• Journal of the Korean Society for Precision Engineering
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• v.19 no.11
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• pp.75-82
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• 2002

Welding is used not only for the shipbuilding, but also for the repairing of ships. While repairing of ships, it is inevitable to weld new materials with degraded materials. In this case, it is predicted that the strength of both the sections is not identical each other. In this study, the respective welded joints in terms of mechanical properties such as microstructure, mechanical strength and fatigue crack propagation, with the component obtained from the barge used for a long-term period, were analyzed. It was found that the material degradation had a significant effect on the welded joints. The fatigue crack propagation in welded sections showed a big difference. The rate of fatigue crack growth of degraded material for both heat affected zone and parent metal was faster than that of new material. By contrast, the result from identical materials showed that the rate of fatigue crack growth of the heat-affected zone was slower than that of parent metal.

• Journal of Welding and Joining
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• v.16 no.6
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• pp.86-96
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• 1998

This study proposes the analysis method of time series ultrasonic signal using the chaotic feature extraction for degradation extent evaluation. Features extracted from time series data using the chaotic time series signal analyze quantitatively degradation extent. For this purpose, analysis objective in this study is fractal dimension, lyapunov exponent, strange attractor on hyperspace. The lyapunov exponent is a measure of the rate at which nearby trajectories in phase space diverge. Chaotic trajectories have at least one positive lyapunov exponent. The fractal dimension appears as a metric space such as the phase space trajectory of a dynamical system. In experiment, fractal correlation) dimensions, lyapunov exponents, energy variation showed values of 2.217∼2.411, 0.097∼ 0.146, 1.601∼1.476 voltage according to degardation extent. The proposed chaotic feature extraction in this study can enhances precision ate of degradation extent evaluation from degradation extent results of the degraded materials (SA508 CL.3)

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.4
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• pp.97-103
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• 2004

In general the starting current of single phase induction motor is 3 to 6times of the rated current It make flickering an electric lamp, dispersion a TV screen, insulation destructing an electric motor and momentary blazing of house wiring. Thus it happens losing an electric power loss and reducing an efficiency and a life of home electrical apparatus. In this paper, we proposed the method of reducing staring current with 3.7(%) using TRIAC and ACCT(alternated current transformer) in order to improve the above problem And also we verified semipermanent system with using semiconductor element.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.728-731
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• 1995

Miniaturzed specimen technology permits mechanical bechanical behavior to be determined using a minimum volume of material. because it is almost impossible to sample the conventional specimen for the fracture toughness test without damage to the rotor. In addition, it is different to collect a large amount of actual turbine rotor steels. Hence seven kinds of specimen with different degradation levels were prepared by isothermal aging heat treatment at 630 .deg. C. Test material was 1Cr-1Mo-0.25V steel which was widely used for turbine rotor material. The relation between fracture toughness and DBTT was investigated The characteristics of minaturized impact speciments technique was discussed. Finally, the estimating method of fracture toughness using a single impact specimen was introduced.

• Journal of the Korean Society of Safety
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• v.25 no.1
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• pp.22-26
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• 2010

Material degradation should be considered to assess integrity and residual life of high temperature equipments. However, the property data reflecting degradation are not sufficient for practical use. In this study, mechanical properties of 1Cr-1Mo-0.25V casting steel generally used for turbine casing were measured and variation of microstructure was observed. Degradation was simulated by isothermal heat treatment.

• Journal of the Korean Institute of Educational Facilities
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• v.4 no.3
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• pp.5-14
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• 1997

The purpose of this study is to present basic data in order to improve the efficiency and the objectivity of diagnosing educational structures built with the reinforced concrete. For achieving the purpose, this paper, firstly, researches damage aspects of 22 public educational of facilities in Seoul, and summarizes the results of that research. Through the analysis and the evaluation of damage aspects, this paper shows the conclusions as follows; (1) Main damage to reduce structural capacities of building is the differential settlement. (2) Though the steel corrosion is occurred by several factors, the main cause is the faulty construction. (3) To prevent the damage development, a proper repair strategy is very important.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2005.10a
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• pp.350-354
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• 2005

본 연구에서는 건설폐기물에 포함되어있는 폐콘크리트를 사용하여 $200^{\circ}C,\; 300^{\circ}C,\;400^{\circ}C,\;500^{\circ}C$로 각 온도에 따라 열화 처리한 후 분쇄하여 시멘트 페이스트 분리량과 골재의 물리적 특성을 파악하였다. 열화 처리의 온도가 높아질수록 시멘트 페이스트의 분리율은 높아졌으며, 압축강도는 낮아지는 경향을 보였다.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.287-288
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• 2009

In this study, the degree of deterioration on the tunnel lining concrete due to crack and leakage was evaluated by field-investigating the conventional tunnels constructed a long time ago. By examining the exterior, conducting the non-destructive test and collecting cores for the tunnel concrete linings, this study evaluated the compressive strength and the permeability, and also performed instrumental analyses.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.222-227
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• 2001

Nonlinear acoustic effect has been considered as an effective tool for the evaluation of material degradation. In this paper, the applicability of nonlinear acoustic effect to the evaluation of degradation of 2.25Cr-1Mo steel is investigated. Firstly, a number of 2.25Cr-1Mo steel samples were heat-treated, and their damage mechanism was examined. Secondly, Ultrasonic nonlinear parameter was measured. Nonlinear acoustic parameter was found to be clearly sensitive to the material degradation.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.210-215
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• 2001

The ferritic 2.25CrMo steel has been used for high temperature structure applications such as turbine rotors, boilers and pressure vessels in fossil plant and petroleum chemical facilities. However, this steel is known to result in aging degradation due to temper embrittlement, carbide induced brittleness and softening of matrix after long time exposure to high temperature. This research investigated the microstructural and mechanical changes after artificial degradation treatment and evaluated the degree of degradation by several nondestructive methods. The decrease of electrical resistivity and increase of magnetic Barkhausen noise(RMS voltage) with increasing aging time were observed. The change of electrical resistivity and Barkhausen noise showed a good correlation with the ductile-brittle transition temperature.