Viscosities and sintering rates of a two-dimensional granular composite

The effective sintering rates and viscosities of two-dimensional granular composites are studied using discrete computational models. The composites consist of randomly mixed soft and hard spheres on a triangular lattice. The numerical formulation is based on a requirement of quasistatic equilibrium for each particle in the packing, Two distinct models are employed: the truss model in which only force equilibrium is enforced for each particle, and the beam model in which force and moment equilibrium are enforced for each particle. The differences between the two models are illustrated by the specific problem studied. The effective composite properties display a transition from soft to hard behavior at a well-defined fraction of hard particles. If contacts between hard particles resist interpenetration, shear, and bending (bonded case), the transition coincides with the site percolation threshold. If contacts between hard particles can slide and bend but resist inter-penetration (sliding case), the transition coincides with percolation of triangular units. Thresholds and scaling of effective viscosities and sintering rates are computed. Because of the mathematical analogy between linear viscous and elastic deformations, these results can also be used to predict the effective moduli and coefficients of thermal expansion of such composites.

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