• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.850-853
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• 2006

This paper presents a primary study for a new method of enhancing measurement using impedance analysis method, which is widely used for structure health monitoring. Many of skyscrapers, bridges, tunnels, which have been built up several years, and nearly reached their operating life due to aging crack, material deterioration, and so on. therefore, the health monitoring technique has obtained considerable attention. The usage of the PZT sensor is proposed, and the coupling torque of bolt-connection overlapping beam is assumed. By using the torque wrench, it is easy to apply torque of different values to each bolt. The coupling torque is adjusted gradually from $3N{\cdot}m\;to\;0N{\cdot}m$ with the decrement of $1N{\cdot}m$. Simultaneously, the impedance peak variation is measured. The peak frequency variation can be determined through the change of bolt coupling torque.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.409-412
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• 1997

The phenomenon of water tree degradation of underground distribution power cables is taking place in polymeric insulation materials under the existence of water and application of electric stress, but water tree is not easy to observe, o water tree features in power cables are shown after cutting and dying with methyleneblue. In previous method, it is impossible to acquire continuous treeing data, and when the insulation material has been cut, the micro crack(water tree) has been damaged. In this paper, to overcome these deflects, the etching method is made use of making needle electrode about 170[${\mu}{\textrm}{m}$] diameter, and AgNO$_3$(silver nitrate) solution is used as liquid electrode to accelerate the growth of water trees. As a result of this study, water tree is observed in real-time with microscope. Electrical tree owing to water treeing is initiated at low electric field and grown with discontinuous. Namely, water tree is shown up a different characteristics of tree growth.

• Journal of Welding and Joining
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• v.13 no.2
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• pp.12-24
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• 1995

Recently, more researches have been actively performed for the assessment of material degradation and residual-life of elevated temperature plant components, as some of domestic fossil power plants become older than 30 years. In this paper, results of on_site residual life assessment are reported for main steam pipes of Youngwol power station #2 which have operated since 1965. For critical weld locations such as butt welds branch welds, Y_sections and a T-section, replication technique and hardness measurement technique were employed for life_assessment. When cracks were detected by conventional NDT tests, crack growth life was calculated using a computer code. On the other hand, for matrix of pipes, residual life was quantitatively estimated by an analytic method and material degradation was estimated qualitatively using diameter measurement data and grain-boundary etching method. Also, direction in further improvement of on-site life assessment techniques are proposed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.12
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• pp.1142-1149
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• 2003

The strength and characteristics of the soldering interface of the power semiconductor chip in a power module has been firstly surveyed by the peel strength measurement method. A power module is combined with several power chips which generally has 30∼400$\textrm{mm}^2$ chip area to allow several tens or bigger amps in current rating, so that the traditional methods for interface characterization like shear test could not be applied to high power module. In this study power diode modules were fabricated by using lead-tin solder with 10${\times}$10$\textrm{mm}^2$ or 7${\times}$7$\textrm{mm}^2$ soldering interface. The peel strengths of soldered interfaces were measured and then the microscopic investigation on the fractured surfaces were followed. The peel test indicated that the crack propagated either through the bulk of the soft lead-tin solder which has 55-60 kgf/cm peel strength or along the interface between the solder and the plated nickel layer which has much lower 22 kgf/cm strength. This study showed that the peel test would be a useful method to quantify the solderability as well as to recognize which is the worst interface or the softest material in a power module with a large soldering area.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.1
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• pp.103-111
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• 2021

Naju Seokdanggan, Treasure No. 49, was dismantled and reconstructed due to poor performance. During construction, the crack area was reinforced and the inclination was improved. It is necessary to analyze the stiffness changes before and after the reconstruction of these cultural properties, and to establish a database of related information. In addition, there is a need for research on a scientific non-destructive testing method capable of predicting or evaluating the reinforcing effect. In this study, a simple equation for estimating the overall stiffness of the structural system was derived from information on the elasticity coefficient and the natural frequency measured by vibration tests before and after reconstruction work, and the applicability of the equation was examined. If the stiffness of important cultural properties is regularly investigated by the suggested method, it is judged that it can be used as data to estimate the time when structural safety diagnosis is necessary or when repair or reinforcement is necessary.

• Fire Science and Engineering
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• v.27 no.2
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• pp.46-53
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• 2013

The architecture environment has changed. The corresponding design criteria should be changed. From July 27th, 2005 the Korea Standard of the fire door changed concerning the smoke resistance test which made the door gap structure more elaborate. However the National Fire Safety Codes are applied by the old data's of England. Which in case differs in the actual construction to the blue print, making the safety standard too excessive. Analyze the results and the phenomenon that occurs due to the difference between design and reality. The National Fire Safety Codes should be revised to leakage crack calculation is presented. Difference of the air flow for the smoke protection due to the stack effect analyzed. Living patterns and evacuation patterns of the apartment reflect and reasonable air flow measurement method are presented.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.184-188
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• 2008

Performance degradation of concrete structures is generally caused by structural deteriorations, such as cracks. It may result in serious defects of concrete structures. Methods of damage detection are used a visual angle of human or non-destructive test, and they are using various sensors. Problems of crack damage detection are occurred to directions of cracks by using 1 axial type of accelerometer in concrete element. In addition, these sensors are not used to occurring fire in RC building. Thermocouple sensors are able to using measurement of temperature in fire, and then deformations of main element and structures are not used. In this study, fundamental studies for development of multiple function sensor using 3 axial type of accelerometer and electric resistance property of thermocouple sensors are discussed estimation to stability of structures when happened form active load or fire, and so on.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.99-99
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• 2008

To grow the large diameter GaN with high structure and optical quality has been obtained by hydride vapor phase epitaxy(HVPE) method. In addition to the nitridation of $Al_2O_3$ substrate, we also developed a "step-growth process" to reduce or to eliminate the bowing of the GaN substrate caused by thermal mismatch during cool down after growth. The as-grown 380um thickness and 75mm diameter GaN layer was separated from the sapphire substrate by laser-induced lift-off process at $600^{\circ}C$. A problem with the free-standing wafer is the typically large bowing of such a wafer, due to the built in the defect concentration near GaN-sapphire interface. A polished G-surface of the GaN substrate were characterized by room temperature Double crystal X-ray diffraction (DCXRD), photoluminescence(PL) measurement, giving rise to the full-width at half maximum(FWHM) of the rocking curve of about 107 arcsec and dislocation density of $6.2\times10^6/cm^2$.

• International Journal of Highway Engineering
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• v.15 no.2
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• pp.11-18
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• 2013

PURPOSES : This study presents the noise level and frequency characteristics investigated in the national highways with the consideration of various measuring conditions and/or methods. METHODS : The noise levels on the asphalt concrete pavement(ACP) and the jointed plain concrete pavement(JPCP) of the national highway were measured and analysed with respect to three variables, i.e., pavement type, surface condition, and measurement distance. The PASS-By method is utilized for the noise measurement and then using CPB spectrum analysis method with 1/3 octave bandwidth, the noise levels and frequency characteristics were calculated for two-second periods before and after the peak noise. RESULTS : Depending on the pavement type, the noise level was changed as the average noise levels are 73.3dB(A) and 78.3dB(A) for ACP and JPCP, respectively. With respect to the effect of surface condition, the average noise levels for crack H(high), M(medium), and L (low) sections are 77.4dB(A), 77.4dB(A), and 78.1dB(A), respectively. Regarding the measurement distance, 1.2meter difference in measuring location reduces 1.6dB(A) of noise level; the average noise levels at 5.3m and 7.5m from the centerline of outer lane are 72.8dB(A) and 71.2dB(A), respectively. It should be noted that the noise levels are slightly different as a function of vehicle speed and type. However, the overall trends for each case was similar. It was found that the domain frequency bands for ACP and JPCP were 400Hz~2000Hz and 500Hz~2000Hz, respectively. CONCLUSIONS : Based on the analysis with the measured noise date from national highway, it was concluded that the noise level and frequency band vary depending on the various conditions. It was also found that some variables significantly affect the noise level while others do not. With further systematic investigation, the comprehensive noise characteristics on the national highway can be achieved. Using such database, it is possible to develop the fundamental noise reduction technology.

• The Korean Journal of Ceramics
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• v.3 no.2
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• pp.73-81
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• 1997

In this paper, it is intended to present more reproducible and quantitative method for adhesion assemssement. In scratch test, micromechanical analysis on the stress state beneath the indenter was carried out considering the additional blister field. The interface adhesion was quantified as work of adhesion through Griffith energy approach on the basis of the analyzed stress state. The work of adhesion for DLC film/WC-Co substrate calculated through the proposed analysis shows the identical value regardless of distinctly different critical loads measured with the change of film thickness and scratching speed. On the other hand, uniaxial loading was imposed on DCL film/Al substrate, developing the transverse film cracks perpendicular to loading direction. Since this film cracking behavior depends on the relative magnitude of adhesion strength to film fracture strength, the quantification of adhesion strength was given a trial through the micromechanical analysis of adhesion-dependence of film cracking patterns. The interface shear strength can be quantified from the measurement of strain $\varepsilon$s and crack spacing $\lambda$ at the cessation of film cracking.