• 동력기계공학회지
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• 제3권4호
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• pp.51-56
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• 1999

The ultrasonic method, which is well known as nondestructive test method, is widely used to evaluate the material damage due to degradation. However, this method is just used for measuring the crack size and the thickness loss of the tube. The purpose of this study is to investigate the applicability of the ultrasonic technique for the evaluation of marine diesel engine exhaust valve and to suggest the correlations between the ultrasonic characteristics and valve degradation. From the evaluation of the results obtained, the technique of using the ultrasonic property was founds to be a efficient method to evaluate the degree of marine diesel engine exhaust valve by nondestructive test.

• 한국해양공학회지
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• 제14권4호
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• pp.68-72
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• 2000

The ultrasonic method, which is well known as nondestructive test method, is widely used to evaluate the material damage due to degradation. However, this method is just used for measuring the crack size and the thickness loss of the tube. The purpose of this study is to investigate the application of the ultrasonic technique for the evaluation of marine diesel engine exhaust valve and to suggest the correlation between the ultrasonic characteristics and valve degradation. From the evaluation of the results obtained, the technique of using the ultrasonic property was founds to be a efficient method to degree of marine diesel engine exhaust valve by nondestructive test.

• 한국구조물진단유지관리공학회 논문집
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• 제5권4호
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• pp.155-160
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• 2001

KS-code(KS B 0896) for nondestructive ultrasonic testing classifies the quality level by relative flaw size only. But flaw position is more important than the flaw size. Test blocks having artificial holes near surface show lower yield load than the blocks having deeply located holes from the surface. So, level calibration table was proposed for classifying the quality level of welded steel structures.

• 비파괴검사학회지
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• 제37권2호
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• pp.115-121
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• 2017

The nonlinear ultrasonic technique is a potential nondestructive method to evaluate material degradation, in which the ultrasonic nonlinearity parameter is usually measured. The ultrasonic nonlinearity parameter is defined by the elastic nonlinearity coefficients of the nonlinear Hooke's equation. Therefore, even though the ultrasonic nonlinearity parameter is not equal to the elastic nonlinearity parameter, they have a close relationship. However, there has been no experimental verification of the relationship between the ultrasonic and elastic nonlinearity parameters. In this study, the relationship is experimentally verified for a heat-treated aluminum alloy. Specimens of the aluminum alloy were heat-treated at $300^{\circ}C$ for different periods of time (0, 1, 2, 5, 10, 20, and 50 h). The relative ultrasonic nonlinearity parameter of each specimen was then measured, and the elastic nonlinearity parameter was determined by fitting the stress-strain curve obtained from a tensile test to the 5th-order-polynomial nonlinear Hooke's equation. The results showed that the variations in these parameters were in good agreement with each other.

• 연구논문집
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• 통권28호
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• pp.229-238
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• 1998

비파괴평가의 대상이 되는 소재나 부품은 관련 표준시험편을 이용하여 평가되고, 표준시험편은 평가대상과 동일 또는 유사한 재질로 제작되어야 한다고 규정하고 있다. 따라서 비파괴평가가 요구되는 소재나 부품을 생산, 외국에 수출하기 위해서는 반드시 공인된 설비와 품질관리 체계로부터의 인증이 선행되어야 한다. 본 논문에서는 초음파를 이용한 항공기용 Udimet 720Li 디스크의 비파괴평가를 위하여 ASTM에 규정되어 있는 4340강 초음파 표준시험편의 적용타당성을 제시하였다. 현미경 시험을 통하여 Udimet 720Li 합금의 미세조직을 규명하고, 고출력 초음파 분석시스템을 이용한 펄스의 위상값을 측정하는 방법으로 4340강 표준시험편 및 Udimet 720Li 합금의 초음파 속도와 감쇠값을 구하였다. 결론적으로 4340강 초음파 표준시험편이 Udimet 720Li 디스크의 평가를 위한 표준시험편으로 사용될수 있음을 증명하였다.

• 대한기계학회논문집A
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• 제24권1호
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• pp.52-61
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• 2000

The role of quantitative nondestructive evaluation of defects is becoming more important to assure the reliability and the safety of structure, which can eventually be used for residual life evaluation of structure on the basis of fracture mechanics approach. Although ultrasonic technique is one of the most widely used techniques for application of practical field test among the various nondestructive evaluation technique, there are still some problems to be solved in effective extraction and classification of ultrasonic signal from their noisy ultrasonic waveforms. Therefore, crack size determination through a neural network based on the back-propagation algorithm using back-scattered ultrasonic signals is established in this study. For this purpose, aluminum plate containing vertical or inclined surface breaking crack with different crack length was used to receive the back-scattered ultrasonic signals by pulse echo method. Some features extracted from these signals and sizes of cracks were used to train neural network and the neural network's output of the crack size are compared with the true answer.

• 비파괴검사학회지
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• 제29권4호
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• pp.283-292
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• 2009

Laser-based ultrasonic sensing requires the probe with fixed fecal length, but this requirement is not essential in laser-based ultrasonic generation. Based on this fact, we designed a pulsed laser-based ultrasonic wave propagation imaging (UWPI) system with a tilting mirror system for rapid scanning of target, and an in-line band-pass filtering capable of ultrasoaic mode selection. 1D-temporal averaging, 2D-spatial averaging, and 3D-data structure building algorithms were developed far clearer results allowing fur higher damage detectability. The imaging results on a flat stainless steel plate were presented in movie and snapshot formats which showed the propagation of ultrasound visible as a concentric wavefield emerging from the location of an ultrasonic sensor. A hole in the plate with a diameter of 1 mm was indicated by the scattering wavefields. The results showed that this robust UWPI system is independent of focal length and reference data requirements.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.389-392
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• 2000

This paper provide nondestructive test method of concrete by applying ultrasonic pulse test. Whinstone aggregates produced from cheju island are used for coarse aggregate. The purpose of this study is to contribute to the standardization of nondestructive test for estimating compressive strength of concrete manufactured from cheju island. According to experimental results, it is found that compressive strength of Whinstone aggregates concrete shows higher than that of granite stone concrete, whereas ultrasonic pulse of Whinstone aggregates concrete shows lower that of granite concrete Based on the results of this study, estimation formula compressive strength by ultrasonic pulse test are presented in Fig 2.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.348-352
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• 1995

In the conventional linear elasticity, ultrasonic velocity is determined by elastic modulus and density of te medium which ultrasonic wave propagates through. But, practical ultrsonic wave depends on the stress acting in the medium, and as the stress increases such dependency becomes nonlinear. This nonlinear dependencyof ultrasonic velocity on stress can be identified by using nonlinear elastic modulus up to 4th order. In thid paper, with the above background relationships between nonlinear elastic modulus and the internalstatus of materials, normal, plastic deformed or heat stressed, are discussed. For this purpose, a new type of measuring system extended from the general nondestructive UT(ultrasonic test) equipment is constructed.

• Journal of the Korean Wood Science and Technology
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• 제31권6호
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• pp.45-54
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• 2003

The density and strength of wood is affected by degradations and defects, such as voids and knots. Old wooden structures such as traditional cultural properties have been deteriorated by these types of defects. They were evaluated by a visual observation that is difficult to evaluate the inner deterioration in structures. In this study, three nondestructive testing techniques were investigated to detect the wooden structural members. Ultrasonic stress wave tests, drilling resistance tests and visual inspections were used to examine the structural wood members. Patterns of Resistograph using by drilling resistance tests could indicate the features of internal wood such as voids, knots, decay, fungi, and so on. The technique just like as ultrasonic stress wave tests, however, difficult to detect exactly area where small amounts of internal deterioration in logs are. In spite of results of ultrasonic stress wave test, the internal deterioration of wooden structural members could be evaluated by the relationship between ultrasonic stress wave tests and drilling resistance tests.