Interplay between forces, particle rearrangements, and macroscopic stress fluctuations in sheared two-dimensional granular media

Recent studies have established correlations between nonaffine motion and macroscopic stress fluctuations in sheared granular media. However, a comprehensive examination of the relationship between nonaffine motion, macroscopic stress fluctuations, and interparticle forces remains lacking. We investigated this interplay in simulations of two-dimensional granular media during stick-slip events under plane shear. We found that, during most large slip events, particles with the greatest nonaffine motion, as quantified by Dₘᵢₙ², initially coalesce into one or two dominant connected clusters. These clusters coincide with the region exhibiting the greatest instantaneous reduction in interparticle forces, indicating a significant correlation between interparticle force fluctuations and particle rearrangements. Furthermore, the magnitude of the greatest nonaffine motion within these clusters correlates strongly with the magnitude of macroscopic stress fluctuations during slip events. This correlation increased when the nonaffine motion of particles in a neighborhood around the point of greatest nonaffine motion was included in the analysis, suggesting that plastic events are best understood as regional rather than pointlike occurrences. Our results held for various interparticle friction coefficients. Our findings suggest that elastoplastic models should consider plastic events as regional rather than pointlike and highlight the importance of studying the propagation of particle rearrangements.