Experimental verification of 2D Cosserat chirality with stretch-micro-rotation coupling in orthotropic metamaterials with granular motif

Chiral effects in 2D Cosserat continuum model may arise from coupling between stretching deformations and the micro-rotation for hemitropic materials. An orthotropic 2D chiral Cosserat continuum is introduced to account for this type of coupling. The expected chiral effects are verified through an experimental effort using a specimen with granular motif. A granular micro-mechano-morphology is considered that leads to 2D orthotropic macro-scopic response. The resultant metamaterial is designed by the aid of micro-macro links provided by the granular micromechanics model, where the relationship between micro-rotation is exploited as well as the coupling of shear and normal responses of grain-pair interactions. A square specimen is fabricated by 3D printing and subjected to unidirectional compression. The specimen deformation field is characterized using digital image correlation (DIC) via mesoscale analyses. The predicted displacements and micro-rotations are found to closely follow their measured counterparts. Moreover, the measured reaction-displacement response agrees well with that predicted by the continuum model. The results demonstrate that it is possible to rationally design micro-mechano-morphologies that yield desired emergent behavior at the macroscale.(c) 2015 The Authors. Published by Elsevier Ltd.