Cumulative damage modeling of solid lubricant coatings that experience wear and interfacial fatigue

Solid lubricating coatings comprise a large segment of tribological materials and under a spherical contact the coating/substrate interface experiences cyclic shear stress that leads to delamination of the coatings from the substrate and premature failure. The polymeric solid lubricating coating used in this study is an expanded PTFE/epoxy composite. The coatings experience cumulative damage caused by interfacial fatigue and wear ultimately leading to failure. Using a finite element simulation of the contact conditions and experimental data, a numerical analysis of the coupled failure modes was completed. The results of the modeling offer insight to designers on considerations in extending the lives of coatings subject to cyclic stresses. The experimental data for cycles to failure versus coating thickness fall closely to the fit for the cumulative damage model. This result also shows that these coatings experience failure primarily from interfacial fatigue under these pin-on-disk experimental conditions.