Equations for particle motions and bulk stresses are derived based on a balance of frictional contact forces on a test particle. Very high particle concentrations are considered, so that contact forces dominate and hydrodynamic interaction is negligible. The analysis is restricted to homogeneous flows of statistically homogeneous suspensions in which the particles are planarly oriented and straight. An explicit solution is given for the case where the friction force between contacting particles is proportional to their relative velocity. Particle motion is then essentially affine, and stresses are quadratic in both particle concentration and particle aspect ratio.