Evidence of lubricant slip on steel surface in EHL contact

The limiting traction provided by typical elastohydrodynamically lubricated (EHL) contacts leads to the postulation that liquid lubricants are subject to limiting shear stress, which is generally accepted as an intrinsic property of the lubricants. The results of recent optical EHL research show that lubricant at EHL contacts may slip on the Cr-coated glass surface under certain circumstances. This paper presents further evidence that high pressure EHL film can slip on a steel surface. Because the steel/steel contacts are common in typical traction drives and the interfaces are therefore oil/steel, the deduction of the limiting shear stress of lubricants from the measured limiting traction may simply reflect a property of the system should boundary slippage occur.

► Evidence of EHL oil film slip on STEEL surface is obtained.
► For measurements of limiting shear stress, boundary slip must be addressed.
► Direct observation of entrapped 5P4E (polyphenyl ether) being ruptured.