K. L. Kuttler and Meir Shillor,

Existence of a weak solution for the problem of frictional contact between
a viscoelastic body and a rigid foundation is established. Contact is modelled
with the Signorini condition. Friction is described by a slip rate dependent
friction coefficient and a nonlocal, regularized, contact stress. The existence
in the case of a friction coefficient that is a graph, which describes the jump
from static to dynamic friction, is established, too. The proofs employ the
theory of set-valued pseudomonotone operators applied to approximate
problems and a priori estimates.