Mechanics of Two-Phase Auxetic Chevron Mechanical Metamaterial

Auxetic materials has two major categories: one is cellular/foam like materials, which experience auxetic effect due to the rotation of ribs or shape-change of pores, the other class is multi-phase composites, which experience auxetic effect due to the deformation of soft phase and the kinematic deformation of hard phase. The first category experiences dramatic volume change upon external loads. While the second category experiences small deformation upon external loads. The first materials have been extensively explored; however, very little efforts have been made on the second materials. In this study, new two-phase auxetic mechanical metamaterial with chevron structures are designed. The new designs significantly expand the auxetic materials in the second category. FE models of this new family of materials are developed in ABAQUS, in which the design parameters can vary in very large ranges defined in Python script. Auxeticity in different material orientations is quantified both analytically and numerically. Design spaces with auxeticity are identified via more than one hundred FE simulations. To prove the concept, selected designs are fabricated via a multi-material 3D printer (Stratasys Connex3) and uni-axial tension tests are performed to measure the effective Poisson’s ratio and the stress-strain behavior.