Evolution Of Force Chains Research Articles

Visualization of force networks in 2D dense granular materials

Dense granular matter is a conglomeration of discrete solid and closely packed particles. As subjected to external loadings, the stress is largely transmitted by heavily stressed chains of particles forming a sparse network of larger contact forces. To understand the structure and evolution of force chains, a photoelastic technique was improved for determining stresses and strains in the assemblies of photoelastic granular disks in this paper. A two-dimensional vertical slab was designed. It contains 7200 polydispersed photoelastic disks and is subjected to a localized probe penetrating at the top of the slab to mimic the cone penetration test. The interparticle contact force distribution was found a peak around the mean value, a roughly exponential tail for greater force and a dip toward zero for smaller force. The force chain network around the probe tip was depicted, and the contact angle distribution of particles in force chains was found to be well aligned in the directions of major principal stress.

Noncoaxiality and force chain evolution

Classical plasticity is predicated on the coaxiality between the principal directions of stress and plastic strain rate. However, there is now extensive evidence which show that these directions are necessarily noncoaxial for cohesionless granular systems. We investigate the micromechanical origins of noncoaxiality in specimens undergoing strain localization, from the standpoint of force chain evolution and associated kinematics. Connections to macroscopic trends in simple shear and biaxial tests are discussed.

Uncovering the secrets to relieving stress: discrete element analysis of force chains in particulate media

The traditional analyses for structures that are either built upon (for example, foundations), or are used for storage and handling of particulate solids (for example, bins, silos, hoppers, and bunkers) cannot account for important processes originating in the evolution of microscale particle kinematics and kinetics. Until recently, the complexity of these processes could only be perceived through macroscale experiments, but information derived from these experiments lacks the necessary level of detail that is needed for sound theoretical development. Limited information on the evolution of microstructural properties in deforming particulate solids emerged through ingenious experiments using photoelastic techniques. These techniques revealed the complex microstructural fabric and force propagation, the evolution of which governs what is observed as the constitutive response of the material. More recently, numerical simulations using the discrete element method have also proven to be powerful tools --- effectively providing a virtual laboratory for studying microstructural evolution. We use the discrete element technique to examine the propagation of forces within a particulate solid that is subject to an indenting rigid flat punch on its surface. Particular attention is given to the formation, evolution and collapse of ``force chains'' (that is, quasi-linear chains of load-bearing particles). These force chains are surrounded by a weak network of particles that, despite carrying only a small amount of the load, provides the necessary stability for such chains to persist. A mathematical framework for the characterisation of these chains is used to investigate the evolution of the force chain network with indentation, with a focus on microstructure, force chain lengths, and length distributions. Finally, the first steps toward establishing correlations across multiple length scales are made by linking the macroscopic load-penetration response to the underlying evolution of contact forces and force chains.