The normal press is more sensitive to roughness at the rough
convex peak points is twice to three times as the Hertzian stress
when Ra¼0.4 μm if oil film thickness is less than 0.5 μm at
contact areas. The direct contact at rough peak will lead to a
larger stress. The surface roughness with big value results in
severe stress concentration at both surface and subsurface. The
shear stress is obvious concentrating at both sides of contact
areas.