Mechanical properties and prediction models of shorts and oat flour

Thumbnail Image
Qu, Qiuya
Journal Title
Journal ISSN
Volume Title
University of Guelph

Mechanical properties of two cohesive materials were investigated by experimental and numerical methods. Both direct shear and triaxial tests were conducted to measure the flow parameters (cohesion and the angle of internal friction) of two cohesive materials, shorts and oat flour. The effects of the shear rate and vertical force in direct shear test and the confining pressure and vertical displacement rate in triaxial test were examined. In 45 direct shear tests of shorts and oat flour, the shear rate did not significantly affect the flow parameters. In 54 triaxial tests of the same materials the effect of vertical displacement rate was small. Cohesion was not significantly different for both tests, whereas the angles of internal friction were significantly different. Cohesion was 34.8 kPa for shorts, 23.5 kPa for oat flour; the angle of internal friction was 27.8° from direct shear tests and 31.0° from triaxial tests for shorts, 31.6° from shear tests and 36.7° from triaxial tests for oat flour. The constants ( q and Cd ) of Drucker-Prager yield criterion were also obtained from triaxial test data. q was 0.24 for shorts, 0.29 for oat flour. Cd was 42.5 kPa for shorts, 27.8 kPa for oat flour. The two constants were not significantly influenced by vertical displacement rate. The relationship between equivalent stress and equivalent strain, and the relationship between volumetric strain and equivalent strain were determined from triaxial data. The effect of the test factors (confining pressure and vertical displacement rate) on all the parameters in the relationships were examined statistically. The parameters in the relationships between equivalent stress and equivalent strain were not significantly affected by vertical displacement rate. Numerical expressions of these parameters were obtained for use in finite element analyses. The stress-strain relationships were used in a number of finite element analyses of wall pressures during storage and discharge of cohesive materials from a silo. The effects of friction coefficient and hopper opening on the normal wall pressures were examined. Friction between stored material and silo wall was the most important factor affecting wall pressure. When friction coefficient increased from 0.2 to 0.3, the normal wall pressure decreased by about 30% for shorts, and 23% for oat flour. The effect of the hopper opening was not as significant.

oat flour, mechincal properties, prediction models, shorts, internal friction