Effect of phase on the frictional dissipation in systems subjected to harmonically varying loads

When contacting elastic systems are subjected to periodic loading, frictional slip occurs resulting in energy dissipation. Here we investigate the effect of the relative phase of harmonically varying tangential and normal loads on the frictional dissipation in a very simple uncoupled frictional system. We demonstrate that this effect is substantial when the system experiences periods of separation, but more modest when contact is continuous. The maximum dissipation occurs when the normal and tangential loads are approximately π/2 out of phase.