A Numerical Study on Thermal Elastohydrodynamic Lubrication of Coated Polymers

The application of polymers in power-transmitting machine elements, e.g., gears, is limited by moderate thermo-mechanical properties and the detrimental accumulation of contact heat, even with external lubrication. Hence, polymer rolling-sliding elements are often prone to thermo-mechanical overload or abrasive wear. Diamond-like carbon (DLC) coatings are well known from steel applications for enhancing wear resistance and reducing friction. Since preliminary results indicate promising results for such coatings for polymers as well, their influence on the behavior of lubricated polymer contacts is investigated by numerical simulation. For polymer-steel contacts, the mechanical and thermophysical properties of coating and polymer are varied. The contact geometry is dominated by a local conformity, in which most of the deformation is related to the polymer. The DLC coatings affect film thickness and hydrodynamic pressure only little even for untypical high coating thicknesses. In contrast, the contact temperature decreases already for very thin coatings due to enhanced heat removal. Hence, DLC coatings can act as a thermal barrier protecting the polymer from detrimental heat and protecting the polymer from abrasive wear.