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The role of microstructure in the incremental behavior of granular materials

The role of microstructure in the incremental behavior of granular materials V. Magnanimo , N. Kumar and S. Luding MSM - University of Twente (NL). We observe the (often disastrous) MACROSCOPIC behavior and we want to model it ….

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The role of microstructure in the incremental behavior of granular materials

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  1. The role of microstructure in the incremental behavior of granular materials V. Magnanimo, N. Kumar and S. Luding MSM - University of Twente (NL)

  2. We observe the(often disastrous) MACROSCOPIC behavior • and we want to model it …. • ….how is this related with the MICROSCOPIC structure?

  3. Evolution of microstructure Evolution of the microstructure [Behringer (Duke)]

  4. Evolution of microstructure Inhomogeneity & anisotropy, instabilities & structures, rotations [Luding (UT)]

  5. Experimental background

  6. Experimental background

  7. Experimental background • Triaxial compression samples • prepared with: • dry deposition • moist tamping • Yang, Li and Yang (2008) Geotechnique58(4) 237-248

  8. ISOTROPIC SYSTEM

  9. Coordination number: HISTORY of the sample • Magnanimo et al. (2008) EPL 8134006

  10. Elastic moduli We apply (m = inf)an incremental strain eijand measure the variation in stress sijafter relaxation • Calvetti et al. (2003) RivistaItaliana di Geotecnica 3 • Magnanimo et al. (2008) EPL 81 34006 • Sibille et al. (2009) EJECE 13(2) 187-201

  11. Amplitude of the increment

  12. Elastic moduli dependence on microstructure G/B • Magnanimo et al. (2008) EPL 8134006

  13. ANISOTROPIC SYSTEM • undrained biaxial test

  14. Evolution of stress and fabric Deviatoric fabric Shear Stress Fdev=√3 J2Fc sdev=√3 J2s definition of fabric O.I. Imole et al. KONA (2013), Kumar et al. ActaMechanica (under review)

  15. Elastic moduli We apply purely deviatoricperturbations along the path

  16. Incremental elastic behavior

  17. How small is small? Small enough before any local rearrangement happens

  18. Bulk modulus

  19. Anisotropy modulus

  20. Shear modulus

  21. Theoretical prediction undrained cyclic biaxial test

  22. Incremental elastic behavior

  23. Fdev=√3 J2Fc

  24. Simple constitutive model Luding and PerdahciogluCIT (2011), Magnanimo and Luding, GranularMatter (2011)

  25. Undrained biaxial test: calibration Shear Stress DeviatoricFabric Initial state: isotropic volume fraction 0.711

  26. Undrained CYCLIC biaxial test: prediction Shear Stress DeviatoricFabric Initial state: isotropic volume fraction 0.711

  27. Isobaric compression

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