A micropolar hypoplastic model for granular materials and its FEM implementation

In this paper a micropolar continuum or so called Cosserat continuum is proposed to take into account particle, rotations and size effects in cohessionless granular materials like sand. A 4-node element with translation and rotation degrees of freedom is implemented into a finite element program for solving plane strain problems. The constitutive model is based on the concept of hypoplasticity. The constitutive equations for the stresses and the couple stresses are incrementally non-linear tensor-valued functions of the rate type. The mean grain diameter serves as an internal length, thus the predicted shear band thickness is mesh independent, provided the element size is small enough.