• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.3
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• pp.276-282
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• 2013

This paper proposes an ultrasonic method for measurement of linear and hysteretic interfacial stiffness of contacting surfaces between two steel plates subjected to nominal compression pressure. Interfacial stiffness was evaluated by the reflection and transmission coefficients obtained from three consecutive reflection waves from solid-solid surface using the shear wave. A nonlinear hysteretic spring model was proposed and used to define the quantitative interfacial stiffness of interface with the reflection and transmission coefficients. Acoustic model for 1-D wave propagation across interfaces is developed to formulate the reflection and transmission waves and to determine the linear and nonlinear hysteretic interfacial stiffness. Two identical plates are put together to form a contacting surface and pressed by bolt-fastening to measure interfacial stiffness at different states of contact pressure. It is found from experiment that the linear and hysteretic interfacial stiffness are successfully determined by the reflection and transmission coefficient at the contact surfaces through ultrasonic pulse-echo measurement.

• Journal of the Korean Society for Nondestructive Testing
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• v.9 no.2
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• pp.42-49
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• 1989

It has not been performed to inspect the underclad cracking in Korea nuclear plant since there is no Code Requirements for inspection. However, underclad cracks in nuclear pressure vessels were reported firstly in 1970. The objection of this study is to be established the ultrasonic inspection techniques for underclad cracking. The ultrasonic inspection of bimetalic stainless steel weld is very difficult by high attenuation and multiple scattering at weld surface and weld/base metal interface. The various inspection methods using $70^{\circ}$ refracted longitudinal wave, 50/70 tandem transducer, $45^{\circ}\;and\;60^{\circ}$ single shear wave are compared. Experiments on limited specimens applied same condition to nuclear pressure vessels shows that $70^{\circ}$ refracted longitudinal wave method is the best one for the detection of underclad cracks. 50/70 tandem transducer using SPOT(Satellite Pulse Observation Technique) is more effective for underclad crack sizing than other sizing methods.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.4
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• pp.355-361
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• 2012

This paper presents an experimental study on the detection and location of nonlinear scattering source due to the presence of fatigue crack in a laboratory specimen. The proposed technique is based on a combination of nonlinear elastic wave spectroscopy(NEWS) and time reversal(TR) focusing approach. In order to focus on the nonlinear scattering position due to the fatigue crack, we employed only one transmitting transducer and one receiving transducer, taking advantage of long duration of reception signal that includes multiple linear scattering such as mode conversion and boundary reflections. NEWS technique was then used as a pre-treatment of TR for spatial focusing of reemitted second harmonic signal. The robustness of this approach was demonstrated on a cracked specimen and the nonlinear TR focusing behavior is observed on the crack interface from which the second harmonic signal was originated.

• Journal of the Korea Computer Industry Society
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• v.2 no.9
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• pp.1199-1208
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• 2001

Program slicing is a program decomposition technique to improve the effectiveness of program testing and maintenance. In this paper I propose a method for slicing object-oriented programs and show its correctness. Also, I propose the class interface slicing technique which can eliminate irrelevant data members, subobjects, and methods from the class declaration parts of the given program. And I show its correctness. Finally, I propose the class hierarchy slicing technique which can compute the declarative parts affecting or affected by the given data member. These techniques may be used for information analysis in some area such as class testing.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.3
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• pp.242-247
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• 2009

The ability of time reversal techniques to focus ultrasonic beams on the source location is important in many aspects of ultrasonic nondestructive evaluation. In this paper, we investigate the time reversal beam focusing of ultrasonic array sensors on a defect in layered media. Numerical modeling is performed using the commercially available software which employs a time domain finite difference method. Two different time reversal approaches are considered - the through transmission and the pulse-echo. Linear array sensors composed of N elements of line sources are used for signal reception/excitation, time reversal, and reemission in time reversal processes associated with the scattering source of a side-drilled hole located in the second layer of two layer structure. The simulation results demonstrate the time reversal focusing even with multiple reflections from the interface of layered structure. We examine the focusing resolution that is related to the propagation distance, the size of array sensor and the wavelength.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.3
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• pp.241-262
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• 2012

Some applications require structural health monitoring in inaccessible components. This paper presents a technique useful for Structural Health Monitoring of double wall structures, such as double wall steam pipes and double wall pressure vessels separated from an ultrasonic transducer by three layers. Detection has been demonstrated at distances in excess of one meter for a fixed transducer. The case presented here is for one of the layers, the middle layer, being a fluid. For certain transducer configurations the wave propagating in the fluid is a wave with low velocity and attenuation. The paper presents a model based on wave theory and finite element simulation; the experimental set-up and observations, and comparison between theory and experiment. The results provide a description of the technique, understanding of the phenomenon and its possible applications in Structural Health Monitoring.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.4
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• pp.371-382
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• 2001

The recognition of such natural wave guides as plates, rods, hollow cylinders, multi-layer structures or simply an interface between two materials combined with an increased understanding of the physics and wave mechanics of guided wave propagation has led to a significant increase in the number of guided wave inspection applications being developed each year. Of primary attention Is the ability to inspect partially hidden structures, hard to access areas, and teated or insulated structures. An introduction to some physical consideration of guided waves followed by some sample problem descriptions in pipe, ice detection, fouling detection in the foods industry, aircraft, tar coated structures and acoustic microscopy is presented in this paper. A sample problem in Boundary Element Modeling is also presented to illustrate the move in guided wave analysis beyond detection and location analysis to quantification.

• Journal of the Korean Ceramic Society
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• v.43 no.4 s.287
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• pp.247-252
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• 2006

Joining Yittria Stabilized Zirconia (YSZ) to NiCr metal was fabricated using YSZ/NiCr Functionally Graded Materials (FGM) Interlayer by hot pressing process. Microscopic observations demonstrate that the composition and microstructure of YSZ/NiCr FGM distribute gradually in stepwise way, eliminating the macroscopic ceramic/metal interface such as that in traditional ceramic/metal joint. The thermal characteristics of this YSZ/FGM/NiCr joint were studied by thermal shock testing and therml barrier testing. Thermal shock test was conducted by gas burner rig. Acoustic Emission (AE) monitoring was performed to analyze the microfracture behavior during the thermal shock test. It could be confirmed that FGM was the excellent performance of thermal shock/barrier resistance at above $1000^{\circ}C$.

• Journal of KIISE:Software and Applications
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• v.27 no.11
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• pp.1106-1114
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• 2000

컴퓨터 분야에서 에이전트의 개념은 전자 상거래, 정보 검색과 같은 많은 어플리케이션들에 응용되어 중요 시 되고 있다. 하지만, 아직까지 지능성을 가진 테스트 도구는 없었다. 이 논문에서 제안하는 테스트 에이전트 시스템은 에이전트의 특성을 가지고 테스터를 도와주는 테스트 도구이다. 테스트 에이전트 시스템은 객체지향 테스트 프로세스를 따라 테스터의 일을 대행해 주고, 테스터의 간섭을 최소화 시켜 준다. 이 시스템은 자동 생성된 많은 양의 테스트케이스에서 중복이 없고 일관성 있는 테스트케이스를 지능적으로 선택하여 테스트 시간을 단축시켜 준다. 테스트 에이전트 시스템은 3개의 에이전트 User Interface Agent, Test Case Selection & Testing Agent, Regression Test Agent로 구성된다. 특히 Test Case Selection & Testing Agent은 RE-Rule과 CTS-Rule을 통하여 중복이 없고 일관성 있는 테스트케이스를 지능적으로 선택하며, Regression Test Agent는 RRTIS-Rule을 통해 리그래션 테스트 항목을 지능적으로 선택한다.

• International Journal of Contents
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• v.15 no.1
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• pp.1-9
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• 2019

Since the VR market is expected to have a high growth, this study aimed to investigate the human factor-related determinants of user satisfaction with mobile VR headsets. A pre-study of customer reviews was conducted with the help of semantic network analysis to identify the core keywords for understanding negative and positive predictors of mobile VR headset experiences. Through laboratory testing with three different commercial models, the main study measured and identified the predictors of user satisfaction. From the results, five factors were extracted as valid predictor variables and used for regression analysis. These factors were immersion, VR sickness, usability, wear-ability and menu navigation interface. All the five predictors were proved to be significant determinants of the perceived user satisfaction with mobile VR headsets. Usability was the strongest predictor, followed by VR sickness and wear-ability. Practical and theoretical implications of the results were discussed.