Evidence of Ductile Tearing Ahead of the Cutting Tool and Modeling the Energy Consumed in Material Separation in Micro-Cutting

[+] Author and Article Information
Sathyan Subbiah

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

Shreyes N. Melkote1

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332shreyes.melkote@me.gatech.edu


Corresponding author.

J. Eng. Mater. Technol 129(2), 321-331 (Sep 11, 2006) (11 pages) doi:10.1115/1.2712471 History: Received February 18, 2006; Revised September 11, 2006

Orthogonal cutting experiments using a quick-stop device are performed on Al2024-T3 and OFHC copper to study the chip–workpiece interface in a scanning electron microscope. Evidence of ductile tearing ahead of the tool at cutting speeds of 150mmin has been found. A numerical finite element model is then developed to study the energy consumed in material separation in micro-cutting. The ductile fracture of Al2024-T3 in a complex stress state ahead of the tool is captured using a damage model. Chip formation is simulated via the use of a sacrificial layer and sequential elemental deletion in this layer. Element deletion is enforced when the accumulated damage exceeds a predetermined value. A Johnson–Cook damage model that is load history dependent and with strain-to-fracture dependent on stress, strain rate, and temperature is used to model the damage. The finite element model is validated using the cutting forces obtained from orthogonal micro-cutting experiments. Simulations are performed over a range of uncut chip thickness values. It is found that at lower uncut chip thickness values, the percentage of energy expended in material separation is higher than at higher uncut chip thicknesses. This work highlights the importance of the energy associated with material separation in the nonlinear scaling effect of specific cutting energy in micro-cutting.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 2

(a) Indentation; (b) machining (12)

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Figure 3

Quick-stop device (33)

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Figure 4

Sectioning sample for SEM observation

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Figure 5

Ductile tearing in Al2024-T3

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Figure 6

Ductile tearing in ductile metals by void formation (36)

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Figure 7

Ductile tearing in OFHC copper

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Figure 8

Crack at the interface and zone of material separation

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Figure 9

Finite element model mesh and boundary conditions

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Figure 10

Sacrificial layer separates the chip from the workpiece

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Figure 11

Orthogonal tube cutting

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Figure 12

Comparing model and experimental forces

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Figure 13

Contour plot of pressure stress

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Figure 14

Contour plot of individual stress components σ11, σ22, and σ33

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Figure 15

Plot of stresses straight ahead of the tool

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Figure 16

Percentage of energy spent in the chip, sacrificial layer, friction, and subsurface

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Figure 1

The size-effect in metal cutting




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