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

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ellipsoid (rye). The seed moisture varied from 10.5% to 12%, and in the case of
rapeseed it was 8%.
To achieve a specific orientation of seeds in the sample the researchers made
use of the phenomenon of the formation of an angle of natural repose and the effect
of grains arranging themselves usually with the long axis towards the generatrix of
the cone formed by the seeds. The method of sample preparation for the triaxial
compression test is illustrated in figure 3.4. Grain was poured with a steady flow
from the funnel through a rectangular outlet of 8 x 24 mm in size into a rubber
diaphragm placed in a two-part cylindrical mould. The funnel, placed at the wall of
the mould, was lifted up as the mould was filled with grain, so that the outlet hole
was always positioned about 20 mm above the top of the freely formed surface of
grain poured. After complete filling of the mould, the cylindrical top cover of the
sample was fixed in place. Next, vacuum was generated within the grain sample,
which gave the sample rigidity of shape, and that permitted its placement inside
a pressure chamber without risk of disturbing the spatial structure of the medium
created in the course of sample formation. The angle between the freely formed
surface of poured grain and the base of the sample was varied by tilting the mould
away from the vertical in the course of grain pouring. As grains tend to orient
themselves so that their long axis is parallel to the generatrix of the cone of natural
repose, varying the tilt of the mould with relation to the vertical resulted in a change
of the preferred spatial orientation of the grains with relation to the sample-related
system of reference.
Fig. 3.4. The method of sample preparation for the triaxial compression test
For further tests six values of sample inclination were chosen: β = –20 o , –10 o ,
0 o , 10 o , 20 o and 30 o (fig. 3.4). The angle of natural repose of the grain was about 20 o .
Additionally, for purposes of comparison, grain was poured into a vertical mould