The shear test should simulate the circumstances in which the powder behave in an handling equipment. Only the size of the specimen is small but, all other circumstances should be the same as in the handling equipment, such as pressure humidity and others.
For many processes, the mechanical properties of powders are responsible for the behavior of the powders. The mechanical properties can be achieved by measuring the shear stress. Measuring the shear stresses by various pressure, we achieve an boundary over which the forces can not grow. This boundary we call YIELD LOCUS. The diagram presenting the yield locus as function of the shear stresses and the pressure is called DIAGRAM OF MOHR. Depending of circumstances there is possible that other inter-particular forces then frictional forces, like cohesive, electrostatic, magnetic, forces Van-Der-Walls, magnetic and others, influences the behavior of powders. This forces predict the position of the Yield locus in the diagram of Mohr.
The properties of the powder can be vary during the process and coarse problems if changes leads to more cohesive powder. Powders can be changed in required direction by mixing other components or treat the powder mechanically or chemically. The shear test can monitor this changes and help us to find the right mixture, treatment or watch over the changes during the production.