Parametric Experimentation to Evaluate Chiral Bars Representative of Granular Motif

The recent wide-ranging interest in chiral materials motivates the need to understand the mechanisms that underlie mechanical chirality. This paper investigates the emergent chiral mechanical behavior of bars in relationship to microscale deformation mechanisms. The focus is upon (meta)material systems with granular motif that exploit couplings between stretch, shear and rotation such that the designed bar exhibits non-standard transverse motion under extension. To this end, a 1D-micropolar model is derived using the granular micromechanics paradigm to predict macroscale chirality based upon grain-scale interactions. The model provides micro-macro links necessary for designing the physical (meta)material system conceived as a granular bar. The validity of the derived model is then investigated through parametric experimentation using the designed system fabricated through 3D printing. The granular bar is varied with regard to two geometrical parameters that describe the interaction between two adjacent grains, thereby providing parametric spaces with respect to the considered geometrical parameters. Tensile experiments on the granular bar are analyzed using digital image correlation (DIC) to extract multiscalar deformation fields. The DIC results serve as the basis for investigating the unusual motions predicted by the 1D model by comparing the predicted displacement and rotation fields with those obtained experimentally.