• Title/Summary/Keyword: 종파속도

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Mode Characteristics of Longitudinal Guided Waves in Buried Steel Pipes (매립된 파이프에서 유도초음파의 종파 모드 특성)

  • Lee, Ju-Won;Shin, Sung-Woo;Na, Won-Bae;Kim, Jae-Min
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2010.04a
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    • pp.674-677
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    • 2010
  • 본 논문에서는 지반에 매립된 파이프에서 전파되는 유도초음파의 종파 모드 특성을 분석하였다. 지상 배관과는 달리 매립 배관에서는 주변 매질로 유도초음파의 누설이 발생할 수 있으며, 이로 인하여 유도초음파의 감쇠가 상대적으로 커질 수 있다. 따라서 본 연구에서는 유도초음파의 여러 특성들 중 종파 모드의 감쇠 특성을 중점적으로 분석하였다. 감쇠에 영향을 미치는 지반의 파동 특성(밀도, 체적종파속도, 체적횡파속도)을 결정하기 위하여 포화도와 다짐을 고려하였다. 포화도가 증가할수록 지반의 체적종파속도와 체적횡파속도는 감소하며, 다짐된 지반은 밀도와 체적종파속도, 체적횡파속도를 증가시킨다. 이와 같은 조건으로 결정된 지반의 파동 특성치와 배관의 물성치를 바탕으로 유도초음파 종파 모드의 감쇠 곡선을 계산하고, 특성을 분석하였다. 결과적으로 포화도가 증가할수록 종파 모드의 감쇠는 감소하는 경향을 나타내었고, 다짐이 증가할 경우 감쇠는 전반적으로 증가하는 경향을 나타냄을 알 수 있었다.

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Influence of Moisture Content on Longitudinal Wave Velocity in Concrete (수분 함유량이 콘크리트의 종파 속도에 미치는 영향에 관한 연구)

  • Lee, H.K.;Lee, K.M.;Kim, J.S.;Kim, D.S.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.19 no.4
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    • pp.259-269
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    • 1999
  • Elastic wave velocity measurement technique such as impact-echo method and ultrasonic pulse velocity method has been successfully used to evaluate the moduli and strength of concrete. However, estimation results obtained by the NDT methods do not agree well with real things because longitudinal wave velocity is influenced by various factors. In this paper, among several factors influencing P-wave velocity, the influence of moisture content in concrete was investigated through the experiment. Test results show that longitudinal wave velocity is significantly affected by the moisture content of concrete, i.e., the lower moisture content. the lower velocity. Moisture content influences rod-wave velocity measured by impact-echo method stronger than ultrasonic pulse velocity measured by transmission method. During drying process with ages. the difference of increasing rate between longitudinal wave velocity and compressive strength of concrete is gradually increased. Therefore, to establish more accurate relationship between longitudinal wave velocity and strength, the difference of the increasing rate should be considered.

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A study on the variation of rock properties of weathered granites (화강암의 풍화현상에 수반되는 물성변화의 특성)

  • 김영화;장보안
    • The Journal of Engineering Geology
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    • v.2 no.1
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    • pp.36-46
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    • 1992
  • Granite core samples and bulk samples were first subjected to petrographic examination to determine weathering degrees. Secondly, their physical or mechanical properties including specific gravity, porosity, sonic wave velocity and uniaxial compressive strength were measured. The results were correlated to investigate the influences between properties including physical and mechanical properties, weathering degrees, and rock textures. Porosity and P wave velocity were found the most useful indices in determining the weathering degrees of granites.

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Evaluation of the State of Rocks in Load Steps by Low-frequency Ultrasonic Flaw Detection (저주파 결함 탐지법에 의한 하중 단계에 따른 암석 내부의 상태 평가)

  • Kang, Seong-Seung;Kim, Jongheuck;Noh, Jeongdu;Na, Tae-Yoo;Jang, Hyongdoo;Ko, Chin-Surk
    • The Journal of Engineering Geology
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    • v.27 no.1
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    • pp.51-58
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    • 2017
  • The purpose of this study was to quantitatively evaluate the state of rocks in load steps by using the low-frequency ultrasonic flaw detection method. The initial Vp-velocities measured with a CND tester were in the order of Z-axis < X-axis < Y-axis, with 1687.5 m/s along the X-axis, 1690.7 m/s along the Y-axis, 1548.3 m/s along the Z-axis, and an average of 1642.2 m/s. The overall average of the Q vlaues, measured with a Silver Schmidt hammer, was 62.6, which corresponds to a uniaxial compressive strength of ~105 MPa. The Vp-velocity, measured with a low-frequency ultrasonic flaw detector at load steps of 50%, 60%, 70%, and 80%, typically decreases in the order of X-axis < Y-axis < Z-axis with increasing load steps. This oder contrasts with that of the initial Vp-velocities. As the load step increases the factors that reduce the Vp-velocity in the X-axis direction are more influential than those in the Y-axis or Z-axis directions. This indicates that the initial state of rocks can vary and is dependent on the stress state.

Analysis of Weathered State on a Halo Stone Buddha, Unju Temple of Hwasun, Korea Using Low Frequency Flaw Detector (저주파 결함 탐지기를 활용한 화순 운주사 광배석불의 풍화상태 분석)

  • Kang, Seong-Seung;Ko, Chin-Surk;Kim, Cheong-Bin;Jang, Bo-An
    • The Journal of Engineering Geology
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    • v.23 no.3
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    • pp.235-246
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    • 2013
  • P-wave velocity was measured by the low frequency flaw detector in order to analyze the weathered state of a halo stone Buddha, Unju temple, Hwasun, Korea. By the results of laboratory tests on a fresh acidic tuff with the same rock of a halo stone Buddha, average absorption, average P-wave velocity, and average uniaxial compressive strength were 5.38%, 4,008 m/s, and 70.1 MPa, respectively. The results correspond to moderately strong rock. Average P-wave velocity of a halo stone Buddha measured by the low frequency flaw detector was 2,257 m/s in the left zone, 3,437 m/s in the right zone, and 2,802 m/s overall. Weathering index of a halo stone Buddha was 0.45 in the left zone, 0.21 in the right zone, and 0.33 overall. Comparing the results of a halo stone Buddha with them of laboratory tests, weathered state of a halo stone Buddha was analyzed highly weathered state in the left zone and moderately weathered state in the right zone. Furthermore, it suggests that the left zone of a halo stone Buddha was affected weathering more than the right one. Overall a halo stone Buddha corresponds to moderately weathered state of weathering degrees. In conclusion, it is considered that low frequency flaw detector may be applicable as a valuable method on analyzing the P-wave velocity of the stone cultural heritage with an irregular surface.

Measurement of Longitudinal and Transverse Wave Speed in Solid Materials Using Immersion Ultrasonic Testing (수침 초음파 시험법을 이용한 고체의 종파와 횡파 속도의 측정)

  • Shin, Yo-Sub;Yoon, Yeo-Ho;Kim, Young-H.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.28 no.1
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    • pp.40-45
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    • 2008
  • Immersion ultrasonic testing (UT) was used to determine elastic moduli of solid materials instead of the widely-used contact UT method. Conventionally, immersion UT is only used for determining the longitudinal wave speed. However, in this research, transverse wave speed was measured through finding transverse wave echoes caused by mode-conversion at material's boundary. Also, even in the cases when wave speeds could not be determined due to unknown thickness, Poisson's ratio was able to be calculated from the ratio of longitudinal and transverse wave speeds. This technique was verified for several materials, and it was found that higher accuracy was obtained by immersion UT method for materials either with relatively high wave speed or with relatively small Poisson's ratio. This technique thus will be suitable fur ceramics or high strength materials.

Preliminary Tomographic hversion for the Crustal Characteristics in the Central Region of South Korea (남한 중부지역의 지각특성 구명을 위한 토모그라피 역산에 의한 예비적 연구)

  • Lee, Duk-Kee;Kyung, Jai-Bok;Chung, Tae-Woong
    • Journal of the Korean earth science society
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    • v.22 no.1
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    • pp.20-29
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    • 2001
  • P wave traveltime delays has been measured and a preliminary tomouaphic inversion has been performed using the data collected from the network deployed by Korea National University of Education in the southcentral part Korea. The maximum variation in relative traveltime residuals is almost 0.7 seconds. A large azimuthal variation in traveltime residuals is observed at the stations in the northwestern part of the study area. This might indicate the existence of lateral velocity heterogeneity beneath the study area. Although, the inverted tomographic image seems to be correlated with the tectonic boundary between Kyunggi Massif and Okcheon Belt, the confidence level is presently low. We should place on the importance of this study for finding preferable inversion parameters and predicting probable result. Better tomographic image of the study area can be obtained in the near future when the data are accumulated.

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A New Method for Characterization of Composites by Ultrasonics (초음파를 이용한 복합재료 기계적 특성값의 새로운 특정 방법)

  • 장필성;전홍재
    • Composites Research
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    • v.13 no.2
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    • pp.1-7
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    • 2000
  • A new ultrasonic test method is proposed to obtain elastic constants of unidirectional composite materials nondestructively. In the proposed test method, only longitudinal transducers are used to measure wave velocities by through-transmission method. An aluminum wedge and a flat aluminum rectangular block are placed on each side of the test specimen. Oblique incident longitudinal wave is transmitted from a wedge to the specimen and the mode conversions are occurred sequentially at two interfaces between the specimen and aluminium. Measuring wave velocities converted to longitudinal waves in the rectangular block give all information to determine elastic constants of the composites. In order to determine shear stiffness coefficients, transverse wave velocity is measured indirectly from received longitudinal wave. Effects of anisotropy on waves are also considered in this study.

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Application of One-Sided Stress Wave Velocity Measurement Technique to Evaluate Freeze-Thaw Damage in Concrete (콘크리트 동결-융해 손상의 비파죄 평가를 위한 One-Sided 응력파 속도 측정기법의 적용에 관한 연구)

  • Lee, Joon-Hyun;Park, Won-Su
    • Journal of the Korean Society for Nondestructive Testing
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    • v.20 no.4
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    • pp.269-275
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    • 2000
  • It is well recognized that damage resulting from freeze-thaw cycles is a serious problem causing deterioration and degradation of concrete. In general, freeze-thaw cycles change the microstructure of the concrete ultimately leading to internal stresses and cracking. In this study, a new method for one-sided stress wave velocity measurement has been applied to evaluate freeze-thaw damage in concrete by monitoring the velocity change of longitudinal and surface waves. The freeze-thaw damage was induced in a $400{\times}350{\times}100mm$ concrete specimen in accordance with ASTM C666 using s commercial testing apparatus. A cycle consisted of a variation of the temperature from -14 to 4 degrees Celsius. A cycle takes 4-5 hours with approximately equal times devoted to freezing-thawing. Measurement of longitudinal and surface wave velocities based on one-sided stress wave velocity measurement technique was made every 5 freeze-thaw cycle. The variation of longitudinal and surface wave velocities due to increasing freeze-thaw damage is demonstrated and compared to determine which one is more effective to monitor freeze-thaw cyclic damage progress. The variation in longitudinal wave velocity measured by one-sided technique is also compared with that measured by the conventional through transmission technique.

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Comparison of Longitudinal Wave Velocity in Concrete by Ultrasonic Pulse Velocity Method and Impact-Echo Method (초음파 속도법과 충격반향기법에 의한 콘크리트의 종파 속도 비교)

  • Lee, Hoi-Keun;Lee, Kwang-Myong;Kim, Young-H.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.23 no.2
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    • pp.98-106
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    • 2003
  • Nondestructive test (NDT) provides much information on concrete without damage of structural functions. Of NDT methods, elastic wave propagation methods, such as ultrasonic pulse velocity (UPV) method and impact-echo (IE) method, have been successfully used to estimate the strength, elastic modulus, and Poisson's ratio of concrete as well as to detect the internal microstructural change and defects. In this study, the concretes with water-binder ratio ranging from 0.27 to 0.50 and fly ash content of 20% were made and then their longitudinal wave velocities were measured by UPV and IE method, respectively. Test results showed that the UPV is greater than the longitudinal wave velocity measured by the If method, i.e., rod-wave velocity obtained from the same concrete cylinder. It was found that the difference between the two types of velocities decreased with increasing the ages of concrete and strength level. Moreover, for the empirical formula, the dynamic Poisson's ratio, static and dynamic moduli of elasticity, and velocity-strength relationship were determined. It was observed that the Poisson's ratio and the modulus of elasticity determined by the dynamic method are greater than those determined by the static test. Consequently, for the more accurate estimation of concrete properties using the elastic wave velocities, the characteristics of these velocities should be understood.