Regimes of Granular Shear Flows

In 1990, Babic et al. published a paper describing the stress and strain-rate relations in a simple shear flow of granular materials. They found that as the solid concentration increases keeping all other parameters constant, the stress at first was nearly proportional to the square of the strain-rate, then went through a sharp transition and finally became independent of the strain-rate at high solid concentrations. In 1991, Hopkins and Louge published a paper describing the microstructure of granular shear flows. It was observed that microstructures formed in shear flows. These microstructures were more prominent for inelastic particles. In 2000, Zhang and Rauenzahn published a paper describing the contact duration between colliding particles. They showed the effect of contact time in stress relaxation and demonstrated viscoplastic behavior of granular materials. Based on these findings it is conceptualized that stress and strain-rate relations depend on the internal structures of the granular materials. That is, stress and strain-rate relations for granular materials must include the evolution of the internal structure as an integral part of the constitutive relation.