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Open AccessArticle

NDE Detection Techniques and Characterization of Aluminum Wires Embedded in Honeycomb Sandwich Composite Panels Using Terahertz Waves

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Department of Automotive Engineering, Woosuk University, Chonbuk 565-701, Korea
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Division of Mechanical System Engineering, Chonbuk Natl. University, Jeonbuk 561-756, Korea
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Department of Mechanical and Automotive Engineering, Songwon University, Gwangju 502-210, Korea
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Department of Manufacturing Design Engineering, Jeonju University, Jeonbuk 560-759, Korea
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Center for Nondestructive Evaluation, Iowa State University, Ames, IA 50011, USA
*
Author to whom correspondence should be addressed.
Materials 2019, 12(8), 1264; https://doi.org/10.3390/ma12081264
Received: 17 March 2019 / Revised: 15 April 2019 / Accepted: 16 April 2019 / Published: 17 April 2019
(This article belongs to the Special Issue Non-destructive Inspection)
For many years, scientists have been aware of the importance of terahertz waves (T-rays), which have now emerged as an NDE (nondestructive evaluation) technique for certain ranges of the electronic spectrum. The present study deals with T-ray scanning techniques of honeycomb sandwich composite panels with a carbon-fiber-reinforced plastic (CFRP) skin as well as the refractive index (n), and the electrical conductivity (α) of glass fiber-reinforced plastic (GFRP) composites. For this experiment, the degree of penetration to FRP composites is investigated for the THz transmitted power based on the angle in the electric field (E-field) direction vs. the direction of the unidirectional carbon fibers. Also, when CFRP skin honeycomb sandwich panels are manufactured for use in aerospace applications, aluminum wires are twisted together into the one-sided surface of the honeycomb sandwich panels to protect against thunderstorms. The aluminum wires are partly visible because they are embedded in the CFRP skin on the honeycomb sandwich panels. After finishing work with a paintjob, the wires become invisible. Thus, detecting the aluminum wires is a key issue for product monitoring. Based on a simple resistor model, an optimal scanning method is proposed to determine the preferred scan orientation on the baseline of the E-field in the direction of fibers to evaluate the level of transmission of T-rays according to the frequency bandwidth. Thus, the combination of angles required to detect the aluminum wires embedded with carbon fibers on the surface of the composite panels can be determined. View Full-Text
Keywords: T-ray; honeycomb sandwiches; aluminum wires; refractive index; fiber direction T-ray; honeycomb sandwiches; aluminum wires; refractive index; fiber direction
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Im, K.-H.; Kim, S.-K.; Jung, J.-A.; Cho, Y.-T.; Woo, Y.-D.; Chiou, C.-P. NDE Detection Techniques and Characterization of Aluminum Wires Embedded in Honeycomb Sandwich Composite Panels Using Terahertz Waves. Materials 2019, 12, 1264.

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