4 pagesInternational audienceStrain in granular materials in quasistatic conditions under varying stress originate in (I) contact deformation and (II) rearrangements of the contact network. Depending on sample history and applied load, either mechanism might dominate. One may thus define rheological regimes I and II accordingly. Their properties are presented and illustrated here with discrete numerical simulation results on sphere packings. Understanding the microscopic physical origin of strain enables one to clarify such issues as the existence of macroscopic elasticity, the approach to stress-strain relations in the large system limit and the sensitivity to noise
