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

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The modulus of compressibility E i was determined on the basis of the resultant
material strain, sum of reversible (elastic) and irreversible (plastic) strain [174]:
1
E
=
1
K
+
1
i
H o
.
(6.4)
Examples of experimental values for wheat grain are presented in Table 6.1 [174].
Table 6.1. Modulus of compressibility, elasticity and plasticity of wheat grain [174]
Minor principal
stress
(kPa)
Modulus
of compressibility
E i (MPa)
Modulus
of elasticity
K (MPa)
Modulus
of plasticity
H o (MPa)
20.7
34.5
48.3
62.1
3.3
4.5
6.4
7.9
8.8
11.1
13.6
16.2
5.3
7.7
12.1
15.3
Volumetric elasticity of granular material is closely related to the elasticity of
individual grains. Modulus of elasticity of seeds of individual plant species varies
within a broad range. In the case of wheat, Young modulus determined for cylindrical
samples cored from the grain endosperm falls within the range of 0.2-3 GPa depending
on the cultivar [55] (figure 6.2). With increasing grain moisture, Young modulus
decrease to stabilize at moisture levels above 22% [41]. Modulus of elasticity depends
on the protein content and on the type of endosperm [84]. For vitreous grains,
the values of the modulus are about 30% higher than for mealy grains [58, 171].
Fig. 6.2. Young modulus of wheat endosperm as influenced by moisture content [55]