(600f) Contact Pair Distribution and Jamming in Dense Non-Brownian Bidisperse Suspensions

Dense non-Brownian suspensions exhibit shear thickening, a phenomenon where viscosity increases with applied shear stress. We study the well-known model where this is due to a stress-driven transition from low stresses, predominantly lubrication interactions to frictional contacts at high stresses. We investigate the shear-thickened regime using stress-controlled simulations via the Lubricated-Flow Discrete Element Method (LF-DEM), applying a normalized shear stress of varying value, focusing on σ/σ₀ = 100. Simulations span volume fractions 0.72 ≤ φ ≤ 0.80 and bidispersity levels δ = 1.0 to 4.0, further characterized by the small particle volume fraction ζ = 0.25, 0.50, and 0.75. While prior studies suggest that the relative viscosity ηᵣ follows the Maron-Pierce law, ηᵣ = (1 − φ/φₘ)⁻², with φₘ being the maximum packing fraction, our results indicate a better fit with a generalized power law: ηᵣ = (1 − φ/φₘ)⁻ᵝ, with β ≈ 2.3. Interestingly, this scaling also holds for the normal stress components and the particle pressure Π. We summarize this behavior with a unified expression: y_rheo ≈ (1 − φ/φₘ)⁻ᵝ, where y_rheo represents ηᵣ, Σₓₓ, Σᵧᵧ, or Π. Contact pair distributions reveal distinct patterns: at low bidispersity (δ = 1.4), contacts align along the compression axis, while at high bidispersity (δ = 4.0), large-large particle contacts increasingly align along the flow direction as ζ increases. Higher ζ promotes preferential alignment of large particles in the flow direction. We also investigate shear jamming, where the suspension transitions to a jammed state due to the emergence of rigid microstructures. Using the pebble game algorithm, we identify rigid clusters and find that jamming can occur when the instantaneous fraction of rigid particles m_rig > 0.80. Additionally, particle softness and interparticle friction influence the onset of jamming: softer particles delay jamming due to increased deformation.