Transcript Effect of Mean Stress on Rolling Contact Fatigue Sina Mobasher Moghaddam Ph.D. Research Assistant Mechanical Engineering Tribology Laboratory (METL) November 14, 2013

Effect of Mean Stress on
Rolling Contact Fatigue
Sina Mobasher Moghaddam
Ph.D. Research Assistant
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
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Outlines
• Butterfly-wing formation in bearing steel
– Background and Motivation
– Stress Analysis
– METL suggested theory
– Results comparison and validation
• Effect of compressive stress on torsion fatigue
– Instrument Design
– Fatigue life reduction
– Failure mode change
– FEM simulation
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
Butterfly Wings
Detrimental Effect on RCF
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• In some applications bearings may last
only 10% of their 𝐿10 life [i.e. wind
turbines]
• The large costs associated with bearing
replacement (about 0.5 M$) makes clean
energy expensive
• Butterflies are believed to be one of the
major reasons for this premature failure
• Despite the extensive experimental
studies in the last 60 years, there is
almost no model capable of simulating
butterflies
Butterflies Observed by Vincent [1](top)
and Grabulov [2](Bottom)
[1] Vincent A., Lormand G., Lamagnere P., Gosset L., Girodin D., “From White Etching Areas Formed Around Inclusions To Crack
Nucleation In Bearing Steels Under Rolling Contact Fatigue”, ASTM International, 1998
[2] A. Grabulov, R. Petrov , H.W. Zandbergen , 2009, “EBSD investigation of the crack initiation and TEM/FIB analyses of the
microstructural changes around the cracks formed under Rolling Contact Fatigue (RCF)” International Journal of Fatigue 32 (2010) 576–
583
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
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Butterfly Wing Characteristics
ORD
•
•
•
•
•
Butterfly structure is made of
highly saturated ultra fine ferrite
grains
Two wings located along a line
which forms a 45° angle with
Over Rolling Direction (ORD)
Subsurface cracks are frequently
observed to be initiated from
butterflies
In this analysis, ORD is from
right to left in all cases
Surface traction is set to -0.05
Wing Span
Debonded
Region
Coarse Grains
50-100 nm
Crack
Fine Grains
5-10 nm
Schematic of a pair of butterfly
wings
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
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•
•
Stress Analysis
Inclusion presence induces stress concentrations in the surrounding
matrix
When dealing with fatigue problems, it is important to consider stress
history
𝜏𝑎
𝜏𝒎
Comparison of centerline stresses for two domains with
and without embedded inclusion
𝐷𝑖𝑛𝑐 = 16𝜇, b=100𝜇, 𝑃𝑚𝑎𝑥 = 2.0 GPa
Damage Equation for
Butterfly Modeling
𝜏𝑎
+ |𝜏𝑚 |
𝑑𝐷
2
=
𝑑𝑁
𝜎𝑟 1 − 𝐷
𝑚
𝜏𝑎
+ |𝜏𝒎 |
𝟐
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
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Butterfly Wing Evolution
Butterfly wing orientation, direction, and size are consistent with the
experimental observations
Color spectrum of
Butterfly formation
butterfly wing
according to Grabulov[1]
formation
Butterfly formation according
to METL model prediction
[1] A. Grabulov, R. Petrov , H.W. Zandbergen , 2009, “EBSD investigation of the crack initiation and TEM/FIB analyses of the
microstructural changes around the cracks formed under Rolling Contact Fatigue (RCF)” International Journal of Fatigue 32 (2010) 576–
583
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
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Effect of Depth on Butterfly Growth
𝑑𝑖𝑛𝑐 < 0.5
Larger lower wing
0.38 b
0.42 b
0.5 𝑏 < 𝑑𝑖𝑛𝑐 < 1.0 𝑏
Larger upper wing
0.7 b
0.8 b
1.0 𝑏 < 𝑑𝑖𝑛𝑐
Secondary upper wing
0.4 b
0.6 b
1.1 b
1.1b
[1] M.-H.Evans,etal.,”Effect of Hydrogen on Butterfly and White Etching Crack (WEC) Formation under Rolling Contact Fatigue
(RCF),Wear(2013), http://dx.doi.org/10.1016/j.wear.2013.03.008i
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
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S-N Curve for Butterfly Formation
Damage equation is calibrated by
curve fitting to Torsion Fatigue
data
𝜏𝑎
+ |𝜏𝑚 |
𝒅𝑫
= 2
𝒅𝑵
𝝈𝒓 𝟏 − 𝑫
𝒎
Integration from
𝑫𝒑𝒓𝒊𝒔𝒕𝒊𝒏𝒆 to 𝑫𝒄𝒓𝒊𝒕𝒊𝒄𝒂𝒍
𝑵𝒂𝒑𝒑𝒆𝒂𝒓𝒂𝒏𝒄𝒆
𝟏
𝝈𝒓
=
𝟏 + 𝒎 𝜏𝑎 + |𝜏𝑚 |
2
𝒎
S-N curve for butterfly formation
[1] Takemura H, et al. , “ Development of New Life Equation for Ball and Roller Bearings”, NSK Motion & Control No. 11 (October 2001)
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
Effect of Inclusion Size on Butterfly
Wing Span
• For comparison, the wingspan to inclusion diameter ratio is compared
• The model results lie within the bounds of the experimental results and show the
same trend
Butterflies around a
16 𝜇 inclusion
Butterflies around a 2
𝜇 inclusion
[1] Lewis , Tomkins, ” A fracture mechanics interpretation of rolling bearing fatigue“, Proc IMechE Part J: J Engineering Tribology,(2012)
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
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Debonding on Inclusion/ Matrix
Interface
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To find the debonding regions, stresses should be resolved along the
inclusion/ matrix interface
Stress transformation formulas in
of debonding
(A & B)
2D areAreas
employed
for this purpose
and deformation (C) observed
by (Grabulov[1])
Schematic showing the reversal of
METL
Model prediction
(bold,
shear
in presence
of compressive
show the
stress black
along arches
the inclusionmatrix
debonding
areas)
interface
[1] A. Grabulov, R. Petrov , H.W. Zandbergen , 2009, “EBSD investigation of the crack initiation and TEM/FIB analyses of the
microstructural changes around the cracks formed under Rolling Contact Fatigue (RCF)” International Journal of Fatigue 32 (2010) 576–
583
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
Prediction of Crack Initiation
Locations
45°
•
•
•
11
10𝜇
Cracks are commonly observed on
top of the upper wing and bottom of
the lower wing
Mode I loading is suggested as the
main factor for crack development
in vicinity of the inclusion
FEM results show maximum tensile
stress during loading history is
higher on top of the upper wing and
bottom of the lower wing
Maximum tensile stress resolved
along the butterfly edges
[1] Lewis , Tomkins, ” A fracture mechanics interpretation of rolling bearing fatigue“, Proc IMechE Part J: J Engineering Tribology,(2012)
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
Effect of Compressive Stress on
Torsion Fatigue
• RCF is a shear dominated phenomena
• There is a large compressive stress
present in the contact zone
• A custom made set of clamps are
designed to apply high compressive
stress (up to 2.5 GPa) on torsion
specimens to better simulate RCF
failure
Custom made clamps: a) exploded view
b) as they appear after assembly
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Stress history at 0.5b
Schematic of Hertzian contact zone in
clamp/ specimen interface
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
Effect of Compressive Stress on
Torsion Fatigue Life
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• Application of compressive clamps reduced the torsion fatigue life
• The reduction is up to in one order of magnitude in high cycle fatigue
Steel B
Steel C
Steel E
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
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Effect of Compressive Stress on
Fracture Mode
As opposed to helical fracture surfaces for
pure torsion tests, broken specimens form cup
& cone pairs
Initiation cracks are due to torsion while
multiple cracks grow in the propagation stage
Initiation
cracks
0.9 𝑆𝑢𝑠
0.8 𝑆𝑢𝑠
0.7 𝑆𝑢𝑠
0.6 𝑆𝑢𝑠
0.5 𝑆𝑢𝑠
0.4 𝑆𝑢𝑠
0.3 𝑆𝑢𝑠
0.5 𝑆𝑢𝑡
0.6 𝑆𝑢𝑡
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Propagation
cracks
Initiation and propagation cracks in sample failed
specimens
Mechanical Engineering Tribology Laboratory (METL)
Sample failed specimens at different
load levels
November 14, 2013
FEM Model
Life Prediction and Failure Simulation
• A user defined subroutine is
developed to apply a
Hertzian pressure profile at
the center of the specimen
• FEM results show similar
crack patterns to
experiments
• Life prediction is successful
implementing the damage
mechanics
Without compressive stress
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With compressive stress
S-N Curve: Experiment vs. FEM
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013
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Summary and Future Work
• Summary
– Damage mechanics is used to model butterfly wing formation in
bearing steel
– The model predicts butterfly shape and size with respect to inclusion
diameter and depth successfully
– S-N curve for wing development is in corroboration with experiments
– Effect of compressive stress on torsion fatigue life and fracture mode is
studied
• Future Work
– Explore capabilities of damage mechanics to model DERs, WEBs, and
WECs in bearings
– Conduct RCF tests to expand a data base for different types of
microstructural changes in bearings
– Experimental and analytical investigation of effect of steel cleanliness
on torsion fatigue and RCF
Mechanical Engineering Tribology Laboratory (METL)
November 14, 2013