Abstract
Janssen's equation is widely used to calculate the powder pressure in a silo. Physical properties necessary for the powder pressure calculation are bulk density, wall friction factor and stress ratio. In the physical properties, bulk density and wall friction factor can be measured directly by the mechanical tests of the powder. But the stress ratios are evaluated indirectly from the Yield Loci of powder beds. Therefore, if the evaluated results of stress ratios differ by the approximation methods of a yield locus, it would be considered that the approximation methods affect the calculated results of powder pressures. But few studies on the effects of approximation method of Yield Locus on stress ratios can be found.
In this paper, we describe Yield Locus from shear test results by Coulomb's equation, Warren-Spring's equation and our proposed equation and evaluate stress ratios. We also evaluated the stress ratio using the equation recommended by ISO and compared it with other methods. Furthermore, we calculated the powder pressure in a silo from the stress ratios by Janssen's equation. These calculated results are compared with experimental results and the effectiveness of our proposed equation is confirmed.
