• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.2
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• pp.357-363
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• 1995

Disbond size of adhesively bonded single lap and double lap joints CFRP composite specimens has been evaluated using acousto-ultrasonic(AU) technique. Frequency spectra for all specimens were obtained by measuring peak amplitude of the stress wave propagated through the bond-lines. By analyzing these frequency spectra, peak amplitude was found to be proportional to fractional bonding area and to be maxima at the fundamental and the third order higher harmonic frequencies of specimen thickness mode. The disbond size can be evaluated quantitatively and this technique can be applied to real structures if the reference specimens are prepared in advancve.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.2
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• pp.152-162
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• 2001

Laser-generated ultrasonic technique which is one of the reliable nondestructive evaluation techniques has been applied to evaluate the integrity of structures by analyzing the characteristics of signal obtained from surface crack. Therefore, the signal analysis of the laser-generated ultrasonics is absolutely necessary for the accurate and quantitative estimation of the surface defects. In this study, one-sided measurement by laser-generated ultrasonic has been applied to evaluate the depth of the surface-breaking crack in the materials. However, since the ultrasonic waveform excited by pulse laser is very difficult to distinguish the defect signals, it is necessary to consider the signal analyses of the transient waveform. Wavelet Transform(WT) is a powerful tool for processing transient signals with temporally varying spectra that helps to resolve high and low frequency transient components effectively. In this paper, the analyses of the surface-breaking crack of the ultrasonic signal excited by pulse laser are presented by employing the WT analyses.

• Journal of the KSME
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• v.28 no.4
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• pp.387-393
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• 1988

본 SP시험법은 사용되는 시편이 미소하다는 장점 때문에 재질의 평가나 더불어 비파괴검사의 일환으로서 이용할 수 있음을 서명해 왔다. 현존하고 있는 거대구조물들의 잔존수명평가가 요 구되는 있는 지금, 정량적인 경년변화측정방법으로서 SP시험법은 높은 가능성을 내포하고 있는 시험법으로 여겨지며, 이 방법을 현장에 정착시키기 위해선 산. 학. 연의 공동연구체제가 필요 하다고 할 수 있다.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.11
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• pp.29-36
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• 2007

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.2
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• pp.130-137
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• 2000

Ultrasonic technique which is one of the most common and reliable nondestructive evaluation techniques has been applied to evaluate the integrity of structures by analyzing the characteristics of signal scattered from internal defects. Therefore, the numerical analysis of the ultrasonic scattered field is absolutely necessary for the accurate and quantitative estimation of internal defects. Various modeling techniques now play an important role in nondestructive evaluation and have been employed to solve elastic wave scattering problems. Because the elastodynamic boundary element method is useful to analyze the scattered field in infinite media. it has been used to calculate the ultrasonic wavefields scattered from internal defects. In this study, a review of the boundary element method used for elastic wave scattering problems is presented and, as examples of the boundary element method, the scattered fields due to a circular cavity subjected to incident SH-wave and due to a surface-breaking crack subjected to incident Rayleigh wave are illustrated.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.3
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• pp.206-212
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• 2000

The guided wave mode conversion phenomena were investigated for the NDE of a plate-like structure with thickness variation. The ratios of reflection and transmission (R/T) were measured via the self-calibrating procedure which allows us to obtain experimental guided wave data in a more reliable way regardless of the coupling uncertainty between transducer & specimen. The results on R/T could be used to determine the thickness reduction of the structure. It was shown that not only the incident modes but also the converted ones need to be considered in the self-calibrating guided wave inspection to extract a reasonable correlation between experimental data & the thickness variation. Through this study, the potential of guided wave inspection as a quantitative NDE technique was explored based on the combined concept of self-calibration & multi-mode conversion in guided wave scattering problems.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.5
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• pp.532-541
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• 2001

Developments of nondestructive evaluation techniques for reduction of strength or toughness by aging of material have been carried out, and the method using electrical resistivity is one of them. In this study, to examine the application of electrical resistivity to the evaluation of degradation of metallic alloy, ten different non-magnetic materials were selected as test materials. Electrical resistivities measured by DC two-point probe method and those measured by non-contact type eddy current method were compared with each other. In addition, to examine the application possibility of four-point probe technology in field, the electrical resistivities for 1Cr-lMo-0.25V steel measured by DC two-point probe method and four-point probe method were compared with each other Differences between two measured values for the 1Cr-1Mo-0.25V steel were 0.6%. Therefore, the four-point probe method can be applied to the estimation of the degradation of metallic alloy. ect.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.6
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• pp.411-419
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• 1999

It has been well recognized that a long term service at elevated temperature of $350^{\circ}C{\sim}550^{\circ}C$ induces embrittlement damage due to carbide precipitation and/or P, Sb and Sn segregation at grain boundaries and thereby deteriorates the grain boundary strength of heat resisting components in the energy-related plants. Therefore, it is very important to assess quantitatively the extent of embrittlement damage of heat resisting components to secure the reliable and efficient service condition and to prevent brittle failure in service. However, because fracture tests are limited in size and number of specimen obtained from the structural components, nondestructive test method is required. In this study, the optimum electrochemical parameters are investigated and discussed to evaluate nondestructive embrittlement damage for aged 2.25Cr-1Mo steels by means of electrochemical polarization test method (ECPTM) in proper corrosive environment. In addition, the electrochemical test results are compared with embrittlement degree evaluated by semi-nondestructive SP test.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.2
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• pp.141-147
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• 2014

A nondestructive ultrasonic technique was applied to evaluate the thermal characteristics and degradation of synthetic polymer resin (plastics) with better cost-effectiveness and functionality than glass and metal. Thermoplastic and transparent acrylic resin (PMMA) specimens were annealed at below the glass transition temperature ($T_g$), and the propagation characteristics (attenuation and velocity) were measured. The attenuation increased and the velocity decreased with thermal degradation. The results showed that the thermal aging of the specimens could be evaluated quantitatively and that the Tg could be evaluated qualitatively.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.437-443
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• 2010

In recent years, as nano scale structured thin film technology has emerged in various fields such as the materials, biomedical and acoustic sciences, the quantitative nondestructive adhesion evaluation of thin film interfaces using ultra high frequency scanning acoustic microscopy(SAM) has become an important issue in terms of the longevity and durability of thin film devices. In this study, an effective technique for investigating the interfaces of nano scale structured thin film systems is described, based on the focusing of ultrasonic waves, the generation of leaky surface acoustic waves(LSAWs), V(z) curve simulation and ultra high frequency acoustical imaging_ Computer simulations of the V(z) curve were performed to estimate the sensitivity of detection of micro flaws(i.e., delamination) in a thin film system. Finally, experiments were conducted to confirm that a SAM system operating at a frequency of 1 GHz can be useful to visualize the micro flaws in nano structured thin film systems.