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Research Papers

Analysis of the Electric and Thermal Effects on Mechanical Behavior of SS304 Subjected to Electrically Assisted Forming Process

[+] Author and Article Information
Tianhao Jiang

State Key Laboratory of Mechanical
System and Vibration,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: jth@sjtu.edu.cn

Linfa Peng

State Key Laboratory of Mechanical
System and Vibration,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: penglinfa@sjtu.edu.cn

Peiyun Yi

State Key Laboratory of Mechanical
System and Vibration,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: yipeiyun@sjtu.edu.cn

Xinmin Lai

State Key Laboratory of Mechanical
System and Vibration,
Shanghai Jiao Tong University,
Shanghai 200240, China;
Shanghai Key Laboratory of Digital
Manufacture for Thin-Walled Structures,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: xmlai@sjtu.edu.cn

1Corresponding author.

Manuscript received April 11, 2015; final manuscript received November 24, 2015; published online January 6, 2016. Assoc. Editor: Brad L. Kinsey.

J. Manuf. Sci. Eng 138(6), 061004 (Jan 06, 2016) (10 pages) Paper No: MANU-15-1169; doi: 10.1115/1.4032118 History: Received April 11, 2015; Revised November 24, 2015

Significant improvements in deformation resistance and ductility of metals are observed in the electrically assisted forming (EAF) process. Both electroplastic effect (EPE) induced by electric current and thermal effect associated with Joule heating have been proposed to explain the phenomenon. However, there are still arguments in the contribution of the EPE in EAF process. In this paper, both electrically assisted tension tests (EAT) and thermally assisted tension tests (TAT) were conducted on SS304 specimens at the same temperature. The existence of EPE is investigated, and the contribution of EPE is also distinguished with thermal effect numerically by considering the initial yield stress, dislocation hardening, and martensite phase transformation. It is shown when the temperature is around 34 °C, the electric current of 50 A/mm2 in EAT induces additional stress reduction of 16% in the short-range internal stress (effective stress) involved in the initial yield stress and volume reduction of 45.2% in martensite formation compared with results in TAT. However, the effect is not obvious for the cases of 100 A/mm2 and 150 A/mm2 when the temperature is above 100 °C. By comparing the storage coefficient and recovery coefficient of dislocation in EAT and TAT, it indicates that electric current has no additional activation effect on dislocation movement of SS304.

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Figures

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Fig. 1

Dimensions of tensile specimen (unit: millimeter)

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Fig. 2

Schematic of electrically assisted tensile setup

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Fig. 3

Schematic of temperature measuring point in the specimen

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Fig. 8

Variation of short-range internal stress σ∗ obtained in EAT and TAT: (a) the relation of σ∗ and current density and (b) comparison of σ∗ activated by electric and thermal factors

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Fig. 7

Flow behavior in TAT tests with various temperatures: (a) true stress–strain curves till fracture and (b) comparison of true stress obtained in both EAT and TAT at similar thermal situation

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Fig. 6

Flow behavior in EAT tests with various current densities: (a) true stress–strain curves till fracture and (b) stress reduction at certain strain compared with room-temperature flow behavior

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Fig. 5

Temperature fluctuation during EAT tests: (i) average temperature and max temperature versus true strain and (ii) thermal pictures at certain period. (a) 50 A/mm2, (b) 100 A/mm2, and (c) 150 A/mm2.

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Fig. 4

Schematic of thermally assisted tensile setup

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Fig. 9

Comparison of experimental value and analytical value: (a) comparison results obtained in EAT test and (b) comparison results obtained in TAT tests

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Fig. 10

Coefficients to Eq. (17) fitted to experimental results

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Fig. 15

Comparison of martensite fraction in 0 A/mm2, TAT and 50 A/mm2

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Fig. 16

Hardness measurement

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Fig. 17

Comparison of experimental value with theoretical value predicted by Olson's equation in 0 A/mm2, TAT and 50 A/mm2

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Fig. 11

Relation of hardening rate and true strain treated inelectric pulses with 0 A/mm2, 50 A/mm2, 100 A/mm2, and 150 A/mm2

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Fig. 12

(a) Locations for the measurement of martensite phase and (b) temperature distribution and martensite volume when current density is 50 A/mm2 and true strain is 0.35

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Fig. 13

Volume of martensite obtained in 0 A/mm2, 50 A/mm2, 100 A/mm2, and 150 A/mm2

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Fig. 14

Comparison of martensite fraction obtained in 100 A/mm2 and 150 A/mm2 with that in TAT

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