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NDE Inspection of Terahertz Waves in Wind Turbine Composites
David Kuei Hsu,임광희,이길성,박제웅,우용득 한국정밀공학회 2012 International Journal of Precision Engineering and Vol. No.
An investigation of terahertz waves was made for the nondestructive evaluation of composite materials and structures in the wind turbine. The modalities of the terahertz radiation used were time domain spectroscopy (TDS) and continuous wave (CW). The composite materials and structures investigated include both non-conducting polymeric composites and conducting carbon fiber composites. Terahertz signals in the TDS mode resembles that of ultrasound; however, unlike ultrasound, a terahertz pulse was able to detect a smaller crack hidden behind a larger crack. This was demonstrated in thick GFRP (glass fiber reinforced plastics) laminates of the wind turbine using saw slots. In carbon composites the penetration of terahertz waves is quite limited and the detection of flaws is strongly affected by the angle between the electric field direction of the terahertz waves and the intervening fiber directions. The structures used in this study included both solid laminates and the parts in the wind turbine. The defects and anomalies investigated by terahertz radiation were foreign material inclusions, simulated disband, delamination and mechanical impact damage. The effectiveness and limitations of terahertz radiation are defined and noted for the NDE of composites.
Terahertz Radiation NDE of Composite Materials for Wind Turbine Applications
박제웅,임광희,양인영,김선규,강성준,조영태,정종안,David Kuei Hsu 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.
Nondestructive testing technique using T-ray (terahertz ray) has received more interest as a new capability tool in engineeringapplication. So, T-ray time-domain spectroscopy was used for inspecting and evaluating physical property and defect characteristicsin FRP composite materials for a use of wind energy. First of all, a general refraction mode and transmission mode was utilized forcalculating a refractive index (n) based on the well-machined sample. In order to obtain the terahertz ray refractive index, a refractivemode and a transmission mode technique was defined for solving a refractive coefficient (n), with which refractive index of GFRPcomposites, balsa and epoxy for a use of wind turbine blades could be obtained. A method of wind turbine blade composites havingone and two saw-cuts delaminations and some angles/ directions was suggested based on the E-field vector. The time of flight in Trayusing evaluating a T-ray transmission mode agreed with that using T-ray time-domain spectroscopy with the wind turbine blade. Also, in CFRP composites, T-ray propagation is limited because the carbon fibers are blocking the T-ray. Therefore, we have analyzeddifference between E-field vector in T-ray and the carbon fiber direction. Also, it was found that a T-ray time domain data in thickGFRP composite laminates seemed to show peaks with a regular spacing (Δt) which was obvious with the close relation between TOFand FFT.
Advanced T-Ray Nondestructive Evaluation of Defects in FRP Solid Composites
임광희,이길성,양인영,양용준,서영환,David Kuei Hsu 한국정밀공학회 2013 International Journal of Precision Engineering and Vol.14 No.6
Nondestructive testing technique using T-ray (terahertz ray) receives attention these days as a new field of test engineering. In this study, T-ray time-domain spectroscopy was used for inspecting and evaluating physical property and defect characteristics in FRP composite material. Also, general refraction and transmission mode of this T-ray spectrography was used for finding refraction coefficient (n) and for obtaining T-ray image. First, in order to obtain the terahertz ray refraction index, refractive and transmission mode technique was induced, with which refraction index of GFRP composites, balsa and epoxy of wind turbine blade could be obtained. In GFRP and CFRP composites, T-ray propagation faces hindrance by carbon fiber. Accordingly, the authors have analyzed directional dependence between E-field of T-ray and the carbon fiber. Also, evaluating method of wind turbine blade composites having two (2) saw-blade delaminations integrally inserted was presented in this study. It was found that the time of flight of T-ray using T-ray transmission mode technique coincides well with that using refractive index in the wind turbine blade.