Shear band analysis of granular materials considering effects of particle shape

Biaxial simulation tests with flexible membrane boundaries and Cosserat theory are used to investigate the effect of the particle shape on the properties of a shear band of granular materials. Three kinds of special particle shapes are quantified by the aspect ratio (AR) and the AR values for disks, squared, and elongated grains which are 1.00, 0.88, and 0.50, respectively. The peak and residual stress ratios and dilatancy increase as the AR decreases. A measurement of inclinations and thicknesses of X shear bands based on the porosity is proposed here. For DEM simulation and bifurcation analysis, the predicted maximal inclination of the shear band increases with the AR decreasing. However, the predicted maximal and minimal thicknesses of the shear band for DEM simulation and bifurcation analysis decrease with the AR decreasing. Based on Cosserat theory, a new empirical equation with fewer material constants which describe the relation between the stress ratio and shear strain is proposed, and this equation is in good agreement with DEM data. The predicted particle rotation and displacement in the shear band are both comparing well with DEM data for three kinds of particle shapes. Furthermore, the rotation of a particle in the shear band gradually decreases on successively considering $\text{AR}=1.00,0.88$, and 0.50.