and computational analysis of the mechanical properties of composite auxetic lattice structures

In this work, the influence of a compliant hyperelastic polymeric phase infiltrated inside stiff auxetic lattices is studied through experimental and numerical approaches. Samples were fabricated using material jetting technology (MJT). The design principle mimics examples of biological materials which combine stiff and compliant materials to attain high superior mechanical properties exceeding the rule of mixtures of both constituent. Two negative Poisson's ratio lattice designs are considered, namely Hexaround and Warmuth cell. Their effective elasto-mechanical properties are investigated through finite element method (FEM) using a homogenization strategy with periodic boundary conditions. A comparison of mechanical properties between lattices and composite lattices, for multiple lattice/matrix volume fractions is discussed and numerical models are validated through a series of compression tests. Results suggest that filling lattices could increase Young's modulus, peak stress, plateau stress and delayed densification of the lattice, hence improving both specific energy absorption (SEA) and absorption efficiency of the considered architectured materials. The improvements are attributed to the presence of the matrix acting as a structural support, modifying lattice failure mode from layerwise to shear band breaking. These results expand the design principles for new energy absorption devices based on architectured materials.