• International Journal of Highway Engineering
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• v.20 no.3
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• pp.1-9
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• 2018

PURPOSES : In order to evaluate a crack resistance at cold joint, sealing tape was adopted to apply at cold joint instead of typical tack coat material(RSC-4). The sealing tape was made by hot sealing material. The crack resistance as function of environmental and traffic loading was measured with visual observation. METHODS : In this study, the crack resistance was evaluated as function of environmental and traffic loading. The freeze-thaw method was adopted for environmental loading of asphalt pavement. condition. The damage of cold joint under freeze-thaw action is initiated by ice expansion load and accelerated by the interfacial damage between new and old asphalt pavement. The traffic loading was applied with wheel tracking machine on the cold joint area of the asphalt pavement for 3 hours at $25^{\circ}C$. The evaluation of crack resistance was measured with visual observation. The freeze-thaw results shows that the sealing tape was significantly increased the crack resistance based on. RESULTS : To estimate the crack resistance at cold joint area due to the environmental loading, the Freeze-thaw test was conducted by exposing the product to freezing temperature(approximately $-18^{\circ}C$) for 24 hours, and then allowing it to thaw at $60^{\circ}C$ for 24 hours. The tack coat material(RSC-4) was debonded after 21 cycles of the Freeze-thaw test. The first crack was observed after 14 freeze-thaw cycle with RSC-4 material. But, the sealing tape was not debonded after 24 cycle test. Also, the sealing tape shows the better performance of the crack resistance under the traffic loading with wheel track test. The crack was generated the under traffic loading with RSC-4(tack coating), however, the crack was not shown with sealing tape. It indicates that the sealing tape has a strong resistance of tensile stress due to traffic loading. CONCLUSIONS :Based on limited laboratory test result, a performance of crack resistance using the sealing tape is better than that of general tack coat material(RSC-4). It means that the sealing tape is possible to extend a pavement service life because the crack, one of the main pavement distresses, will be delayed.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.618-629
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• 2001

This paper presents a result of failure analysis and reliability evaluation for high voltage ceramic capacitors. The failure modes and failure mechanisms were studied in two ways in order to estimate component life and failure rate. The causes of failure mechanisms for zero resistance phenomena under withstanding voltage test in high voltage ceramic capacitors molded by epoxy resin were studied by establishing an effective root cause failure analysis. Particular emphasis was placed on breakdown phenomena at the ceramic-epoxy interface. The validity of the results in this study was confirmed by the results of accelerated testing. Thermal cycling test for high voltage ceramic capacitor mounted on a magnetron were implemented. Delamination between ceramic and epoxy, which might cause electrical short in underlying circuitry, can occur during curing or thermal cycle. The results can be conveniently used to quickly identify defective lots, determine $B_{10}$ life estimation each lot at the level of inspection, and detect major changes in the vendors processes. Also, the condition for dielectric breakdown was investigated for the estimation of failure rate with load-strength interference model.

• Journal of Adhesion and Interface
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• v.21 no.2
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• pp.65-70
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• 2020

Epoxy adhesive was mainly used to combine different composite materials. Epoxy adhesive was a typical thermosetting resin that can be bonded by changing from a linear structure to a three-dimensional network structure by curing reaction of epoxy and hardener. The curing conditions of epoxy adhesive were different with different types of hardener such as mixing ratio, curing time, and temperature. These curing conditions affected to the adhesive property of epoxy adhesive. In industry, it was difficult to proceed the applying epoxy adhesive and combining two parts immediately. The adhesive property decreased by humidity and pre-curing of epoxy adhesive in waiting time between two processes. In this paper, the glass fiber reinforced composite (GFRC) was combined with epoxy adhesive and adhesion property between epoxy adhesive and GFRCs was evaluated using single lap shear test. The different waiting times and humidity conditions were applied to epoxy adhesive in room temperature and adhesive property decreased as the waiting time increased. In small amount of humidity, the adhesive property increased because a small amount of moisture in the surroundings accelerated the curing reaction. In certain amount of humidity, however, the adhesion property decreased.

• Journal of the Korea Concrete Institute
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• v.25 no.6
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• pp.621-630
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• 2013

Several techniques for steel corrosion detection are proposed and HCP (half cell potential) technique is widely adopted for field investigation. If concrete has cracks on surface, steel corrosion is rapidly accelerated due to additional intrusion of chloride and carbon dioxide ions. This study is for an evaluation of HCP in cracked concrete exposed chloride attack. For this work, RC (reinforced concrete) beams are prepared considering 3 w/c ratios (0.35, 0.55, and 0.70) and several cover depths (10~60 mm) and various crack widths of 0.0~1.0 mm are induced. For 35 days, SST (salt spraying test) is performed for corrosion acceleration, and HCP and corrosion length of rebar are evaluated. With increasing crack width, w/c ratios, and decreasing cover depth, HCP measurements increase. HCP evaluation technique is proposed considering the effects of w/c ratios, crack width, and cover depth. Furthermore anti-corrosive cover depths are obtained through Life365 program and the results are compared with those from this study. The results shows relatively big difference in cracked concrete, however provide similar anti-corrosive conditions in sound concrete.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.424-429
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• 2018

In this study, an expansion joint that is susceptible to waterhammer was tested for its vibration durability. The operation data for the hydraulic actuator was the expansion length of the expansion joint when the waterhammer occurred. In the case of the vibration durability test, the internal temperature status of the expansion joint was assumed to be a stress factor and a lifespan prediction model was assumed to follow the Arrhenius model. A test was carried out by increasing the internal temperature status at $30^{\circ}C$, $50^{\circ}C$, and $65^{\circ}C$. By a linear transformation of the lifespan data for each temperature, a constant value and activation energy coefficient was induced for the Arrhenius equation and verified by comparing the value of a lifetime prediction model with the experimental value at $85^{\circ}C$. The failure modes of the ongoing or finished test were leakage, bellows separation, and internal deformation. In the future, a composite lifespan prediction model, including two more stress factors, will be developed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.9
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• pp.784-793
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• 2017

A two-axis gimbal-type X-band antenna mounted on an observation satellite can efficiently transmit high-capacity image data to a ground station regardless of both the satellite position and the orbital motion. However, this X-band antenna induces unnecessary micro-jitter which can degrade the image quality of the high-resolution observation satellite. Therefore, to achieve the high-resolution image quality from the observation satellite, micro-jitters have been required to be isolated. In this study, to resolve aforementioned drawback, we proposed blade gear using a shape memory alloy (SMA) applied to azimuth stage of X-band antenna. To investigate the rotational basic characteristics of the proposed SMA blade gear, we performed rotational static loading test. Futhermore, to evaluate the cycle to failure of the gear, accelerated life test was conducted. The temperature test was conducted to confirm rotational basic characteristics at various temperature conditions. To verify the isolation performance for micro-jitter, we performed micro-jitter measurement test.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.45 no.5
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• pp.49-55
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• 2013

To explore the paper materials for restoration of the Annals of the Joseon Dyansty, durability of the three type of the traditional Korean Papers were estimated in this study, through moist heat artificial aging test. Three types(D, F, and G) which showed the best preservation performance in dry heat and UV treatment in the previous study were selected and artificial accelerated aging treatment with moist-heat process was conducted; the viscosity change rate was D>G>F; folding endurance G>D>F; $L^*$ value F>D>G; $a^*$ and $b^*$ change rate D>G>F; brightness decrease rate D>G>F, suggesting paper F showed the least change rate in physical/optical properties. Also the CLSM image observation showed fair coherence among fibers and confirmed paper mulberry. And in FDI extraction from each sample, paper F showed the highest value. Overall, paper F (traditional glossy paper) showed the highest stability against thermal treatment. It confirms that paper F is suitable as restoration paper for tributary remains including the annals of the Joseon Dynasty for its steady strength/viscosity decrease rate and color change rate.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.15 no.1
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• pp.83-93
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• 1982

In this work, lipid oxidation and the kinetics of the oxidation reaction in fried file-fish meat were investigated when sun-dried file-fish was stored under the conditions of various water activities and temperature, 35, 45, 55 and $35/55^{\circ}C$. The storage stability and the development of browning by oxidative rancidity were also discussed. Monolayer coverage value of water content in dried file-fish was $8.03\%$ at $0.21\;a_w$Lipid oxidation at $35^{\circ}C$ was developed with increasing water activity but at $45^{\circ}C$and $55^{\circ}C$ it was rapidly progressed without clear differences between water activities except $0.44\;a_w$. The rate of reaction was more sensitive to storage temperature than to water activity. Browning in methanol-chloroform fraction was developed linearly by the progress of lipid oxidation which suggested that lipid oxidation was greatly influential to the development of browning in dried fish meat. In kinetical analysis the oxidation followed a zero order reaction mechanism as a function of carbonyl value. The activation energies obtained from the Arrhenius plot ranged 9.0 to 10.8 Kcal/mol and $Q_10$ values, 1.6-1.7. Shelf-lives at the storage of 35,45 and $55^{\circ}C$ ranged 58 days to 8 days. And in the fluctuating temperature storage at $35/55^{\circ}C$, shelf-lives were 17, 16, 15 and 13 days at 0.44, 0.52, 0.65 and $0.75\;a_w$, respectively. The shelf-lives for assessed from the accelerated shelf-life test were 125, 123, 120 and 106 days at 0.44, 0.52, 0.65 and $0.75\;a_w$, respectively, in the case of storage at $25^{\circ}C$.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.6
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• pp.1163-1168
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• 2011

Most transformers use insulating and cooling fluids derived from petroleum crude oil, but mineral oil has some possibility of environmental pollution and fire with explosion. vegetable oil fluids extracted from seed has superior biodegradation and fire-resistant properties including an exceptionally high fire point enhancing fire safety. In this study, it is aimed at the practicality of substituting natural ester dielectric fluid for mineral oil in liquid insulation system of transformers. As a rise in coil winding temperature has a direct influence on transformer life time, it is important to evaluate the temperature rise of coil winding in vegetable oil in comparison with mineral oil. Four transformers for the test are designed with 10KVA, 13.2KV, one phase unit. The temperature are directly measured in insulating oil of these transformers with the two sorts of natural ester and mineral oil dielectric fluid respectively. Experiment for aging carry out two means. First means remained $120^{\circ}C$ that transformer of mineral oil were operated at 185% load. Second means is that insulating oils of two natural ester and mineral oil were aged by thermal cycles repeating from $30^{\circ}C$ to $120^{\circ}C$. For the heating, Transformers were operated at 185% load. For the cooling, cooling system was operated in the chamber. Samples were analyzed at 42, 63, 93, 143, 190, 240 300cycles. Analysis contents are dielectric strength, total acid value. Mineral oils compared results of first means with results of second means. And compared two sort natural esters respectively with mineral oil in second means.

• Journal of Pharmaceutical Investigation
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• v.41 no.6
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• pp.331-336
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• 2011

The instability of hirsutenone (HST), a potential therapeutic candidate for the treatment of atopic dermatitis (AD) and ovarian carcinoma, is one of the main concerns for the development of drug product. In the present study, aqueous stability of HST was investigated by kinetic analysis, and the effect of several factors covering temperature, nitrogen gas ($N_2$) flushing, and selection of proper antioxidant was compared. Cosolvent system composed of distilled water and methanol (9:1 v/v) was used as a vehicle to dissolve HST at the concentration of $200{\mu}g/mL$. Samples of aqueous solution were prepared under the absence or presence of antioxidants, such as ascorbic acid (AA), sodium edetate (EDTA), and ascorbyl palmitate (AP), and subjected for stability test. The degradation of HST in aqueous solution was followed by the first order kinetics with an extremely short half life of less than a week at room temperature, and was accelerated as the temperature increased. $N_2$ flushing brought a little enhancement in stability compared to control solution, but the effect was insufficient. The addition of AA and EDTA (0.1%) significantly enhanced the stability of HST at $40^{\circ}C$, but the addition of AP (0.01%) was limited due to its water insolubility and revealed no promising result. The stability of HST was increased proportionally by the amount of AA added, showing the difference in degree of stabilization as an order of magnitude. Finally, we conclude that HST was stabilized by the addition of a suitable antioxidant, suggesting AA as the most effective stabilizer.