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Research Papers: Elastohydrodynamic Lubrication

Permeation of Lubricant Trapped Within Pocket Into Real Contact Area on the End Surface of Cylinder

[+] Author and Article Information
Akira Azushima, Akira Yanagida, Shojiro Tani

Department of Mechanical Engineering, Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogya-ku, Yokohama 240-8501, Japan

J. Tribol 133(1), 011501 (Dec 02, 2010) (6 pages) doi:10.1115/1.4002745 History: Received February 08, 2010; Revised September 15, 2010; Published December 02, 2010; Online December 02, 2010

Knowledge on the behavior of lubricant trapped in a surface pocket is important for improving metal forming technology, since the trapped lubricant affects friction and surface finishing. The permeation phenomena at higher reduction in height were quantitatively observed during the upsetting of cylinders with a central conical dent using the new fluorescence direct observation apparatus developed by the authors. Moreover, the permeation phenomena were estimated using a rigid-plastic finite element analysis model incorporating the compressibility of the lubricant. From the experimental results, it was quantitatively observed that over a reduction in height of 37%, the outline of the central conical dent became blurred, and the lubricant trapped within the conical dent permeated into the peripheral real contact area. It was also quantitatively observed that the volume of the lubricant trapped within the conical dent decreased gradually and abruptly with increasing reduction in height up to and above 36%, respectively. From the numerical results, it was estimated that the trapped lubricant permeated when the hydrostatic pressure generated within the lubricant pocket exceeded the die pressure at higher reduction in height.

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Figures

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Figure 3

Relationship between visible light intensity and oil film thickness

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Figure 4

Dimensions of specimen

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Figure 5

Surface appearance of specimen observed using digital microscope

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Figure 6

Surface profile of tip of asperity observed using laser microscope

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Figure 7

FE model with trapped lubricant

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Figure 8

Appearance of interface between sapphire die and end surface of cylinder

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Figure 9

Profiles of end surface of cylinder specimen

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Figure 10

Relationship between volume and reduction in height

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Figure 11

Micrograph and profile of workpiece after upsetting at reduction in height of 50%

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Figure 12

Equivalent strain distributions at eight different reductions in height

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Figure 1

Schematic representation of compression apparatus

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Figure 2

Schematic representation of measurement part of apparatus (a) and magnification of interface between die and workpiece (b)

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Figure 13

Comparison of variations of conical dent profiles obtained from experimental observations and FE simulations

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Figure 14

Relationships among reduction in height, hydrostatic pressure, equivalent stress, and average die pressure

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