• 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.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.544-550
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• 1997

In this study, the advanced on-sided stress wave velocity measurement method was applied to investigate the effects of composition, age and moisture content in concrete. Two concrete specimens that have different composition were used to figure out the change of the Longitudinal and Surface wave velocity due to different composition. The other concrete specimen was cast and the Longitudinal and Surface wave velocity was monitored during curing process. After 28-day old, the effect of moisture content in the concrete specimen to the stress wave velocity is presented in this paper during the time period 43-74 days after casting. For drying process. an aggregate drying oven was used. A conventional ultrasonic through transmission method was used to compare with the results determined by the one-sided method.

• Journal of the Korean Society for Nondestructive Testing
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• v.11 no.2
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• pp.22-31
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• 1991

Various types of ultrasonic techniques have been used for the estimation of compressive strength of concrete structures. However, conventional ultrasonic velocity method using only longitudial wave cannot be determined the compressive strength of concrete structures with accuracy. In this paper, by using the introduction of multiple parameter, e. g. velocity of shear wave, velocity of longitudinal wave, attenuation coefficient of shear wave, attenuation coefficient of longitudinal wave, combination condition, age and preservation method, multiple regression analysis method was applied to the determination of compressive strength of concrete structures. The experimental results show that velocity of shear wave can be estimated compressive strength of concrete with more accuracy compared with the velocity of longitudinal wave, accuracy of estimated error range of compressive strength of concrete structures can be enhanced within the range of ${\pm}$10% approximately.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.537-543
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• 1997

A new procedure for the advanced one-side measurement of longitudinal wave and surface wave velocities in concrete is presented in this paper. Stress waves are generated in a consistent fashion with a DC solenoid. Two piezoelectric accelerometers are mounted on the surface of a specimen as receivers. Stress waves propagate along the surface of the specimen and are detected by the receivers. In order to reduce the large incoherent noise levels of the signals, signals are collected and manipulated by a computer program for each velocity measurement. For a known distance between the two receivers and using the measured flight times, the velocities of the longitudinal wave and the surface wave are measured. The velocities of the longitudinal wave determined by this method are compared with those measured by conventional methods on concrete, PMMA and steel.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.3
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• pp.502-509
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• 2001

In this paper, when stress waves are propagated along the reinforced direction of the composite, the characteristic equation of Rayleigh wave is derived. The relationships between velocities of stress waves and Rayleigh wave are studied for anisotropic ratios(E(sub)11/E(sub)12 or E(sub)22/E(sub)11). The increments of anisotropic ratios is made by using known material properties and being constant of basic properties. When the anisotropic ratios are increased, Rayleigh wave velocities to the shear wave velocities are almost equal to 1 with any anisotropic ratios. Rayleigh wave velocities to the longitudinal wave velocities and Shear wave velocities ratio to the longitudinal wave velocities are almost identical each other, they are between 0.12 and 0.21. When the anisotropic ration is very high, that is, E(sub)11/E(sub)22=46.88, Rayleigh wave velocities and the shear wave velocities are almost constant with Poissons ratio, longitudinal wave velocities are very slowly increased with the increments of Poissons ratios. When E(sub)11(elastic modulus of the reinforced direction)and ν(sub)12 are constant, Rayleigh wave velocities and the shear wave velocities are steeply decreased with the increments of anisotropic ratios and the velocities of longitudinal wave are almost constant with them. When E(sub)22(elastic modulus of the normal direction to the fiber) and ν(sub)12 are constant, Rayeigh wave velocities is slowly increased with the increments of anisotropic ratios, the shear wave velocities are almost constant with them, the longitudinal wave velocities are steeply increased with them.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.2 s.95
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• pp.138-144
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• 1999

Longitudinal wave and shear wave velocity changes of PMMA Polymer meterial under the the unidirection load were measured. The Third-order elastic modulus and acousto-elastic modulus of PMMA are obtained. The theoretical and experemental values of the velocity change of each wave by stress are compared each other and the validity of theoretical expression is examinated.

• Journal of the Korea Concrete Institute
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• v.12 no.6
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• pp.67-74
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• 2000

The usage of nondestructive testing on early-aged concrete leads to enhacned safty and allows effective scheduling of construction, thus making it possible to maximize the time and cost efficiencies. In this study, a reliable nondestructive strength evaluation method for early-aged concrete using the longitudinal wave velocity is proposed. Compression tests were performed to examine factors influencing the velocity-strength relationship of concrete, such as water-cement (w/c) ratio, fine aggregate ratio, curing temperature, and curing condition. The test results show that a change in the w/c ratio and curing temperature has minor effect on the velocity-strength relationship/ However, curing condition significantly influences the velocity-strength relationship of early-aged concrete. Moreover, the longitudinal wave velocity increases with decreasing fine aggregate ratio. It is concluded from this study that the strength evaluation of early-age concrete can be achieved by a nonlinear equation which considers the effects of curing condition and fine aggregate ratio.

• International Journal of Reliability and Applications
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• v.5 no.1
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• pp.1-13
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• 2004

It is recently well recognized that the technique for the one-sided stress wave velocity measurement in structural materials provides measurement in structural materials provides valuable information on the state of the material such as quality, uniformity, location of cracked or damaged area. This technique is especially effective to measure velocities of longitudinal and Rayleigh waves when access to only one surface of structure is possible. However, one of problems for one-sided stress wave velocity measurement is to get consistent and reliable source for the generation of elastic wave. In this study, the laser based surface elastic wave was used to provide consistent and reliable source for the generation of elastic wave into the materials. The velocities of creeping wave and Rayleigh wave in materials were measured by the one-sided technique using laser based surface elastic wave. These wave velocities were compared with bulk wave velocities such as longitudinal wave and shear wave velocities to certify accuracy of measurement. In addition, the mechanical properties such as poisson's ratio and specific modulus(E/p) were calculated with the velocities of surface elastic waves.

• Journal of Ocean Engineering and Technology
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• v.24 no.4
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• pp.32-37
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• 2010

This study presents the attenuation characteristics of the first guided longitudinal wave mode propagating in water-filled, buried steel pipes in order to investigate the effects of soil saturation and compaction on the attenuation patterns. For numerical calculation of attenuation, 10 different combinations of S-wave velocity, P-wave velocity, and soil densities were considered. From the attenuation dispersion curves, which were obtained using Disperse software, we determined that the attenuation decreases as saturation increases, whereas it increases as compaction increases. Over the frequency range from 0.2 to 0.4 MHz, the first longitudinal wave mode has attenuations that are relatively lower than for other ranges, is faster than the first flexural wave mode, and is sensitive to defects aligned in the axial direction. Hence, the first longitudinal wave mode over the mentioned frequency range would be the proper choice for long-range buried pipelines that transport water.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.336-341
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• 2004

This research investigates the feasibility of ultrasonic microscope for nondestructive assessment of thermal degradation in artificially aged commercial Co-base superalloy, FSX414. This alloy has been used for high temperature structure applications such as stationary gas turbine blade and nozzle chamber in fossil plant. Microstructural change was found that the fine carbides became coarser and spheroidized in matrix as aging time increased. The leaky surface acoustic wave velocity gradually decreases by a maximum of 4.7% with increasing aging time up to 4,000hours. However, the longitudinal wave velocity has a little change. Also, it has a good correlation between leaky surface acoustic wave velocity and Vickers hardness. Consequently, LSAW can be used to examine the degree of degradation in thermally aged Co-base superalloy.