  Motivated by roughness-induced adhesion enhancement (toughening and
strengthening) in low modulus materials, we study the detachment of a sphere
from a substrate in the presence of both viscoelastic dissipation at the
contact edge, and roughness in the form of a single axisymmetric waviness. We
show that the roughness-induced enhancement found by Guduru and coworkers for
the elastic case (i.e. at very small detachment speeds) tends to disappear with
increasing speeds, where the viscoelastic effect dominates and the problem
approaches that of a smooth sphere. This is in qualitative agreement with the
original experiments of Guduru's group with gelatin. The cross-over velocity is
where the two separate effects are comparable. Viscoelasticity effectively
damps roughness-induced elastic instabilities, and make their effects much less
important.
