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

Journal Article · Wed Mar 21 00:00:00 EDT 2007 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.2718104· OSTI ID:21054934

Lee, C; Shen, Y; Lo, C C. H.; Nakagawa, N ^[1]

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1. Center for NDE, Iowa State University, Ames, Iowa 50011 (United States)

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.

• OSTI ID: 21054934
• Journal Information: AIP Conference Proceedings, Vol. 894, 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); ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
DIRECT CURRENT
EDDY CURRENT TESTING
EDDY CURRENTS
FILMS
HEAT RESISTING ALLOYS
LAYERS
MHZ RANGE
NICKEL BASE ALLOYS
RESIDUAL STRESSES
SUBSTRATES
SURFACES