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

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Relating the modulus of elasticity of a material deposit with the Young modulus
and Poisson coefficient of the granules of the medium and with the average pressure
and the material packing parameters permits correct physical interpretation of elastic
reactions in a bulk of granular material. Studies by Horabik and Molenda [65] showed
that the Hertz formula permits also the description of the behaviour of grain within
a broad range of moisture content (fig. 6.3). At the current stage of the research, the
application of the relation derived by Walton for a big number of bodies like granular
plant material permits only qualitative analysis of the phenomenon.
Fig. 6.3. Contact area of wheat grain with smooth surface as influenced by moisture content and
normal load [65]
Granular material volumetric elasticity has a very strong influence on the
pressure transmitted by the granular material onto the structure of the container or
silo [98, 99]. For the purpose of solving practical problems, an empirical value of
modulus of elasticity of granular material in bulk is usually adopted, constant for
a given range of pressure values [139, 148]. In the case of granular materials of
plant origin, the value of the modulus is strongly related to moisture content.
Stasiak and Molenda [154] showed that the modulus of elasticity of wheat grain,
determined under the conditions of uniaxial compression at the vertical pressure
of 100 kPa and grain moisture content of 10% was 22 MPa, and at grain moisture
content of 20% decreased to 11 MPa, while Poisson constant ν did not depend on
grain moisture and oscillated around 0.2. Modulus of elasticity of corn kernels in
bulk determined by Frontczak and Metzger [53] in uniaxial compression test at