Granular Shear Flows of Flexible Fibers

Flexible fibrous particles are widely encountered in nature and industry, e.g., plant stover, glass fiber, and paper pulp. Previous studies indicate that the deformability of the fibers has a significant impact on the properties of the bulk materials and the fiber suspensions. Here, the shear flows of flexible fibers are simulated using the Discrete Element Method (DEM) to systematically explore the effect of particle flexibility on the flow behavior and constitutive laws. In the simulations, a fiber is formed by connecting a number of spheres in a straight line using deformable and elastic bonds. The forces/moments induced by the bond deformation resist the relative normal, tangential, bending, and torsional movements between two bonded spheres. The bond stiffness determines the difficulty of particle deformation, and the bond damping accounts for the energy dissipation in the particle vibration process. The simulation results show that the elastically-bonded fiber particles have smaller coefficient of restitution compared to the rigidly connected particles. In addition, the coefficient of restitution decreases as the bond stiffness decreases and the bond damping coefficient increases. As a result, smaller stresses are obtained for the granular flows of the fibers with lower bond stiffness and larger bond damping coefficient. For the flexible fibers, besides the kinetic energy, the potential energy is also generated due to bond deformation. It is found that during shear flows at a specified shear rate, the average potential energy per fiber increases as the bond stiffness decreases and the bond damping coefficient decreases.