Radial pressure exerted by piston rings

The local pressures exerted by 15 in diameter rings closed to a circular shape by 36 point loads were measured with strain gauges. Departures from the theoretical open shape and from a circle when closed by tangential end forces, which simulated uniform pressure, did not predict the variations in local pressure. Double integration of pressures around the rings led to the open shape defects of the same order of magnitude as the measured values. Variations in local pressure exerted by actual piston rings can only be determined by direct, multipoint measurement.