• 비파괴검사학회지
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• 제37권2호
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• pp.84-90
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• 2017

An ultrasonic synthetic aperture focusing technique (SAFT) using a root mean square (RMS) velocity model is proposed for pulse-echo immersion testing to improve the computational efficiency. Considering the immersion ultrasonic testing of a steel block as an example, three kinds of imaging were studied (B-Scan, SAFT imaging based on ray tracing technology and RMS velocity). The experimental results show that two kinds of SAFT imaging have almost the same imaging performance, while the efficiency of RMS velocity SAFT imaging is almost 25 times greater than the SAFT based on Snell's law.

• 비파괴검사학회지
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• 제28권1호
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• pp.40-45
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• 2008

고체의 탄성 계수를 구하기 위한 방법으로 초음파의 종파와 횡파 속도를 측정하기 위하여 기존의 접촉식 초음파 시험법 대신 수침 초음파 시험법을 사용하였다. 통상적으로 수침법에서 종파 에코만 고려하는 것과 달리 모드 변환에 의한 횡파 에코를 찾아서 횡파 속도를 측정하였다. 물질의 두께를 알 수 없어 종파와 횡파 속도를 구할 수 없는 경우에도 두 속도의 비를 이용하여 포아송비를 구할 수 있었다. 다양한 재료를 대상으로 이 방법을 적용한 결과, 속도가 빠른 재료이거나, 포아송비가 작을수록 수침법에 의해 측정한 값이 정확하여 이러한 특징을 가진 세라믹이나 고강도 재료가 이 방법을 통한 종파와 횡파 속도 측정에 적당함을 알 수 있었다.

• 비파괴검사학회지
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• 제28권6호
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• pp.519-523
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• 2008

Poisson's ratio is one of elastic constants of elastic solids. However, it has not attracted attention due to its narrow range and difficult measurement. Transverse wave velocity as well as longitudinal wave velocity should be measured for nondestructive measurement of Poisson's ratio. Hard couplant for transverse wave prevents transducer from scanning over specimen. In the present work, a novel measurement of Poisson's ratio distribution was proposed. Immersion method was employed for the scanning over the specimen. Echo signals of normal beam longitudinal wave were collected. Transverse wave modes generated by mode conversion were identified. From transit time of longitudinal and transverse waves, Poisson's ratio can be determined without information of specimen thickness. This technique was demonstrated for aluminum and steel specimens.

• 비파괴검사학회지
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• 제24권4호
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• pp.348-353
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• 2004

이 연구는 터빈베어링의 신뢰성을 평가하기 위하여 초음파 C-Scan 방법을 적용한 기술이다. 수침법에 관한 연구는 실험실과 현장검사 적용에 광범위하게 사용되는 기술이다. 여기에서는 C-Scan 방법을 이용하여 베어링의 모재와 Babbitt 금속간 경계부의 상태를 평가하였다. 수침법 C-Scan 방법에 의한 초음파 영상은 베어링 경계부의 상태를 확인하는데 효과적인 방법으로 사용될 수 있었다. 초음파 영상의 분해능을 높이기 위하여 집속형 탐촉자를 사용하고, Babbitt 금속과 베어링 모재간의 접합경계면에서 발생하는 초음파 음압 반사율을 측정하여 결함의 검출과 면적을 추정할 수 있었다. 초음파 수침법은 베어링 접합부의 박리위치와 박리면적의 경계면을 결정하여 크기를 계산하는데 아주 유용하게 사용될 수 있는 기술이며, 이 연구에서 개발된 기술은 화력발전소에서 사용되고 있는 터빈베어링의 건전성을 확보하는데 적용되었다.

• 비파괴검사학회지
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• 제26권3호
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• pp.153-161
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• 2006

A simulation program SIMULTSONIC is under development at CNDE to help determine and/or help optimize ultrasonic probe locations for inspection of complex components. SIMULTSONIC provides a ray-trace based assessment for immersion and contact modes of inspection. The code written in Visual C++ operating in Microsoft Windows environment provides an interactive user interface. In this paper, a description of the various features of SIMULTSONIC is given followed by examples illustrating the capability of SIMULTSONIC to deal with inspection of canonical objects such as pipes. In particular, the use of SIMULTSONIC in the inspection of very thin-walled pipes (with 450 urn wall thickness) is described. Ray trace based assessment was done using SIMULTSONIC to determine the standoff distance and the angle of oblique incidence for an immersion mode focused transducer. A 3-cycle Hanning window pulse was chosen for simulations. Experiments were carried out to validate the simulations. The A-scans and the associated B-Scan images obtained through simulations show good correlation with experimental results, both with the arrival time of the signal as well as with the signal amplitudes.

• 비파괴검사학회지
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• 제30권6호
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• pp.548-557
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• 2010

An ultrasonic resonance scattering spectroscopy technique is developed and applied for reconstructing elastic constants of a transversely isotropic cylindrical component. Immersion ultrasonic measurements are performed on tube samples made from a boron/aluminum composite material to obtain resonance frequencies and dispersion curves of different guided wave modes propagating in the tube. Theoretical analysis on the acoustic resonance scattering from a transversely isotropic cylindrical tube is also performed, from which complete backscattering and resonance scattering spectra and theoretical dispersion curves are calculated. A sensitive change of the dispersion curves to the elastic properties of the composite tube is observed for both normal and oblique incidences; this is exploited for a systematic evaluation of damage and elastic constants of the composite tube samples. The elastic constants of two boron/aluminum composite tube samples manufactured under different conditions are reconstructed through an optimization procedure in which the residual between the experimental and theoretical phase velocities (dispersion curves) is minimized.

• 한국자동차공학회논문집
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• 제16권5호
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• pp.8-14
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• 2008

For nondestructive inspection of electron beam (EB) welding part in automotive power transmission assembly, a pulse-echo ultrasonic testing apparatus in water immersion has been applied using the ultrasonic waves with a frequency of 10MHz. However various problems have appeared during the ultrasonic inspection, which led to some significant mistakes in automatic quality evaluation of the welding parts. Experimental study showed that the state of water couplant medium containing some amount of contaminants, rusts and anti-corrosion agents had considerable influences on the reduction of ultrasonic amplitudes during wave propagation. The amplitude reduction depending on the coupling medium state could bring about some mis-diagnoses for defects in the welding parts. The results proposed that for a reliable inspection of defects in welds the state of water medium should be kept in about 15 volume fractions (vol.%) of anti-corrosion agents and in minimized contaminants.

• 비파괴검사학회지
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• 제29권6호
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• pp.586-590
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• 2009

Poisson's ratio, one of elastic constants of elastic solids, has not attracted attention due to its narrow range and difficult measurement. Transverse wave velocity as well as longitudinal wave velocity should be measured for nondestructive measurement of Poisson's ratio. Rigid couplants for transverse wave is one of obstacle for scanning over specimen. In the present work, a novel measurement of Poisson's ratio distribution was applied. Immersion method was employed for the scanning over the specimen. Echo signals of normal beam longitudinal wave were collected, and transverse wave modes generated by mode conversion were identified. From transit time of longitudinal and transverse waves, Poisson's ratio was determined without the information of specimen thickness. Poisson's ratio distribution of the carbon steel weldment was mapped. Heat affected zone of the weldment was clearly distinguished from base and filler metals.

• 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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• 제12권3호
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• pp.33-39
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• 1992

This paper presents a summary of the immersion ultrasonic test to analyze the quality of diffusion bonding parts. The most important property of diffusion bonding parts is bonding strength, and that can be obtained by shear test. By comparing among data obtained by ultrasonic test(C-Scan) and those by shear test (bonding strength), these data are shown to be in good relation. Therefore ultrasonic C-Scan test result can be used successfully in quantitative quality control for diffusion bonded parts.