Discrete element investigation into Cosserat effects of granular materials: The measurement of couple stress and Cosserat modulus

Granular materials can be modeled as Cosserat continua at the macroscale. However, whether the Cosserat effect of granular materials exists has been controversial. In this paper, by using discrete element method (DEM), the macroscopic stresses like couple stress and the normalized modulus like Cosserat modulus in representative volume element (RVE) of granular materials are compared under two boundary conditions. The results shows that the couple stress and Cosserat modulus are not found in the RVEs under the displacement and rotation boundary, but are found under strain and moment boundary. The Cosserat modulus is significantly affected by size effect, as well as particle arrangement and aspect ratio. In addition, the presence of strain gradients can lead to an increase in the Young's modulus of granular materials, indicating that granular materials are affected by both strain and strain gradients. At the same time, two shear moduli are also measured and discussed.