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.