OBSERVATIONS IN TRANSIENTLY LOADED EHL CONTACTS UNDER PURE SLIDING CONDITIONS

An elastohydrodynamically lubricated contact is experimentally investi gated during transient loading and pure sliding motion. This is a comb ination of motions where lubricant film failures sometimes occur. The experimental setup consists of a empty set 70 mm ball segment mounted on a pendulum. The ball segment can be rotated while it impacts a lubr icated glass disc. The deformation of the surfaces in the contact regi on is studied by means of optical interferometry and high-speed video recording equipment. Two poly-alpha-olefin-type lubricants with viscos ities of 94 and 2600 mm(2)/s are used in the experiments. The squeeze velocity, i.e., the normal approach velocity, is approximately 0.06 m/ s, giving an impact time of about 20 ms. The sliding velocity is varie d from 0 to 34 m/s. Some of the observed phenomena are that lubricant film breakdown occurs at high sliding velocities while full film is ma intained at no or low sliding velocity and that the traditional horses hoe-shaped fringes are found even for this load situation. At very hig h sliding velocities; the interferograms are distorted from their norm al circular shape to a pear-like shape.