Multiscalar DIC analyses of granular string under stretch reveal non-standard deformation mechanisms

Abstract

Mechanical tests designed to measure classical behavior do not provide information underlying the macroscale response. Multiscalar digital image correlation (DIC) can be employed in these experiments to expose the micromechanisms that lead to the emergent macroscale behavior. A multiscalar DIC methodology was applied to study the extensional behavior of a particular granular string with chiral properties. DIC was performed at the macroscale in which the underlying microstructure is overlooked and the construct is treated as a continuum bar. Further, the underlying microstructure was exploited in a microscale DIC analysis to expose the rich deformation regimes. In addition, a mesoscale analysis was carried out to extract the rigid body motions that characterize a granular material system. These analyses were performed for two types of surface patterns and measurement uncertainties were quantified. The microscale results show that the grain string can be treated as a granular material composed of a set of nearly rigid grains that store elastic energy through intergranular mechanisms. Further, the results reveal non-standard deformation mechanisms that underlie the chiral granular string subjected to extension. These mechanisms include grain rotations that are coherent as opposed to gear-like grain rotation. More notably, grain transverse displacements are observed that are controlled by the behavior of the grain interconnections.