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Hydrodynamic Lubrication

Bubble Structures Between Two Walls in Ultrasonic Cavitation Erosion

[+] Author and Article Information
A. Abouel-Kasem1

Faculty of Engineering, Mechanical Engineering Department, King Abdulaziz University, P.O. Box 344, Rabigh 21911, Kingdom of Saudi Arabia; Department of Mechanical Engineering,  Assiut University, Assiut 71516, Egyptabouelkasem@yahoo.com

S. M. Ahmed

Faculty of Engineering, Mechanical Engineering Department,  Majmaah University, P.O. Box 165, Almajma’a 11952, Kingdom of Saudi Arabiashemy2001@yahoo.com

1

Corresponding author.

J. Tribol 134(2), 021702 (Mar 19, 2012) (9 pages) doi:10.1115/1.4005217 History: Received September 04, 2010; Revised September 21, 2011; Published March 15, 2012; Online March 19, 2012

The cavitation bubble structures for the stationary specimen method were clarified for various distances, h, between the stationary specimen and the horn-tip surface. The generated cavitation bubbles constituted a huge number of tiny bubbles and bubble clusters of different sizes. The maximum cluster size was 1.4 mm. The observed cavitation patterns systematically changed during tests from the subcavitating state to the supercavitating state with respect to the separation distance, h. For h <4 mm, the bubbles have a definite trajectory, and the pressure patterns manifest a circular shape as a result of streaming induced by ultrasonic cavitation. The feature morphology of the eroded surfaces revealed that the predominant failure mode was fatigue. In the light of the material failure features and the cavitation patterns, it is also deduced that the important mechanism to transfer the cavitation energy to the solid is shock pressures accompanied by collapsing clusters.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 7

Atypical pressure-sensitive film maps developed at test time of 3 s for h = 4.1 mm (a) and h = 1.8 mm (b)

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Figure 8

Photographs illustrating the bubble sizes and their collapses taken at different times on the time displacement diagram

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Figure 9

SEM photograph illustrating the impact damaged sites and the removal of material

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Figure 10

Progress of cracks forming fatigue striations

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Figure 11

Fracture surface showing fatigue striations

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Figure 1

Schematic view of test apparatus for cavitation bubbles-capture

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Figure 2

Time – displacement diagram for horn tip

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Figure 3

Photographs illustrating the cavitation patterns for different separation distances, h, between the horn tip and stationary specimen and at the marked times 1–7 on the time-displacement shown in Fig. 2

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Figure 4

Cavitation aspects for vibratory specimen method taken at the marked times 1–7 on the time-displacement shown in Fig. 2

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Figure 5

Enlarged photograph of actual streaming patterns generated at 2 kHz [23]

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Figure 6

Enlargement of photographs 2 and 3 shown in Fig. 3 for various distances, h

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