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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Korean Society for Nondestructive Testing
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Journal DOI :
The Korean Society for Nondestructive Testing
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Volume & Issues
Volume 36, Issue 3 - Jun 2016
Volume 36, Issue 2 - Apr 2016
Volume 36, Issue 1 - Feb 2016
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Using Lamb Waves to Monitor Moisture Absorption in Thermally Fatigued Composite Laminates
Lee, Jaesun ; Cho, Younho ;
Journal of the Korean Society for Nondestructive Testing, volume 36, issue 3, 2016, Pages 175~180
DOI : 10.7779/JKSNT.2016.36.3.175
Nondestructive evaluation for material health monitoring is important in aerospace industries. Composite laminates are exposed to heat cyclic loading and humid environment depending on flight conditions. Cyclic heat loading and moisture absorption may lead to material degradation such as matrix breaking, debonding, and delamination. In this paper, the moisture absorption ratio was investigated by measuring the Lamb wave velocity. The composite laminates were manufactured and subjected to different thermal aging cycles and moisture absorption. For various conditions of these cycles, not only changes in weight and also ultrasonic wave velocity were measured, and the Lamb wave velocity at various levels of moisture on a carbon-epoxy plate was investigated. Results from the experiment show a linear correlation between moisture absorption ratio and Lamb wave velocity at different thermal fatigue stages. The presented method can be applied as an alternative solution in the online monitoring of composite laminate moisture levels in commercial flights.
Developing an Early Leakage Detection System for Thermal Power Plant Boiler Tubes by Using Acoustic Emission Technology
Lee, Sang Bum ; Roh, Seon Man ;
Journal of the Korean Society for Nondestructive Testing, volume 36, issue 3, 2016, Pages 181~187
DOI : 10.7779/JKSNT.2016.36.3.181
A thermal power plant has a heat exchanger tube to collect and convert the heat generated from the high temperature and pressure steam to energy, but the tubes are arranged in a complex manner. In the event that a leakage occurs in any of these tubes, the high-pressure steam leaks out and may cause the neighboring tubes to rupture. This leakage can finally stop power generation, and hence there is a dire need to establish a suitable technology capable of detecting tube leaks at an early stage even before it occurs. As shown in this paper, by applying acoustic emission (AE) technology in existing boiler tube leak detection equipment (BTLD), we developed a system that detects these leakages early enough and generates an alarm at an early stage to necessitate action; the developed system works better that the existing system used to detect fine leakages. We verified the usability of the system in a 560MW-class thermal power plant boiler by conducting leak tests by simulating leakages from a variety of hole sizes (ⵁ2, ⵁ5, ⵁ10 mm). Results show that while the existing fine leakage detection system does not detect fine leakages of ⵁ2 mm and ⵁ5 mm, the newly developed system could detect leakages early enough and generate an alarm at an early stage, and it is possible to increase the signal to more than 18 dB.
Evaluating Interfacial Adhesion Properties of Pt/Ti Thin-Film by Using Acousto-Optic Technique
Park, Hae-Sung ; Didie, David ; Yoshida, Sanichiro ; Park, Ik-Keun ;
Journal of the Korean Society for Nondestructive Testing, volume 36, issue 3, 2016, Pages 188~194
DOI : 10.7779/JKSNT.2016.36.3.188
We propose an acousto-optic technique for the nondestructive evaluation of adhesion properties of a Pt/Ti thin-film interface. Since there are some problems encountered when using prevailing techniques to nondestructively evaluate the interfacial properties of micro/nano-scale thin-films, we applied an interferometer that combined the acoustic and optical methods. This technique is based on the Michelson interferometer but the resultant surface of the thin film specimen makes interference instead of the mirror when the interface is excited from the acoustic transducer at the driving frequency. The thin film shows resonance-like behavior at a certain frequency range, resulting in a low-contrast fringe pattern. Therefore, we represented quantitatively the change in fringe pattern as a frequency spectrum and discovered the possibility that the interfacial adhesion properties of a thin film can be evaluated using the newly proposed technique.
Study on Signal Processing in Eddy Current Testing for Defects in Spline Gear
Lee, Jae Ho ; Park, Tae Sung ; Park, Ik Keun ;
Journal of the Korean Society for Nondestructive Testing, volume 36, issue 3, 2016, Pages 195~201
DOI : 10.7779/JKSNT.2016.36.3.195
Eddy current testing (ECT) is commonly applied for the inspection of automated production lines of metallic products, because it has a high inspection speed and a reasonable price. When ECT is applied for the inspection of a metallic object having an uneven target surface, such as the spline gear of a spline shaft, it is difficult to distinguish between the original signal obtained from the sensor and the signal generated by a defect because of the relatively large surface signals having similar frequency distributions. To facilitate the detection of defect signals from the spline gear, implementation of high-order filters is essential, so that the fault signals can be distinguished from the surrounding noise signals, and simultaneously, the pass-band of the filter can be adjusted according to the status of each production line and the object to be inspected. We will examine the infinite impulse filters (IIR filters) available for implementing an advanced filter for ECT, and attempt to detect the flaw signals through optimization of system design parameters for detecting the signals at the system level.
Designing a Highly Sensitive Eddy Current Sensor for Evaluating Damage on Thermal Barrier Coating
Kim, Jong Min ; Lee, Seul-Gi ; Kim, Hak Joon ; Song, Sung Jin ; Seok, Chang Seong ; Lee, Yeong-Ze ;
Journal of the Korean Society for Nondestructive Testing, volume 36, issue 3, 2016, Pages 202~210
DOI : 10.7779/JKSNT.2016.36.3.202
A thermal barrier coating (TBC) has been widely applied to machine components working under high temperature as a thermal insulator owing to its critical financial and safety benefits to the industry. However, the nondestructive evaluation of TBC damage is not easy since sensing of the microscopic change that occurs on the TBC is required during an evaluation. We designed an eddy current probe for evaluating damage on a TBC based on the finite element method (FEM) and validated its performance through an experiment. An FEM analysis predicted the sensitivity of the probe, showing that impedance change increases as the TBC thermally degrades. In addition, the effect of the magnetic shield concentrating magnetic flux density was also observed. Finally, experimental validation showed good agreement with the simulation result.
Cure Monitoring of Epoxy Resin by Using Fiber Bragg Grating Sensor
Lee, Jin-Hyuk ; Kim, Dae-Hyun ;
Journal of the Korean Society for Nondestructive Testing, volume 36, issue 3, 2016, Pages 211~216
DOI : 10.7779/JKSNT.2016.36.3.211
In several industrial fields, epoxy resin is widely used as an adhesive for co-curing and manufacturing various structures. Controlling the manufacturing process is required for ensuring robust bonding performance and the stability of the structures. A fiber optic sensor is suitable for the cure monitoring of epoxy resin owing to the thready shape of the sensor. In this paper, a fiber Bragg grating (FBG) sensor was applied for the cure monitoring of epoxy resin. Based on the experimental results, it was demonstrated that the FBG sensor can monitor the status of epoxy resin curing by measuring the strain caused by volume shrinkage and considering the compensation of temperature. In addition, two types of epoxy resin were used for the cure-monitoring; moreover, when compared to each other, it was found that the two types of epoxy had different cure-processes in terms of the change of strain during the curing. Therefore, the study proved that the FBG sensor is very profitable for the cure-monitoring of epoxy resin.
Experimental and Numerical Validation of the Technique for Concrete Cure Monitoring Using Piezoelectric Admittance Measurements
Kim, Wan Cheol ; Park, Gyuhae ;
Journal of the Korean Society for Nondestructive Testing, volume 36, issue 3, 2016, Pages 217~224
DOI : 10.7779/JKSNT.2016.36.3.217
This paper presents a new technique for monitoring the concrete curing process using embedded piezoelectric transducers via admittance measurements. When a piezoelectric transducer is embedded in a structure, the electrical impedance (admittance) of the transducer is coupled with the mechanical impedance of the host structure, which allows monitoring of the structural condition. In this study, the admittance signatures are used for monitoring the concrete curing process. This new method is based on an admittance-based sensor diagnostic process, in which the capacitance values of the piezoelectric transducers are dependent on the strength of the host structure. We numerically and experimentally investigated the variations in capacitive value during the curing process. The results demonstrate that there is a clear relationship between the concrete curing status and the slope, this indicates that the proposed method could be efficiently used for monitoring the curing status of a concrete structure.
Reliability Evaluation of Fiber Optic Sensors Exposed to Cyclic Thermal Load
Kim, Heon-Young ; Kang, Donghoon ; Kim, Dae-Hyun ;
Journal of the Korean Society for Nondestructive Testing, volume 36, issue 3, 2016, Pages 225~230
DOI : 10.7779/JKSNT.2016.36.3.225
Fiber Bragg grating (FBG) sensors are currently the most prevalent sensors because of their unique advantages such as ease of multiplexing and capability of performing absolute measurements. They are applied to various structures for structural health monitoring (SHM). The signal characteristics of FBG sensors under thermal loading should be investigated to enhance the reliability of these sensors, because they are exposed to certain cyclic thermal loads due to temperature changes resulting from change of seasons, when they are applied to structures for SHM. In this study, tests on specimens are conducted in a thermal chamber with temperature changes from -
for 300 cycles. For the specimens, two types of base materials and adhesives that are normally used in the manufacture of packaged FBG sensors are selected. From the test results, it is confirmed that the FBG sensors undergo some degree of compressive strain under cyclic thermal load; this can lead to measurement errors. Hence, a pre-calibration is necessary before applying these sensors to structures for long-term SHM.
Excessive Leakage Measurement Using Pressure Decay Method in Containment Building Local Leakage Rate Test at Nuclear Power Plant
Lee, Won Kyu ; Kim, Chang Soo ; Kim, Wang Bae ;
Journal of the Korean Society for Nondestructive Testing, volume 36, issue 3, 2016, Pages 231~235
DOI : 10.7779/JKSNT.2016.36.3.231
There are two methods for conducting the containment local leakage rate test (LLRT) in nuclear power plants: the make-up flow rate method and the pressure decay method. The make-up flow rate method is applied first in most power plants. In this method, the leakage rate is measured by checking the flow rate of the make-up flow. However, when it is difficult to maintain the test pressure because of excessive leakage, the pressure decay method can be used as a complementary method, as the leakage rates at pressures lower than normal can be measured using this method. We studied the method of measuring over leakage using the pressure decay method for conducting the LLRT for the containment building at a nuclear power plant. We performed experiments under conditions similar to those during an LLRT conducted on-site. We measured the characteristics of the leakage rate under varies pressure decay conditions, and calculated the compensation ratio based on these data.
Application on Long Range Pipeline Inspection by Guided Waves
Lee, Jaesun ;
Journal of the Korean Society for Nondestructive Testing, volume 36, issue 3, 2016, Pages 236~239