Strona 2_redak - Instytut Agrofizyki im. Bohdana Dobrzańskiego ...

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a) Glass Beads
Considering Rolling Friction
b) White Rice
Considering Rolling Friction
Profile of Free Surface by Experiment
Discharging Time - 0.25 s
Slit Width - 130 mm
Fig. 3.12. Comparison between simulation and experimental results [146]
formation of macroscopic deformation, and especially the explanation of the
mechanisms of dilation of the material. In classical theories of granular material,
the dominant role in the occurrence of dilatation has been attributed to mutual
displacement of the granules. In the micro-structural approach, the source of
dilation was sought in the mutual rotation of the granules. However, the reduction
of the interactions to the consideration of forces solely in the contact points of the
granules permits mutual rotation of granules without mobilizing the resistance to
motion at the points of contact, e.g. through the rotation of neighbouring granules
in opposite directions (fig. 3.13 a). Such rotation of granules does not lead to
dilation. In reality, granules have rough surface, and the contact surface area is
limited. Substituting the contact points with contact area (fig. 3.13 b), the authors
included the equations of rotational motion in a form analogous to the equation of
linear motion in tangential direction (visco-elastic element and dry friction). Like
in the case of tangential displacement, the frictional element in rotational motion
is activated when the force moment M is greater than friction resistance.
Computer simulations made by Iwashita and Oda [72] showed that the modified
method creates quite new possibilities of interpretation.