• 비파괴검사학회지
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• 제13권3호
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• pp.7-13
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• 1993

AISI 4130 금속재를 사용한 균열 컴팩터 인장시편의 파괴거동이 음향방출(AE) 및 초음파 C-scan을 이용하여 조사되었다. 모든 시편들을 특정 수준의 하중까지 증가시키면서, 크랙 개구변위 (COD)와 더불어 여러가지의 음향방출 인자들을 얻었다. 크랙 선단의 크랙 개구변위와 손상(소성)역을 계산하기 위하여 탄소성 유한요소 해석이 수행되었다. 펄스-반사, 침수형으로한 초음파 C-scan은 손상역 크기와 상사시키기 위하여 행해졌다. 유한요소 해석 결과와 측정된 크랙개구변위는 만족할 정도로 일치하였다. 음향방출 결과에서, 시험시편들은 연성거동을 나타내었다. 총 사상수대 크랙 개구변위의 기울기는 크랙 개시점을 결정하는 데에 유용하였다. 예비 시험적인 C-scan 화상은 손상역의 초음파 진폭변화를 보여주었고, 손상역의 형상 및 크기가 유한요소 결과와 정성적으로 부합되었다. 손상역 크기에 관한 추가적인 연구가 요약되었다.

• 한국전기전자재료학회논문지
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• 제32권3호
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• pp.207-212
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• 2019

A flat-type piezoelectric ceramic ultrasonic transmitter was successfully fabricated for application in acoustic devices with cone-free diaphragms. The transmitter, possessing a center frequency of 40.6 kHz, exhibited a higher displacement characteristic for a multilayer type compared with a single layer type. Surface roughness treatment of an Al elastic diaphragm influenced a slight increase (1.1 dB) in the sound pressure level (SPL) at $10V_{rms}$ due to the enlarged surface area. The fabricated multilayer piezoelectric ceramic ultrasonic transmitter showed increasing SPL with increasing input voltage, with a maximum SPL of approximately 123.6 dB at $10V_{rms}$. This implies a doubly increased SPL density of $3.6dB/mm^3$, superior to that of a commercial open-type transmitter with a cone.

• 한국전기전자재료학회논문지
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• 제27권5호
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• pp.286-291
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• 2014

In this study, novel ultrasonic rotary motor of hexadecagon shape stator was proposed. Stator of the hexadecagon ultrasonic motor was composed of an elastic ring and ceramics. The elastic ring had sixteen sides and sixteen angular points. Eight ceramics were attached on the outer surface of the eight sides of the ring. When rotor of cylindrical shaft was inserted inside of the ring stator, central lines of the sixteen sides of the stator hold the shaft by the slight pressures(frictions). This slight pressure was a preload of the motor and it could be controlled by radius and thickness of the ring. When two sinusoidal voltages which have 90 degree phase difference were applied to each four ceramics, elliptical displacements of inner surface of the ring were obtained. These elliptical displacements of the inner surface rotated the shaft rotor through the frictions. The proposed hexadecagon ultrasonic motor was designed and analyzed by using the finite element method (FEM), depending on materials of the elastic ring. Based on the FEM results, one model of motor which showed maximum displacement at contact points was chosen and fabricated. And characteristics of the motor were compared with simulated results. When the motor was fabricated with these results, EL20ET0.5CT0.5CW2 model showed 115[rpm] speed about input voltage of 60[Vrms] at 65.6[kHz]. And the maximum torque of 6[gfcm] was obtained. From these results, the hexadecagon shaped ultrasonic motor can be used to actuator for optical device which needs detailed position control. Also it can be used to medical and portable device by reducing size and weight.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 Techno-Fair 및 추계학술대회 논문집 전기물성,응용부문
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• pp.175-176
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• 2008

An ultrasonic motor of high torque with a new configuration for application in automobiles is proposed. The newly designed stator is two sided vibrator consisting of a toothed metal disk with a piezoelectric ceramic ring bonded on both faces of the disk which generates a flexural traveling wave along the circumference of disk. In this configuration, the displacement on the surface of stator may not be confined. It also produces a large vibrating force and amplitude because the vibrator is sandwiched by two piezoelectric plates. It is possible to increase the torque by improving the vibration characteristics. To compute the vibration mode of the motor of diameter 48 mm, the finite element method was used. A 6th mode was chosen as the operation mode with a resonance frequency of about 64.4 kHz. According to this design and measured its performance, a prototype was fabricated. The performance measurement of the prototype motor showed that its stall torque was about 1.8 Nm and efficiency was 37 % at 60 % of the maximum torque.

• 대한의용생체공학회:의공학회지
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• 제27권3호
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• pp.117-124
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• 2006

Recently, active research has been going on to measure the elastic modulus of human soft tissue with medical ultrasound imaging systems for the purpose of diagnosing cancers or tumors which have been difficult to detect with conventional B-mode imaging techniques. In this paper, a real-time ultrasonic elasticity imaging system is implemented in software on a Pentium processor-based ultrasonic diagnostic imaging system. Soft tissue is subjected to external vibration, and the resulting tissue displacements change the phase of received echoes, which is in turn used to estimate tissue elasticity. It was confirmed from experiment with a phantom that the implemented elasticity imaging system could differentiate between soft and hard regions, where the latter is twice harder than the former, while operating at an adequate frame rate of 20 frames/s.

• 비파괴검사학회지
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• 제30권5호
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• pp.458-463
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• 2010

음향 비선형성은 재료 물성의 미세한 변화에 민감하기 때문에, 이를 측정하는 비선형 초음파 기술은 재료의 열화나 피로를 평가할 수 있는 기법으로 연구되어 왔다. 하지만 벌크파를 이용하는 일반적인 비선형 초음파 기법은 얇은 판재에 적용하는 것에는 여러 한계가 있다. 이와 같은 경우에는 비선형 Lamb 파의 사용을 생각할 수 있지만, Lamb 파는 벌크파와 매우 다른 전파 특성을 가지고 있어 그 비선형 특성에 대한 별도의 연구를 필요로 한다. 이를 위해 본 연구에서는 Lamb 파에서 비선형성에 의해 전파하면서 누적 성장할 수 있는 2차 고조파 모드의 발생 조건을 분석하였으며, 그 결과 네 가지 조건, 즉 (1) phase matching, (2) non-zero power flux, (3) group velocity matching, (4) non-zero out-of-plane displacement 를 제시하였다. 그리고 제시된 조건으로 알루미늄 판재에 대책 실험한 결과 이론 예측과 동일하게 전파 거리에 따라 2차 고조파 성분의 크기와 비선형 파라미터가 증가하였고, Al6061-T6 과 Al1100-H14에서 측정된 상대적인 비선형 파라미터의 비율이 이론적인 비율과 근접함을 보였다.

• 대한기계학회논문집A
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• 제38권7호
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• pp.711-717
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• 2014

본 논문에서는 초고주기피로영역의 가속시험 방법인 초음파 피로시험에 대해 20 kHz 근처에서 시험편 게이지부의 동적거동을 유한요소해석으로 검토하였다. 실제 실험에서 시험편에 작용하는 응력은 시험편의 형상과 변위를 통해 식으로 계산되는데 여기서 가정하는 시험편의 형상과 실제 시험편의 형상에 차이가 발생한다. 실험으로 구해진 응력과 유한요소 동적 해석의 결과를 비교하고 형상차이에 따른 응력분포를 확인하였다. 또한, 이론적으로 생각하는 초음파 피로시험기의 동적 거동을 가시적으로 확인하여 초음파 피로시험의 정확성을 확보하였다.

• 한국안전학회지
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• 제32권5호
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• pp.62-68
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• 2017

It is necessary to analyze on the compressive strength among material properties of concrete for confirming damages of architectures due to large explosion. A non destructive test is known as the representative methods estimating compressive strength and ultrasonic pulse velocity, rebound hardness test are widely used because of their simplicity, convenience. But combined method supplementing two types is applied at now as they are affected by the characteristics of test specimen. In this research to check damages on the members of structure before and after explosion, the characteristics of compressive strength are compared and analyzed through a real explosion test prior to full scale structures. The test results showed that the larger the TNT powder and the shorter the distance, the greater the decrease in strength before and after the explosion and that the largest displacement and moment for the explosive load and the greatest decrease in the strength at the central part. Due to the surface condition and the thickness variation of the concrete specimens, the standard deviation value is the smallest in the combining method of fusion of the ultrasonic method and rebound hardness method. Thus, the combining method can be one of appropriate methods to evaluate the strength in the reinforced concrete structures damaged by the explosion.

• Corrosion Science and Technology
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• 제19권4호
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• pp.163-173
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• 2020

Cavitation corrosion in many industrial plants has recently become a serious issue. Cavitation corrosion has generally been investigated using a vibratory method based on ASTM G32 standard, and the test can be divided into direct cavitation and indirect cavitation. Cavitation corrosion test uses the vibration frequency of the horn of 20 kHz with constant peak-to-peak displacement amplitude. In this work, the peak-to-peak amplitude was controlled from 15 ㎛ to 85 ㎛, and electrochemical measurements were obtained during indirect cavitation. The relationship between cavitation corrosion rate and electrochemical properties was discussed. Corrosion steps of carbon steel at the initial stage under cavitation condition in 3.5 % NaCl can be proposed. When the cavitation strength is relatively low, corrosion of the steel is more affected by the electrochemical process than by the mechanical process; but when the cavitation strength is relatively high, corrosion of the steel is affected more by the mechanical process than by the electrochemical process. This work confirmed that the critical ultrasonic amplitude of 0.42 %C carbon steel is 53.8 ㎛, and when the amplitude is less than 53.8 ㎛, the corrosion effect during the cavitation corrosion process is higher than the mechanical effect.

• 비파괴검사학회지
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• 제28권4호
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• pp.352-357
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• 2008

구조물의 안전 보장 문제에 있어 재료의 파손 이전에 미세균열을 검출하는 것은 매우 중요하다. 비선형 초음파 기법은 일반적인 초음파 기법보다 미세결함에 민감하기 때문에 이를 이용하여 비파괴적으로 구조물이나 재료의 건전성을 진단하는 방법이 주목받고 있다. 계면접촉에 의한 비선형 초음파 효과는 초음파가 내부의 미세 균열에 입사될 때 미세균열면에서 응력과 변위가 비선형 관계를 가지고, 이에 의해 파가 왜곡되어 그 결과 고조파 성분이 발생하는 현상이다. 본 연구에서는 이러한 비선형 초음파 기법의 적용가능성을 알루미늄 시편에 인위적으로 발생시킨 피로균열을 대상으로 실험적으로 검증하고자 하였다. 이를 위해 V-노치를 갖는 A16061의 피로균열 시험편을 준비하고, 균열방향으로 2차 고조파 성분의 크기를 측정하였다. 실험결과 미세균열에서 고조파 성분이 크게 발생하며 이 기법에 의한 균열깊이 측정이 일반적인 반사파의 6 dB drop법보다 정확함을 확인하였다.