Some aspects of frictional damping as applied to vibrating beams

Abstract It is suggested that more use could be made in the damping of structural vibrations than is currently practised, of the energy dissipating properties of plane contacting metal surfaces subjected to relative slip. Some recent work on surface finish shows that the adverse effects of fretting corrosion can be reduced. Frictional damping of the forced vibrations of a cantilever beam is investigated at frequencies up to 170 c/s for steel-steel, cast iron-steel and brass-steel mating surfaces. The condition for maximum energy dissipation is found to be when the vibration amplitude at the damping position is one-half the undamped amplitude. The energy dissipation is shown to be independent of the coefficient of friction of the contacting surfaces. A simple theoretical analysis gives a fair prediction of the beam response and in particular suggests that the coefficient of friction for the various surface combinations reduces by almost a half, from near zero slip amplitude to a slip velocity of 3 in/sec. The actual contact surface area, as indicated by the fretted scar, is found to be very small and independent of the geometrical contact surface area; the actual contact pressure being about 40 lbf/in 2 .