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Research Papers: Lubricants

The Effect of Deformation Speed on Frictional Behavior by Tip Test

[+] Author and Article Information
Ki-Ho Jung

Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Koreamark.jung@kaist.ac.kr

Yong-Taek Im1

Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Koreaytim@kaist.ac.kr

1

Corresponding author.

J. Tribol 132(3), 031801 (Jun 16, 2010) (6 pages) doi:10.1115/1.4001556 History: Received December 02, 2009; Revised April 06, 2010; Published June 16, 2010; Online June 16, 2010

In this study, a tip test was carried out under various ram velocities of 0.01 mm/s, 0.1 mm/s, 1.0 mm/s, and 5.0 mm/s to investigate the effect of deformation speed on friction using the commercially available AL6061-O. For experiments, four different lubrication conditions with grease, corn oil, VG100, and VG32 were used to investigate the lubrication characteristics. During the test, temperature was measured in the specimen by a K-type thermocouple to determine the temperature increase induced by heat generation due to plastic deformation. In the present investigation, the linearity between tip distance and experimentally measured maximum load was consistently observed in spite of different orders of ram velocity and types of lubrication. As the ram velocity increased, loads were reduced for liquid lubricants and increased for grease. To better understand such a lubrication phenomenon, white-light interferometer microscopy and laser confocal microscopy were used to observe and compare surface topographies on the bottom and circumferential side of the deformed specimens at various experimental conditions, which formed lubrication pockets incurring hydrodynamic pressure of liquid lubricants. Finally, the effect of deformation speed on the level of shear friction factors at the punch and die interfaces was characterized by the finite element simulations and was determined to be expressed as an exponential function depending on the lubricant. This investigation demonstrates the capability of the tip test to experimentally characterize the effect of deformation speed on the frictional behavior for practical use.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the tip test used in experiments

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Figure 2

Stress-strain curves obtained from the compression test at different compression speeds of 0.01 mm/s, 0.1 mm/s, 1.0 mm/s, and 5.0 mm/s

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Figure 3

Load versus stroke curves obtained from the tip test using the lubricant of (a) grease, (b) corn oil, (c) VG100, and (d) VG32 for different deformation speeds

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Figure 4

Variations in maximum nondimensional load measured versus deformation speed

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Figure 5

Viscosity variation in (a) grease, (b) corn oil, VG100, and VG32 depending on shear rate

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Figure 6

Measured temperature data at the center of the specimen of AL6061-O at a ram velocity of 5.0 mm/s

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Figure 7

Surface topographies on the bottom of deformed specimens at different strokes by a white-light scanning interferometer microscope at deformation speeds of 0.1 mm/s and 5.0 mm/s (16)

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Figure 8

Surface topographies on the bottom of deformed specimens tested with grease, corn oil, VG100, and VG32 at a deformation speed of 5.0 mm/s

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Figure 9

Surface topographies of the circumferential side of the deformed AL6061-O specimen at deformation speeds of (a) 0.1 mm/s and (b) 5.0 mm/s with VG32 by a laser confocal microscope (OLS-4000)

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Figure 10

Surface topographies of the circumferential side of the deformed AL6061-O specimen at deformation speeds of (a) 0.1 mm/s and (b) 5.0 mm/s with grease by a laser confocal microscope (OLS-4000)

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Figure 11

Plots of normalized maximum load versus tip distance obtained from the tip test result

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Figure 12

Comparison of shear friction factors at the punch interface (mfp) versus deformation speed

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