Stress transmission in wet granular materials

Abstract

We analyze stress transmission in wet granular media in the pendular state by means of three-dimensional molecular-dynamics simulations. We show that the tensile action of capillary bonds induces a self-stressed particle network organized in two percolating "phases" of positive and negative particle pressures. Various statistical descriptors of the microstructure and bond force network are used to characterize this partition. Two basic properties emerge: 1) the highest particle pressure is located in the bulk of each phase; 2) the lowest pressure level occurs at the interface between the two phases, involving also the largest connectivity of the particles via tensile and compressive bonds. When a confining pressure is applied, the number of tensile bonds falls off and the negative phase breaks into aggregates and isolated sites.

Cohesive, frictional powders: contact models for tension

“…Since effects like liquid and possibly permanent solid bridges are not subject of the present study, we refer to the detailed literature, see Refs. [5,9,19,20,24,68,69,74,87,88,90] and references therein.…”

“…[40,91,92] and references therein. The challenge here is to reduce the tremendous amount of information on the contact level, like contact-orientation and -force probability distribution functions [68], to the relevant macroscopic properties related to bulk-moduli, anisotropy and inhomogeneity in the contact network. The quest for a macroscopic constitutive model based on microscopic contact parameters is still ongoing.…”

Force transmission in dry and wet granular media

“…Although the stress tensor is by definition a macroscopic quantity, it can be shown that an equivalent quantity σ i , called 'particle stress', can be defined for each particle i of a granular packing in static equilibrium [41,42,20]:…”

“…The morphology of each phase is approximately filamentary with variable thickness and a large interface between them. A detailed analysis of this structure shows that the particles at the interface between the two phases have a weak pressure and the largest negative or positive pressures are located at the heart of each phase [20].…”

“…However, in contrast to cohesionless media, the distribution of weak compressive forces is affected by tensile forces [19]. In wet granular media in the pendular state, the tensile action of capillary bonds bridging the gaps between neighboring particles gives rise to a network of self-equilibrated forces [20]. This network is likely to control features such as particle aggregation and the enhanced shear strength of wet granular media.…”