NDE characterization and inspection techniques of trailing edges in wind turbine blades using terahertz waves

Abstract

Terahertz waves (T-ray) were extensively studied for the nondestructive evaluation of the characterization of trailing edges composed with composite materials. The NDE system consisted of both continuous wave (CW) and time domain spectroscopy (TDS). The FRP composites were utilized for both trailing edges of wind energy (non-conducting polymeric composites) and carbon fiber composites with conducting properties. The signals of T-ray in the TDS mode almost resembles that of ultrasound waves; however, a terahertz pulse could not penetrate a material with conductivity, unlike ultrasound. The refractive index (n) was utilized as one of the material properties, so a method was suggested to obtain the “n” in the materials. The data of refractive index (n) were utilized due to obtained data for the trailing edges. The trailing edges were scanned for charactering and inspecting. C-scan and B-scan images were obtained and the optimal NDE techniques were suggested for complicated geometry samples by terahertz radiation. In particular, the penetrating time-of-flight (TOF) of T-ray corresponded with the calculated TOF for the trailing edges with greater thickness (about 70 mm).

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Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. 2015R1D1A3A01016775/2018R1D1A1 B07049775) and also experimentally helped by the CNDE at Iowa State University, USA.

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Correspondence to Kwang-Hee Im.

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Recommended by Associate Editor Tae June Kang

Kwang-Hee Im has been at Woosuk University since 2000 and is board member of the World Federation of Nondestructive Evaluation Centers (WFNDEC) from 1998 to present. He is currently a Full Professor of Automotive Engineering at Woosuk University.

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Im, K., Kim, S., Jung, J. et al. NDE characterization and inspection techniques of trailing edges in wind turbine blades using terahertz waves. J Mech Sci Technol 33, 4745–4753 (2019). https://doi.org/10.1007/s12206-019-0915-8

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Keywords

  • T-ray
  • FRP
  • Refractive index
  • Balsa
  • Continuous wave
  • Trailing edge
  • Wind energy