Granular packings and fault zones

The failure of a two-dimensional packing of elastic grains is analyzed using a numerical model. The packing fails through formation of shear bands or faults. During failure there is a separation of the system into two grain-packing states. In a shear band, local ``rotating bearings'' are spontaneously formed. The bearing state is favored in a shear band because it has a low stiffness against shearing. The ``seismic activity'' distribution in the packing has the same characteristics as that of the earthquake distribution in tectonic faults. The directions of the principal stresses in a bearing are reminiscent of those found at the San Andreas Fault.

Fragmentation dynamics within shear bands--a model for aging tectonic faults?

A numerical model for packing of fragmenting blocks in a shear band is introduced, and its dynamics is compared with that of a tectonic fault. The shear band undergoes a slow aging process in which the blocks are being grinded by the shear motion and the compression. The dynamics of the model have the same statistical characteristics as the seismic activity in faults. The characteristic magnitude distribution of earthquakes appears to result from frictional slips at small and medium magnitudes, and from fragmentation of blocks at the largest magnitudes. Aftershocks to large-magnitude earthquakes are local recombinations of the fragments before they reach a new quasi-static equilibrium. The …

Self-assembly and rheology of dipolar colloids in simple shear - studied by multi-particle collision dynamics

Magnetic nanoparticles in a colloidal solution self-assemble in various aligned structures, which has a profound influence on the flow behavior. However, the precise role of the microstructure in the development of the rheological response has not been reliably quantified. We investigate the self-assembly of dipolar colloids in simple shear using hybrid molecular dynamics and multi-particle collision dynamics simulations with explicit coarse-grained hydrodynamics; conduct simulated rheometric studies and apply micromechanical models to produce master curves, showing evidence of the universality of the structural behavior governed by the competition of the bonding (dipolar) and erosive (ther…

Abstracts from the CECAM workshop on computer simulations of cellular automata

Self-assembly and rheology of dipolar colloids in simple shear studied using multi-particle collision dynamics.

Magnetic nanoparticles in a colloidal solution self-assemble in various aligned structures, which has a profound influence on the flow behavior. However, the precise role of the microstructure in the development of the rheological response has not been reliably quantified. We investigate the self-assembly of dipolar colloids in simple shear using hybrid molecular dynamics and multi-particle collision dynamics simulations with explicit coarse-grained hydrodynamics, conduct simulated rheometric studies and apply micromechanical models to produce master curves, showing evidence of the universality of the structural behavior governed by the competition between the bonding (dipolar) and erosive …