• 제목, 요약, 키워드: Ultrasonic velocity

검색결과 708건 처리시간 0.037초

아세틸화 처리가 대나무재의 초음파 전달 속도에 미치는 영향 (Effect of Acetylation on Ultrasonic Velocity of Bamboo)

  • 강호양;이관영
    • 목재공학
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    • v.25 no.3
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    • pp.8-15
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    • 1997
  • The ultrasonic velocity and dynamic MOE of acetylated bamboos were investigated using PUNDIT, a transit time measuring device for longitudinal ultrasonic propagation. Bamboo specimens were boiled in acetic anhydride for 2, 4 and 6 hours, and the maximum average WPG (Weight Percentage Gain) of 19% was obtained at 6 hours. The volumes of acetylated bamboos increase with boiling time and WPG, while as WPG increases their oven-dry densities generally increase with a concave around 5% WPG. This oven-dry density pattern likely influences the trends of ultrasonic velocity and dynamic MOE. which generally decrease with a convex around 5% WPG. It is postulated that during boiling extractives in a bamboo move and aggregate at its surfaces transiently, resulting in the increase of ultrasonic velocity and dynamic MOE. To explain the fact that ultrasonic velocity varies with WPG a simple model was proposed and some ultrasonic properties of a transmitted wave were examined.

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구상흑연주철에서 초음파 전파속도에 미치는 흑연형상의 영향 (The Effect of Graphite Morphology on the Propagation of Ultrasonic Wave in Ductile Cast Iron)

  • 이계완;양노석;박온수
    • 한국주조공학회지
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    • v.9 no.3
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    • pp.228-236
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    • 1989
  • The relationships between nodularity, tensile property and ultrasonic velocity were studied in ductile iron castings having similar matrix structure. Also, the effects of heat treatment and the number of graphite nodules on the ultrasonic velocity were investigated. The results were as follows 1. The ultrasonic velocity increased proportionally with increassing nodularity and tensile strength. 2. The ultrasonic velocity in annealed and normalized state decreased average 1.7% and 3.4% respectively than that in as cast state. 3. The ultrasonic velocity increased with increasing the number of graphite nodules. Therefore, ductile iron castings can be evaluated in the only case of castings having the same manufacturing history by ultrasonic velocity.

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퀜칭한 SCM 440 강에서 초음파 전파특성에 미치는 템퍼링온도의 영향 (The Effect of Tempering Temperature on Ultrasonic Velocity Property at the Quenched SCM 440 Steel)

  • 이계완;김문일;박은수
    • 열처리공학회지
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    • v.4 no.3
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    • pp.54-62
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    • 1991
  • The effect of tempering temperature on the ultrasonic propagation velocity at SCM 440 steel quenched from $870^{\circ}C$ and $1000^{\circ}C$ has been studied by metallurgical and crystallographical observation. The measurements of ultrasonic velocity were made on the specimen by appling an immersion ultrasonic pulse-echo technique with a constant frequency of 10 MHz. The quenched microstructure of this steel was a lath martensite. As the tempering temperature was increased, the martensite was transformed into the tempered martensite composed of cementite and carbide. The ultrasonic velocity increased with increasing the tempering temperature. It was thought that these were resulted from the microstructural transformation. The change of ultrasonic propagation velocity with quenching and tempering heat treatment was resulted from microstrain due to the change of internal stress. Considering these results concerning to the change of ultrasonic propagation velocity. the phenomena of microstructural transformation were estimated. Consequently, it was thought that the degree of quenching and tempered heat treatment of steel could be nondestructively evaluated with the change of ultrasonic propagation velocity.

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초음파속도법에 의한 고강도 콘크리트의 압축강도 추정에 관한 연구 (Estimating Compressive Strength of High Strength Concrerte by Ultrasonic Pulse Velocity Method)

  • 임서형;강현식
    • 한국구조물진단유지관리공학회 논문집
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    • v.5 no.3
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    • pp.123-130
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    • 2001
  • The purpose of this study is to suggest the non-destructive equation for the estimation of concrete strength by ultrasonic pulse velocity at the Age of 28day compressive strength of $600{\sim}1000kg/cm^2$. For this purpose, selected test variables were water-hinder ratio, replacement ratio of silica fume, binder content, maximum size of coarse aggregate and sand-aggregate ratio. From the results, the average increase or decrease of ultrasonic pulse velocity is 61m/sec for each 1% of moisture content. And the correlation equation between the ultrasonic pulse velocity and the compressive strength of concrete is as follows. $F_c=896.3V_p-3514$ ($R^2$ = 0.81) where, $F_c$ : compressive strength($kgf/cm^2$), $V_p$ : ultrasonic velocity(km/sec).

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목재 초음파 전달속도에 대한 온도의 영향 (Temperature Effect on Ultrasonic Stress Wave Velocity of Wood)

  • 강호양
    • 목재공학
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    • v.27 no.1
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    • pp.50-55
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    • 1999
  • Since ultrasonic stress wave velocity varies with wood temperature and moisture content, ultrasonic stress wave could be a tool to predict wood moisture content if temperature effect could be eliminated. This temperature effect was investigated by measuring the velocities of ultrasonic stress waves transmitting through air, a metal bar and a dimension lumber at various temperatures. For air the velocity and amplitude of the ultrasonic stress wave increase with temperature, while for a metal bar and a dimension lumber those decrease as temperature increases. However all three materials showed velocity hystereses with a temperature cycle. The effect of temperature and moisture content on stress wave velocity of a dimension lumber was depicted in the form of a three dimensional graph. The plot of stress wave velocity vs. wood moisture content was well fitted by two regression equations: a exponential equation below 46% and a linear equation above 46%.

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The Change of Ultrasonic Transmission Velocity by Wood Decay

  • Hwang, Won-Joung;Lee, Hyun-Mi;Park, Young-Ran;Lee, Dong-Heub
    • 목재공학
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    • v.42 no.2
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    • pp.214-221
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    • 2014
  • The deterioration in wood by the brown-rot fungus (Fomitopsispalustris) and the white-rot fungus (Trametesversicolor) were measured using ultrasonic velocity. Those were used for the decay exposure and 4 wood species of wood as the test specimens, Pinusdensiflora, Larixkaempferi, Pinuskoraiensis and Pinusrigida, were chosen with both the brown- and white-rot culture petridish during 12 weeks. After 12 weeks, the decrease rate of ultrasonic velocity was measured at 10~15%. In both brown- and white-rot exposure experiments, P. rigida showed significant decrease in ultrasonic velocity (20%), L. kaempferi on the other hand did not show decrease in ultrasonic velocity. After the fungal exposure experiment, the inside of specimens was investigated by computer tomography (C/T). After C/T investigation, bending tests were performed.

초음파 전파속도법을 이용한 목조 문화유산 흰개미 피해의 정량 평가 (Quantitative Analysis for Termites Damage of Wooden Heritage using Ultrasonic Pulse Velocity)

  • 안재철
    • 건축역사연구
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    • v.24 no.5
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    • pp.41-48
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    • 2015
  • Quantitative analysis of termites damage is important in terms of conservation and maintenance of wooden cultural heritage buildings, because termites makes cavities and decreases the section area of wooden structural members. The purpose of this study is to forecast the range and spread of termites damage in the wooden structural members by using ultrasonic pulse velocity method. Ultrasonic pulse velocity has been used as one of non-destructive test to analysis the internal defect by using difference velocity between medium material and cavity. This method would be effective to analysis termites damages. From the result of the ultrasonic velocity test, the loss rate of area effected by termites damage had a strong correlation with ultrasonic velocity. And it is possible to predict the loss rate of area from by termites damage by using regression equation in the case of structural member of fine tree.

Ultrasonic Velocity and Absorption Measurements for Polyacrylamide and Water Solutions

  • Bae, Jong-Rim;Kim, Jeong-Koo;Yi, Meyung-Ha
    • The Journal of the Acoustical Society of Korea
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    • v.22 no.4E
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    • pp.155-160
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    • 2003
  • Both ultrasonic velocity at 3 MHz and absorption coefficient for the frequency range of 0.2-2 MHz were measured in an aqueous solution of polyacrylamide for the concentration range of 0.5% to 2.5% by weight. Pulse echo overlap method was taken for measuring the ultrasonic velocity over the temperature range of 10-90℃ and the high-Q ultrasonic resonator method was used for the absorption coefficient at 30℃. The velocity exhibited a maximum value at approximately 70℃, 71℃, 72℃, 73℃ and 74℃ in 2.5%, 2.0%, 1.5%, 1.0%, and 0.5% solutions, respectively. The velocity increased with the concentration at a given temperature. The ultrasonic absorption (a/f²) at a given temperature increased linearly with the concentration for the concentration below 1.5%, but suddenly increased for the concentration above 1.5% concentration. The value of a/f² at 1MHz was entirely due to the classical Stoke's viscous effect. The ultrasonic relaxation in polyacrylamide aqueous solutions, which may be the result of structural fluctuations of polymer molecules such as the segmental motion of the polymer chains, was observed, and at 2.5%, the value of a/f² was found to suddenly increase as frequency decreased.

두개의 탐촉자를 사용한 등방성 균일 고체의 초음파 속도 및 두께 동시 측정법 (Simultaneous Measurement of Ultrasonic Velocity and Thickness of Isotropic and Homogeneous Solids Using Two Transducers)

  • 이정기;권진오;김영환
    • 비파괴검사학회지
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    • v.19 no.5
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    • pp.363-368
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    • 1999
  • 시험체의 두께나 초음파 속도를 측정하기 위해서 초음파 펄스-에코법이 널리 사용되고 있다. 초음파 속도를 결정하기 위해서는 초음파 송수신 장치를 포함한 오실로스코우프와 같은 초음파 측정 장치를 사용하여 시험편에서의 초음파진행 시간을 측정하고, 초음파 진행 거리에 해당하는 시험편의 두께를 버어니어 캘리퍼스 또는 마이크로미터와 같은 길이측정 도구를 사용하여 측정한다. 그리고 초음파를 이용하여 시험편의 두께를 측정할 때에는 초음파 속도를 알고 있는 대비 시험편으로 기준을 설정하여야 한다. 본 연구에서는, 대비 시험편 없이 재료의 두께와 초음파 속도를 동시에 구하는 방법을 제시하였다. 재질과 두께를 달리한 여러 시험편에서 측정된 초음파 속도와 두께가 기존의 방법에 의해 측정한 값과 잘 일치하였다.

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기체온도 측정을 위한 초음파 계측에 관한 연구 (A Study on Ultrasonic Technique for Measuring Gas Temperature)

  • 윤천한;최영;전흥신
    • 대한기계학회논문집B
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    • v.23 no.7
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    • pp.893-900
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    • 1999
  • Measuring temperature with ultrasonic wave apparatus is desirable in the cue of gas below $300^{\circ}$ because of the fact that the temperature of gas is the function of only sound velocity. In this study, being used a heatable wind channel and a blower. the variation of temperature is observed in accordance with flow rate(air velocity). The frequency modulation method is used to measure the temperature which is varying in hot air flow up to $100^{\circ}$. The length changed in the position of ultrasonic sensors is considered. Also. the effects of air velocity at the same temperature and various facing angles of ultrasonic sensors are considered. As a result of this study. it has been found that the temperature in gas flow is correctly measured regardless of both the distance of ultrasonic sensors and the variation of air velocity. and that there is just a little influence of facing angles.