1. The elastohydrodynamic (EHD) regime

1.1 The lubricated hertzian contact

Hertzian contacts are those subjected to high Hertz pressures in excess of 200 MPa.

EHD lubrication occurs in contacts between non-conforming surfaces, which are subject to a punching effect: mainly between gear teeth, in bearings in contact with the track/rolling element, and in cam/push-button contacts.

It is also found in biomechanics, in the joints of the lower limbs. Contact pressure is very low (in the megapascal range), but porous, water-rich cartilage has a very low Young's modulus of the order of 10 to 100 MPa (