Abstract
Using a “Coke-Tester” which is a sophisticated split-cell type tensile strength tester, a new method for measuring the yield locus of a low stress region of a loosly packed cohesive powder is proposed.
The movable cell is pulled horizontally while in the vertical direction a compressive stress is applied by weights placed on the surface of the sample powder. Failure of the powder bed commences when the state of stress in the bed reaches the plastic equilibrium. If the vertical compressive stress coincides with the major principal stress σ1, the measured tensile strength indicates the minor principal stress σ3, and therefore a Mohr failure circle is obtained for each measurement. By drawing an envelop around Mohr's failure circles obtained for several values of σ1, PYL is determined corresponding to the specified porosity of the bed. This method is also useful for evaluating the unconfined yield strength of the powder bed.
