The contact problem between two solid bodies has been studied, conside
ring the existence of a third thin body separating the two bodies, wit
h a viscoplastic behaviour law of Norton-Hoff type. The limit problem
corresponding to the first order solution of the asymptotic problem is
investigated, from the mathematical point of view. Several equivalent
variational formulations of the model are derived. The existence and
uniqueness of the solution of the material surface model are then stud
ied. Lastly, error estimates between the three-dimensional problem and
the limit two-dimensional model are obtained.