1、91 FTM6vComparing Surface Failure Modes in Beatingsand Gears: Appearances versus Mechanismsby: Charles A. Moyer, The Timken companyAmerican Gear Manufacturers AssociationTECHNICAL PAPERComparing Surface Failure Modes in Bearings and Gears: AppearancesversusMechanismsCharles A. MoyerThe Timken Compan
2、yTheStatementsandopinionscontainedhereinare thoseof the authorandshould notbe conslruedasan official actionoropinion of the American Gear ManufacturersAssociation.ABSTRACT:For gear systems and rolling element beatings, there are similar designations for the failures that are identifiedwithintheir re
3、spective contact surfaces. By concentrating on the contact tribo-system, it is possible to go beyond theappearance and determine the mechanisms that promote or prevent contact fatigue damage.It is also important to identify the lubricant regimewithinthe contact. This can be donewith the modified lam
4、bda ratio.This is a ratio of the central film thickness occurring within a contact divided by the composite roughness of the twosurfaces forming the contact, the roughness being modified to match the contact width occurring in the direction ofmotionThe contact fatigue modes are identifiedover arange
5、 of modified lambda values. An attempt is made to describe thefailure modes and interpret the wear,fracture and/or fatiguemechanisms that lead to the failure initiation. Consideringthe similarity in appearance of the gear and bearing failure modes and yet the considerablydifferent relative surfacemo
6、tions and _aetions of the twocontacts, this comparison helpsprovide insight into thebasic causes of the failures andperhaps suggests methods to avoid them.Copyright 1991American Gear Manufacturers Association1500 King Street, Suite 201Alexandria, Virginia, 22314October, 1991ISBN: 1-55589-603-0COMPAR
7、ING SURFACE FAILURE MODES IN BEARINGSAND GEARS: APPEARANCES VERSUS MECHANISMSCharles A. MoyerThe Timken CompanyConsiderable work has been done toINTRODUCTION accomplish this, and more remains to bedone, but by being able to understandIn the 1960s and early 1970s, expected failure modes based on know
8、nconsiderable work was done to identify the operating conditions and applying this tovarious modes of damage that ended the the design cycle, significant improvementslives of rolling element bearings in bearing performance have been achieved.(1)(2)(3)(4)(5). A simple summary of For line contact bear
9、ings, the primeall the damage modes that could lead to factors are (i) significantly cleanerfailure is given in Table 1. In bearing steel, (2) much improved surface finishes,applications that have insufficient or which includes roughness, waviness andimproper lubricant, or have contaminants other fa
10、ctors beyond R (the arithmetic(water, solid particles) or poor sealing, center-line average of 9oughness), and (3)failures such as excessive wear, geometry that optimizes internal stresscorrosion or excessive vibration can profiles so that even under high load oroccur rather than contact fatigue, no
11、naligned conditions much more uniformUsually other components in the overall stresses can be maintained along thesystem besides bearings also suffer. Over contact line.the years, builders of transmissions,axles and gear boxes that comprise such It would seem the same developmentsystems have understo
12、od the need to path has been occurring for gear contacts.improve the operating environment within Thus, it may be we can review the failuresuch units so that some system life modes that occur in gears and, based onimprovements have taken place, the understanding of what mechanismsunderlie the variou
13、s failure modes thatThose of us who manufacture bearings have been identified, see what designrealized that identifying the damage modes changes may be appropriate that would alsowas not enough but that an understanding extend gear performance life beyondof the causes and underlying mechanisms at pr
14、esent limits.play was important to improve the abilityto predict bearing life in these variety One way to do this is to compare theof systems. However, whenever adverse modes of damage identified in line contactoperating conditions prevailed and actual bearings and gears to determine what islife was
15、 below expected life, it was happening within their respective contactsrecognized that the understanding of modes that cause the final failures. Since bothof failure within bearings could be used bearings and gears function primarily withto determine what improvements were needed fluid lubrication,
16、a tribological model ofto allow bearings to have extended life line contact, as shown in Fig. 1, can beeven under adverse conditions, the starting point to discuss theTABLE iDAMAGE CLASSIFICATION FOR BEARINGSI. FATIGUEContact Fatigue - Subsurface OriginInclusion - within macroshear classical shear s
17、tress zone below contact surfaceInclusion - near surface zone of microshear greatly influenced by surface roughness(asperities)Subcase Fatigue - origin near case-core interface if yield strength is exceeded by appliedstressContact Fatigue - Surface OriginOrigin at the end of contact aggravated by ed
18、ge geometryMultiple origins of micropitting (peeling or frosting)Point Surface Origin - at localized stress risers (dents, grooves, surface inclusions)II. PLASTIC FLOWBrinelling or debris dentingLoad excursions above the material yield pointYielding aggravated by high temperature excursionsIII. WEAR
19、A. AdhesiveNormal - mild or “controlled“ - usually identified as “run-in“Severe - irreversible scuffing, scoring, smearing or seizureB. AbrasiveNormal - usually 3 body system, medium to fine particles that are also associated with“run- in“Severe - grooving, gouging, denting with ridges that cause se
20、rious surface stress risersC. CorrosiveWater or acidic constituents from lubricant breakdown or temperature chemicallyaggressive additives in lubricantD. FrettingMicroscale adhesive and abrasive wearCorrosion involvement depending on environment and contactsThe two cylinders under load determinethe
21、Hertzian contact area on the X-Y planeshown on Fig. i. The cylinder lengthmechanisms that contribute to the various along the Y axis and 2b, the widthfailure modes reported, of contact along the X axis, form theHertzian contact shown by the straightTHE BASIC LINE CONTACT MODEL dashed lines. The Hert
22、zian contactpressure reaches a maximum P as indicatedWhether gears or roller bearings, the by the dotted lines above the contactcontacting surfaces can be represented as rectangle. P directly relates to thetwo cylinders. It is possible to include sub-surface principal and shear stressestransverse pr
23、ofiles or radii on these to be discussed later.cylinders and determine the appropriateelliptical or truncated elliptical contact If there is sufficient lubricant informed; but for this discussion two simple the entering meniscus to the contact, ancylinders of the same or different radii elastohydrod
24、ynamic lubricant (EHL) film(h)are sufficient. Under running conditions, will be formed. Recognizing that theeach cylinder has surface velocities cylindrical surfaces have some amount ofeither close to the same or considerably roughness, the lubricant film(h) anddifferent that results in tangential o
25、r roughness (O-) can be compared to give anfrictional forces within the contact that indication of the quality of the lubricantcan range from less than one percent to operating regime within the contact. Thatwell over twenty percent of the normal is, the EHL film(h) divided by theforce that forms a
26、rectangular contact composite roughness of the two surfaces(_)area between the two cylinders, provide h/_ or lambda (_).2Testing on ball and roller contacts, Maximum Contactas for example in a tapered roller bearing -_Pressure(P)(6), demonstrates that the contact itself (2b) actually operates as a f
27、unctional ad_- c_C_Iw_e _ _ _k.,-,_._filter and only the surface roughness -“ wavelengths that are approximately _ _/ Z axis; I“ _:one-fourth (2b) up to twice (2b) are /, _ 1.0), the shear stress will bebelow the surface and contribute only to +-0.3 ,material related fatigue. As the velocity ldiffer
28、ence increases (larger slide/rollratio) and_or with considerable surfacecontact ( Am 3.0 Subsurfac_l_atigue Important Minor Importantinclusion _ -Ratio 3-1.0 Subsurface/Near Surface Important “Sharp“/High ImportantMostly Inclusion Asperities ImportantRatio 1-0.3 Some Inclusion, Some Somewhat Importa
29、nt Important for Surface SomewhatSurface Related spalling for gears(18).(3) PSO - point surface origin - fan shaped spall propagation starting on the surface.(4) GSC - geometric stress concentration starting at end of line contact.Both forms of surface distress are reduced A fair volume of material
30、aroundby reduction in surface roughness or these “localized“ stress risers may alsoincreasing the oil film. That be highly stressed and may be influencedmicropitting could be related to fatigue by material cleanness. Of course, GSC andwas demonstrated by Macpherson and Cameron edge stress problems c
31、an be overcome with(25) in some specific sliding disk tests adequate design and proper profilethey conducted in the early 1970s. They geometry for the application. For linecalled the “new form“ of gear failure, contact, as in gears or tapered roller“Fatigue Scoring.“ The work of Cummins bearings, fr
32、om a fatigue standpoint, onlyand Doyle (17) reinforce this conclusion the largest debris particles are capablethat micropitting is fatigue, of life-limiting dents in bearings or deepscratches in gears.There are also localized stressrisers that can occur either from handling SUMMARYdamage before runn
33、ing, large debrisparticles going through the contact or It is possible with the tribologyserious misalignment that causes end of line contact model to consider all thecontact edge damage. Within the bearing factors that influence and interact withincontact, failures from these stress the loaded conc
34、entrated contact. Two ofrisers are termed point surface origin the important factors are the film(PSO) i.e. spalling from a localized point thickness (h) and combined surfacethat propagates much as the “spalling“ roughness (_). Together in the modifiedDrago describes for gears. At the end of lambda,
35、 they are an indicator of thecontact, the failure is called, geometric lubricant regime operating in a gearstress concentration (GSC). These stress contact or roller bearings. A corollaryrisers are usually generated well beyond to this model is the stress fieldthe elastic limit for the contact mater
36、ial developed below the concentrated contactso, based on their size relative to the that consists of subsurface shear stresslubricant film, they may influenCemfatigue_ and near surface shear stresses related tolife almost independently of . In the surface asperities. These shearbearings, the defects
37、 from debris are stresses are important in theobserved as isolated, pronounced dents, understanding of near surface plasticwhile in gears the debris develop long deformation accumulation and near surfacescratches or a series of grooves and and subsurface fatigue.ridges from the considerable slidingp
38、resent in the contacts9The three basic mechanisms that lead 7. Wellauer, E. J. and Holloway, G. A.,to metal loss in steel gears or bearings “Application of EHD Oil Film Theoryare abrasive wear, adhesive wear and to Industrial Gear Drives,“ Trans.fatigue, in the presence of various levels ASME JEI, p
39、p 626-634, May 1976.of plastic deformation. Very often inreal operating contacts all three of these 8. Moyer, C. A. and Bahney, L. L.,mechanisms exist together and all “Modifying the Lambda Ratio tocontribute to the nucleation and Functional Line Contacts“, STLE Trib.propagation of the fractures tha
40、t lead to Trans. Vol. 33,4, pp 535-542, 1990.the loss of material. An aid toseparating out the primary mechanism is a 9. Moyer, C. A., “Power Densitycareful examination of the contact surface Development: The Role of Improvedand the debris formed, optical Line Contact Performance“, AGMA Tech.microsc
41、opes, scanning electron Paper 89 FTM3, Nov. 1989.microscopes, particle size analyses andferrography may be required to clearly i0. Kannel, J. W. and Tevaarwerk, J. L.identify the actual mechanisms present. “Subsurface Stress Evaluations UnderRolling/Sliding Conditions,“ ASMETable 3 presents the appr
42、oximate Trans. JOT, Vol. 106, pp 96-103, Jan.relationship of contact fatigue mode for 1984.bearings and the modified lambda ratio.Although it is based on fatigue, an Ii. Fessler, H. and Ollerton, E.,understanding of the other mechanisms at “Contact Stresses in Toroids Underwork that degrade gear and
43、 bearing Radial Loads,“ British Journal ofperformance and that also relate to _ may Applied Physics Vol. 8, pp 387-593,allow Table 3 to be used in a broader Oct. 1957.sense. Our review of the various surfaceand near surface damage modes in gears and 12. Zhou, R. S., Cheng, H. S. and Mura,the develop
44、ment of cracks and fractures T., “Micropitting in Rolling andthat precede the formation of debris, when Sliding Contact Under Mixedcompared to the development of fatigue Lubrication,“ ASME Trans. JOT, Vol.cracks for bearings, makes the iii, pp 605-613, Oct. 1989.relationships in Table 3 a reasonable
45、starting point for defining the lubricant 13. Vingsbo, O., “Wear and Wearregime in gears. Mechanisms,“ ASME Proceedings of Wearof Materials Conference, Ed. K.Ludema, W. Glaeser and S. Rhee, ppREFERENCES 620-635, 1979.I. Littmann, W. E., “The Mechanism of 14. Jahanmir, S., “The Relationship ofContact
46、 Fatigue,“ NASA Symp. Tangential Stress to Wear ParticleInterdisciplinary Approach to the Formation Mechanisms,“ ASMELubrication of Concentrated Contacts, Proceedings of Wear of MaterialsNew York, July 1969. Conference, Ed. K. Ludema, pp238-247, 1985.2. Tallian, T. E., Baile, G. H., Dalal,H. and Gus
47、tafsson, O. G., Rolling 15. Suh, N. P., “An Overview of theBearing Damage, A Morphological Delamination Theory of Wear,“ Wear,Atlas, SKF Industries, Revere Press, 44, pp 1-16, 1977.Phil., 1974.16. Rigney, D. A. and Glaeser, W. A.,3. Wren, F. J. and Moyer, C. A., “Modes “The Significance of Near Surf
48、aceof Fatigue Failures in Rolling Microstructure in the Wear Process,“Element Bearings,“ Proceed. I.Mech. E. ASME Proceedings of Wear of MaterialsVol. 179, pt 3D, pp 236-247, 1964-65. Conference, Ed. Ludema, pp 41-46,1977.4. Widner, R. L. and Littmann, W. E.,“Bearing Damage Analysis,“ Symp. 17. Cumm
49、ins, R. A. and Doyle, E.D.,Mechanical Failures by Mech. Failures “Interpretation of Gear Wear,“ ASLEPrevention Group, NBS, May 1974. Trans. Vol. 25, 4, pp 502-510, Oct.1982.5. Fitzsimmons, B. and Clevenger, H. D.,“Contaminated Lubricants and Tapered 18. , “National Standard-Roller Bearing Wear,“ ASLE Trans. Nomenclature of Gear Tooth FailureVol. 20, 2, pp 97-107, 1977. Modes,“ AGMA Standard, ANSI/AGMA110.04-1980.6. Leaver, A. H., Sayles, R. S., andThomas, T.R., “Mixed Lubrication and 19. Drago, R. J., “Failure Modes,“Surface Topography of Rolling Chapter 6, Fundamentals of Gea
