  We report on rheometry measurements to characterize critical behavior in two
model shear thickening suspensions: cornstarch in water and glass spheres in
oil. The slope of the shear thickening part of the viscosity curve is found to
increase dramatically with packing fraction and diverge at a critical packing
fraction phi_c. The magnitude of the viscosity and the yield stress are also
found to have scalings that diverge at phi_c. We observe shear thickening as
long as the yield stress is less than the stress at the viscosity maximum.
Above this point the suspensions transition to purely shear thinning. Based on
these data we present a dynamic jamming phase diagram for suspensions and show
that a limiting case of shear thickening corresponds to a jammed state.
