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Research Papers

Crystallographic Effects on Microscale Machining of Polycrystalline Brittle Materials

[+] Author and Article Information
Siva Venkatachalam

Corning Incorporated,
One Riverfront Plaza,
Corning, NY 14831

Xiaoping Li

Professor
Department of Mechanical Engineering,
National University of Singapore,
Singapore 119260, Singapore

Omar Fergani

Research Assistant
George W. Woodruff
School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332

Jiang Guo Yang

Professor
School of Mechanical Engineering,
Donghua University,
Shanghai 200051, China

Steven Y. Liang

George W. Woodruff
School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF Micro- AND Nano-Manufacturing. Manuscript received January 25, 2013; final manuscript received July 23, 2013; published online September 25, 2013. Assoc. Editor: Stefan Dimov.

J. Micro Nano-Manuf 1(4), 041001 (Sep 25, 2013) (9 pages) Paper No: JMNM-13-1010; doi: 10.1115/1.4025255 History: Received January 25, 2013; Revised July 23, 2013

This paper studies the effects of crystallography on the microscale machining characteristics of polycrystalline brittle materials on a quantitative basis. It is believed that during micromachining of brittle materials, plastic deformation can occur at the tool-workpiece interface due to the presence of high compressive stresses which leads to chip formation as opposed to crack propagation. The process parameters for such a machining process are comparable to the size of the grains, and hence crystallography assumes importance. The crystallographic effects include grain size, grain boundaries (GB), and crystallographic orientation (CO) for polycrystalline materials. The size of grains (crystals), whose distribution is analyzed as a log-normal curve, has an effect on the yield stress of a material as described by the Hall–Petch equation. The effects of grain boundary and orientation have been considered using the principles of dislocation theory. The microstructural anisotropy in a deformed polycrystalline material is influenced by geometrically necessary boundaries (GNB) and incidental dislocation boundaries (IDB). The dislocation theory takes both types of dislocations into account and relates the material flow stress to the dislocation density. The proposed analysis is compared with previously reported experimental data on polycrystalline germanium (p-Ge). This paper aims to provide a deeper physical insight into the microstructural aspects of polycrystalline brittle materials during precision microscale machining.

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References

Figures

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Fig. 1

Microstructure effects in machining [36]

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Fig. 2

(Left) Sample grain structure of Alumina (Al2O3) and (right) lognormal distribution for grain size

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Fig. 3

(Left) Machining model: a—depth of cut; h—undeformed chip thickness; f—feed; b—width of cut; and κ—cutting edge angle (reproduced from Ref. [10]) and (right) facing operation

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Fig. 4

Experimental force data extracted from Ref. [10]

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Fig. 5

(Left) Schematic of the grain map in polycrystalline germanium and (right) SEM picture of the grain map of polycrystalline germanium

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Fig. 6

Comparison of predicted forces with corresponding experimental values

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Fig. 7

Force comparison for grains A and B

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Fig. 8

Main effects plot for cutting force (Fc)

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Fig. 9

Main effects plot for thrust force (Ft)

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Fig. 10

Main effects plot for shear angle (ϕ)

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