• Journal of the Korean Wood Science and Technology
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• v.32 no.3
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• pp.8-14
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• 2004

Nondestructive evaluation (NDE) technique method using a resonance frequency mode was carried out for woodceramics produced at different carbonizing temperatures (600℃, 800℃, 1000℃, 1200℃, 1500℃) at the phenol resin impregnation rate of 70%, for three kinds of species (Pinus densifora, Pinus koraiensis, Larix leptolepis), respectively. There was a poor relationship between density and static bending MOR. However, close correlations were found between dynamic MOE_d and static bending MOR, and between static MOEs and MOR. Especially, the correlation coefficient was highest between MOE_d and static bending MOR. Therefore, the MOE_d using the resonance frequency mode is useful as a NDE method for predicting the MOR of woodceramics produced at different carbonizing temperatures.

• Journal of the Korean Wood Science and Technology
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• v.31 no.2
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• pp.31-37
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• 2003

Among the nondestructive evaluation (NDE) methods for wood defect detection, ultrasonic wave has been considered as competitive technique in terms of economics and workability. Until now, researches on application of NDE methods for wood have focused mainly on standing tree and logs. Recently, some attempts have been conducted with NDE technique, for evaluation of wooden structural members. However, wooden structural members are different from others (standing tree or log) in various aspects. Expecially when some parts or whole member are covered with other materials, they can't be evaluated appropriately on general NDE methods. For the purpose of development of proper NDE technique for the wooden structural members, the ultrasonic wave transmission process investigated on artificial defect in wood. First, various types of transmission process were assumed, and then the transmission times were predicted respectively. Predicted times were compared with the measured time of ultrasonic wave and then a suitable type of transmission process is determined. In case of the ultrasonic wave doesn't transmit directly due to defect, it is reflected once only at the opposite surface of member, and the path is accord with the line of shortest length.

• Journal of Advanced Engineering and Technology
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• v.11 no.4
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• pp.245-251
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• 2018

Terahertz waves (T-ray) was extensively studied for the NDE (nondestructive evaluation) of characterization of trailing edges for a use of turbines composed with composite materials. The used NDE system were consisted of both CW(Continuous wave) and TDS (Time domain spectroscopy). The FRP composites were utilized for two kinds of 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 (Time domain spectroscopy) mode resembles almost that of ultrasound waves; however, a terahertz pulse could not penetrate a material with conductivity unlike ultrasound. Also, a method was suggested to obtain the "n" in the materials, which is called the refractive index (n). The data of refractive index (n) could be solved for the trailing edges. The trailing edges were scanned for characterization and inspection. C-scan and B-scan images were obtained and best optimal NDE techniques were suggested for complicated geometry samples by terahertz radiation. Especially, it is found that the defect image of T-ray corresponded with defect locations for the trailing edges of wind mill.

• Journal of the Korean Society of Systems Engineering
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• v.12 no.1
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• pp.59-71
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• 2016

The Nuclear and Fossil Steam Turbines record a considerable number of failures annually. Some of these failures reported are as result of blade failure. The failure of the L-0 blade in a Steam Turbine is one of the most reported blade failure in Nuclear and Fossil steam turbines. This paper seeks to identify the best Non Destructive Evaluation (NDE) method or methods to be used in the steam turbine L-0 blades inspection process. The development of systems engineering processes presents an opportunity to apply NDE inspection to the L-0 blades. This process apply computer modelling of the L-0 using ANSYS and by simulating the stresses experienced by the L-0 blade during operation it is possible to identify the most susceptible areas for crack formation and growth. The results from these models compared to industry data for validation. The analysis of these results used to predict the most probable failure location and failure modes. Therefore NDE inspection can be applied to these areas with greater degree of accuracy. This would be beneficial in the increasing the accuracy in the detection of cracks and hence save inspection time and the overall inspection cost. Furthermore, not only the location for crack formation and NDE inspection determined but also best the NDE inspection technique/techniques to be applied appropriately on the L-0 blade are prescribed.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.3
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• pp.174-183
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• 1997

Turbine rotor disc consists of disc, bore, keyway, hub, and rim in which the typical defects are located. And these part of disc has very complicated geometry, therefore proper transducer selection, wedge design, fabrication, classification and evaluation of the signal identification are required. In this research, test block with the artificial flaws at keyway and boresurface parts have been used in order to establish the ultrasonic inspection technique for flaw detectability on disc. The analysis of the signals from the test blocks was performed. The wedges were designed according to the curvature from the discs. All the ultrasonic signals were collected and identified for evaluation. The ultrasonic inspection technique for the flaw-detection was established from this research. And it is proved that the result of this research can be applicable in the field inspection.

• Journal of the Korean Wood Science and Technology
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• v.41 no.5
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• pp.466-473
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• 2013

Nondestructive evaluation (NDE) technique method using a resonance frequency mode was carried out for heat-treated wood under different conditions. The effect of heat treatment on the bending strength and NDE technique using the resonance frequency by impact hammer and force transducer mode for Korean paulownia, Pinus densiflora, Lidiodendron tulipifera and Betula costata were measured. The heat treatment temperature has been investigated at $175^{\circ}C$ and $200^{\circ}C$, respectively. There were a close relationship of dynamic modulus of elasticity and static bending modulus of elasticity to MOR. In all conditions, It was found that there were a high correlation at 1% level between dynamic modulus of elasticity and MOR, and static modulus of elasticity and MOR. However, the result indicated that correlation coefficient is higher in dynamic modulus of elasticity to MOR than that in static modulus of elasticity to MOR. Therefore, the dynamic modulus of elasticity using resonance frequency by impact hammer mode is more useful as a nondestructive evaluation method for predicting the MOR of heat-treated wood under different temperature and species conditions.

• Journal of the Korean Society for Nondestructive Testing
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• v.9 no.2
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• pp.25-36
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• 1989

This essay is a general review of the application of ultrasonic NDE techniques to the performance assessment and characterization of composite materials. A brief review of ultrasonic input-output characterization of a composite plate by shear waves is presented. A theoretical development of ultrasonic wave propagation in isotropic and anisotropic media excited, respectively, by a circular transducer and an oscillatory point source is summarized. Some experimental results are described in which ultrasonic velocity and attenuation measurements give insight into material degradation of fatigued composite laminates. Ultrasonic determination of the elastic constants of a composite plate and an experimental attempt at ultrasonic testing of an isotropic plate containing a crack are also included. A recent effort for the characterization of viscoelastic materials using the ultrasonic NDE technique is outlined. Finally, the reliability of ultrasonic NDE is briefly touched upon.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.1
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• pp.1-21
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• 2001

It will be shown how models can simulate all the elements of an ultrasonic NDE measurement system, including the pulser/receiver, cabling, transducer(s), and the acoustic/elastic waves fields. When combined, these models form what is called the electroacoustic measurement model. It will be demonstrated how this electroacoustic measurement model can be used to conduct parametric transducer and system studies and how the model can form the basis for experimentally characterizing all the elements of the ultrasonic measurement system, using purely electrical measurements.

• Journal of Magnetics
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• v.16 no.2
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• pp.173-176
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• 2011

Fe-Cr alloys with different Cr contents were prepared by an arc melting technique. The alloys were isochronally aged in the range from $400^{\circ}C$ to $900^{\circ}C$ with $50^{\circ}C$ steps with a holding time of 100 hours. The ageing produced embrittlement in the alloys due to either the formation of a Cr-rich ${\alpha}'$ phase or a $\sigma$ phase at high temperatures. Magnetic Hysteresis Loop (MHL) and Micro-Vickers hardness were measured at each step to correlate the magnetic and mechanical properties. Coercivity and hardness of the alloys were increased and remanence decreased up to 500-$550^{\circ}C$ due to formation of a Cr-rich ${\alpha}'$ phase. Beyond 500-$550^{\circ}C$ range, the coercivity and hardness decreased and remanence increased due to the coarsening or dissolution of the Cr-rich ${\alpha}'$ phase. In the Fe-48% Cr alloy, formation of the $\sigma$ phase at $700^{\circ}C$ reduced the maximum induction of the alloy significantly.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.45 no.5
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• pp.56-62
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• 2008

This paper proposes the use of decision tree classification for the measuring pattern recognition from industrial Computed Radiography(CR) images used in nondestructive evaluation(NDE) of steel-tubes. It appears that NDE problems are naturally desired to have machine learning techniques identify patterns and their classification. The attributes of decision tree are taken from NDE test procedure. Geometric features, such as radiative angle, gradient and distance, are estimated from the analysis of input image data. These factors are used to make it easy and accurate to classify an input object to one of the pre-specified classes on decision tree. This algerian is to simplify the characterization of NDE results and to facilitate the determination of features. The experimental results verify the usefulness of proposed algorithm.