Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
(A) The coefficient of friction as a function of number of revolutions in the pin-on disk test. (B) The optical profile images of worn discs and the calculated cross-section areas of the wear tracks. This image is reprinted from ref. [113].
