• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.6
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• pp.807-815
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• 2004

In order to evaluate the static stability of hybrid carbody structures of Korean Tilting Train eXpress(TTX) caused by degradation of composites under ground environments, T300/AD6005 graphite/epoxy composite specimens were exposed to accelerated environmental conditions including ultraviolet radiation, temperature and moisture fer 2000 hours. It was found that the stiffness and strength of composites after aging were lower than those of unexposed specimens, and decreased as the aging time increases. The values of the degraded properties were used in the static analysis to check the static stability of hybrid carbody structures caused by environmental degradation of composites. The results shown that the structural stability of hybrid carbody structures was affected by the degradation of composites after exposure to accelerated aging environments.

• Journal of The Korean Society of Agricultural Engineers
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• v.50 no.3
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• pp.51-58
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• 2008

Ninety five percent of the agricultural reservoirs were constructed by earth or rock. There are 18,000 agricultural dams and reservoirs in Korea. Therefore, it is easy to evaluate or identify their problems. Reservoirs should be repaired before too late. It is required to guarantee the proper functions of the existing agricultural dams and reservoirs in time to minimize the damage. In this study, in order to evaluate degradation of agricultural reservoir, grasps the safety of reservoir choosing for agriculture of 25 reservoirs which are distributed in Chungbuk region rural and analyzed using possibility as reservoir of agricultural usage. The degradation was evaluated by a compilation of the result where embankment and structure were separately handled, measured and then multiplied scores for each categories. By activating this research, current status of agricultural reservoir and degradation status will be easily measured. In addition, the research could be also used as a tool for an effective control or maintenance.

• Elastomers and Composites
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• v.52 no.2
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• pp.131-135
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• 2017

Zinc nitrate hexahydrate [$Zn(NO_3){\cdot}6H_2O$] and sodium hydroxide [NaOH] were used as source reagents in the preparation of ZnO nanoparticles in an aqueous solution containing deionized water and ethanol in a ratio of 2:5 (v/v). ZnO nanoparticles were heated in an electric furnace at $700^{\circ}C$ for 2 h under an atmosphere of inert argon gas. The morphological and structural properties of the nanoparticles were characterized by scanning electron microscopy (SEM) and powder X-ray diffractometry (XRD). UV-vis spectrophotometry was used to analyze the photocatalytic degradation of 3-nitrophenol with ZnO nanoparticles as photocatalyst under ultraviolet irradiation at 254 nm. Evaluation of the kinetic of the photo-catalytic degradation of 3-nitrophenol indicated that the degradation of 3-nitrophenol with ZnO nanoparticles obeyed the pseudo-first order reaction rate model.

• Journal of Surface Science and Engineering
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• v.52 no.1
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• pp.16-22
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• 2019

The structural change of DLC coatings during long-term wear test and dicing test under the low loading condition was investigated. DLC coatings were applied for the precision injection molds of a modified SNCM steel for the extension of life and the micro-diamond blades for the high cutting efficiency and the increase in life. A ball-on-disc wear tests in the mold steel and a dicing tests in the micro-diamond blades were conducted to understand degradation of DLC coatings. The degradation of DLC coatings for the injection mold steel and the micro-diamond blades during the wear and dicing tests were studied with Raman Spectroscopy. Raman peaks were divided two bands(D band and G band) to study the degradation process of DLC structure. By the wear test, polished condition of wear marks were observed to be maintained until 10 hrs of wear test period is given, but small striation marks appeared in 20 hours wear test. It was observed that $I_D/I_G$ ratios changed as the degradation of DLC coatings is proceeded during the wear tests and the dicing tests. It is suggested that the change in $I_D/I_G$ value possibly reflected from the composition of $sp^2$ and $sp^3$ bondings in DLC layers relevant to the change in mechanical and physical property.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.132-132
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• 2009

To achieve the commercialization of PEM fuel cell, the durability problem must be solved. Recently, many researchers have focused on this durability problem and degradation studies about membrane and electrode have been reported. But durability characteristics of gas diffusion layer is not much reported yet. Durability of GDL is very important to maintain the performance of PEM fuel cell because the main function of GDL is a path of fuel and water and the GDL degradation causes the loss of the GDL function. In this study, the degradation of GDL, especially, the mechanical degradation process was investigated with the leaching test. The effect of water dissolution was observed through the test and the amount of GDL degradation was measured with various measurement methods such as weight measurement, static contact angle measurement, scanning electron microscope. After 2,000 hours test, the GDL showed structural damage and loss of hydrophobicity.

• Steel and Composite Structures
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• v.27 no.4
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• pp.417-426
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• 2018

This paper presents the seismic behaviors and restoring force model of ring beam joints of steel tube-reinforced concrete column structure under cyclic loading. First, the main failure mode, ultimate bearing capacity, stiffness degradation and energy dissipation capacity are studied. Then, the effects of concrete grade, steel grade, reinforcement ratio and radius-to-width ratios are discussed. Finally, the restoring force model is proposed. Results show that the ring beam joints of steel tube-reinforced concrete column structure performs good seismic performances. With concrete grade increasing, the ultimate bearing capacity and energy dissipation capacity increase, while the stiffness degradation rates increases slightly. When the radius-width ratio is 2, with reinforcement ratio increasing, the ultimate bearing capacity decreases. However, when the radius-to-width ratios are 3, with reinforcement ratio increasing, the ultimate bearing capacity increases. With radius-to-width ratios increasing, the ultimate bearing capacity decreases slightly and the stiffness degradation rate increases, but the energy dissipation capacity increases slightly.

• KIEAE Journal
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• v.7 no.4
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• pp.141-146
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• 2007

It is necessary to guarantee the safety, serviceability and durability of reinforced concrete structures over their service life. However, concrete structures represent a decrease in their durability due to the effects of external environments according to the passage of time, and such degradation in durability can cause structural degradation in materials. In concrete structures, some degradations in durability increase the corrosion of embedded rebars and also decrease the structural performance of materials. Thus, the structural condition assessment of RC materials damaged by corrosion of rebars becomes an important factor that judges needs to apply restoration. In order to detect the damage of reinforced concrete structures, a visual inspection, a nondestructive evaluation method(NDE) and a specific loading test have been employed. However, obscurities for visual inspection and inaccessible members raise difficulty in evaluating structure condition. For these reasons, detection of location and quantification of the damage in structures via structural response have been one of the very important topics in system identification research. The main objective of this project is to develope a methodologies for the damage identification via static responses of the members damaged by durability. Six reinforced concrete beams with variables of corrosion position and corrosion width were fabricated and the damage detections of corroded RC beams were performed by the optimization and the conjugate beam methods using static deflection. In results it is proved that the conjugate beam method could predict the damage of RC members practically.

• Steel and Composite Structures
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• v.10 no.3
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• pp.207-222
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• 2010

Fire incident in buildings is common, so the fire safety design of the framed structure is imperative, especially for the unprotected or partly protected bare steel frames. However, software for structural fire analysis is not widely available. As a result, the performance-based structural fire design is urged on the basis of using user-friendly and conventional nonlinear computer analysis programs so that engineers do not need to acquire new structural analysis software for structural fire analysis and design. The tool is desired to have the capacity of simulating the different fire scenarios and associated detrimental effects efficiently, which includes second-order P-D and P-d effects and material yielding. Also the nonlinear behaviour of large-scale structure becomes complicated when under fire, and thus its simulation relies on an efficient and effective numerical analysis to cope with intricate nonlinear effects due to fire. To this end, the present fire study utilizes a second-order elastic/plastic analysis software NIDA to predict structural behaviour of bare steel framed structures at elevated temperatures. This fire study considers thermal expansion and material degradation due to heating. Degradation of material strength with increasing temperature is included by a set of temperature-stress-strain curves according to BS5950 Part 8 mainly, which implicitly allows for creep deformation. This finite element stiffness formulation of beam-column elements is derived from the fifth-order PEP element which facilitates the computer modeling by one member per element. The Newton-Raphson method is used in the nonlinear solution procedure in order to trace the nonlinear equilibrium path at specified elevated temperatures. Several numerical and experimental verifications of framed structures are presented and compared against solutions in literature. The proposed method permits engineers to adopt the performance-based structural fire analysis and design using typical second-order nonlinear structural analysis software.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.3
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• pp.507-528
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• 2014

In the ship and offshore structure design, age-related problems such as corrosion damage, local denting, and fatigue damage are important factors to be considered in building a reliable structure as they have a significant influence on the residual structural capacity. In shipping, corrosion addition methods are widely adopted in structural design to prevent structural capacity degradation. The present study focuses on the historical trend of corrosion addition rules for ship structural design and investigates their effects on the ultimate strength performance such as hull girder and stiffened panel of double hull oil tankers. Three types of rules based on corrosion addition models, namely historic corrosion rules (pre-CSR), Common Structural Rules (CSR), and harmonised Common Structural Rules (CSR-H) are considered and compared with two other corrosion models namely UGS model, suggested by the Union of Greek Shipowners (UGS), and Time-Dependent Corrosion Wastage Model (TDCWM). To identify the general trend in the effects of corrosion damage on the ultimate longitudinal strength performance, the corrosion addition rules are applied to four representative sizes of double hull oil tankers namely Panamax, Aframax, Suezmax, and VLCC. The results are helpful in understanding the trend of corrosion additions for tanker structures.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.2
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• pp.131-138
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• 2013

The high damping rubber bearings contributed to reduce a seismic force transmitted to upper structures, the material properties of rubber changes with time and the rubber with age-related degradation can affect the seismic response of structures and equipments. Therefore the seismic response of structure considering age-related degradation of isolators should be evaluated. In this paper, the stiffness and damping for isolators were defined using the aging data proposed by other researchers. The reactor containment building and the auxiliary building were selected to conduct the nonlinear analysis and the natural frequency, maximum responses, floor response spectrum(FRS) were evaluated with time using the four earthquakes with different frequency contents. According to the analysis results, the seismic responses are increased by the age-related degradation of isolators and the detail inspections should be conducted up to 20 years because it was presented that the change of FRS was high during this period.