• Journal of the Korean Society for Precision Engineering
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• v.22 no.3 s.168
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• pp.123-129
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• 2005

The unbalance of the power output, noise, and vibration is happened by the disproportionate pressure variation in the cylinder. For this reason, decrease of the pressure in the cylinder and increase of the residual gas effect on the engine performance. If the abnormal combustion is continued, the crack would be occurred in the engine block. And it could be broken down. For the normal combustion of the SI engine, it is important to supply the balanced mixture by each operating condition. In this study, it was tested the combustion characteristics in the cylinder according to the abnormal adjusting of intake & exhaust valve. This test is willing to set a basic data's analysis fur developing an automotive diagnosis system by analyzing the pressure in the cylinder, the output signal of MAP sensor, the exhaust gas, etc.

• Composites Research
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• v.15 no.4
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• pp.32-36
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• 2002

Recently, the applications of composite materials become broader to civil engineering as well as mechanics and aerospace engineering. Cracks on the civil structures like bridges can cause stress concentration, which induces Peak splitting of fiber Bragg grating sensor and it makes strain measurements difficult. In this study, 4-point bending test of concrete beam with initial crack reinforced by composite patch was conducted in order to verify the effects of the stress concentration on the peak signal of FBG sensor and a novel method for signal maintenance.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.909-914
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• 2007

In this paper, an overload detecting algorithm for an excavator is presented. The proposed overload detecting algorithm is based on the time series analysis especially moving window. The main purpose of this paper is to prevent a damage or crack from the fatigue in advance. 16 channel sensors data are considered and maximum stress is computed by a sensor fusion method every moving window. After the maximum stress every window is compared with a given threshold, this overload detecting algorithm decides overload or not.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.149-152
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• 2005

In order to extend the life time of building and civil infra-structure, nowadays, patch type carbon sheets are widely used as repairing meterials. Repaired concrete columns and beams with carbon sheets gain their stiffness and strength, but they lose toughness and show brittle failure behaviors. Usually, the cracks of concrete structures are visible with naked eyes and the status of the structure in the life cycle is estimated with visible inspection. After repairing of the structure, crack visibility is blocked by repaired carbon sheets. Therefore, structural monitoring after repairing is indispensible and self diagnosis method with optical fiber sensor is very useful. In this paper, peel-out effects is detected with optical fiber sensors and the strain difference between main structure and repaired carbon sheets when they separate each other.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.2
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• pp.95-103
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• 1993

In the manufacturing field, some traditional manufacturing and machining methods become weakened the productivity, the external competitive power, and accuracies of the products. In these point of view, the unmanned and intelligent manufacturing systems are proposed by some manufacturing companies. The real-time monitoring technology of the cutting tool conditions i.e. tool wear, tool breakage, crack, and chipping anre necessarily reauired to realize those system, especially. In this study, we constructed the multi- sensing system using the acceleration sensor, the current sensor, and the loadmeter of a machine tool. Also, we analyzed the nose breakage, the massive signal, and some monitoring features by means of the developed system.

• Journal of the Korean Geosynthetics Society
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• v.19 no.4
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• pp.41-50
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• 2020

Since cracks in concrete structures expedite corrosion of reinforced concrete over a long period of time, regular on-site inspections are essential to ensure structural usability and prevent degradation. Most of the safety inspections of facilities rely on visual inspection with naked eye, so cost and time consuming are severe, and the reliability of results differs depending on the inspector. In this study, a portable measuring device that can be used for safety diagnosis and maintenance was developed as a device that measures the width and length of concrete cracks through image analysis of cracks photographed with a camera. This device captures the cracks found within a close distance (3 m), and accurately calculates the unit pixel size by laser distance measurement, and automatically calculates the crack length and width with the image processing algorithm developed in this study. In measurement results using the crack image applied to the experiment, the measurement of the length of a 0.3 mm crack within a distance of 3 m was possible with a range of about 10% error. The crack width showed a tendency to be overestimated by detecting surrounding pixels due to vibration and blurring effect during the binarization process, but it could be effectively corrected by applying the crack width reduction function.

• Composites Research
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• v.17 no.5
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• pp.15-24
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• 2004

Longitudinal strains (${\varepsilon}_x$) of the core and skin layers in glass fiber reinforced plastic (GFRP) cross-ply composite laminates have been measured using the embedded optical fiber sensor of absolute extrinsic Fabry-Perot interferometer (A-EFPI). Transmission optical microscopy was used to investigate the damage behavior around the A-EFPI sensor. Foil-type strain gauges bonded on both the upper and lower surfaces were used for the measurement of the surface strains. It was shown that values of ${\varepsilon}_x$ in the interior of the skin layer and the core layer measured by embedded A-EFPI sensor were significantly higher than that of the specimen surface measured by strain gauges. The experimental results agreed well with those from finite element analysis on the basis of uniform stress model. Large strains in the core layer led to the occurrence of many transverse cracks which drastically reduced the strain at failure of optical fiber sensor embedded in the core layer.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.369-370
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• 2005

LTCC (Low Temperature Cofired Ceramic) technology is one of technologies which can realize SIP (System-In-a-Package). In this paper realization of gas sensor using LTCC technology was described. In the conventional gas sensor structure, wire bonding method is generally used as an interconnection method whereas in the LTCC sensor structure, via was used for the interconnection. As sensing materials, $SnO_2$ was adopted. The effect of frit glass portion on the adhesion of the sensing material to the LTCC substrate and the electrical conductivity of the sensing material were analyzed. AgPd, PdO, Pt was added to the sensing material as an additive for improving the gas sensitivity and electrical conductivity and the effect of the amount of additives in the sensing material on the electrical conductivity was investigated. The effect of the amount of frit glass in the termination on the sensor performance, especially mechanical integrity, was considered and the crack initiation and propagation in the boundary between the sensing material and the termination was studied.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.26 no.3
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• pp.306-312
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• 2017

Press rolls are constantly exposed to physical and heat stresses on their surface and are prone to crack, bruise, and spall if the accumulated stress goes beyond the critical point. Such surface phenomenon can cause them to lose their functionality and eventually lead to a halted production line. Eddy current testing can be considered a useful method to investigate the surface of the roll. The method involves the application of a high intensity magnetic field onto the surface of the roll, and thereby finding any early stage of possible defects. When the method was applied for roll inspection, the cross section of the sensor was regulated as per the overall testing speed. A smaller cross sectional area implied a better resolution but a longer testing time. In this paper, a convenient method to increase both overall system resolution and inspection speed of eddy current roll inspection is suggested by using a devised array sensor structure.

• 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.