Sina Mobasher Moghaddam- STLE

Purdue Schaeffler Monthly Update

Butterfly Wing FormationIn Bearing SteelSina Mobasher MoghaddamPhD Research Assistant

May 16, 2014Mechanical Engineering Tribology Laboratory (METL)

#


OutlinesMotivationBackgroundButterfly wing modeling:Stress solutionSuggested theoryEffect of inclusion depthEffect of inclusion sizeEffect of applied loadS-N curve for butterfly formationDebonding at inclusion/ matrix interfaceCrack initiation Summary & conclusion

#


RCF Failure MechanismsFailure in rolling elements mostly occurs due to two different phenomena:Surface pittingSubsurface spallingIf a bearing is well installed and lubricated, and operates under the right load, the main mode of failure is subsurface spallingCracks initiate underneath the surface and grow to the surface to cause the final failure

Surface initiated crack observed by [1](top) compared to subsurface initiated crack observed at METL facilities (bottom)- Note the difference in the crack depth [1] A. OILA,S.J. BULLPhase transformations associated with micropitting in rolling/sliding contacts, JOURNAL OF MATERIALS SCIENCE 40 (2005) 4767 4774

#


Butterfly WingsDetrimental Effect on RCFIt has been frequently observed that matrix microstructure alters in the regions adjacent to the non-metallic inclusionsThese material alteration is commonly referred to as Butterfly- WingsCracks often form in the vicinity of butterfly wingsDespite 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)

#


4May 16, 2014

Butterfly Wing CharacteristicsSchematic of a pair of butterfly wings

#


Stress Concentration due to Inclusion Presence

Inclusion presence induces stress concentrations in the surrounding matrixThis stress concentration can culminate in microstructural alteration and premature crack initiation

#


x/b=-1.0x/b=-0.5x/b=0.0x/b=0.5x/b=1.0Shear Stress VariationDuring One Load PassShear stress variation during Hertzian load approach and departureShear stress contours at no single time step resemble the two- wing butterfly shapesIt is well known that wing formation is a cyclic phenomenonHence, any stress based approach to model butterfly formation should look at the loading history during each load pass

#


Effect of Surface Traction Alternating and Mean Shear StressAlternating shear stress There are four regions of maximum alternating shear stress around inclusionAll these regions are equally affected by surface tractionMean shear stressThere are four regions of maximum mean shear stress around the inclusionTwo of them are strongly depended on surface traction

#


Damage MechanicsSuggested Model for Butterfly FormationButterfly formation is a fatigue related phenomena alternating shear stress should be consideredButterfly wing formation is a depended on rolling direction (surface traction) mean shear stress should be consideredThe fatigue model should take both alternating and mean shear stress into accountSuggested damage law is:

#


Chronological Evolutionof Butterfly Wing

Butterfly Wing EvolutionColor spectrum of Butterfly Wing Formation

#


Butterfly Wing ShapeComparison with ExperimentsButterfly wing orientation, direction, and size are consistent with the experimental observations

Butterfly formation according to METL model prediction

Butterfly formation according to Grabulov[1][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

#


Experimental Data by Nelias et. al. [1] show butterfly formation frequency versus depthMost of the researchers have directly related butterfly formation to stress level which does not match over the whole span Damage Parameters obtained from torsion fatigue match closely with the experimental data

[1] Nelias. D, et. al. Role of Inclusions, Surface Roughness and Operating Conditions on Rolling Contact Fatigue, Transactions of the ASME, April 1999, Vol. 121Effect of Depth onButterfly Occurrence Frequency

#


12May 16, 2014

0.7 b0.8 b0.38 b0.42 b1.1 b0.4 b0.6 b1.1b

[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.2013.03.008iEffect of Depth on Butterfly Shape

#


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 comparedSimulations show that the relative wingspan to inclusion size increases as the inclusion diameter decreases

#


Effect of Inclusion SizeComparison with Experimental Data[1] Lewis , Tomkins, A fracture mechanics interpretation of rolling bearing fatigue, Proc IMechE Part J: J Engineering Tribology,(2012) The model is exercised for different inclusions diametersThe results are compared with experimental data provided in [1] The model results lie within the bounds of the experimental results and show the same trend

#


Effect of Load Level on Wing Formation

[1] Takemura H, et al. , Development of New Life Equation for Ball and Roller Bearings, NSK Motion & Control No. 11 (October 2001)Color spectrum indicating butterfly formation at different load levels

#


S-N Curve for Butterfly Formation

Damage equation is calibrated by curve fitting to Torsion Fatigue data

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)

#


Schematic showing the reversal of shear in presence of compressive stress along the inclusion- matrix interface

Debonding on Inclusion/ Matrix InterfaceStress Transformation[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) 576583It is suggested that debonding at inclusion/ matrix interface can be the reason for crack initiation[1]To find the debonding regions, stresses should be resolved along the inclusion/ matrix interface

Stress transformation formulas in 2D are employed for this purpose

#


Debonding on Inclusion/ Matrix InterfaceSimulation vs. Experiments[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)Resolved shear stress along the inclusion matrix interface has for maxima regions corresponding to debonding areas observed by [1]

#


Summary & ConclusionDamage mechanics is used to model butterfly wing formation in bearing steelAlternating and mean shear stress are suggested to be effective in butterfly wing formationThe model predicts butterfly shape and size with respect to inclusion diameter and depth successfullyS-N curve for wing development is in corroboration with experiments

#


Sina Mobasher Moghaddam- STLE

Documents

Transcript of Sina Mobasher Moghaddam- STLE