  We investigate dilation-induced surface deformations in a Discontinuous Shear
Thickening (DST) suspension to determine the relationship between dilation and
stresses in DST. Video is taken at two observation points on the surface of the
suspension in a rheometer while shear and normal stresses are measured. A
roughened surface of the suspension is observed as particles poke through the
liquid-air interface, corresponding to dilation. Dilation events are found to
be intermittent and localized spatially. Shear and normal stresses also
fluctuate between high- and low-stress states, and dilation is observed
frequently in the high stress state. On the other hand, a complete lack of
dilation is observed when the stresses remain at low values for a several
seconds. Dilation is most prominent while the stresses grow from the low-stress
state to the high-stress state, and the dilated region tends to span the entire
surface by the end of the stress growth period. Dilation is found only at
stresses and shear rates in and above the shear thickening range. These
observed relations between surface dilation and stresses confirm that dilation
and stresses are coupled in the high-stress state of DST.
