The document provides an overview of bearing failure analysis, including failure mode classifications, causes of bearing failures, and methods to secure evidence for analysis. It details factors leading to premature failure such as lubrication issues, misalignment, and material defects, emphasizing the importance of examining damaged bearings for root cause analysis. Practical exercises are included to aid in understanding various types of bearing failures and their identification.

1. Bearing Failure Analysis
2013-09-13 ©SKF Slide 1 [Code]
SKF [Organisation]

2. 2013-09-13 ©SKF Slide 2 [Code]
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Bearing failure analysis
Overview:
•Load path patterns
•Failure mode classification
•How to secure evidence
•Hands-on exercises

3. 2013-09-13 ©SKF Slide 3 [Code]
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Bearing failure analysis
The best way to become expert is to examine damaged bearings. Evidence will emerge
to allow root cause analysis and hence corrective action. Many of ball and roller bearings
never attain their calculated life expectancy. .
The calculated life expectancy of any bearing is based on four assumptions:
1.Good lubrication in proper quantity will always be available to the bearing.
2.The bearing will be mounted without damage.
3.Dimensions of parts related to the bearing will be correct.
4.There are no defects inherent in the bearing.

4. 2013-09-13 ©SKF Slide 4 [Code]
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Bearing failure analysis
Even if all the four conditions are met, the bearing may still
fail due to fatigue of bearing material.
Three major classifications of premature spalling are
lubrication, mechanical damage, and material defects.

5. 2013-09-13 ©SKF Slide 6 [Code]
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Bearing failure analysis
Most bearing failures can be attributed to one or more of the
following causes:
1. Defective bearing seats on shafts and in housings.
2. Misalignment.
3. Faulty mounting practice
4. Incorrect shaft and housing fits.
5. Inadequate lubrication.
6. Ineffective sealing.
7. Vibration while the bearing is not rotating
8. Passage of electric current through the bearing.
9. Transportation, storage and handling.

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Load paths

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Normal radial load zones…

8. 2013-09-13 ©SKF Slide 9 [Code]
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Normal radial load zones…
Stationary outer ring
Rotating inner ring
Constant unidirectional loads

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Normal radial load zones
Stationary inner ring
Rotating outer ring
Constant unidirectional load

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Combined (radial and axial) load
Stationary outer ring
Rotating inner ring
Constant unidirectional radial and axial loads

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Pure Axial load

12. 2013-09-13 ©SKF Slide 13 [Code]
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Misalignment of outer ring

13. 2013-09-13 ©SKF Slide 15 [Code]
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Ovalised outer ring

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Out of round housing

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Tight fit - preloading

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Eccentric radial load

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Imbalance

18. 2013-09-13 ©SKF Slide 20 [Code]
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Failure mode classification
• Causes of failures have identifiable characteristics
• Failure mechanisms have identifiable failure modes
• Observed damage can identify failure causes

19. 2013-09-13 ©SKF Slide 21 [Code]
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Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation
Forced fracture
Fatigue fracture
Thermal cracking
Overload
Indentation
Indents from debris
Indents by handling
Moisture corrosion
Fretting corrosion
Excessive voltage
Current leakage
Adhesive wear
Abrasive wear
Surface initiated fatigue
Subsurface fatigue
Failure modes

20. 2013-09-13 ©SKF Slide 22 [Code]
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Subsurface fatigue
• Repeated stress changes
• Material structural
• Micro cracks under the surface changes
• Crack propagation
• Flaking and peeling
Surface initiated fatigue
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation
Subsurface fatigue

21. 2013-09-13 ©SKF Slide 23 [Code]
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Fatigue spall

22. 2013-09-13 ©SKF Slide 24 [Code]
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Edge loading

23. 2013-09-13 ©SKF Slide 25 [Code]
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True brinelling

24. 2013-09-13 ©SKF Slide 26 [Code]
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Surface initiated fatigue
• Surface distress
• Reduced lubrication
• Sliding motion
• Severity micro cracks
40 µm
Surface initiated fatigue
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation
Subsurface fatigue

25. 2013-09-13 ©SKF Slide 29 [Code]
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Abrasive wear
• Progressive removal of material
• Accelerating process
• Inadequate lubrication
• Ingress of dirt particles
Adhesive wear
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation
Abrasive wear

26. 2013-09-13 ©SKF Slide 30 [Code]
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Wear

27. 2013-09-13 ©SKF Slide 32 [Code]
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• Smearing / skidding / galling
• Material transfer / friction heat
• Tempering / rehardening with stress
concentrations and cracking or flaking
• Low loads
• Accelerations
Adhesive wear
Adhesive wear
Abrasive wear
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation

28. 2013-09-13 ©SKF Slide 33 [Code]
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• It is a material transfer from one
surface to another high temperature
resulting in tempering and
rehardening of material
Adhesive wear
Adhesive wear
Abrasive wear
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation

29. 2013-09-13 ©SKF Slide 34 [Code]
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150° - 177° C (300° - 350° F)
177° - 205° C (350° - 400° F)
205° - 260° C (400° - 500° F)
+ 260° C (+ 500° F)
+ 540° C (+ 1000° F)
Temperature discoloration
• SKF Bearings can be used at temperatures up to
125° C (~ 250° F)
• Higher temperatures may cause loss of Hardness
• Loss of 2-4 points of Rockwell Hardness reduces life 50%

30. 2013-09-13 ©SKF Slide 35 [Code]
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• Oxidation / rust
• Chemical reaction
• Etching (water / oil
mixture)
Corrosion
Fretting corrosion
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation
Moisture corrosion
Rust will form if water or corrosive agents reach the in side of the bearing In
such quantities that the lubricant can not provide adequate protection.

31. 2013-09-13 ©SKF Slide 36 [Code]
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Ineffective sealing

32. 2013-09-13 ©SKF Slide 37 [Code]
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False brinelling…
• Rolling element / raceway
• Micro movements / elastic deformations
• Vibrations
• Corrosion / wear: shiny or reddish depressions
• Stationary: Damage at rolling element spacing
• Rotating: Damage exhibits parallel flutes
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation
Moisture corrosion
Fretting corrosion

33. 2013-09-13 ©SKF Slide 38 [Code]
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Fretting corrosion
• Rolling element / raceway
• Micro movements / elastic deformations
• Vibrations
• Corrosion / wear: shiny or reddish depressions
• Stationary: Damage at rolling element spacing
• Rotating: Damage exhibits parallel flutes
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation
Moisture corrosion
Fretting corrosion

34. 2013-09-13 ©SKF Slide 39 [Code]
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Advanced fretting…

35. 2013-09-13 ©SKF Slide 40 [Code]
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Advanced fretting

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• High current = sparking
• Instant localized heating
leads to melting and/or
welding
• Craters up to 100 µm
Electrical erosion
Current leakage
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation
Excessive voltage

37. 2013-09-13 ©SKF Slide 42 [Code]
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Electrical erosion – excessive voltage

38. 2013-09-13 ©SKF Slide 43 [Code]
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• Low current intensity
• Shallow craters
closely positioned
• Development of
flutes on raceways
and rollers, parallel
to rolling axis
• Dark gray
discoloration
Electrical erosion
Current leakage
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation
Excessive voltage

39. 2013-09-13 ©SKF Slide 44 [Code]
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Vibration

40. 2013-09-13 ©SKF Slide 45 [Code]
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Current leakage

41. 2013-09-13 ©SKF Slide 46 [Code]
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Hybrid deep groove
ball bearing
Insocoat
Electric current passage solutions

42. 2013-09-13 ©SKF Slide 47 [Code]
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• Static or shock loads
• Plastic deformations
• Depressions at rolling element spacing
• Handling damage
Overload
Indentation
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation
Overload
Indents by handling
Indents from debris

43. 2013-09-13 ©SKF Slide 48 [Code]
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Installation damage

44. 2013-09-13 ©SKF Slide 49 [Code]
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• Localized overloading
• Over-rolling of particles = dents
• Caused by soft / hardened steel / hard mineral
particles
Debris denting
Indentation
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation
Overload
Indents by handling
Indents from debris

45. 2013-09-13 ©SKF Slide 50 [Code]
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• Localized overloading
• Nicks caused by hard /
sharp objects
Handling damage…
Indentation
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation
Overload
Indents by handling
Indents from debris

46. 2013-09-13 ©SKF Slide 51 [Code]
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Handling damage

47. 2013-09-13 ©SKF Slide 52 [Code]
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CRB roller damage

48. 2013-09-13 ©SKF Slide 53 [Code]
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• Stress concentration exceeds tensile strength
• Impact / overstressing
Forced fracture…
Forced fracture
Fatigue fracture
Thermal cracking
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation

49. 2013-09-13 ©SKF Slide 54 [Code]
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Forced fracture…

50. 2013-09-13 ©SKF Slide 55 [Code]
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• Exceeding fatigue
strength under
bending
• Crack initiation /
propagation
• Finally forced fracture
• Rings and Cages
Fatigue fracture
Forced fracture
Fatigue fracture
Thermal cracking
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation

51. 2013-09-13 ©SKF Slide 56 [Code]
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Thermal cracking
• High sliding and / or
insufficient lubrication
• High friction heat
• Cracks at right angle to
sliding direction
Forced fracture
Fatigue fracture
Thermal cracking
Electrical erosion
Wear
Corrosion
Fracture
Fatigue
Plastic deformation

52. 2013-09-13 ©SKF Slide 58 [Code]
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Securing evidence
• Collect operating data, monitoring data
• Collect lubricant samples
• Check bearing environment(s)
• Assess bearing(s) in mounted condition
• Mark mounting position(s)
• Remove, mark and bag bearing(s) and parts
• Check bearing seats

53. 2013-09-13 ©SKF Slide 59 [Code]
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Conducting the analysis
Examine Bearing(s) and Parts
• Record visual observations
• Use the Failure Modes to eliminate improbable possible causes and
determine the original cause of the failure.
• Contact external resources for assistance, if needed
• Initiate corrective action, if desired

54. 2013-09-13 ©SKF Slide 60 [Code]
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False brinelling