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

19
horizontald deformation of the sample. Elasto-optical photographs show that the
load is transmitted by columns of particles oriented in the direction of maximum
compressive stress. The points of contact around the columns transmit only a
limited amount of the load applied, but ensure stability of the columns that
transmit most of the load. The distribution of forces obtained is highly similar to
that presented earlier by Drescher and De Josselin de Jong [44] in their work
concerned with verification of the theoretical model of granular medium flow.
12
10
8
6
4
2
0 2 4 6 ,%
o
2
25.6%
12
10
8
6
4
2
0 2 4 6 ,%
o
-29
23.1%
10
8
6
4
2
0
0
2 4 6 ,% o 2 4 6 ,%
o
-49
-86
20.8%
15.8%
8
6
4
2
Fig. 3.2. Distribution of probability density of angle of contact normal directions in the assembly
of rods of cross section (ratio of length of axes 1.4 [83])
Konishi et al. [83] applied the distribution of unit normal directions at contact
points for the description of the packing structure of particles. Figure 3.2 presents
the obtained distributions of contact normal directions for the particular variants of the
experiment in an undeformed sample. The authors adopted an approximation of the
distribution of normal directions by means of an ellipse. The long axis of the ellipse in
undeformed state is perpendicular to the plane of deposit pouring. The effect is more
pronounced in the case of flatter particles and in the case of lubricated particles
that display higher anisotropy. The numbers in figure 3.2 represent the direction
of the long axis of the ellipse (higher) and the degree of anisotropy (lower). The
parameters were calculated according to the relation [130]:
long axis direction:
1
β = arctg(A / B) , (3.1)
2
degree of anisotropy:
2 2
M = A + B
* 100 ,
(3.2)