Strength Deterioration of Nonfractal Particle Aggregates in Simple Shear Flow

Abstract

The restructuring of a non-fractal particle aggregate in simple shear flow was simulated by Stokesian dynamics approach. We studied the deformation and the resultant strength change of aggregate by surrounding flow under the condition that the cohesive strength of aggregate is comparable with the fluid stress. In particular, we focused on how the aggregate deteriorates due to the fluid stress exerted on it periodically. The image analysis was applied to visualized simulation results for quantitative estimation of irreversible change in aggregate configuration.We examined the structural change of aggregate from various perspectives, i.e., the outer shape, the internal strength and the fluid stress on the surface of the aggregate. The simulation results show that the aggregate gets squashed after intricate restructuring process and it elongates along with streamline as experimentally observed in the previous study. Regarding the internal strength, the weakest point locally develops in the aggregate by periodically-varying fluid stress. Combination of rotation and elongation effects of shear flow is complexly-involved in the deterioration of internal strength of aggregate.

Universal Breakup of Colloidal Clusters in Simple Shear Flow

“…Where most of the simulation techniques differ substantially is in the description of hydrodynamic interactions among particles, which play a crucial role in properly describing the interactions of particles with the fluid. Several models have been used to account for hydrodynamic interactions, including lattice-Boltzmann simulation, finite element method, free-draining approximation, , and Stokesian dynamics (SD). − The free-draining approximation is the simplest and hence the most commonly used model in colloidal science because it completely neglects interparticle hydrodynamic interactions, thus substantially reducing the computational cost of the simulations. However, several publications have demonstrated the importance of including hydrodynamic interactions to properly describe the dynamics of hard spheres − and of interacting particles, , as well as the formation of colloidal gels …”

Numerical investigation of the respective roles of cohesive and hydrodynamic forces in aggregate restructuring under shear flow

“…On the other hand, modeling and simulation of aggregates in shear flow have enabled scientists to investigate the aggregate behavior at a more fundamental level, where the physics at play can be selectively implemented to see their relative impact on aggregate behavior. Recent aggregate studies through simulations have complemented experimental results [7,9,10], proving the viability of numerical studies. Such numerical investigations of aggregation dynamics and aggregate restructuring have been conducted at infinitely low Reynolds conditions using Stokesian Dynamics [11], or even using the Free Draining Approximation (FDA) in which the fluid-particle interactions are simplified to consider only Stokesian drag [12].…”

“…This happens through re-distribution of the hydrodynamic stresses and the cohesive forces within the aggregate [15]. When the hydrodynamic forces are not balanced by the combined cohesive forces within an aggregate, it will restructure and/or eventually break [10].…”

“…Finally, studies resolving the hydrodynamics using SD and their impact on aggregation [11,25], restructuring [10,26,27] and breakage kinetics [5] have shown how aggregates evolve under different hydrodynamic stresses, but are still not numerous enough to cover the full set of parameters at play. For example, Horii et al [10] did not include the tangential forces which have been seen to be rather crucial in restructuring. Furthermore, since SD uses multipole expansion of the velocity field to solve the linear Stokes equations, it is restricted to low Reynolds number conditions.…”

Mechanical Behavior of 3D Crack Growth in Transparent Rock-Like Material Containing Preexisting Flaws under Compression

“…In the crack evolution process of brittle materials containing preexisting flaws, usually two types of crack are observed, which are wing cracks originating from the tips of preexisting flaws and secondary cracks. Wing cracks are usually caused by tension, while secondary cracks may develop due to shear [16]. Wing cracks initiation in rocks is favored with respect to secondary cracks because of lower toughness of the materials in tension than in shear [17][18][19][20].…”