Research Papers: NDE

A Nondestructive Evaluation Method: Measuring the Fixed Strength of Spot-Welded Joint Points by Surface Electrical Resistivity

[+] Author and Article Information
Akira Shimamoto

e-mail: shimamot@sit.ac.jp

Keitaro Yamashita

e-mail: yamashita-kn@nifty.com
High-Tech Research Center,
Saitama Institute of Technology,
1690 Fusaiji Fukaya,
Saitama 369-0293, Japan

Hirofumi Inoue

Mito Industry Co., Ltd.,
6 Kandakitanorimonocho, Chiyoda,
Tokyo 101-0036, Japan
e-mail: hi_inoue@mitokogyo.co.jp

Sung-mo Yang

Division of Mechanical & Advanced
Materials Engineering,
Chonbuk National University,
664-14 Duckjin-dong,
Jeonju 561-756, Korea
e-mail: yangsm@moak.chonbuk.ac.kr

Masahiro Iwata

e-mail: rd@emic-jp.com

Natsuko Ike

e-mail: et.factory@emic-jp.com
Densijiki Industry Co., Ltd.,
1-13-10 Funado, Itabashi,
Tokyo 174-0041, Japan

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the Journal of Pressure Vessel Technology. Manuscript received May 27, 2011; final manuscript received October 6, 2012; published online March 18, 2013. Assoc. Editor: Tribikram Kundu.

J. Pressure Vessel Technol 135(2), 021501 (Mar 18, 2013) (7 pages) Paper No: PVT-11-1133; doi: 10.1115/1.4007957 History: Received May 27, 2011; Revised October 06, 2012

Destructive tests are generally applied to evaluate the fixed strength of spot-welding nuggets of zinc-plated steel (which is a widely used primary structural material for automobiles). These destructive tests, however, are expensive and time-consuming. This paper proposes a nondestructive method for evaluating the fixed strength of the welded joints using surface electrical resistance. A direct current nugget-tester and probes have been developed by the authors for this purpose. The proposed nondestructive method uses the relative decrease in surface electrical resistance, α. The proposed method also considers the effect of the corona bond. The nugget diameter is estimated by two factors: RQuota, which is calculated from variation of resistance, and a constant that represents the area of the corona bond. Since the maximum tensile strength is correlated with the nugget diameter, it can be inferred from the estimated nugget diameter. When appropriate measuring conditions for the surface electrical resistance are chosen, the proposed method can effectively evaluate the fixed strength of the spot-welded joints even if the steel sheet is zinc-plated.

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Fig. 1

Surface electrical resistivity measurements using four-point probe method

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Fig. 2

Relationship between the surface electrical resistivity and specimen thickness

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Fig. 3

Influence of electrode distance s2 and specimen thickness, t, on surface resistance, R

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Fig. 4

Specimen size and geometry

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Fig. 5

Effect of welding current on tensile shear strength for different welding force (welding time 15 cycle, t = 1.4 mm)

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Fig. 6

Effect of welding current on tensile shear strength for different welding times (electrode force 2.5 kN, t = 1.4 mm)

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Fig. 7

Relationship between the shear strength and elongation (t = 0.9 mm)

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Fig. 8

Apparatus for measurement of nugget

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Fig. 9

Example of the surface electrical resistance distribution in the normal welding condition

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Fig. 10

Relationship between the thickness and surface electrical resistivity

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Fig. 11

Relationship between the tensile shear force Fmax and the measured nugget diameter D

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Fig. 12

Example of specimen shape after shear tests (t = 1.4 mm)

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Fig. 13

Cross section of nugget

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Fig. 14

Surface electrical resistance distribution

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Fig. 15

Relationship between the tensile shear force Fmax and the estimated nugget diameter Deff



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