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Research Papers: Multiphase Flows

Development of a Novel Oil Cavitation Jet Peening System and Cavitation Jet Erosion in Aluminum Alloy, AA 6063-T6

[+] Author and Article Information
A. Sahaya Grinspan1

Technical Centre, Advanced Engineering, Ashok Leyland, Chennai 600103, Indiasahayagrinspan.a@ashokleyland.com

R. Gnanamoorthy

 Indian Institute of Information Technology, Design and Manufacturing (IIITD&M) Kancheepuram, IIT Madras Campus, Chennai 600 036, India

1

Corresponding author.

J. Fluids Eng 131(6), 061301 (May 14, 2009) (8 pages) doi:10.1115/1.3129134 History: Received September 19, 2008; Revised March 23, 2009; Published May 14, 2009

Compressive residual stresses that improve fatigue strength of material are obtained by peening the surface. Unlike traditional processes, a novel process of oil cavitation jet peening was developed. The process is based on implosion generated by the oil cavitation jet that plastically deforms the surface, imparting compressive residual stresses. The process developed involves injection of a high-speed oil jet (230m/s) through a suitably designed nozzle, into an oil-filled chamber containing the specimen to be peened. The region of cavitation generation, growth, and collapse, at the various cavitation numbers, was recorded using high-speed photography. To optimize the process parameters, a simple erosion test was performed in aluminum alloy, AA 6063-T6, specimens. The impact pressure generated during the implosion of cavitation bubbles causes plastic deformation and erosion of the surface. The surface deformation and cavitation jet erosion in the exposed specimens were characterized using optical and scanning electron microscopies. The standoff distance, which measures jet impact zone of the specimen from nozzle, was optimized at 15 mm in a cavitation number (which is a measure of pressure ratio across the nozzle) of 0.0017. The surface deformation produced by collapse of the oil bubble was similar to impact of oil droplet on the surface. The material removal mechanism during implosion of the bubble is predominately by ductile shear deformation.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Pressure and velocity change in a jet in the cavitation condition.

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Figure 2

Schematic of the oil cavitation jet peening system developed: (a) oil cavitation jet peening system and (b) illustration of cavitation jet structure observation system employed

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Figure 3

Parameters involved in oil cavitation jet peening

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Figure 4

Sequence of images showing the oil cavitation jet structures at various upstream pressures: (a) 20 MPa, (b) 30 MPa, (c) 40 MPa, (d) 50 MPa, and (e) 60 MPa

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Figure 5

Cavitation jet length at various upstream pressures

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Figure 6

Cavitation jet diameter at various upstream pressures

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Figure 7

Schematic depicting the oil cavitation jet structures under different upstream pressures

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Figure 8

Micrographs showing the surface of aluminum alloy, AA6063-T6, eroded by oil cavitation jet under various SODs: (a) SOD=10 mm, (b) SOD=15 mm, and (c) SOD=25 mm

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Figure 9

Micrograph showing the sectional view of aluminum alloy, AA6063-T6, eroded by oil cavitation jet under a SOD of 15 mm

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Figure 10

Mechanism of oil jet cavitation erosion on ductile materials: (a) collapse of clouds and/or bubbles, and pressure wave emission; (b) bubble oscillates and deforms near the surface; (c) implosion of bubble and micro jet formation; (d) subsequent implosion of another bubble of oil cavitation jet forms craters; and (e) initiated the cracks in the rims, crack growth, and fragmentation of rims due to radial force

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