Prediction of micropitting damage in gear teeth contacts considering the concurrent effects of surface fatigue and mild wear

Abstract

A B S T R A C TThe present paper studies the occurrence of micropitting damage in gear teeth contacts. An existing general micropitting model, which accounts for mixed lubrication conditions, stress history, and fatigue damage accumulation, is adapted here to deal with transient contact conditions that exist during meshing of gear teeth. The model considers the concurrent effects of surface fatigue and mild wear on the evolution of tooth surface roughness and therefore captures the complexities of damage accumulation on tooth flanks in a more realistic manner than hitherto possible. Applicability of the model to gear contact conditions is first confirmed by comparing its predictions to relevant experiments carried out on a triple-disc contact fatigue rig. Application of the model to a pair of meshing spur gears shows that under low specific oil film thickness conditions, the continuous competition between surface fatigue and mild wear determines the overall level as well as the distribution of micropitting damage along the tooth flanks. The outcome of this competition in terms of the final damage level is dependent on contact sliding speed, pressure and specific film thickness. In general, with no surface wear, micropitting damage increases with decreasing film thickness as may be expected, but when some wear is present micropitting damage may reduce as film thickness is lowered to the point where wear takes over and removes the asperity peaks and hence reduces asperity interactions. Similarly, when wear is negligible, increased sliding can increase the level of micropitting by increasing the number of asperity stress cycles, but when wear is present, an increase in sliding may lead to a reduction in micropitting due to faster removal of asperity peaks. The results suggest that an ideal situation in terms of surface damage prevention is that in which some mild wear at the start of gear pair operation adequately wears-in the tooth surfaces, thus reducing subsequent micropitting, followed by zero or negligible wear for the rest of the gear pair life. The complexities of the interaction between the contact conditions, wear and surface fatigue, as evident in the present results, mean that a full treatment of gear micropitting requires a numerical model along the lines of that applied here, and that use of overly simplified criteria may lead to misleading predictions.

The Influence of Slide–Roll Ratio on the Extent of Micropitting Damage in Rolling–Sliding Contacts Pertinent to Gear Applications

“…Other factors, including the magnitude and direction of sliding, level of Hertz contact pressure, material and running-in, have also been shown to have a significant influence on micropitting by several authors [6][7][8][9][10][11][12]. In addition to these experimental studies, a number of authors have attempted to predict the onset and progression of micropitting on gear teeth using numerical contact models [8,[13][14][15].…”

Propagation of Large Spalls in Rolling Bearings

“…(8). (8) Where N i is the number of stress cycles to failure at stress S i , and n i is the number of cycles applied at stress S i .…”

“…This situation has pushed research to investigate, understand and predict SRCF. One example of damage development very much related to SRCF is surface distress, also known as micropitting or grey staining, recent work can be found in the following publications [3][4][5][6][7][8]. Another important example of failure mode related to SRCF is spalls propagating from surface pre-damage, e.g.…”

Assessing the effectiveness of data-driven time-domain condition indicators in predicting the progression of surface distress under rolling contact

“…However, due to ongoing trends of reducing oil viscosities and increasing power densities, both of which lead to reduced lubricant film thicknesses and associated increase in metal-to-metal contact, modern machine elements often fail through damage initiated at roughness asperity contacts. Perhaps the most important type of such asperity contact initiated damage in bearings and gears is micropitting [13,14]. Micropitting occurs through rolling contact fatigue caused by the cyclic stresses on the surface asperity level, as distinct from pitting which occurs due to cyclic Hertzian stress on the contact level and results in pits that are comparable in size to the contact size.…”