effect of mean stress on rolling contact fatigue
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Effect of Mean Stress on Rolling Contact Fatigue. Sina Mobasher Moghaddam Ph.D. Research Assistant. Outlines. Butterfly-wing formation in bearing steel Background and Motivation Stress Analysis METL suggested theory Results comparison and validation - PowerPoint PPT PresentationTRANSCRIPT
Slide 1
Sina Mobasher Moghaddam
Ph.D. Research Assistant
Effect of Mean Stress on Rolling Contact Fatigue
November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
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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
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
Butterfly WingsDetrimental Effect on RCF
In some applications bearings may last only 10% of their 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
[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) 576583
Butterflies Observed by Vincent [1](top) and Grabulov [2](Bottom)
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
Wing Span
Debonded Region
Coarse Grains
50-100 nm
Crack
Fine Grains
5-10 nm
ORD
Butterfly Wing Characteristics
Schematic of a pair of butterfly wings
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
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
Stress Analysis
Inclusion presence induces stress concentrations in the surrounding matrix
When dealing with fatigue problems, it is important to consider stress history
Comparison of centerline stresses for two domains with and without embedded inclusion
, b=100= 2.0 GPa
Damage Equation
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
Butterfly Wing Evolution
Butterfly wing orientation, direction, and size are consistent with the experimental observations
Color spectrum of butterfly wing formation
Butterfly formation according to Grabulov[1]
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) 576583
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
0.7 b
0.8 b
0.38 b
0.42 b
1.1 b
0.4 b
0.5
Secondary upper wing
0.6 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
Effect of Depth on Butterfly Growth
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
S-N Curve for Butterfly Formation
Damage equation is calibrated by curve fitting to Torsion Fatigue data
Integration from to
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)
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
Effect of Inclusion Size on Butterfly Wing Span
[1] Lewis , Tomkins, A fracture mechanics interpretation of rolling bearing fatigue, Proc IMechE Part J: J Engineering Tribology,(2012)
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 inclusion
Butterflies around a 2 inclusion
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
Schematic showing the reversal of shear in presence of compressive stress along the inclusion- matrix interface
Debonding on Inclusion/ Matrix 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) 576583
Areas of debonding (A & B) and deformation (C) observed by (Grabulov[1])
METL Model prediction (bold, black arches show the debonding areas)
To find the debonding regions, stresses should be resolved along the inclusion/ matrix interface
Stress transformation formulas in 2D are employed for this purpose
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
Prediction of Crack Initiation Locations
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
[1] Lewis , Tomkins, A fracture mechanics interpretation of rolling bearing fatigue, Proc IMechE Part J: J Engineering Tribology,(2012)
Maximum tensile stress resolved along the butterfly edges
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
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
Stress history at 0.5b
Custom made clamps: a) exploded view b) as they appear after assembly
Schematic of Hertzian contact zone in clamp/ specimen interface
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
Effect of Compressive Stress on Torsion Fatigue Life
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
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
Effect of Compressive Stress on Fracture Mode
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Initiation cracks
Propagation cracks
0.6
0.5
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 and propagation cracks in sample failed specimens
Sample failed specimens at different load levels
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
FEM ModelLife Prediction and Failure Simulation
Without compressive stress
With compressive stress
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
S-N Curve: Experiment vs. FEM
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)
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
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November 14, 2013
Mechanical Engineering Tribology Laboratory (METL)