  Formulating a consistent theory for rigid-body dynamics with impacts is an
intricate problem. Twenty years ago Stewart published the first consistent
theory with purely inelastic impacts and an impulsive friction model analogous
to Coulomb friction. In this paper we demonstrate that the consistent impact
model can exhibit multiple solutions with a varying degree of dissipation even
in the single-contact case. Replacing the impulsive friction model based on
Coulomb friction by a model based on the maximum dissipation principle resolves
the non-uniqueness in the single-contact impact problem. The paper constructs
the alternative impact model and presents integral equations describing
rigid-body dynamics with a non-impulsive and non-compliant contact model and an
associated purely inelastic impact model maximizing dissipation. An analytic
solution is derived for the single-contact impact problem. The models are then
embedded into a time-stepping scheme. The macroscopic behaviour is compared to
Coulomb friction in a large-scale granular flow problem.
