Research Papers

Spatially Resolved Characterization of Geometrically Necessary Dislocation Dependent Deformation in Microscale Laser Shock Peening

[+] Author and Article Information
Youneng Wang, Jeffrey W. Kysar, Sinisa Vukelic, Y. Lawrence Yao

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

J. Manuf. Sci. Eng 131(4), 041014 (Jul 15, 2009) (9 pages) doi:10.1115/1.3160370 History: Received July 08, 2008; Revised April 17, 2009; Published July 15, 2009

As the laser spot size in microscale laser shock peening is in the order of magnitude of several microns, the anisotropic response of grains will have a dominant influence on its mechanical behavior of the target material. Furthermore, conventional plasticity theory employed in previous studies needs to be re-examined due to the length scale effect. In the present work, the length scale effects in microscale laser shock peening have been investigated. The crystal lattice rotation underneath the shocked surface was determined via electron backscatter diffraction. From these measurements, the geometrically necessary dislocation (GND) density that the material contains has been estimated. The yield strength increment was then calculated from the GND distribution by using the Taylor model and integrated into each material point of the finite element method (FEM) simulation. Finite element simulations, based on single crystal plasticity, were performed for the process both with and without considering the GND hardening, and the comparison has been conducted.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Experimental setup

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Figure 2

Deformed geometry of shocked line by using SPM with scan area=80×80 μm2 and data scale=1 μm

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Figure 3

The crystal lattice curvature and coordinate system

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Figure 4

The three effective slip systems in the aluminum single crystal of [11¯4] orientation

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Figure 5

The scheme FEM simulation of spatially resolved GND dependent deformation

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Figure 6

Crystal lattice rotation by EBSD measurement

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Figure 7

Crystal lattice rotation by FEM simulation without considering length scale effects

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Figure 8

The distribution of geometrically necessary dislocation density (in m−2) from EBSD measurement, corresponding to Fig. 6

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Figure 9

The distribution of geometrically necessary dislocation density (in m−2) from FEM simulation, corresponding to Fig. 7

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Figure 10

Plane strain slip systems corresponding to (11¯4) orientation and GND distribution (a) in each slip system (in m−2) by FEM simulation, (b) in slip system i, (c) in slip system ii, and (d) in slip system iii

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Figure 11

Temporal evolution for four discrete material points of (a) lattice rotation and (b) geometrically necessary dislocation density

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Figure 12

Hardening by geometrically necessary dislocation density (in Pa)

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Figure 15

Total shear strain distribution: (a) without considering length scale effects, (b) only considering length scale effects, and (c) only considering the hardening of statistically-stored dislocation

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Figure 14

Comparison of normal displacement of the shocked surface by FEM with length scale effects and without considering length scale effects

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Figure 13

Temporal evolution for four discrete material points of strength increment by geometrically necessary dislocation density




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