Micromechanical Origin of Rate Independence of the Stress in Sheared Granular Materials

R Gautam and PR Nott, PHYSICAL REVIEW LETTERS, 134, 158201 (2025).

DOI: 10.1103/PhysRevLett.134.158201

The stress in slowly sheared granular materials is independent of the shear rate, but individual particles transmit momentum at a rate proportional to the shear rate. How a rate-dependent microscopic momentum flux leads to a rate-independent macroscopic stress is a fundamental, unanswered question. Another prominent feature is the occurrence of large stress fluctuations. Here, we show that the two features are closely related. The fluctuations arise from recurrent jamming-yielding dynamics, with deformation being elastic in the jammed phases and yielding occurring in short bursts. These findings lead to an explanation for the rate independence of the stress.

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