• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.3
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• pp.193-199
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• 2015

Active thermography techniques have the capability of inspecting a broad range simultaneously. By evaluating the phase difference between the defected area and the healthy area, the technique indicates the qualitative location and size of the defect. Previously, the development of the defect detection method used a variety of materials and the test specimen was done. In this study, the proposed technique of lock-in is verified with artificial specimens that have different size and depth of subsurface defects. Finally, the defect detection capability was evaluated using comparisons of the phase image and the amplitude image according to the size and depth of defects.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.4
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• pp.321-327
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• 2007

In lock-in thermography, a phase difference between the defect area and the healthy area indicates the qualitative location and size of the defect. To accurately estimate these parameters, the shearing-phase technique has been employed which gives the shearing-phase distribution. The shearing-phase distribution has maximum, minimum, and zero points that help determine quantitatively the size and location of the subsurface defect. In experiment, the proposed technique is verified with artificial specimen and these related factors are analyzed.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.1
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• pp.43-50
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• 2007

In this study, Hybrid Separate Learning Algorithm(SLA) consisting of Support Vector Machine(SVM) and Artificial Neural Network(ANN) has been used for developing the defect diagnostic algorithm of the aircraft turbo-shaft engine in the off-design range considering altitude variation. Although the number of teaming data and test data highly increases more than 6 times compared with those required for the design condition, the proposed defect diagnostics of gas turbine engine using SLA was verified to give the high defect classification accuracy in the off-design range considering altitude variation.

• Journal of the Korean Institute of Gas
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• v.16 no.2
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• pp.18-24
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• 2012

This research seeks to evaluate damage on type II gas cylinder by an acoustic emission test when executing 20000 cycles fatigue test and thereafter burst test. Used gas cylinders in the experimental are three types as follows; one is sound cylinder, others are cylinders which contain longitudinal and transverse artificial defect. The size of artificial defect is a depth of 3 mm, width of 3 mm and length of 50 mm. In the case of the cylinder which artificial defect, unlike the expectation that it will burst in low pressure, the burst pressure of the cylinder did not differ much according to whether or not there were defects. However, when there was longitudinal defect, the location of burst was near the location of defect. This leads to the effect in which the thickness of the composite material becomes thinner according to the length of the longitudinal defect and this is judged to have an effect on the location of initiation and growth of crack in the liner. Also, for the acoustic emission signal, when there is longitudinal defect, the ratio of an event occurring at defect position among overall hits is more than 50 %, and the source location also accords very precisely with defect position.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.11 s.170
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• pp.1922-1928
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• 1999

Rotary bending fatigue tests were carried out to investigate the influence of artificial defects on fatigue limit in annealed and austempered ductile iron. Obtained main results are as follows : (1) Artificial defect(micro hole type, dia.<0.4 mm) on specimen surface did not bring about a obvious reduction of fatigue limit in austempered ductile iron(ADI) as compared with annealed ductile iron. (2) According to the investigation of $\sqrt{area}_c$ which is the critical defect size to crack initiation at artificial defect, $\sqrt{area}_c$ of ADI is larger than that of annealed ductile iron. This shows that the situation of crack initiation at artificial defect in ADI is more difficult in comparison with annealed ductile iron. (3) One of the reasons for the low rate of crack initiation from artificial defect in ADI is that the resistance of matrix to crack initiation is higher than that of annealed ductile iron. (4) In case that the $\sqrt{area}$ of artificial defect and graphite nodule is the same, the rate of crack initiation from graphite nodule is higher than that from artificial defect. This reason is that the serious ruggedness around graphite nodule is formed by austempering treatment.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.5
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• pp.341-348
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• 2015

Active infrared thermography methods have been known to possess good fault detection capabilities for the detection of defects in materials compared to the conventional passive thermal infrared imaging techniques. However, the reliability of the technique has been under scrutiny. This paper proposes the lock-in thermography technique for the detection and estimation of artificial subsurface defect size and depth with uncertainty measurement.

• Nuclear Engineering and Technology
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• v.20 no.3
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• pp.170-178
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• 1988

An automated ultrasonic flaw detection system was developed for thin-walled and short tubes such as Zircaloy-4 tubes used for cladding heavy-water reactor fuel. The system was based on the two channels immersion pulse-echo technique using 14 MHz shear wave and the specially developed helical scanning technique, in which the tube to be tested is only rotated and the small water tank with spherical focus ultrasonic transducers is translated along the tube length. The optimum angle of incidence of ultrasonic beam was 26 degrees, at which the inside and outside surface defects with the same size and direction could be detected with the same sensitivity. The maximum permissible defects in the Zircaloy-4 tubes, i.e., the longitudinal and circumferential v notches with the length of 0.76mm and 0.38mm, respectively and the depth of 0.04 mm on the inside and outside surface, could be easily detected by the system with the inspection speed of about 1 m/min and the very excellent reproducibility. The ratio of signal to noise was greater than 20 dB for the longitudinal defects and 12 dB for the circumferential defects.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.1
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• pp.54-61
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• 2001

A software package to classify acoustic emission (AE) signals using the wavelet transform and the neural network was developed Both of the continuous and the discrete wavelet transforms are considered, and the error back-propagation neural network is adopted as m artificial neural network algorithm. The signals acquired during the 3-point bending test of specimens which have artificial defects on weld zone are used for the classification of the defects. Features are extracted from the time-frequency plane which is the result of the wavelet transform of signals, and the neural network classifier is tamed using the extracted features to classify the signals. It has been shown that the developed software package is useful to classify AE signals. The difference between the classification results by the continuous and the discrete wavelet transforms is also discussed.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2018.06a
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• pp.235-237
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• 2018

많은 분야에서 기기설비들의 고장, 결함은 안전과 관련되어 있기 때문에 연구가 활발히 진행되고 있다. 주로 데이터를 취득하여 제품의 유지보수 및 품질을 향상시키는 연구로 고장을 나타내는 특성 인자를 추출하여 고장진단을 하는 것이다. 하지만, 과거의 룰 기반 결함 탐지 기법은 예외의 경우를 탐지하기 어렵다는 문제를 가져왔다. 최근 들어 인공지능이 특성 인자를 쉽게 추출할 수 있다는 장점으로 인해 인공지능과 결합된 고장진단 시스템이 많이 제안되고 있다. 본 논문에서는 인공지능의 추세와 인공지능과 결합된 고장진단 시스템을 소개한다.

• Journal of the Korean Institute of Gas
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• v.15 no.2
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• pp.27-32
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• 2011

In this paper a new defect length estimation algorithm using SQI(self quotient image) is presented for the MFL(magnetic flux leakage) inspection of underground gas pipelines. Gas pipelines are magnetized by the permanent magnets of the MFL PIG(pipeline inspection gauge) when the PIG runs through pipelines. If defects or corrosions exist in the pipeline, magnetic leakage flux is increased. The MFL signals measured by hall sensors are analyzed to estimate defect length using SQI. For 74 real defects carved in KOGAS pipeline simulation facility(KPSF) the accuracy of defect length estimation of the proposed algorithm was compared with that of conventional methods.