  How friction affects adhesion is addressed. The problem is considered in the
context of a very stiff sphere adhering to a compliant, isotropic, linear
elastic substrate, and experiencing adhesion and frictional slip relative to
each other. The adhesion is considered to be driven by very large attractive
tractions between the sphere and the substrate that can act only at very small
distances between them. As a consequence, the adhesion behavior can be
represented by the Johnson-Kendall-Roberts model, and this is assumed to
prevail also when frictional slip is occurring. Frictional slip is considered
to be resisted by a uniform, constant shear traction at the slipping interface,
a model that is considered to be valid for small asperities and for compliant
elastomers in contact with stiff material. A model for the interaction of
friction and adhesion, known to agree with some experimental data, is utilized.
This model is due to Johnson, and its adhesion-friction interaction is assumed
to stem, upon shrinkage of the contact area, from a postulated reversible
energy release associated with frictional slip. This behavior is considered to
arise from surface microstructures generated or eliminated by frictional slip,
where these microstructures store some elastic strain energy in a reversible
manner. The associated reversible energy release rate is derived from the
energy exchanges that occur in the system. The Johnson model, and an asymptotic
analysis of it for small amounts of frictional slip, is shown to be consistent
with the reversible energy release rate that we identify.
