Structural change in non-fractal particle clusters under fluid stress

The restructuring of particle clusters having a dense packing structure under fluid stress is investigated numerically. The rearrangement of particles in the cluster and the breakage of their interparticle bonds in simple shear flow are examined by the Lagrangian-type simulation. The hydrodynamic force exerted on multiple particles is estimated by Stokesian dynamics approach. The interparticle force is calculated from the retarded van der Waals potential based on the Lifshitz theory. The simulation results show that the particle cluster rotates with the rotation of the surrounding flow and deforms due to the fluid stress along the principal axes of the stress tensor. These complex effects bring the irreversible change of the internal structure to the cluster. It is found that the structural change of the cluster can be explained by the initial rearrangement of primary particles and the successive crack growth that takes a long time. Such a long-term structural change is analogous to that of the fatigue crack growth of solid materials. We discuss the dynamics of the restructuring of a dense cluster from this point of view and propose a mathematical model which describes the restructuring process in a flow field.