• 한국압력기기공학회 논문집
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• 제6권1호
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• pp.23-28
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• 2010

To enhance the reliability of ultrasonic testing system, MOST(Ministry of Science and Technology) bulletin 2004-13 was published in 2004.6 requiring performance demonstration in ultrasonic examination and MEST(Ministry of Education, Science and Technology) 2009-37 was published in 2009.9(formerly MOST bulletin 2004-13). In order to meet the MEST bulletin requirement and increase the reliability of ultrasonic testing, all the ultrasonic examination procedure and equipment should be performance demonstrated and qualified. In this paper, generic procedure for the ultrasonic examination of dissimilar metal welds are described and new technique are introduced.

• 비파괴검사학회지
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• 제11권2호
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• pp.42-47
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• 1991

Nondestructive evaluation study was made on creep damage materials by ultrasonic spectrum analysis. The evaluation methods was developed in order to predict the change of ultrasonic attenuation with increasing creep damage. A new algorithm for the improvement of measuring accuracy of ultrasonic attenuation using a spectrum analysis has been developed. Normally, the ultrasonic attenuation is evaluated from 1st and 2nd peak values of the pulse-echo ultrasonic wave. The algorithm developed is incorporated in a measuring system which consists of a personal computer with ultrasonic apparatus and a digital storage oscilloscope. By the spectrum analysis method, it become popssible to describe approximately the attenuation change with increassing creep damage in Cr-Mo-V forging.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.268-271
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• 2004

Non-contact technique should be developed for receiving ultrasonic wave for on-line monitoring of processing defects of fiber reinforced composites, since couplant must be applied on composite materials when conventional ultrasonic testing technique was used. Restriction of conventional ultrasonic testing technique was proven by transmitting and receiving ultrasonic wave on CFRP in various direction of wave propagation with various incident angle of ultrasonic beam. Air-coupled transducer and laser interferometer were applied for non-contacting reception of ultrasonic wave in fiber reinforced composite materials. Air-coupled transducer has optimal sensitivity and frequency band of 300kHz has homogeneous characteristics on direction of wave propagation.

• 비파괴검사학회지
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• 제33권2호
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• pp.232-240
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• 2013

This paper presents recent advances in damage visualization algorithms of laser generated ultrasonic propagation imaging(UPI) system. An effective damage evaluation method is required to extract correct information from raw data to properly characterize anomalies present in structure. A temporal-reference free imaging system provides easy and rapid defect inspection capability with less computational complexity. In this paper a number of methods such as ultrasonic wave propagation imaging(UWPI), anomalous wave propagation imaging(AWPI), ultrasonic spectral imaging(USI), wavelet ultrasonic propagation imaging(WUPI), variable time window amplitude mapping(VTWAM), time point adjustment(TPA), time of flight and amplitude mapping(ToF&Amp) and ultrasonic wavenumber imaging(UWI) are discussed with instances of successful implementation on various structures.

• 비파괴검사학회지
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• 제28권3호
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• pp.279-284
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• 2008

The firmness of fruit is one of the most important quality factors and is highly correlated to the elastic modulus. In this study, the ultrasonic transmission method was applied to evaluate the elastic modulus of the apple. In order to transmit and receive the ultrasonic wave through the whole apple, the ultrasonic measurement setup consisted of ultrasonic pulser, two specially fabricated ultrasonic transducers for fruit and digital storage oscilloscope. Ultrasonic parameters such as ultrasonic wave velocity, apparent attenuation, and peak frequencies were analyzed. The elastic modulus of apple was measured by using compression test apparatus. The correlations between ultrasonic parameters and elastic modulus were analyzed. A multiple linear regression model describing the relationship between elastic modulus and ultrasonic parameters was proposed.

• 비파괴검사학회지
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• 제22권6호
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• pp.621-626
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• 2002

The amplitude of a back-wall echo depends on the reflection coefficient of the interface between a transducer and a test material when using contact pulse-echo ultrasonic testing. A couplant is used to transmit ultrasonic energy across the interface, but has an influence on the amplitude of the pulse-echo signal. To investigate the couplant effect on pulse-echo ultrasonic testing, back-wall echoes are measured by using various couplants made of water and glycerine in a carbon and austenitic stainless steel specimens. The amplitude of the first back-wall echo and the apparent attenuation coefficient increases with the acoustic impedance of the couplant. The couplant having a higher value of the transmission coefficient is more effective for flaw detection. The reflection coefficient should be known in order to measure the attenuation coefficient of the test material.

• 비파괴검사학회지
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• 제32권5호
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• pp.540-544
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• 2012

위상배열 기술에 기반을 둔 통상의 초음파검사에서처럼, 자왜형 원거리 초음파검사에서도 실시간 수신신호 처리를 위해 복잡한 전자회로들을 사용하여왔다. 본 연구는 위상 보상, 노이즈 필터링, 파형 변환 등과 같은 필수적인 작업들을 기존의 하드웨어 접근보다는 소프트웨어 접근을 이용하여 수행할 때, 보다 유연하고 효율적인 실시간 신호처리가 가능해진다는 것을 보여준다. 이는 비용효율적인 원거리 초음파검사 시스템 구축과 검사 결과 분석에 기여할 것이다.

• 비파괴검사학회지
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• 제37권1호
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• pp.37-43
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• 2017

초음파탐상법을 이용하여 마이크로미터의 크기 작은 결함을 검출하기 위해서는 높은 공진주파수와 큰 분해능의 초음파 변환기가 필요하다. 초음파 변환기의 공진주파수와 분해능은 변환기에 사용된 압전소자의 두께, 후면재 및 탐상 시스템 간의 전기 임피던스 정합과 밀접한 관련이 있으며, 이 중 전기 임피던스 매칭은 초음파 변환기와 초음파탐상 시스템 사이의 서로 다른 입 출력단을 연결하는 과정에서, 두 연결단의 전기적 임피던스 차이에 의한 에너지 반사와 손실을 줄이는 중요한 역할을 한다. 임피던스 정합에서 흔히 많이 사용하는 방법은 LC-정합회로이다. 이러한 LC-정합을 통해 탐상 시스템과 초음파 변환기의 전기 임피던스를 $50{\Omega}$으로 맞추어 두 연결단 사이의 임피던스 차이를 보정해 줌으로서 초음파 변환기에서 발생되는 전기신호의 손실을 줄 수 있다. 본 연구에서는 15 MHz의 공진주파수를 가지는 광대역 수침형 초음파 탐촉자를 제작하고 광대역 특성을 갖는 초음파 변환기를 위한 LC 임피던스 정합법을 적용하였다.

• 비파괴검사학회지
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• 제24권2호
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• pp.151-157
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• 2004

초음파검사는 재료의 표면 또는 내부에 존재하는 불 연속부를 검출하기 위해, 초음파를 재료에 전달시켜 검사하는 비파괴검사법의 일종이다. 이러한 일반 초음파검사 방법 및 일반 결함평가 방법은 복잡한 형상에서 반사되는 신호로부터 결함을 구분하기가 어려워 결함의 평가 및 검사결과에 신뢰성이 떨어지고 있는 실정이다. 따라서 이러한 crack성 결함의 발생 가능성이 높으나 기존의 초음파검사 방법으로는 결함 판별에 어려움이 있는 설비에서의 검사방법 및 결함평가 방법의 제고가 필수 불가결한 실정이다. 본 연구에서는 위상배열 초음파를 사용하여 크랙 검출능력이 높고 길이 평가가 가장 정확한 방사각도를 규명하고, 주요발전설비중 하나인 터빈에 적용하였다. 기존의 초음파 검사 방식이 아닌 위상배열 초음파를 이용하여 결함의 크기를 평가할 수 있는 신 기법 및 이를 이용하여 터빈 블레이드 루트부 내에 존재하는 미세 결함에 대하여 크기평가 방법 및 결함탐지 방법에 대하여 고찰하였다.

• Journal of Biosystems Engineering
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• 제38권3호
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• pp.192-198
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• 2013

Purpose: Methods for non-destructive estimation of product quality have been reported in various industrial fields, but the application of ultrasonic techniques for the agricultural products of potatoes, pears, apples, watermelons, kiwis and tomatoes etc. have been rarely reported since the application of a contact-type ultrasonic transducer in agricultural products is very difficult. Therefore, this study sought to determine the firmness of apples using non-contact ultrasonic techniques. Methods: For this experiment, an ultrasonic experimental tester using a non-contact ultrasonic transducer was created, and a signal processing program was used to analyze the acquired ultrasonic reflected signal. Also, a universal testing machine was used to measure firmness parameters of the apples such as bioyield strength, a firmness factor, after the ultrasonic tests had been performed. Results: Six distance correction factors were calculated to obtain consistent values of ultrasonic properties regardless of the distance between the transducer and the surface of the subject. We developed prediction models of the bioyield strength using the distance correction factors. Conclusions: The optimum prediction model of the bioyield strength of apples using a non-contact ultrasonic technique was a multiple regression model ($R^2=0.9402$).