• Journal of the Korean Society for Precision Engineering
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• v.13 no.11
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• pp.92-99
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• 1996

The contact pressure in jointed plates was measured by means of an improved ultrasonic technique. In order to get calibration curve, the relationship between contact pressure and ratio of boundary and bottom echo of normal beam probes were obtained for the calibration blocks with various surface roughness. The ratio of boundary and bottom echoes were measured for the upper/under plates locally compressed with uniform pressure, and the distribution of contact pressure was obtaines. The measured pressure has a good agreement with results of FEM analysis. Thus the proposed ultrasonic method in this work is very useful to measure the contact pressure.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.4
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• pp.561-571
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• 1997

In this paper, the fundamental equations are developed for the pulsatile laminar flow generated by changing the oscillatory flow with $0{\leq}f{\leq}48Hz$ into a steady one with $0{\leq}Re{\leq}2500$ in a rigid circular pipe. Analytical solutions for the wave propagation factor k, the axial distributions of cross-sectional mean velocity $u_m$ and pressure p are schematically derived and confirmed experimentally. The axial distributions of centerline velocity and pressure were measured by using Pitot-static tubes and strain gauge type pressure transducers, respectively. The cross-sectional mean velocity was calculated from the centerline velocity by applying the parabolic distribution of the laminar flow and it was confirmed by using the ultrasonic flowmeter. It was found that the axial distributions of cross-sectional mean velocity and pressure agree well with theoretical ones and depend only on the Reynolds number Re and angular velocity $\omega$.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.280-285
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• 2000

It is very important to evaluate the surface or subsurface microstructure because of their influences on mechanical properties of materials. Surface SH-wave which is horizontally polarized shear wave traveling along near surface and subsurface layer is an attractive technique for material evaluation. The destructive method is widely used for the estimation of material degradation but it has a great difficulty in preparing specimens from in-service industrial facilities. In this study, nondestructive evaluation for degraded structural materials used at high temperature though surface SH-wave method is discussed. 2.25Cr-1Mo steel specimens which were prepared by the isothermal aging heat treatment at $650^{\circ}$ were evaluated though ultrasonic nondestructive evaluation techniques investigating the change of sound velocity, attenuation coefficient and amplitude spectra. In addition, it has verified experimentally the frequency-dependence of attenuation coefficient though wavelet analysis method.

• International Journal of Advanced Culture Technology
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• v.10 no.3
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• pp.339-345
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• 2022

In this paper, the effect of porosity on the acoustic phase velocity of the 3D printed Kelvin closed-cell structure was investigated using the spectral phase analysis. Since Kelvin cells bring about the large amount of scattering, acoustic pulses in ultrasonic measurements undergoes a distortion of waveforms due to the dispersion effect. In order to take account on the dispersion, mathematical expressions for calculating the phase velocity of longitudinal waves propagating normal to the plane of the Kelvin structure are suggested by introducing a complex wave number based on Fourier transform. 3D Kelvin structure composed of identical unit-cells, a polyhedron of 14 faces with 6 quadrilateral and 8 hexagonal faces, was developed and fabricated by 3D CAD and 3D printer to represent the micro-structure of porous materials such as aluminum foam and cancellous bone. Total nine samples of 3D Kelvin structure with different porosity were made by changing the thickness of polyhedron. Ultrasonic pulse of 1MHz center frequency was applied to the Kelvin structures for the measurement of the phase velocity of ultrasound using the TOF(time-of-flight) and the phase spectral method. From the experimental results, it was found that the acoustic phase velocity decreased linearly with the porosity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.751-756
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• 2010

Ultrasonic nonlinearity is very sensitive to changes in material properties. This paper describes the study of the correlation between heat treatment and ultrasonic nonlinearity by taking nonlinear factors into consideration. A modified formula was proposed for ultrasonic velocity. This formula indicated that the changes occurring in nonlinearity during heat treatments cause changes in the ultrasonic velocity. The experimental results show that the relative nonlinearity parameters calculated from the modified ultrasonic velocities and the ratio of amplitudes of the second harmonic and fundamental wave are in good agreement. The experimental results prove that heat treatment can result in changes in material nonlinearity. Moreover, the relative nonlinearity parameter calculated from the modified velocity formula is has a large value. Since this parameter has high sensitivity to changes in nonlinearity, it can be used to represent the relative nonlinearity change calculated in this study by using the modified formula for ultrasonic velocity.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.18-24
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• 2015

Non-destructive testing (NDT) methods are widely used in the construction industry to diagnose the defects/strength of the concrete structure. However, it has been reported that the results obtained from NDT are having low reliability. In order to resolve this issue, four kinds of NDT test (ultrasonic velocity measurements by P-wave and S-wave and the impact resonance methods by longitudinal vibration and deformation vibration) were carried out on 180 concrete cylinders made with two kinds of mix proportions. The reliability of the NDT results was analyzed and compared through the measurement of the actual compressive strength of the concrete cylinders. The statistical analysis of the results was revealed that the ultrasonic velocity method by S-wave is having lowest coefficient of variation and also most capable of stable observation. Analytical equations were established to estimate the compressive strength of the concrete from the obtained NDT results by relating the actual compressive strength. Moreover the equation established by the ultrasonic velocity method by S-wave had the highest coefficient of determination. Further studies on the stability of non-destructive testing depending on various mixing conditions will be necessary in the future.

• Journal of the korean Society of Automotive Engineers
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• v.10 no.3
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• pp.38-44
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• 1988

It is important to control the axial forces of high tension bolts such as the automobile, construction machine, aircraft, marine engine bolts. However, the direct method to measure the axial forces of bolts practically have not been found out. The ultrasonic techniques is based on the principles that the bolt tensile elongation and ultrasonic velocity changes are proportional to the axial force below the yield point of the materials. From the result of the experiment, the coefficient of acoustoelasticity k could be measured as - 11.18*10$_{-5}$m $m^{2}$k $g_{f}$./.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.5
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• pp.381-388
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• 1998

The ultrasonic method, which is well known as non-destructive test method, is widely used to evaluate the material damage caused by degradation practically. However, this method is just used for measuring the crack size and the thickness loss of tube. The purpose of this study is to investigate the applicability of the ultrasonic technique for the evaluation of carburized material and to suggest the correlations between the ultrasonic characteristics and carburized degradation. The miniaturized specimens($40{\times}20{\times}6.3mm$) are adopted from the HK-40 (25Cr-20Ni-0.4C) centrifugal cast tube after carburization treatment. Carburization was carried at $1200^{\circ}C$ by the pack method. The results of ultrasonic test present that the longitudinal wave velocity increased with the increase of carburized depth. The correlation between the longitudinal wave velocity and carburization was changed with the density and Young's modulus. Therefore, the average velocity in the materials carburized for 336 hours and the unused one were 5,840 m/s and 5,755 m/s at 5 MHz, respectively. With the obtained results from this study, it can be recognized that the technique using the ultrasonic velocity property is very useful method to evaluate the degree of carburized material non-destructively.

• Journal of the Korean Wood Science and Technology
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• v.28 no.2
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• pp.19-24
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• 2000

Effects of the cross-sectional dimension and moisture profile of wood specimens on the ultrasonic sound velocities of radiata pine heartwood and sapwood. Each moisture profile model specimen was made by composing five wood pieces with various moisture contents. As the cross-sectional dimensions decreased the ultrasonic velocities of both heartwood and sapwood decreased by 4~8%. In the ultrasonic signals transmitted through the specimens low frequency components more dominated than high frequency components as the dimension of cross section increased. The specimens with the same average MCs and different moisture profiles showed different ultrasonic velocities. By plotting the ultrasonic velocities against the average moisture contents of the inner three pieces of the moisture profile model specimens it was revealed that three distinct plot patterns existed.

• Journal of the Korean Society for Nondestructive Testing
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• v.9 no.2
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• pp.25-36
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• 1989

This essay is a general review of the application of ultrasonic NDE techniques to the performance assessment and characterization of composite materials. A brief review of ultrasonic input-output characterization of a composite plate by shear waves is presented. A theoretical development of ultrasonic wave propagation in isotropic and anisotropic media excited, respectively, by a circular transducer and an oscillatory point source is summarized. Some experimental results are described in which ultrasonic velocity and attenuation measurements give insight into material degradation of fatigued composite laminates. Ultrasonic determination of the elastic constants of a composite plate and an experimental attempt at ultrasonic testing of an isotropic plate containing a crack are also included. A recent effort for the characterization of viscoelastic materials using the ultrasonic NDE technique is outlined. Finally, the reliability of ultrasonic NDE is briefly touched upon.