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TECHNICAL PAPERS

Micro Scale Laser Shock Processing of Metallic Components

[+] Author and Article Information
Wenwu Zhang, Y. Lawrence Yao

Department of Mechanical Engineering, Columbia University, New York, NY 10027

J. Manuf. Sci. Eng 124(2), 369-378 (Apr 29, 2002) (10 pages) doi:10.1115/1.1445149 History: Received November 01, 2000; Revised July 01, 2001; Online April 29, 2002
Copyright © 2002 by ASME
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Figures

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(a) Modeling of laser shock processing (axisymmetry about the z-axis is assumed; and (b) effects of laser intensity on shock wave pressure (laser pulse duration is 50 ns, interaction coefficient α=0.2, open air, and temperature T=300 K)
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(a) Influence of strain rate on the yield strength of copper (open air and temperature T=300 K); and (b) influence of shock pressure on the yield strength of copper (strain rate=1 s−1 and temperature T=300 K)
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Typical distribution of total strain at the end of a shock pulse (a) radial strain E11; and (b) in-depth strain E22. Pulse energy E=240 μJ(I=4.24 GW/cm2), beam diameter is 12 microns, plasma absorption coefficient AP=0.545 and interaction coefficient α=0.2. Axisymmetry is assumed. Computation domain is 90 microns by 1000 microns, and the region shown is 90 microns (z-direction) by 100 microns (r-direction) for clear view of the results. Deformation in the dented region is magnified by a factor of 3 for viewing clarity.
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SEM micrograph of dents on copper sample produced by laser shock processing (3 laser pulses at each location with each pulse energy E=240 μJ, laser pulse duration=50 ns, pulse repetition rate=1 KHz, beam diameter=12 microns, laser wavelength=355 nm, copper sample thickness=90 microns)
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Comparison of measured and simulated dent profiles (a) E=240 μJ, 2 and 3 pulses; and (b) 2 pulses at E=180 μJ and E=240 μJ. Laser beam diameter is 12 microns, pulse duration is 50 ns, pulse repetition rate is 1 KHz, plasma absorption coefficient AP=0.545, and interaction coefficient α=0.2. Copper sample thickness=90 microns.
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Geometry comparison between experiments and simulations (a) dent slope angle (left axis) and dent depth (right axis) vs. pulse number, E=180 μJ and 240 μJ; and (b) dent slope angle (left axis) and dent depth (right axis) vs. pulse energy, pulse number=2 and 3. AP=0.545, and α=0.2. Copper sample thickness=90 microns.
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Evolution of strain rate in z-direction (in-depth direction) (a) strain rate of points on the centerline; and (b) strain rate of points along the surface and at other locations. (r,z) gives the location of a point, and (0,0) is the center point on the top surface. Single pulse, E=240 μJ,AP=0.545, and α=0.2.
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Typical optical micrograph of dented region (left) produced by laser shock processing at an array of equally spaced locations, spacing=50.8 microns. E=240 μJ, 2 pulses at each location, beam diameter=12 microns. The region on the right of the graph is unprocessed, original copper surface, on which holes were laser drilled to assist observation and positioning in subsequent X-ray diffraction measurements.
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Simulated elastic strains averaged along the depth direction in anticipation of comparison with subsequent X-ray diffraction measurement (a) for X-ray diffraction measurement of Cu (111); and (b) for X-ray diffraction measurement of Cu (311). Two pulses, E=240 μJ,AP=0.545, and α=0.2. E11 is in radial, E22 depth, and E33 circumferential direction.
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Overlapping results of the depth-direction elastic strain Ez(E22) for comparison with subsequent X-ray diffraction measurement of Cu(311), spacing=50.8 microns. Two pulses at each location, E=240 μJ,AP=0.545, and α=0.2.
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Typical distribution of residual stresses (a) radial residual stress S11 and (b) in-depth residual stress S22,E=240 μJ, beam diameter=12 microns. Stress unit: Pascal. Axisymmetry is assumed. Computation domain is 90 microns by 1000 microns, and the region shown is 90 microns by 200 microns for clear view of the results. Deformation in the dented region is magnified by a factor of 3 for viewing clarity.
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Distribution of residual stresses on the top surface and at 70 microns below the top surface (a) radial residual stress S11,E=240 μJ, 2 to 4 pulses; and (b) radial residual stress S11, 2 pulses, E=180, 200 and 240 μJ. Distance from the center is normalized to the radius of laser beam r0, where r0=6 microns.

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