  Highly concentrated or 'dense" particle suspensions can undergo a sharp
increase in viscosity, or shear thickening, under applies stress. Understanding
the fundamental features leading to such rheological changes in dense
suspensions is crucial to optimize flow conditions or to design flow modifiers
for slurry processing. While local changes to the particle environment under an
applied shear can be related to changes in viscosity, there is a broader need
to connect the shear thickening transition to the fundamental organization of
particle-interaction forces which lead to long-range organization. In
particular, at a high volume fraction of particles, recent evidence indicates
frictional forces between contacting particles is of importance. Herein, the
network of frictional contact forces is analyzed within simulated
two-dimensional shear thickening suspensions. Two topological metrics are
studied to characterize the response of the contact force network (CFN) under
varying applied shear stress. The metrics, geodesic index and the void
parameter, reflect complementary aspects of the CFN: one is the connectedness
of the contact network and the second is the distribution of spatial areas
devoid of particle-particle contacts. Considered in relation to the variation
of the viscosity, the topological metrics show that the network grows
homogeneously at large scales but with many local regions devoid of contacts,
indicating clearly the role of stress chain growth in causing the large change
in the rheological response at the shear thickening transition.
