Microstructural Alterations in Hertzian Fatigue

Robert Errichello, GEARTECH

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Martensite Decay Under Moderately High Hertzian

Stress

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Classic Subsurface-Initiated

Macropitting

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Subsurface Orthogonal Shear Stress, o

= 0.256po = maximum alternating orthogonal shear stress (basis of L-P theory) o y = 0.85b = locations of o o z = -0.50b = depth of o o 2 = 0.512po = range of o o

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aglicksoText BoxSubsurface Maximum Shear Stress

Morphology of Classic Subsurface-Initiated Macropitting

A

B

C D

D E

F

A- Macropit entry (end first reached by roller) B- Origin located at inclusions at depth of max orthogonal shear stress o C- Typical near-radial branch cracks D- Serration on crater bottom formed by change in crack direction E- Macropit bottom consisting of series of cracks at depth of max shear stress 45 F- Macropit exit formed by crack rising in the rolling direction at 30

Ref: T.E. Tallian, Failure Atlas for Hertz Contact Machine Elements, ASME, 1999.

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Morphology of Butterflies

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Morphology of IrWEAs & WECs

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Microstructural Alterations inHertzian FatigueMartensite Decay UnderModerately High HertzianStressMartensite decay with DEA, Flat bands, and steep bandsDEA morphology and characteristics of flat and steep bandsDEA morphology and characteristics of flat and steep bands (cont.)Correlation between Hertzian stress, number of cycles, DEA, and WBs Ref: Zwirlein and Schlicht, ASTM 771 (1982)Classic Subsurface-Initiated MacropittingSubsurface Orthogonal Shear StressSubsurface Maximum Shear StressClassic Subsurface-Initiated Macropit (CRB IR)Morphology of Classic Subsurface-Initiated MacropittingOrigin of Classic Subsurface-Initiated MacropittingWhite Etching Areas (WEAs) Below OriginCrack Networks Near Origin (unetched)Butterfly Below Origin (MnS inclusion)Fatigue Beach Marks on Floor of Macropit Crater (SRB IR)Fatigue Beach Marks on Floor of Macropit Crater (SRB IR) (cont.)Mechanisms of subsurface-initiated Hertzian fatigueMorphology of ButterfliesTypical ButterflyTypical ButterflyTypical butterflies emanating from MnS inclusions (etched)Typical butterflies emanating from MnS inclusions (unetched)Typical butterfly emanating from MnS inclusion (unetched)WEA morphology and characteristics of butterfliesWEA morphology and characteristics of butterflies (cont.)WEA morphology and characteristics of butterflies (cont.)WEA morphology and characteristics of butterflies (cont.)Morphology of IrWEAs & WECsTypical irregular white-etching areas (IrWEAs)Typical white-etching cracks (WECs)Morphology and characteristics of IrWEAs and WECsWEA morphology and characteristics of IrWEAs and WECs (cont.)