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A n erpm'mental study of metallic contatninant e,@!cls on sufacesurface defect-such as large inclusion-is beco~ning indentation i n EHL contacts is presented. Partic/es (,re initially uncommon. In the same time, the increase of the contact sphhcal and are composed of M-50 high-carbon steel poruder. Their rec~uirements-in terms higher temperature and diameter ranges from 3 2 to 40 Fm. A n original lzcbricrition system lower amount of oil available-reduce the EHL film thickness. As a consequence, the proportion of rolling bearing with a controlled leuel of contamination was built. Tlte contaminant failures initiated from the surface increases. It is well known distribution and concentration are measured on-line by nil automatic that solid particles in suspension in oil may pass through an particle counter. Tesls are conducted on a truo-disk nrnchine with EHL contact and dent the contacting surfaces. on conditions. may lravel througll lhe EHL the bearing element as well as grinding furrows o r contact only one time, the lubn'cantflow bkng used only once. The improper surface finishing, may be at the origin of a rolling oil is a synthetic one qualiJied under the MI[,-Ld-23699 sj>eci$cation.bearing failure surface initiated. A n optical profilometer is used to describe the indent rqogruphy andOperating oils contain many contaminants prior to the first a CCD video camera to count the number of dents.The test bench is described and the experimental procedure is presented. Specific tests were perjormed to qunlifjr the contanrination bench. The combined qfects of particles concentration ccnd tesf duration on dent distribution ruere studied. Some reszclts o,?. the shape and concentration of indents verstis operating mnrlitiotzs are presented. It is shown that over the range of test conditions considered, the number of indents on the racnuays can be esfittrnturl from the particle concentration i n the oil bulk. This leads to /he conclusion that the particle mtty ratio is close to one, i.e., the concentration of particles inside the EHL contact is close to tlrose i n the Irulk.

An original displacement-based formulation of tooth friction power losses in spur and helical gears is established, which can account for the influence of tooth profile modifications. Several analytical formulas are derived enabling friction losses to be easily estimated for a wide range of gears at the design stage. Numerous comparisons with both the classic formulas in the literature and the results of numerical simulations are presented, which confirm the accuracy of the proposed approach.

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Among prevalent tribological failures, notably in rolling element bearings for wind turbines, an unusual rolling/sliding contact fatigue failure mode has been identified as white etching cracks. White etching cracks are broad subsurface three-dimensional branching crack networks bordered by white etching microstructure, eventually leading to flaking. Reproduction of the failure mode on standard rolling element bearings test rigs has not been mastered yet except with artificial hydrogen charging. Even though these failures have been reported for several decades, there is no evident common denominator in different occurrences. Hence, initiation and propagation mechanisms are not yet fully understood in application. Analyses of the contact conditions of a standard rolling element bearings test rig reproducing white etching cracks on standard and hydrogen precharged inner rings reveal that hydrogen charging seems to modify the white etching cracks initiation mechanism. Based on fractographs, serial sectioning, and scanning electron microscopic analyses, surface initiation and propagation mechanisms are proposed, including influent drivers and possible preventive techniques.

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Power losses in high-speed gears come from the friction between the teeth (sliding and rolling), the lubrication process (dip or jet lubrication), the pumping of a gas-lubricant mixture during the meshing and the losses associated with windage effects. The objective of this paper is to present a number of preliminary experimental and theoretical findings on the prediction of windage losses. Experiments were conducted on a test bench whose principle consists in driving a gear to a given speed and then measuring its deceleration once it has been disconnected from the motor. Results are presented for a disk and 4 different gears with no enclosure and in the absence of lubricant at speeds ranging from 0 to 12, 000 rpm. Two different theoretical approaches have been developed: i) a dimensional analysis based upon the dimensionless groups of terms which account for the flow characteristics (Reynolds number), the gear geometry (tooth number, pitch diameter, face width) and the speed, ii) a quasi-analytical model considering in detail the fluid flow on the gear faces and inside the teeth. It is found that both approaches give good results in comparison with the experimental evidence and two analytical formulas aimed at predicting windage losses in high-speed gears are proposed.

Debris dents produced by solid particles in suspension in oil or grease when they travel through an EHL contact may be at the origin of rolling bearing failures. A summary of an experimental investigation carried out to identify (i) the particle entry ratio, (ii) the mechanisms of particle fragmentation or deformation, (iii) the resulting indentation features, and (iv) the initiation site of subsequent surface damage is presented first. Afterwards, numerical simulations of a dent moving through an EHL contact are performed. A critical slide-to-roll ratio is found. Results of our numerical simulations are analyzed and discussed in relation to the concept of infinite life for rolling bearing applications. [S0742-4787(00)00901-2]