Shear-induced mechanical yielding controls cluster morphology and dynamics in aggregating non-Brownian suspensions
In sheared aggregating suspensions, flow drives both the formation and breakage of particle clusters, whose dynamic evolution influences transport and rheological properties. Understanding these mechanisms remains challenging due to the complex interplay between interparticle forces, hydrodynamic interactions, and shear flow. Using parallelized Accelerated Stokesian Dynamics (PASD) simulations, we investigate cluster microstructure and rotational dynamics, and how their coupling produces suspension stress in sheared, attractive non-Brownian suspensions. When interparticle attraction dominates over separating shear forces, clusters grow until mechanical loading balances maximum interparticle bond strength. We examine how the cluster stresslet depends on cluster size, with both quantities normalized by their mechanical yielding scales. Scaled cluster stresslets collapse onto a master curve exhibiting three distinct regimes: cubic, quadratic, and linear with respect to the scaled radius of gyration $R_g$. In the cubic regime, small, compact clusters behave as rigid bodies, whose hydrodynamic stresslet scales with cluster volume $R_g^3$. As clusters grow into the quadratic regime, low-aspect-ratio clusters preferentially yield under flow, driving a proportional increase in average aspect ratio with size. High-aspect-ratio clusters follow Jeffery rotational dynamics within the flow-gradient plane, spending longer durations aligned with the flow and thereby reducing their time-averaged hydrodynamic stresslet to scale as $R_g^2$. In the linear regime, clusters approach the maximum size sustainable by the interparticle bonds. The internal tension is bounded by the maximum bond strength, limiting the stresslet to an $R_g$ dependence. These findings establish a mechanistic framework connecting microscale cluster morphology and dynamics to macroscale rheology.