(544g) In Elastic Deformation and Segregation in Cohesive Micron Size Particles

Real granular materials often present significant inter-particular cohesive forces resulting from different physical origins: van der Waals forces for small enough grains such as clay particles, powders; or third body in tribology; capillary forces in humid grains as in unsaturated soils or wet snow, and solid bridges in sintered powders or when liquid menisci freeze. Particles go through brittle to ductile deformation as the particle size gets smaller. In shear flow of uniformly sized particles, inter-particle forces and hydrodynamic forces dominate. It can be postulated that after a sufficient amount of time, the flow reaches a steady homogeneous shear state, which does not depend on the initial configuration, characterized by constant time-averaged solid fraction, shear rate and stress tensor. In a cohesion model. the granular shear state is controlled by inertial number(ratio of inertial to shear times) and a dimensionless cohesion number. Contacts in our particles are visco-elastic, frictional and cohesive. The cohesion force is a normal van der Waals type force, equal to the product of the interfacial energy and the contact area. In Couette shear experiments the shearing process causes buildup of inhomogeneous stress structures, such as force chains, which fail when they reach a critical yield stress. In sheared dense granular materials, mean stresses grow linearly with logarithmic shear rate. Shear stresses and normal stresses are computed and compared against experiments in shear cells using particles of different diameters, cohesive strength and dynamic friction.