A frictional Cosserat model for the flow of granular materials through a vertical channel

A rigid-plastic Cosserat model has been used to study dense, fully develope d flow of granular materials through a vertical channel. Frictional models based on the classical continuum do not predict the occurrence of shear lay ers, in contrast to experimental observations. This feature has been attrib uted to the absence of a material length scale in their constitutive equati ons. The present model incorporates such a material length scale by treatin g the granular material as a Cosserat continuum. Thus, localized couple str esses exist, and the stress tensor is asymmetric. The velocity profiles pre dicted by the model are in close agreement with available experimental data . The predicted dependence of the shear layer thickness on the width of the channel is in reasonable agreement with data. In the limit of small epsilo n (ratio of the particle diameter to the half-width of the channel), the mo del predicts that the shear layer thickness scaled by the particle diameter grows as epsilon(-1/3).