5. Conclusions

The flow behavior of binary mixtures of two sizes of glass beads was investigated using both the Schulze Ring Shear Tester and the Discrete Element Method. Both approaches demonstrate that the shear stresses required to achieve steady state flow are greater for binary blends than they are for monodisperse systems. Moreover, DEM simulations well reproduce the experimental observation that the highest measured shear stress is not associated with the highest measured solid fraction for the range of binary mixtures studied. Experimental data further confirm that the flow function coefficient (FFc) of these mixtures is strongly affected by its solid fraction, with unconfined yield strength directly correlating to this parameter. An analysis of the frictional and tensile components of unconfined yield strength reveals that the powder friction has a slightly higher contribution to powder strength than powder adhesion, and that the frictional component follows the same trend as steady state shear stress with mixture composition. Whereas maximum tensile strength corresponded to maximum solid fraction, steady state shear stresses and internal angle of friction values do not. DEM simulation demonstrate that the addition of small adhesive particles reduces the averaged angular velocity of the larger particles, which makes a contribution to a larger shear stress and internal friction angle for binary blends. Furthermore, particle contact type, contact number and force network vary significantly for different blends. It is believed that these factors also contribute to the shear stress difference for blends of varying composition.