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Title: Validation of a Residual Stress Measurement Method by Swept High-Frequency Eddy Currents

Abstract

This paper reports on a swept high-frequency eddy current (SHFEC) measurement method developed for electromagnetic nondestructive characterization of residual stresses in shot peened aerospace materials. In this approach, we regard shot-peened surfaces as modified surface layers of varying conductivity, and determine the conductivity deviation profile by inversion of the SHFEC data. The SHFEC measurement system consists of a pair of closely matched printed-circuit-board coils driven by laboratory instrument under software control. This provides improved sensitivity and high frequency performance compared to conventional coils, so that swept frequency EC measurements up to 50 MHz can be made to achieve the smallest skin depth of 80 {mu}m for nickel-based superalloys. We devised a conductivity profile inversion procedure based on the laterally uniform multi-layer theory of Cheng, Dodd and Deeds. The main contribution of this paper is the methodology validation. Namely, the forward and inverse models were validated against measurements on artificial layer specimens consisting of metal films with different conductivities placed on a metallic substrate. The inversion determined the film conductivities which were found to agree with those measured using the direct current potential drop (DCPD) method.

Authors:
; ; ;  [1]
  1. Center for NDE, Iowa State University, Ames, Iowa 50011 (United States)
Publication Date:
OSTI Identifier:
21054934
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 894; Journal Issue: 1; Conference: Conference on review of progress in quantitative nondestructive evaluation, Portland, OR (United States), 30 Jul - 4 Aug 2006; Other Information: DOI: 10.1063/1.2718104; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; DIRECT CURRENT; EDDY CURRENT TESTING; EDDY CURRENTS; FILMS; HEAT RESISTING ALLOYS; LAYERS; MHZ RANGE; NICKEL BASE ALLOYS; RESIDUAL STRESSES; SUBSTRATES; SURFACES

Citation Formats

Lee, C., Shen, Y., Lo, C. C. H., and Nakagawa, N.. Validation of a Residual Stress Measurement Method by Swept High-Frequency Eddy Currents. United States: N. p., 2007. Web. doi:10.1063/1.2718104.
Lee, C., Shen, Y., Lo, C. C. H., & Nakagawa, N.. Validation of a Residual Stress Measurement Method by Swept High-Frequency Eddy Currents. United States. doi:10.1063/1.2718104.
Lee, C., Shen, Y., Lo, C. C. H., and Nakagawa, N.. Wed . "Validation of a Residual Stress Measurement Method by Swept High-Frequency Eddy Currents". United States. doi:10.1063/1.2718104.
@article{osti_21054934,
title = {Validation of a Residual Stress Measurement Method by Swept High-Frequency Eddy Currents},
author = {Lee, C. and Shen, Y. and Lo, C. C. H. and Nakagawa, N.},
abstractNote = {This paper reports on a swept high-frequency eddy current (SHFEC) measurement method developed for electromagnetic nondestructive characterization of residual stresses in shot peened aerospace materials. In this approach, we regard shot-peened surfaces as modified surface layers of varying conductivity, and determine the conductivity deviation profile by inversion of the SHFEC data. The SHFEC measurement system consists of a pair of closely matched printed-circuit-board coils driven by laboratory instrument under software control. This provides improved sensitivity and high frequency performance compared to conventional coils, so that swept frequency EC measurements up to 50 MHz can be made to achieve the smallest skin depth of 80 {mu}m for nickel-based superalloys. We devised a conductivity profile inversion procedure based on the laterally uniform multi-layer theory of Cheng, Dodd and Deeds. The main contribution of this paper is the methodology validation. Namely, the forward and inverse models were validated against measurements on artificial layer specimens consisting of metal films with different conductivities placed on a metallic substrate. The inversion determined the film conductivities which were found to agree with those measured using the direct current potential drop (DCPD) method.},
doi = {10.1063/1.2718104},
journal = {AIP Conference Proceedings},
number = 1,
volume = 894,
place = {United States},
year = {Wed Mar 21 00:00:00 EDT 2007},
month = {Wed Mar 21 00:00:00 EDT 2007}
}