The mechanism of the increase in oil film
thickness with a steel ball with sub-micrometer
downsteps beside the contact point on a ball under pointcontact elastohydrodynamic lubrication (EHL) condition
was investigated. The film thickness was measured using
a disk-on-ball friction tester with optical interferometry.
The Reynolds equation and finite element method were
used to calculate the pressure and deformation
distributions, respectively. The analytical results showed
that the increase in the oil film thickness was due to the
ball and disk taking a unique deformed shape. This
restricted oil flow from the contact point, causing the film
thickness to increase.