• Journal of the Korean Society for Nondestructive Testing
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• v.2 no.1
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• pp.17-24
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• 1982

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.2
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• pp.108-113
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• 1997

Ultrasonic testing is one of the most widely used method of nondestructive testing for pre-service inspection(PSI) & in-service inspection(ISI) in structures of bridges, power plants, chemical plants & heavy industrial fields. It is very important to estimate safety, life, quality of structures. Also, a lot of research for quantities evaluation & analyses inspection data is proceeding. But traditional portable ultrasonic flaw detector had been following disadvantages. 1) Analog ultrasonic flaw detector decreased credibility of ultrasonic test, because it is impossible for saving data & digital signal processing. 2) Stand-alone digital ultrasonic flaw detector cannot effectively evaluate received signals because of lack of its storage memory. To overcome this shortcoming, we develop the computer based ultrasonic flaw detector for nondestructive testing. It can store the received signal and effectively evaluate the signal, and then enhance the reliability of the testing results.

• 한국정보통신설비학회:학술대회논문집
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• 2002.08a
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• pp.49-52
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• 2002

본 논문에서는 강자성체 물질을 사용하는 구조물들에 발생되는 결함을 와전류탐상을 이용하여 검출하기 위한 비파괴검사방법에 대하여 제시하였다. 와전류탐상은 전자기비파괴검사방법으로 초음파탐상법과 같은 방법에 비교하여 비접촉식이며 고속으로 검사가 가능하다는 장점이 있다. 본 연구에서 사용되는 매질인 강자성체의 경우 비자성체에 비하여 표피효과에 의한 침투깊이가 얇기 때문에 강자성체를 위한 주파수를 별도로 선정하여야 한다. 또한 고속으로 움직이는 경우 속도기전력에 의한 효과를 고려하여야 한다. 본 연구에서는 와전류센서를 제작하여 실제 강자성체에 적용하는 경우 어떠한 특성을 나타내는가에 대하여 고찰하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.4 no.1
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• pp.30-33
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• 1984

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.1-9
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• 2000

This study shows the defect detection and sizing capability of ultrasonic guided waves in the nondestructive inspection of heat exchanger and steam generator tubing. Phase and group velocity dispersion curves for the longitudinal and flexural modes of a sample Inconel tube were presented for the theoretical analysis. EDM(Electric Discharge Machining) wears in tubing under a tube support plate and circumferential laser notches in tubing were detected by an axisymmetric and a non-axisymmetric transducer set up, respectively. EDM wears were detected with L(0, 2), L(0, 3) and L(0, 4) modes and among them L(0, 4) mode was found to be the most sensitive. It was also found that the flexural modes around L(0, 1) mode could be used for the detection and sizing of laser notches in the tubing.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.2
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• pp.135-143
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• 2013

Friction Stir Welding (FSW) was developed, it is successfully commercialized in the field of transportation vehicles. In this study, we analyzed the defects of A2024-T4 alloy using non-destructive test of radiograph, ultrasonic, electrical conductivity and destructive test of microstructure observation, tensile strength. As the results of experiment, mapping of defects was obtained. Fine defects which were not detected in radiograph test were detected in ultrasonic test, and it enabled efficient detection of defects by difference of sound pressure and color. The values of electrical conductivity was decreased as amount of defects was increasing. Joint efficient of defect-free weldment that found by non-destructive and destructive test was 91%. Therefore it was considered that non-destructive test of friction stir welded A2024-T4 Alloy was an efficient method.

• Journal of the Korean Society for Nondestructive Testing
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• v.13 no.4
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• pp.25-31
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• 1994

A system for EMAT, which generates ultrasound by electro-magnectic forces and performs nondestructive testing in noncontact, was established. By linking it with a 3 axis scanning system and a data acquisition and processing system the automation of EMAT testing was attempted. A EMAT sensor was fabricated and the directivity pattern of it was measured. To be suitable automation, it has a transmitter and a receiver in one case and the main beam direction of it can be controlled by the frequency of driving signal. A program which controls the EMAT system, the 3 axis scanner and the data acquisition and processing system was developed. It also processes acquired data and displays the processing results. IBM-PC/AT compatible PC was used as main controller and the stratage of the program is emulation of real devices on the PC monitor. To provide the performance of the established EMAT system, two aluminium blocks containing artificial flaws and a welded aluminium block were tested. The result of the tests were satisfactory.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.4
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• pp.406-414
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• 2001

Ultrasonic guided waves were explored to apply them to the long range inspection of polyethylene coated steel gas pipes. The steel pipes have such dimensions as 190.7mm inside diameter and 5.3mm thickness. The outside surface of the pipe is coated by a polyethylene layer of $1.9{\pm}0.5mm$ thickness. Non-axisymmetric guided waves were excited on the outside surface of the polyethylene coated pipe by using a 0.5MHz transducer with a variable angle shoe. Frequency and phase velocity tuning was used to find optimum guided wave modes for the inspection. The dispersive characteristics of the modes were analyzed in time-frequency representation obtained by short time Fourier transforms. Sample results were presented for artificial defects such as wall thinning and hole.

• Journal of the Korean Society for Nondestructive Testing
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• v.37 no.1
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• pp.37-43
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• 2017

Ultrasonic transducers with high resolution and resonant frequency are required to detect small defects (less than hundreds of ${\mu}m$) by ultrasonic testing. The resonance frequency and resolution of an ultrasonic transducer are closely related to the thickness of piezo-electric materials, backing materials, and the electric impedance matching technique. Among these factors, electrical impedance matching plays an important role because it can reduce the loss and reflection of ultrasonic energy differences in electrical impedance between an ultrasonic transducer and an ultrasonic defects detecting system. An LC matching circuit is the most frequently used electric matching method. It is necessary for the electrical impedance of an ultrasonic transducer to correspond to approximately $50{\Omega}$ to compensate the difference in electrical impedance between both connections. In this study, a 15 MHz immersion ultrasonic transducer was fabricated and an LC electrical impedance circuit was applied to that for having broad-band frequency characteristic.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.6
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• pp.590-596
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• 2004

Neural network-based signal classification systems are increasingly used in the analysis of large volumes of data obtained in NDE applications. Ultrasonic inspection methods on the other hand are commonly used in the nondestructive evaluation of welds to detect flaws. An important characteristic of ultrasonic inspection is the ability to identify the type of discontinuity that gives rise to a peculiar signal. Standard techniques rely on differences in individual A-scans to classify the signals. This paper proposes an ultrasonic signal classification technique based on the information tying in the neighboring signals. The approach is based on a 2-dimensional Fourier transform and the principal component analysis to generate a reduced dimensional feature vector for classification. Results of applying the technique to data obtained from the inspection of actual steel welds are presented.