Logarithmic strengthening of granular materials with shear rate

R. R. Hartley, R. P. Behringer, S. Henkes, D. Bi, B. Chakraborty

Research output: Chapter in Book/Report/Conference proceedingConference Contribution (Conference Proceeding)


Experiments on sheared granular materials show that the stresses grow as the first power of the log of the shear rate, γ. We suggest that this may be evidence of the stress ensemble recently proposed by Henkes, O'Hern, and Chakraborty. The picture that we propose is that under steady shearing, the local force network builds up over time, and then fails when the force on the network exceeds a characteristic value. In analogy to soft glassy rheology, we assume that this is an activated process, but now, with the Boltzmann factor replaced by the stress ensemble analogue. We assume that the probability that a local part of the network fails is proportional to exp[(σ- σm)/σo], where s is the local stress, sm is a failure threshold, and σo is related to the generalized temperature, α, of Henkes and Chakraborty. It is then possible to show that these assumptions lead to logarithmic increases in the stress as a function of γ. This contrasts with the SGR result that the stress grows as the square root of l og(γ).

Original languageEnglish
Title of host publicationPowders and Grains 2009 - Proceedings of the 6th International Conference on Micromechanics of Granular Media
Number of pages4
Publication statusPublished - 2009
Event6th International Conference on Micromechanics of Granular Media, Powders and Grains 2009 - Golden, CO, United States
Duration: 13 Jul 200917 Jul 2009

Publication series

NameAIP Conference Proceedings
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616


Conference6th International Conference on Micromechanics of Granular Media, Powders and Grains 2009
CountryUnited States
CityGolden, CO

Bibliographical note

Copyright 2009 Elsevier B.V., All rights reserved.


  • Granular shear
  • Rate-dependence
  • Soft glassy rheology

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