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Research Papers: Applications

Extraction and Testing of Miniature Compression Specimens From Bearing Balls Subjected to Rolling Contact Fatigue

[+] Author and Article Information
B. D. Allison, N. K. Arakere, H. Yamaguchi

Department of Mechanical and
Aerospace Engineering,
University of Florida,
Gainesville, FL 32611

G. Subhash

Department of Mechanical and
Aerospace Engineering,
University of Florida,
Gainesville, FL 32611
e-mail: subhash@ufl.edu

H. Chin, D. Haluck

Pratt & Whitney,
400 Main Street,
East Hartford, CT 06108

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received April 7, 2013; final manuscript received December 15, 2013; published online February 5, 2014. Assoc. Editor: Xiaolan Ai.

J. Tribol 136(2), 021103 (Feb 05, 2014) (7 pages) Paper No: TRIB-13-1077; doi: 10.1115/1.4026442 History: Received April 07, 2013; Revised December 15, 2013

Extraction and testing of miniature compression specimens from localized regions of components affected by rolling contact fatigue loading can provide significant insight into material degradation. Current ASTM standards for compression testing of cylindrical specimens become too stringent and difficult to achieve when specimen size is reduced to around 1 mm in diameter. The tolerances for surface flatness, parallelism of the loading surfaces, and the perpendicularity between the axis and the loading surfaces play crucial roles in the resulting stress-strain curves under uniaxial compression loading. In this manuscript, a systematic study is performed to quantify the influence of the above geometric parameters on the stress-strain response. Based on the analysis, the allowable geometric tolerances of miniature cylindrical specimens for a valid compression tests are recommended. The analysis results are validated and the usefulness of the method is demonstrated on miniature specimens extracted from the rolling contact fatigue affected regions of high strength M50 bearing balls. The yield stress within the rolling contact fatigue affected region is shown to increase by over 12%.

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Figures

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Fig. 1

Schematics of the geometric imperfections modeled to define allowable limits for (a) edge retention (ratio r/R), (b) perpendicularity (angle Θ), (c) parallelism (height difference, Δh), and (d) 3D FE model containing all three imperfections

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Fig. 2

Stress-strain response with varying fractions of edge retention. Note that the curves are nearly identical even when only 90% of the radius (or 81% of the top surface) is in-plane.

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Fig. 3

Flow curves with varying degrees of perpendicularity. One-degree deviation from perpendicular has negligible effect, while 2.7 deg causes a decrease in modulus and yield strength by less than 1%.

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Fig. 4

Flow curves with varying levels of parallelism. The numbers next to each curve are the elastic modulus and yield strength in MPa. A height difference (Δh) of up to 10 μm has no effect on the flow curve (other than a slight heel at the beginning). The elastic modulus is measured midway in the elastic range.

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Fig. 5

Constitutive response of a specimen with the limiting acceptable tolerances for parallelism, perpendicularity, and flatness compared to an ideal specimen. The imperfect specimen has a small heel at the beginning of the curve, but after this is accounted for, the curves are nearly identical.

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Fig. 6

Locations from which miniature compression specimens were extracted. (a) Schematic showing the plane definitions and RCF affected regions in a ball, (b) Micrograph of the RCF affected region in meridial section after etching, (c) Micrograph of the RCF affected region in equatorial section after etching, and (d) Miniature compression specimens extracted from the RCF affected zone of meridial section.

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Fig. 7

Schematic of the layout for polishing the compression specimens to achieve the required parallelism and flatness tolerances

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Fig. 8

Flatness data of the top surface recorded by the profilometer: (a) scan of the entire area and (b) line scans along the two diagonals used to highlight the flatness of the surface which varies by less than 4 μm over 1.5 mm.

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Fig. 9

Image of the specimen captured by the profilometer for measurement of the perpendicularity of the specimen

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Fig. 10

Machine setup used to perform compression tests. A deflectometer and a load cell were used to record the test data.

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Fig. 11

Representative flow curves for specimens tested. The unloading is shown for only one of the curves for clarity.

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Fig. 12

Average curve fit for each of the set of RCF conditions tested

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