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Research Papers

Deformation Size Effects Due to Specimen and Grain Size in Microbending

[+] Author and Article Information
Sunal Ahmet Parasiz, Reid VanBenthysen, Brad L. Kinsey

Department of Mechanical Engineering, University of New Hampshire, Durham, NH 03824

J. Manuf. Sci. Eng 132(1), 011018 (Feb 12, 2010) (8 pages) doi:10.1115/1.4000943 History: Received November 10, 2008; Revised December 17, 2009; Published February 12, 2010; Online February 12, 2010

Sheet metal forming often consists of bending processes in which gradients of deformation exists through the thickness of the workpiece in a localized deformation area. In microscale bending, these deformation gradients become much steeper, as the changes in the deformation occur over short distances (in the order of micrometers). In addition, with miniaturization, the number of grains that are present through the thickness decreases significantly. In this research, the effect of grain size and specimen size on the deformation distribution through the thickness of microbent sheet specimens was investigated via microhardness evaluations. It was found that the deformation distribution, i.e., hardness profile, is not affected significantly by the grain size when the sheet thickness is large (for 1.625 mm specimens) or by miniaturization of the specimen size when the grain size is fine. However, the deformation distribution of the coarse grained specimens deviates from the fine grained ones and from the 1.625 mm thick sheet specimens when the specimen size is miniaturized.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

The ratio of surface grains to volume grains increases with miniaturization (5)

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Figure 2

Schematic of microbending tooling

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Figure 3

Microhardness measurements through the thickness on half of a 205 μm coarse grained 0.5 mm specimen

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Figure 4

Average contour plots of increase in the hardness after microbending operations on half of the 0.25 mm thick (a) 20 μm fine grained, (b) 130 μm coarse grained, and (c) 190 μm coarse grained sheets

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Figure 5

Average contour plots of increase in the hardness after microbending operations on half of the 0.5 mm thick (a) 22.5 μm fine grained, (b) 205 μm coarse grained, and (c) 285 μm coarse grained sheets

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Figure 6

Average hardness contour plots of increase in the hardness after microbending operations on half of the 1.5 mm thick (a) 19 μm fine grained, (b) 175 μm coarse grained, (c) 280 μm coarse grained, and (d) 660 μm coarse grained sheets

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Figure 7

Microstructure of a 0.5 mm thick, 285 μm coarse grained microbent specimen

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Figure 8

Average hardness profile at the bend area through the thickness of (a) 1.625 mm, (b) 0.5 mm, and (c) 0.25 mm sheets. Note: initial hardness values were subtracted from measured hardness values after bending.

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Figure 9

Average hardness distribution at the bend area through the thickness of (a) 20 μm, (b) 190 μm, and (c) 280 μm grained sheets. Note: initial hardness values were subtracted from measured hardness values after bending.

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Figure 10

Normalized bending force versus displacement curves for (a) 20 μm, (b) 190 μm, and (c) 280 μm grain sized sheets

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Figure 11

Normalized peak bending force versus specimen size curves for 20 μm, 190 μm, and 280 μm grained sheets

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