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Microstructural Alterations in Hertzian Fatigue
Robert Errichello, GEARTECH
1
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Martensite Decay Under Moderately High Hertzian
Stress
2
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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
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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
30
- 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.)