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Rheophysics of wet granular materials

Rheophysics of wet granular materials. S. Khamseh, J.-N. Roux & F. Chevoir. IMA Conference on Dense Granular Flows - Cambridge - July 2013. Dense assembly of frictional spherical grains with capillary forces. F cap. D 0. h. Pendular state Pair-wise interaction. Surface tension g

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Rheophysics of wet granular materials

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  1. Rheophysicsof wet granular materials S. Khamseh, J.-N. Roux & F. Chevoir IMA Conference on Dense Granular Flows - Cambridge - July 2013

  2. Dense assembly of frictional spherical grainswith capillary forces Fcap D0 h • Pendular state • Pair-wise interaction Surface tension g Contact angle θ (=0) Maugis model -F0 θ h Normal and tangential contact forces same as dry grains (Hertz and Coulomb) Liquid bridge - constant volume V - forms once particles touch - disappears for h > D0 = V1/3 2 / 12

  3. Homogeneous steady shear flow Normal stress syy = Pressure P Shear rate Lees-Edwards periodic boundary condition Control - Average shear rate - Normal stress Parameters: - Friction coefficient μ = 0.3 - Number of grains N = 4000 - Stifness number Κ = (E/P)2/3 = 8400 y x z 3 / 12

  4. Two dimensionless numbers Pressure P diameter a mass m Shear rate Inertial number Reduced pressure 4 / 12

  5. Range of saturation / reduced pressure d Roughness Funicular range of validity a = 10-4 mgwater= 7.3 × 10-2 J/m2 P* = 1  P = 2,5 kPa  H = 10 cm in gravity field 5 / 12

  6. Constitutive law: m* (I,P*) and f (I,P*) 6 / 12

  7. Comparison with previous study Cohesion at contact 2D Rognon et al. JFM 2007 P *  f 0,1 0,03 0,02 0,015 I I 7 / 12

  8. Strong effect of distant interactions ! P* = 0,43 – D0 = 0 P* =  Contact (+85% to 20%) h/a 8 / 12

  9. Strong effect of distant interactions ! P* = 0,43 – V = 10-3 D0 = 0,08 D0 = 0,01 D0 = 0 P* =  Distant (+40%) Contact (+85% to 20%) h/a 8 / 12

  10. Contributions to shear stress small contribution of - distant interactions - capillary interactions 9 / 12

  11. Contact duration Coordination number zc I = 10-2 I = 10-2.5 I = 10-3 zd Microstructure Microstructure: Fcap Fcap Clustering effet 10 / 12

  12. 2D Rognon et al. EPL 2006 Contact Anisotropy Average force Anisotropy 80% 20% Microstructure : anisotropy of contact network Receding pairs Approaching pairs y x z 11 / 12

  13. Conclusions Large effect of capillary forces on macroscopic behavior - already for P*  1 Strong influence of distant interactions : clustering effect Shear stress dominated by anisotropy of average force Large fabric anistropy of distant interacting pairs Perspectives Shear localization for small P* Include viscous force Describe liquid transfer Describe larger saturation range Comparison with experiments

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