  If a contact of two purely elastic bodies with no sliding (infinite
coefficient of friction) is subjected to superimposed oscillations in the
normal and tangential directions, then a specific damping appears, that is not
dependent on friction or dissipation in the material. We call this effect
"relaxation damping". The rate of energy dissipation due to relaxation damping
is calculated in a closed analytic form for arbitrary axially-symmetric
contacts. In the case of equal frequency of normal and tangential oscillations,
the dissipated energy per cycle is proportional to the square of the amplitude
of tangential oscillation and to the absolute value of the amplitude of normal
oscillation, and is dependent on the phase shift between both oscillations. In
the case of low frequency tangential motion with superimposed high frequency
normal oscillations, the system acts as a tunable linear damper. Generalization
of the results for macroscopically planar, randomly rough surfaces is
discussed.
