  We show that the detachment of a flat punch from a viscoelastic substrate has
a relatively simple behavior, framed between the Kendall's elastic solution at
the relaxed modulus and at the instantaneous modulus, and the cohesive strength
limit. We find hardly any dependence of the pull-off force on the details of
the loading process, including maximum indentation at preload and loading rate,
resulting much simpler than the case of a spherical punch. Pull-off force peaks
at the highest speeds of unloading, when energy dissipation is negligible,
which seems to be in contrast with what suggested by the theories originated by
de Gennes of viscoelastic semi-infinite crack propagation which associated
enhanced work of adhesion to dissipation. Further qualitative differences with
the dissipation-based model occur to explain the finite size effect.
