Measurements And Analysis Of Granular Stress In A Silo System

Silo effect is an important research direction in granular physics field. Former researcher almost studied the silo effect under the Janssen model, and focused on the measurement of the apparent mass on the bottom of the silo, while the direct measurements of the stresses along the sidewall remain scarce. However, if we analyze the granular matter under the nonlinear elasticity theory, the sidewall stresses is obviously an important boundary conditions.In this thesis, firstly, we measured sidewall friction and silo pressure simultaneously in a cylindrical silo, with an apparatus of which side wall is consisted of two separated up and down parts. As compared the results with the so-called Janssen model of silo stress, certain deviations from the model are always observed, irrespective that a slowly downward motion of silo bottom for "fully mobilized friction" suggested by Vanel etal is carried on or not. Moreover,without the friction mobilization the deviation may increase considerably if a tiny sink of the upper side-wall caused by weight of filled grains is present. The effect can be however eliminated by the friction mobilization. We designed another setup to measure the apparent mass on the bottom and the local stress distributions along the sidewall synchronously. The apparent mass, as a macroscopic property, are found deterministic and stable for many experimental runs, while the mesoscopic stress distribution, which measured with force detectors of several grain diameters, fluctuated strongly from one experiment to the another. Our results show that the local fluctuations do not destroy the deterministic nature of a macroscopic property.Results of this thesis indicate that the distribution of stress among silo bottom and the sidewall is complicated and variant, depend on the preparation history and the deformation of experiment setup. Large fluctuation of local stress even exists in a determinate macro-stress. Therefore, the stress boundary conditions, but not the displacement boundary conditions are commended for analyzing static stress distribution of granular matter with nonlinear elastic theory. In this frame, the history-dependence on preparation of the granular system can attribute to the difference of the boundary condition.