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Research Papers

Characterization of Flow Stress for Commercially Pure Titanium Subjected to Electrically Assisted Deformation

[+] Author and Article Information
James Magargee

Department of Mechanical Engineering,
Northwestern University,
2145 Sheridan Road,
Evanston, IL 60208

Fabrice Morestin

Laboratory of Contact and Structural
Mechanics (LaMCoS),
INSA-Lyon,
20, Avenue Albert Einstein,
Villeurbanne 69621, France

Jian Cao

Department of Mechanical Engineering,
Northwestern University,
2145 Sheridan Road,
Evanston, IL 60208
e-mail: jcao@northwestern.edu

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the Journal of Engineering Materials and Technology. Manuscript received October 23, 2012; final manuscript received April 22, 2013; published online June 18, 2013. Assoc. Editor: Marwan K. Khraisheh.

J. Eng. Mater. Technol 135(4), 041003 (Jun 18, 2013) (10 pages) Paper No: MATS-12-1245; doi: 10.1115/1.4024394 History: Received October 23, 2012; Revised April 22, 2013

Uniaxial tension tests were conducted on thin commercially pure (CP) titanium sheets subjected to electrically assisted deformation using a new experimental setup to decouple thermal–mechanical and possible electroplastic behavior. The observed absence of stress reductions for specimens air-cooled to near room temperature motivated the need to reevaluate the role of temperature on modeling the plastic behavior of metals subjected to electrically assisted deformation, an item that is often overlooked when invoking electroplasticity theory. As a result, two empirical constitutive models, a modified-Hollomon and the Johnson–Cook models of plastic flow stress, were used to predict the magnitude of stress reductions caused by the application of constant dc current and the associated Joule heating temperature increase during electrically assisted tension experiments. Results show that the thermal–mechanical coupled models can effectively predict the mechanical behavior of commercially pure titanium in electrically assisted tension and compression experiments.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Schematic of electrically assisted tension setup

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Fig. 2

Thermal image of electrically assisted tension specimen just prior to fracture (using a current density of 16 A/mm2). Center temperature indicated in top-right corner.

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Fig. 3

Temperature distribution along the axial length of a representative electrically assisted tension specimen during experiment using a current density of 16 A/mm2

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Fig. 4

Temperature distribution along the width of a representative electrically assisted tension specimen during experiment using a current density of 16 A/mm2. Distributions are truncated at edges of specimen width.

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Fig. 5

Maximum temperature measurements of electrically assisted tension tests. Squares mark beginning of tension test.

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Fig. 6

Uniaxial tension behavior in electrically assisted tension tests

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Fig. 7

Comparison of uniaxial tension behavior for air-cooled and noncooled electrically assisted tension tests

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Fig. 8

Tensile strength ratio R(T) as a function of temperature. Compared data is from Nemat-Nasser et al. [40] and electrically assisted tension tests.

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Fig. 9

Validation of modified-Hollomon and Johnson–Cook models with experimental data from baseline room-temperature tension tests

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Fig. 10

Modified-Hollomon and Johnson–Cook model predictions of flow stress behavior in electrically assisted tension tests

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Fig. 11

Error of flow stress models compared to experimental measurements: (top) modified-Hollomon model; (bottom) Johnson–Cook model

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Fig. 12

Thermal softening parameter as a function of temperature

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Fig. 13

Evolution of thermal softening parameter with increasing strain

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Fig. 14

Modified-Hollomon and Johnson–Cook model predictions of compressive flow stress behavior of CP titanium at room temperature and electrically assisted (current density of 26 A/mm2). Experimental data from Ref. [44].

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Fig. 15

Error of flow stress models compared to experimental data from Ref. [44]: (top) modified-Hollomon model; (bottom) Johnson–Cook model

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Fig. 16

(top) Uniaxial true stress–strain response of electrically assisted compression test from Ref. [44]; (bottom) maximum temperature measurement during electrically assisted compression test from Ref. [44]. Squares mark instance of maximum measured temperature (occurs at true strain of 0.1036).

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Fig. 17

Evolution of thermal softening parameter with increasing strain during electrically assisted compression from Ref. [44]. Location of greatest material softening coincides with instance of maximum measured temperature (at a true strain of 0.1036).

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