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Subsurface Defect Detection in Conducting Materials Through Transient Eddy Current NDE and Apparent Conductivity Calculations

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Part of the Lecture Notes in Mechanical Engineering book series (LNME)

Abstract

A novel transient eddy current NDE system has already been developed with double “D” excitation coil and fluxgate as a receiver. By using this system, an artificially engineered subsurface defect in an aluminium plate has been detected by shifting the defect from a depth of 2 mm to 20 mm and by maintaining the total thickness of the plate of 21.5 mm. The defect size is 70 mm long, 1 mm wide and 1.5 mm high. The feature maximum diffusion time, tm that is the time at which the diffusion of eddy current is maximum has been obtained and the same has been correlated with the defect depth. Subsequently, an additional novel technique has been established to measure the thickness of the conducting materials by combining the transient eddy current NDE measurements and apparent conductivity calculations. Here, two features such as maximum diffusion time, tm, and maximum apparent conductivity, σmapp, have been obtained. From this, another parameter maximum diffusion depth, δm, has been calculated and the same has been correlated with the thickness of the aluminium plates The parameters such as tm, σmapp and δm are related to the fundamental expression of diffusion depth (δ =  (2t/σµ)1/2) in time domain eddy current measurements. This work has been further extended to detect the defects in aluminium plates by combining transient eddy current NDE measurements and apparent conductivity calculations. From this work, it has been shown that the depth of the defect is proportional to the maximum diffusion depth, δm.

Keywords

  • Transient eddy current NDE
  • Apparent conductivity
  • Defect detection

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  • DOI: 10.1007/978-981-16-9093-8_10
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Acknowledgements

The authors would like to thank Shri R. Baskaran, Dr. N. V. Chandra Shekar and Dr. Shaju K. Albert for their continuous support and encouragement. The authors would also like to thank Shri Ram and Shri Gautam for their continuous support throughout this work.

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Correspondence to R. Nagendran .

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© 2022 Indian Society for Non-destructive Testing

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Bisht, L., Mohanty, I., Nagendran, R. (2022). Subsurface Defect Detection in Conducting Materials Through Transient Eddy Current NDE and Apparent Conductivity Calculations. In: Mandayam, S., Sagar, S.P. (eds) Advances in Non Destructive Evaluation. NDE 2020. Lecture Notes in Mechanical Engineering. Springer, Singapore. https://doi.org/10.1007/978-981-16-9093-8_10

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  • DOI: https://doi.org/10.1007/978-981-16-9093-8_10

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  • Publisher Name: Springer, Singapore

  • Print ISBN: 978-981-16-9092-1

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