• Proceedings of the KIPE Conference
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• 2002.11a
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• pp.205-208
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• 2002

Thermal design is required with considering thermal stability to verify the reliability of electric power device with using IGBT. Numerical analysis is performed to analyzed the change in thermal resistance with respect to the various thermal density of heating element. Correlations between thermal resistance and heat generation density are established. With using these correlations, performance curve is composed with respect to the change in thermal resistance of cooling conditions for natural convection and forced convection. Thermal fatigue is occurred at the Inside and outside of IGBT by repeated heat load. The crack is occurred between base plate and ceramic substrate for the inside. When the crack length is 4mm, the failure is occurred. Therefore, Thermal design method considering thermal density, thermal fatigue resistance is presented on this study and it is expected to thermal design with considering life prediction.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.11
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• pp.918-923
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• 2008

Since crack detection for laminated composites in-service is effective to improve the structural reliability of laminated composites, it have been tried to detect cracks of laminated composites by various nondestructive methods. An electric potential method is one of the widely used approaches for detection of cracks for carbon fiber composites, since the electric potential method adopts the electric conductive carbon fibers as reinforcements and sensors and the adoption of carbon fibers as sensors does not bring strength reduction induced by embedding sensors into the structures such as optical fibers. However, the application of the electric method is limited only to electrically conductive composite materials. Recently, a piezoelectric method using piezoelectric characteristics of epoxy adhesives has been successfully developed for the adhesive joints because it can monitor continuously the damage of adhesively bonded structures without producing any defects. Polymeric materials for the matrix of composite materials have piezoelectric characteristics similarly to adhesive materials, and the fracture of composite materials should lead to the fracture of polymeric matrix. Therefore, it seems to be valid that the piezoelectric method can be applied to monitoring the damage of composite materials. In this research, therefore, the feasibility study of the damage monitoring for composite materials by piezoelectric method was conducted. Using carbon fiber epoxy composite and glass fiber composite, charge output signals were measured and analyzed during the static and fatigue tests, and the effect of fiber materials on the damage monitoring of composite materials by the piezoelectric method was investigated.

• Journal of Oral Medicine and Pain
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• v.32 no.4
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• pp.403-411
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• 2007

This investigation was carried out to evaluate the effect of Transcutaneous Electric Nerve Stimulation (TENS) to experimentally induced masticatory muscle pain and muscular fatigue. Twenty-nine healthy volunteers (18 men and 11 women, aged $26.1{\pm}4.7$ years) without past history or present symptoms of temporomandibular disorders were participated in this study. All of the subjects were randomly assigned to experimental group and control group, after at least 3 days interval, two groups were reassigned conversely. Subjects assigned to experimental group were received TENS and others assigned to control group were received sham-TENS therapy for 45 minutes, respectively. The changes of Visual Analogue Scale (VAS), Pressure Pain Threshold (PPT), and EMG power spectrum were measured on the masseter muscle both before and after sustained fatiguing contraction in each group. The major findings of this study are as follows : 1. PPTs and median frequencies of masseter muscles were significantly decreased after sustained isometric contraction resulting in muscular fatigue. 2. In experimental group received TENS therapy, PPTs measured both before and after occurrence of experimentally induced muscular fatigue were significantly increased. 3. In experimental group received TENS therapy, the changes of PPTs during sustained isometric contraction resulting in muscular fatigue were significantly decreased. 4. In experimental group received TENS therapy, VAS measured after occurrence of experimentally induced muscular fatigue was significantly decreased. 5. Although there were not statistical significances, endurance time was increased in experimental group received TENS therapy and decreased in control group received sham-TENS therapy. 6. In experimental group received TENS therapy, the changes of median frequencies were the less decreased and the slope of median frequency shift was the more increased during endurance time than in control group, however, there were not statistical significances.

• KEPCO Journal on Electric Power and Energy
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• v.4 no.1
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• pp.25-31
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• 2018

A boiler system transforms water to pressured supercritical steam which drives the running of the turbine to rotate in the generator to produce electricity in power plants. Materials for building the tube system face challenges from high temperature creep damage, thermal fatigue/expansion, fireside and steam corrosion, etc. A database on the creep resistance strength and steam oxidation of the materials is important to the long-term reliable operation of the boiler system. Generally, the ferritic steels, i.e., grade 1, grade 2, grade 9, and X20, are extensively used as the superheater (SH) and reheater (RH) in supercritical (SC) and ultra supercritcal (USC) power plants. Currently, advanced austenitic steel, such as TP347H (FG), Super304H and HR3C, are beginning to replace the traditional ferritic steels as they allow an increase in steam temperature to meet the demands for increased plant efficiency. The purpose of this paper is to provide the state-of-the-art knowledge on boiler tube materials, including the strengthening, metallurgy, property/microstructural degradation, oxidation, and oxidation property improvement and then describe the modern microstructural characterization methods to assess and control the properties of these alloys. The paper covers the limited experience and experiment results with the alloys and presents important information on microstructural strengthening, degradation, and oxidation mechanisms.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.345-352
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• 2016

As aircrafts are being operated at high altitude, wing structures experience various fatigue loadings under cryogenic environments. As a result, fatigue damage such as a crack could be develop that could eventually lead to a catastrophic failure. For this reason, fatigue damage monitoring is an important process to ensure efficient maintenance and safety of structures. To implement damage detection in real-world flight environments, a special cooling chamber was built. Inside the chamber, the temperature was maintained at the cryogenic temperature, and harmonic fatigue loading was given to a wing structure. In this study, piezoelectric active-sensing based guided waves were used to detect the fatigue damage. In particular, a beamforming technique was applied to efficiently measure the scattering wave caused by the fatigue damage. The system was used for detection, growth monitoring, and localization of a fatigue crack. In addition, a sensor diagnostic process was also applied to ensure the proper operation of piezoelectric sensors. Several experiments were implemented and the results of the experiments demonstrated that this process could efficiently detect damage in such an extreme environment.

• International Journal of Safety
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• v.2 no.1
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• pp.17-22
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• 2003

In order to analyze general three dimensional cracks in an infinite body, the symmetric Galerkin boundary element method formulated by Li and Mear is used. A crack is modelled as distribution of displacement discontinuities, and the governing equation is formulated as singularity-reduced integral equations. With the proposed method several example problems for three dimensional cracks in an infinite solid, as well as their growth under fatigue, are solved and the accuracy and efficiency of the method are demonstrated.

• Proceedings of the KIEE Conference
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• 2000.07d
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• pp.2741-2743
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• 2000

내구시험기의 기본적인 구조를 해석하고 분석하여 각종 기구부의 내구성 시험에서 적용대상물에 관계없이 전기유압서보장치의 용량과 적합한 센서들을 조합하여 구성 가능하도록 시험기를 구성하였으며, 본 연구에서 개발된 제어장치와 데이터 수집 소프트웨어는 내구시험 대상물에 관계없이 범용 적으로 사용할 수 있도록 개발하였다.

• Proceedings of the KSR Conference
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• 2003.05a
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• pp.597-603
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• 2003

Air spring system in railway vehicles primarily ensure the air suspension of the vehicle body. The low natural frequency ensures a comfortable ride and an invariably good stiffness. In this paper, the characteristics and durability test was conducted in laboratory by using servo-hydraulic fatigue testing system to reliability evaluation of air spring for electric railway vehicle. The experimental results show that the characteristics and durability of domestic development productions are obtained the good results.

• Journal of the Semiconductor & Display Technology
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• v.1 no.1
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• pp.29-33
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• 2002

In the flip-chip process, the problem like electric defect or fatigue crack caused by the difference of CTE, between chip and substrate board had occurred. Underfill of flip chip to overcome this defects is noticed as important work developing in whole reliability of chip by protecting the chip against the external shock. In this paper, we introduce the underfill methods using mold and plunge and improvement of process and reliability, and the advantage which can be taken from embodiment of device.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.4
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• pp.583-588
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• 2016

The high-temperature steam pipes of thermal power plants are subjected to severe conditions such as creep and fatigue due to the power plant frequently being started up and shut down. To prevent critical pipes from serious damage and possible failure, inspection methods such as computational analysis and online piping displacement monitoring have been developed. However, these methods are limited in that they cannot determine the life consumption rate of a critical pipe precisely. Therefore, we set out to develop a life assessment system, based on a three-dimensional piping displacement monitoring system, which is capable of evaluating the life consumption rate of a critical pipe. This system was installed at the "M" thermal power plant in Malaysia, and was shown to operate well in practice. The results of this study are expected to contribute to the increase safety of piping systems by minimizing stress and extending the actual life of critical piping.