Breakage dynamics and scaling of wet aggregates of rigid particles

The mechanical behaviour of wet particle aggregates is crucial in many granular processes such as wet granulation and soil degradation. However, the interplay of capillary and viscous forces for aggregate stability and breakage have remained elusive due to the complexity of granular dynamics. We use particle dynamics simulations to analyse the deformation and breakage of wet aggregates colliding with a flat wall. The aggregates are composed of spherical particles and the effect of liquid bonds is modelled through capillary and lubrication forces acting between particles. We perform an extensive parametric study by varying surface tension, impact velocity and liquid viscosity in a broad range of values. We show that when lubrication force is neglected, aggregate breakage is fully controlled by the reduced kinetic energy $\xi$ , defined as the ratio of incident kinetic energy to the initial capillary energy. At low values of $\xi$ , the aggregate deforms without breakage due to inelastic energy loss induced by rearrangements and loss of capillary bonds, whereas above a critical value of $\xi$ it breaks into smaller aggregates due to the transfer of kinetic energy from aggregate to fragments. In the presence of lubrication forces, the crossover from capillary to viscous regime is controlled by the capillary number, defined as the ratio of viscous dissipation to capillary energy. We find that the critical value of $\xi$ for aggregate breakage in the viscous regime increases as a power law with capillary number while the effective restitution coefficient follows the same trend as in the capillary regime.