Étude expérimentale et théorique du microgrippage dans les contacts élastohydrodynamiques

Abstract

This paper describes experimental research conducted on a high-speed twin-disk machine. The twin-disk machine, originally designed to simulate the operation of gears, is used at high speed and low load to simulate the operation of high-speed rolling bearings at the inner ring - rolling element contact. Operating conditions, ie, rolling and sliding speeds, contact pressure, lubricant, temperature, disk material combination and surface finish are typical of aerospace practice. The lubricant used in these tests is a tetra ester of five centistoke viscosity at 100 °C, qualified for use in gas turbine engine lubrication systems under the MIL-L-23699 specifications. In the experimental procedure, the scuffing limit is reached by increasing progressively the sliding speed, other operating conditions such as the normal load and the rolling speed being kept constant. The evidence of disk scuffing is a sudden increase of the friction force, which stops automatically the machine at an earlier stage of the damage process. Moreover, a model to estimate the surface and subsurface temperature distribution in the contacting bodies is presented and used to complement our experimental results. Scuffing damages at sliding speeds of up to 40m.s −1 have been obtained. A total of 32 tests have been carried out. Damages observed on the surface of the disks after tests at very high sliding speeds, appear to be similar in nature to those of the inner raceway of rolling bearings subject to skidding. They consist of transfer of component surface material in microscopic patches from a location on one contacting surface to a location on the other contacting surface. The scuffing limits of two material combinations (M50-M50 and M50-16NCD13), for two mean rolling speeds (25 and 50 m/s), three maximum Hertz pressures (0.5, 0.8 and 1 Gpa) and three oil feed temperatures (40, 80 and 120 °C) are presented and discussed. Finally, from this experimental and theoretical investigation, it is proposed to call ‘micro-scuffing damage’ the surface distress observed as a consequence of skidding.