• Journal of Ocean Engineering and Technology
• /
• v.12 no.3 s.29
• /
• pp.31-41
• /
• 1998

Single fiber fragmentation technique was used to evaluate the change of interfacial properties by degradation of fiber tensile strength in the fiber reinforced composites. The influences of fiber tensile strength on the interfacial properties have been evaluated by the fragmentation specimens(weak fiber samples) of glass fiber/epoxy resin that was made using the pre-degraded glass fiber in distilled water at $80^{circ}C$ for specified periods. The effects of the immersion time on the interfacial properties in the distilled water at $80^{circ}C$ also have been evaluated by the fragmentation specimens(original fiber samples) of glass fiber/epoxy resin that was made using the received glass fiber. As the result, the tensile strength of glass fiber was decreased with the increasing of the treatment time in the distilled water at $80^{circ}C$ and the interfacial shear strength was independent of the change of the glass fiber strength in the single fiber fragmentation test. But in the durability test using the single fiber fragmentation specimen, interfacial shear strength decreased with the increasing of the immersion time in distilled water ar $80^{circ}C$. And it turned out that the evaluating of interfacial shear strength using original fiber tensile strength was valuable in the durability test for the water environment by the single fiber fragmentation technique.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.7 s.178
• /
• pp.1673-1680
• /
• 2000

The degradation of a boiler header constructed by a material, 1Cr-0.5Mo steel in a fossil power plant is observed when the header is exposed for a long period to the high temperature and pressure. The present investigations are for evaluating the effect of the degradation on the material, such as its strength changes. Reheat-treated metal is used to compare the mechanical properties of the degraded and that of reheat-treated materials. Through the investigation, following results are obtained 1) the area ratio of ferrite in the reheat-treated material is larger than that of the degraded material, 2) the hardness and tensile strength of the degraded material are lower than that of the reheat-treated material, 3) the ductile-brittle transition temperature(DBTT) increased toward high temperature region, 4) the fatigue crack growth rate(FCGR) of the degraded material is higher than that of the reheat-treated material in the region of low ΔK value while FCGR of the both materials are similar in high ΔK region.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.22 no.4
• /
• pp.20-29
• /
• 2014

This research aims to study the new paradigm of NDE measurement which allows the identification of defect locations and sizes of a certain structure by measuring its surface temperature after applying heat. STS which has a certain defect is applied by the heat of 70000W by a heater. Its difference of STS surface temperature is measured by using Infrared thermography. The estimated result of STS experiment and that of theoretical analysis of Flex-PDE are compared and analyzed to diagnose STS defect. Moreover, this study can save time and money and improve accuracy in contrast to the existing ultrasonic NDE experiment. In addition, the new paradigm of NDT/NDE by reverse-engineering will be valid if the data of thermal analysis and temperature distribution from the specifications of many materials is accumulated and verified.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2017.05a
• /
• pp.160-162
• /
• 2017

When rubber elastomer has contact with fuel, since the component and additive having low molecular weight can flow out, the physical properties of both elastomer and fuel could be hindered. In order to predict the life of the rubber elastomer, this study is to determine the change of weight, thickness, hardness, strain, and compression set as mechanical properties of the sealant rubber O-ring, which was dependent on volume, temperature, and storage time of the contacted fuel. We also determined purity of fuel via GC analysis and measured gross heat of combution. The results could be used as a reference to evaluate the life of the rubber elastomer.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.19 no.8
• /
• pp.77-84
• /
• 2005

The considerations for reminder life of transmission line is gradually higher. It is requisite for investigation of ACSR life to test tensile load of ACSR as a fundamental data. It is vary important to analysis correlations between results of tensile load testing and elapsed years. Estimation of ACSR life can be obtained by statistics processing using mechanical experimental results. It is a general method to use regression analysis as a statistics processing technique. In this paper, we did experiment on tensile strength of ACSR by using a new and due to flame for artificial fire, and gathering due to a flame. The limit of life estimation is decided by basic line using twenty percentage reduction of rate tensile strength. This basic line is like to results of Canada Ontario Hydro-research. There are $480[mm^2]$ ACSR which are experimented on this study.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2007.06a
• /
• pp.242-242
• /
• 2007

무방향성 규소강판을 lamination core 형태로 제작하여 자기적 특성을 조사 하였다. 그 결과 1차, 2차 권선수가 400turns 시료에서 보자력(Hc)과 포화자속밀도(Bs)는 최대값을 나타내었고, 보자력은 0.05Oe, 포화자속밀도는 1.8T 이었다. 현재 국내에서 생산되고 있는 무방향성 규소강판의 자속밀도값 보다 더 우수한 강을 나타내었으며, 열화특성이 자기적 특성에 미치는 영향을 통해 고효율 무방항성 규소강판 개발의 가능성을 확인하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2007.11a
• /
• pp.503-503
• /
• 2007

본 논문에서는 지중배전(22.9kV) 선로에 사용되는 지상변압기를 대상으로 수행한 방열해석 및 개선과 변압기수명연장에 관한 검토 결과를 수록하였다. 변압기의 열화메커니즘에 대한 문헌 조사를 통해 변압기 온도와 수명간의 관계를 작도하였는바, 수명 평가를 위한 핵심 인자로 열에 의한 절연지의 열화에 초점을 맞추었다. 기존 외함에 설치된 방열구중 상부 위치를 상부판에도 변경하는 경우 약25%의 통풍량 증가 효과를 기대할 수 있을 것으로 평가 되었으며 상부판과 내함 사이에 형성되던 고온 영역에서의 온도를 약$15^{\circ}C$정도 낮출 수 있는 것으로 나타났다. 절연지의 인장강도 변화로 평가한 수명예측 곡선에 따르면 약$10^{\circ}C$의 은도 저감은 약10배의 수명 연장 효과를 가져오는 것으로 나타난바, 본 연구에서 확인한 방열구의 위치 변경에 따른 지상기기 내부의 온도 저하는 변압기 수명을 연장하는데 일조할 것으로 기대된다. 기존 지상변압기에서의 방열구조를 통해 변압기 온도와 수명간의 관계를 작도하였는바, 수명 평가를 위한 핵심인자로 효과적으로 방열할 수 있는 새로운 외함의 구조 및 디자인을 제시하고 시뮬레이션을 통해 개선효과를 예측하였다. 또한, 개선된 모델을 가지고 실제 변압기를 제작한 후 부하를 인가하여 개선전과 후에 대한 방열효과를 실증시험을 통해 확인하였다.

• Journal of the Korean Society for Precision Engineering
• /
• v.25 no.5
• /
• pp.77-81
• /
• 2008

Structural components subjected to high frequency vibrations, such as those used in vibrating parts of gas turbine engines, are usually required to avoid resonance frequencies. Generally, the operating frequency is designed at more than resonance frequencies. When a vibrating structure starts or stops, the structure has to pass through a resonance frequency, which results in large stress concentration. This paper presents the transient thermoelastic stress analysis of vibrating cantilever beam using infrared thermography and finite element method (FEM). In FEM, stress concentration factor at the 2nd resonance vibration mode is calculated by the mode superposition method of ANSYS. In experiment, stress distributions are investigated with infrared thermography and dynamic stress concentration factor is estimated. Experimental result is agreed with FEM result within 10.6%. The advantage of this technique is a better immunity to contact problem and geometric limitation in stress analysis of small or micro structures.

• The Journal of Engineering Geology
• /
• v.25 no.2
• /
• pp.227-235
• /
• 2015

In recent years, owing to the frequent occurrence of natural disasters, the inspection and maintenance of structures have become increasingly important on a national scale. However, because most structural inspections are carried out manually, and due to the lack of objectivity in data acquisition, quantitative data are not always available. As a result, researchers are seeking ways to collect and standardize survey data using terrestrial laser scanning, thereby bypassing the limitations associated with visual investigations. However, field data acquired using a laser scanner have been required to measure changes in structure geometry resulting from passive deterioration. In this study, we demonstrate that it is possible to identify the processes of structural deterioration (e.g., efflorescence, leakage, delamination) using intensity data from terrestrial laser scanning. Additionally, we confirm the viability of automated classification of alteration type and objectification of the polygon area by establishing intensity characteristics. Finally, we show that our method is effective for structural inspection and maintenance.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.1A
• /
• pp.28-34
• /
• 2011

In this paper, we proposed the architecture of the Hybrid Quadrature Polar transmitter which has the wideband characteristics available for the SRD(Short Range Device). First, we developed the simulation environment and carried out performance degradation analysis. Second, we considered the slewrate of the VVA(Voltage Variable Attenuator), time delay between magnitude signal and phase signal and the number of bits for DAC(Digital-to-Analog Converter) as the main performance factors. Then we obtained the minimum required values to meet the transmitting performance requirements of 3GPP standards through simulation results. Based on these results, we implemented the Wideband Hybrid Quadrature Polar transmitter platform and varified the performance requirements through practical measurement.