Boundary Layers: Unifying the Impact and Rolling EHL Contacts

Transient effects in elastohydrodynamic lubrication occur due to varying operating conditions and surface features moving through the contact. For rolling/sliding contacts the lubricated contact behaviour is determined by a unifying mechanism characterized by the inlet length (boundary layer). Roughness deformation depends on a single dimensionless parameter representing the ratio inlet length to wavelength. This behavior is shown to generalize to the pure impact problem. The bell shaped film thickness near the periphery of the contact is directly related to the boundary layer velocity profile. Also, the deformation of waviness under impact conditions is shown to depend as a function of the same single parameter as or rolling contacts when the rolling velocity in it is replaced by the local boundary layer velocity in the impact problem. However, contrary to the rolling sliding case where the roughness deformationis constant over the central region of the contact, in the impact problem it varies from a small deformation in the central zone increasing towards the periphery of the contact