Abstract
The angle of internal friction is one of the most important properties of powder and is often used to characterize powdered materials. The angle of internal friction has been generally determined from the slope of yield locus in the previous works. However, it has been reported also in many papers that the shape of yield locus is affected by the external conditions and the properties of the powder particles. Thus the angle of internal friction has not been determined precisely. On account of this reason, it is necessary to consider the shape of yield locus before everything. In this paper, the shape of yield locus was studied to know its dependence on some factors by analysing the mechanisms of the shear test.
The shear test was performed using plastic balls of amorphous polystyrene as the powder, of which viscoelastic property changes with temperature continuously. The yield loci were determined at several temperatures and preconsolidation pressures. The results obtained show that the values of shear index determined from the yield loci, which is the reciprocal of the shear index in Warren Spring's equation, change with temperature and preconsolidation pressure. Furthermore it is seen that the influence of preconsolidation pressure can be substituted by the influence of temperature. As the results, the master curve of shear index vs. preconsolidation pressure could be constructed.
On the other hand, it is considered that the shearing property is affected by the state of packing, which is dividable into the four parts-plastic deformation, elastic deformation, reversible rearrangement and irreversible rearrangement. It can be concluded that the change of shear index is determined by the values of these four contributions.
