Debris denting, spall initiation and propagation in elasto-hydrodynamic lubricated contacts

Gang Xu, Purdue University

Abstract

Surface initiated fatigue caused by debris is one of the most dominant failure modes for lubricated machine elements such as bearings, gears, cam and followers, etc. The existence of debris in lubricant significantly reduces the contact fatigue life. The life reduction is due to the surface damage caused by the debris when it is rolled into the contact. This dissertation presents the analytical, numerical and experimental studies of the debris denting effects on the elastohydrodynamic lubricated contacts. Debris indentation model, thermal elastohydrodynamid lubrication contact model with dent effects, and elasto-plasto hydrodynamic lubrication contact model were developed to investigate debris denting effects. The results indicate that when debris enters a lubricated contact, it will indent the surfaces causing surface damage. Dents in the contact will create high pressure spikes and result in stress concentrations on the surface, which lead to surface initiated failures. Based on the damage mechanics theory, spall initiation and propagation models were developed for both line and point contacts. The results indicate that the crack initiation in lubricated contacts with surface damage is due to the accumulated plastic strain process. This model includes the crack initiation life. Experimental studies on dent initiated spalling and spall initiation location were conducted. The experiments were performed on a ball-on-disk rolling/sliding contact tester and a ball-on-rod fatigue test machine. The experimental results verify the numerical model predictions and the significant life reduction to debris denting effects. Finally, the residual stress effects due to debris denting were studied. The residual stresses are generated in the debris denting process and the over-rolling of dent process. The results indicates that the residual stress effects are strongly influenced by the material properties.

Degree

Ph.D.

Advisors

Sadeghi, Purdue University.

Subject Area

Mechanical engineering

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