On the Study of Thermal Fatigue of Bearing Metals Lining on Steel Plates

Abstract

The strain due to the difference of thermal expansion between the lining metal and the backing metal is considered to cause thermal fatigue in plain bearings where heating and cooling are alternated during run and rest. In the present paper, thermal fatigue tests were carried out on the bearing metals lining on steel plates in lubricating oil, the strain fluctuations being considered in details. The residual strain due to lining is relaxed with time, but the strain recovers to appropriate states through a few thermal cycles. Thereafter, the strains in the metal are decided by the temperature and the lining thickness. Accordingly, in thermal fatigue tests under a given temperature range, the strains of constant amplitude are repeated on test pieces and the mean strain which is the residual strain at the mean temperature is kept constant. The feature of thermal fatigue differs with different bearing metals, white metals showing fine cracks at the surface, copper-lead alloy forming pits in the place of lead. The thermal fatigue strength depends on the temperature range and the lining thickness. The dependences are due to the strain amplitude and the mean strain produced in the test pieces. The failure initiates from the interface when the lining thickness is large under the condition of these strains. When the thermal cycles include the holding time at the maximum and the minimum temperatures, the thermal fatigue strength is lowered because of stress relaxation. The rate of heating and cooling being affected by the viscosity of oil, the fatigue strength is higher in a more viscous oil. These discussions may contribute to the study of thermal fatigue of coating materials in general as well as of bearing metals.