Effective viscosities and sintering rates of composite random packings of spheres

A discrete computational model has been used to study the effective viscosities and sintering rates of composite random packings of spheres. The packings consist of equal-sized spheres, a fraction υ f of which are randomly assigned viscosities much greater than the rest. In all cases the effective properties of the packings experience a soft-to-hard transition. Two extreme types of interactions between contacting hard particles are considered: bonded and sliding. In the bonded case the transition (or rigidity threshold) coincides with the site percolation threshold ( υ f ≈ 0.32). In the sliding case the transition is much higher ( υ f ≈ 1.0). The effective sintering rate of the packing reduces to zero as the site fraction approaches the rigidity threshold. These results are in good agreement with experiments.