• 비파괴검사학회지
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• 제34권2호
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• pp.155-164
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• 2014

탄소섬유강화 복합재료(carbon fiber reinforced plastics; 이하 CFRP)는 금속재료에 비해 중량이 가벼우면서도 비강도와 비강성이 높은 재료로 항공기, 자동차, 선박 등의 다양한 분야에서 적용이 증가하고 있다. CFRP는 정적부하에 대해서는 우수한 역학적 특성을 가진 반면에 고온 다습한 환경에서는 우수한 역학적 특성을 기대할 수 없고, 복합재료의 유용한 기계적 성질이 장시간 주위 환경에 놓여 있어도 충분히 유지되어야 하지만 온도, 습도 등과 같은 환경적 요인으로 수분이 복합재료 내로 침투하여 기지의 분자 배열 및 화학적 성질을 변화시키고 복합재료의 계면 특성 및 구성 재질의 기계적 성질을 저하시킨다. 항공기의 경우 운항 시에 CFRP가 고온 다습한 환경조건에 장시간 노출되게 되면 CFRP 내부로 수분이 흡수되게 되는데 CFRP 내부에 흡수된 수분은 체적팽창을 야기시키고 내부 응력상태를 변화시킬 뿐만 아니라 섬유와 기지의 화학적 결합을 분리시킴으로써 접합강도를 급격히 저하시키게 된다. 따라서 CFRP를 사용하는 항공기의 구조 건전성 확보를 위하여 실제 환경에서의 특성 변화를 연구할 필요가 있다. 본 연구에서는 공기결합 초음파탐상검사(air coupled ultrasonic testing; 이하 ACUT) 시스템을 이용하여 흡습된 CFRP의 비파괴적 특성을 평가하고자 하였다. CFRP 시험편을 직접 제작한 후 고온다습한 환경을 설정하기 위해 항온수조를 이용하여 $75^{\circ}C$의 증류수에 30일, 60일, 120일간 침지하였고, ACUT를 이용하여 흡습에 의한 CFRP 시험편의 특성 변화를 초음파 C-scan 이미지와 흡습 전과 후의 신호의 전파시간 변화를 통해 초음파 신호 특성 변화를 고찰하였다. 또한 전단강도 평가를 통해 흡습에 의한 기계적 특성 변화를 실험적으로 검증하였다.

• The Journal of the Acoustical Society of Korea
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• 제16권1E호
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• pp.24-28
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• 1997

Ultrasonic relaxation measurements for imidazole and its derivative in phosphate buffer exhibit a high peak of absorption at neutral pH. Near neutral pH, protolysis and hydrosis may be neglected and the essential reaction only consists of a direct proton-exchange. The kinetics constants and the volume changes for the proton transfer reaction with the protonated imidazole and 2-methylimidazole have been determined at 25℃. The kinetics constants are 7.2×108s-1M-1for imidazole and 1.7×108s-1M-1 for 2-methylimidazole. The kinetics constants are used to estimate the spectrum of relaxation times and acoustic relaxation amplitude associated with intermolecular and intramolecular proton-exchange reactions in bilogical media. It is concluded that the magnitude of the acoustic absorption reasonalbly attributable to the perturbation of proton-transfer equilibria between imidazole and inorganic phosphate is comparable in magnitude with the acoustic absorption observed in some intact tissues.

• 한국정밀공학회지
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• 제21권10호
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• pp.78-85
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• 2004

The particle amount monitoring technique using ultrasound is proposed to determine the proper maintenance time of the filter in the supply process of pure gas in the unit of oxygen plant. There are advantages that it is adaptable in high temperature and high pressure, and it is not disturbed by being exposed in the gas flow, and it can be implemented very economically. The applicability of the ultrasonic technique is pre-studied through the theoretical analysis for the dependency of attenuation of ultrasonic wave on the particles in the gas flow. For the purpose, absorption, scattering and dispersion models are considered, and the attenuation by absorption and the change rate of the propagation speed are calculated fur the specific range of particle size and the ultrasonic wave frequency. It was expected by simulation that the absorptive attenuation by particles was the most sensitive to the change of particle amount. The experimental result showed high correspondence with the theoretical expectation so that this ultrasound attenuation measurement was proved to be highly effective for monitoring the amount of floating particles in the gas flow.

• 비파괴검사학회지
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• 제36권3호
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• pp.175-180
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• 2016

Nondestructive evaluation for material health monitoring is important in aerospace industries. Composite laminates are exposed to heat cyclic loading and humid environment depending on flight conditions. Cyclic heat loading and moisture absorption may lead to material degradation such as matrix breaking, debonding, and delamination. In this paper, the moisture absorption ratio was investigated by measuring the Lamb wave velocity. The composite laminates were manufactured and subjected to different thermal aging cycles and moisture absorption. For various conditions of these cycles, not only changes in weight and also ultrasonic wave velocity were measured, and the Lamb wave velocity at various levels of moisture on a carbon-epoxy plate was investigated. Results from the experiment show a linear correlation between moisture absorption ratio and Lamb wave velocity at different thermal fatigue stages. The presented method can be applied as an alternative solution in the online monitoring of composite laminate moisture levels in commercial flights.

• 한국농공학회지
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• 제45권6호
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• pp.128-135
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• 2003

This study is performed to examine the physical and mechanical properties of concrete using recycled aggregate and industrial by-products. The test results show that the unit weight, compressive and flexural strength, ultrasonic pulse velocity and dynamic modulus of elasticity are decreased with increasing the content of recycled aggregate. But, the absorption ratio is increased with increasing the content of recycled aggregate. The unit weight is 2,237∼2,307 kg/$\textrm{m}^3$, the absorption ratio is 2.96∼4.12%, the compressive strength is 415∼532 kgf/$\textrm{cm}^2$, the flexural strength is 75∼96 kgf/$\textrm{cm}^2$, the ultrasonic pulse velocity is 4,350∼4,949 m/s and the dynamic modulus of elasticity is $390\times10^3\;∼\;465\times10^3$ kg f/$\textrm{cm}^2$, respectively These recycled aggregate concrete can be used for high strength concrete.

• 대한화학회지
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• 제36권2호
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• pp.329-334
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• 1992

단백질 수용액 중의 초음파흡수 mechanism을 규명하기 위하여 pH 7의 소혈청 albumin(BSA)수용액의 초음파흡수 측정을 주파수 100 kHz에서 1600 MHz에 걸쳐 행하였다. 측정방법은 plano-concave 공명법(0.1${\sim}$10 MHz)과 고분해능 Bragg 반사법(120${\sim}$1600 MHz)을 사용하였다. pH7에서의 초음파흡수스펙트럼은 Davidson-Cole 분포식의 거울상인 분포함수를 사용한 완화곡선과 일치하였다. 이 완화현상을 BSA 분자의 수화평행에 의한 것으로 해석하였다.

• Bulletin of the Korean Chemical Society
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• 제30권1호
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• pp.53-56
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• 2009

At room-temperature, a facile, seedless, and environmentally benign green route for the synthesis of star like PbS nanoclusters at 7 min in aqueous solution of 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIM] [$EtSO_{4}$], room-temperature ionic liquid (RTIL), via ultrasonic irradiation is proposed. The X-ray diffraction studies display that the products are excellently crystallized in the form of cubic structure. An energy dispersive X-ray spectroscopy (EDX) investigation reveals the products are extremely pure. The absorption spectra of the product exhibit band gap energy of about 4.27 eV which shows an enormous blue shift of 3.86 eV that can be attributed to very small size of PbS nanoparticles produced and quantum confinement effect. A possible formation mechanism of the PbS nanoparticles using ultrasonic irradiation in aqueous solution of the RTIL is presented.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1976년도 제7차 하계학술발표회 및 산학협동세미나초록
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• pp.49-52
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• 1976

• Preventive Nutrition and Food Science
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• 제14권4호
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• pp.373-377
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• 2009

Safflower seed extract was prepared by a high-pressure extraction technology and its quality characteristics were compared to that of other conventional extraction techniques, such ultrasonic and reflux extractions. Safflower seeds were extracted with 80% aqueous ethanol by three above extraction methods, and further fractionated with Diaion HP-20 column chromatography to obtain a partially purified safflower seed extract (PPSSE). Among the three extraction techniques examined, the reflux extraction showed the higher yields of EtOH extract and PPE than the ultrasonic and high-pressure extractions. Levels of most phenolic compounds in the EtOH extract of safflower seed are higher in reflux and ultrasonic extractions than the high pressure extraction, but levels of two serotonin aglycones, N-(p-coumaroyl)serotonin (CS) and N-feruloylserotonin (FS), in PPSSE were higher in the high pressure extraction than the reflux and ultrasonic extractions. In addition, color values (L and a) of the PPSSE were higher in the high-pressure extraction than the reflux and ultrasonic extractions, although there were no significant differences in pH and UV maxima absorption spectra among three extraction techniques. These results indicate that the high-pressure extraction technology is a simple and effective extraction for preparation of a high quality of safflower seed extract containing CS and FS with anti-wrinkle activity.

• 지질공학
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• 제23권4호
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• pp.341-352
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• 2013

본 연구에서는 생성 당시의 퇴적환경이 상이한 것으로 알려진 대구지역의 적색 셰일과 흑색 셰일의 물리적 및 역학적 특성을 확인하기 위하여 단위중량, 흡수율, 공극률, 초음파속도, 일축압축강도, 점하중강도, 슬레이크 내구성 및 열화특성 시험 등을 실시하였고, XRD 및 XRF 분석과 SEM 영상 분석을 수행하였다. 시험결과 두 셰일의 단위중량은 유사하였으나 흡수율과 공극률은 적색 셰일이 흑색 셰일보다 더 높았다. 특이하게도 공극률이 높은 적색 셰일의 초음파속도, 일축압축강도, 점하중강도지수 가 흑색보다 더 높은 값을 보였는데 이는 흑색 셰일 내에 발달된 엽층리의 영향인 것으로 판단된다. 열화시험에서는 용액의 산성도가 증가할수록 또 수침시간이 길어질수록 시료의 점하중강도지수와 슬레이크 내구성지수의 저감정도가 심하였으며, 흑색 셰일보다는 공극률이 큰 적색 셰일에서 더 크게 영향을 받는 것으로 나타났다.