the role of microstructure in the incremental behavior of granular materials
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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 …. - PowerPoint PPT PresentationTRANSCRIPT
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The role of microstructure in the incremental behavior
of granular materials
V. Magnanimo, N. Kumar and S. LudingMSM - University of Twente (NL)
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We observe the (often disastrous) MACROSCOPIC behaviorand we want to model it ….
….how is this related with the MICROSCOPIC structure?
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Evolution of microstructure
[Behringer (Duke)]
Evolution of the microstructure
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Inhomogeneity & anisotropy, instabilities & structures, rotations
[Luding (UT)]
Evolution of microstructure
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Experimental background
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Experimental background
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Experimental background
Yang, Li and Yang (2008) Geotechnique 58(4) 237-248
Triaxial compression samples prepared with:
• dry deposition• moist tamping
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ISOTROPIC SYSTEM
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Coordination number: HISTORY of the sample
Magnanimo et al. (2008) EPL 81 34006
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Elastic moduliWe apply (m = inf) an incremental strain eij and measure the variation instress sij after relaxation
Calvetti et al. (2003) Rivista Italiana di Geotecnica 3Magnanimo et al. (2008) EPL 81 34006 Sibille et al. (2009) EJECE 13(2) 187-201
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Amplitude of the increment
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Elastic moduli dependence on microstructure
G/B
Magnanimo et al. (2008) EPL 81 34006
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ANISOTROPIC SYSTEMundrained biaxial test
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O.I. Imole et al. KONA (2013), Kumar et al. Acta Mechanica (under review)
Shear Stress
Evolution of stress and fabricDeviatoric fabric
s dev
=√3
J 2s
F dev=
√3 J 2Fc
definition of fabric
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We apply purely deviatoric perturbations along the path
Elastic moduli
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Incremental elastic behavior
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Small enough before any local rearrangement happens
How small is small?
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Bulk modulus
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Anisotropy modulus
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Shear modulus
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Theoretical predictionundrained cyclic biaxial test
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Incremental elastic behavior
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F dev=
√3 J 2Fc
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Luding and Perdahcioglu CIT (2011), Magnanimo and Luding, Granular Matter (2011)
Simple constitutive model
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Initial state: isotropic volume fraction 0.711
Shear Stress Deviatoric Fabric
Undrained biaxial test: calibration
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Undrained CYCLIC biaxial test: prediction
Initial state: isotropic volume fraction 0.711
Shear Stress Deviatoric Fabric
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Isobaric compression
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