• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.4
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• pp.231-241
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• 2021

Although the deterioration of bridges may occur due to various causes, one of the representative causes is that the chloride used for deicing in the winter penetrates bridge members and results in corrosion. This study aims to quantify the ageing degree resulting from the corrosion of a bridge, apply it to the inelastic dynamic analysis model of the bridge, perform a seismic fragility analysis, and evaluate the relationship between the ageing degree and the seismic fragility curve. It is important to appropriately define the threshold values for each damage state in seismic fragility analyses considering the ageing degree. The damage state was defined using the results of existing experimental studies on the characteristics of the deterioration in the displacement ductility capacity of the pier, according to the ageing degree. Based on the seismic fragility analyses of six types of bridges divided by three types of bearing devices and two pier heights, it was found that the seismic vulnerability tends to increase with the ageing degree. The difference in seismic vulnerability with respect to the ageing degree exhibits a tendency to increase as the damage state progresses from slight to moderate, severe, and collapse.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.3
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• pp.205-214
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• 2018

This paper deals with the experimental study on the hygrothermal ageing effect to the strength of Carbon Fiber Reinforced Plastics (CFRP) materials for marine leisure boat manufactured by vacuum assisted resin infusion method. The experiments performed consist of tensile, flexural and shear tests according to American Society for Testing and Materials (ASTM) and Korean Industrial Standards (KS) test methods. Test coupons are varied from uni-directional(UD, $0^{\circ}$, $90^{\circ}$), Bi-Directional (BD), and Double-Bias (DB) carbon fiber fabrics in conjunction with epoxy resin. The results of tensile test show that tensile strength reduces significantly while not the same degree of reduction is observed for elasticity modulus with respect to the existence of hygrothermal ageing effect. This implies that the tensile strain induced from external load holds steady values but ultimate strength values change widely under hygrothermal ageing effect. In case of the flexural test, $0^{\circ}$ UD shows more strength reduction than $90^{\circ}$ UD while BD has reduced values in both flexural strength and elasticity modulus under hygrothermal ageing effect. It is learned that the bending strain induced from external load and ultimate strength values are reduced with respect to hygrothermal ageing effect. Shear test performed only on DB materials, and the results show marginal reduction in ultimate strength and moderate reduction in elasticity modulus. This means that the shear strain varies more than ultimate shear strength with respect to hygrothermal ageing effect. The experiment conducted in this paper clearly demonstrates the differences in material properties of the CFRP for the consideration of hygrothermal ageing effect. Findings obtained from this experimental study can serve as a fundamental input data for the realistic structural responses of marine leisure boat built in CFRP materials.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.5
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• pp.800-805
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• 2017

The accelerated thermal ageing of CSPE (chlorosulfonated polyethylene) was carried out for 16.82, 50.45, and 84.09 days at $110^{\circ}C$, equivalent to 20, 60, and 100 years of ageing at $50^{\circ}C$ in nuclear power plants, respectively. As the accelerated thermally aged years increase, the insulation resistance and resistivity of the CSPE decrease, and the capacitance, relative permittivity and dissipation factor of those increase at the measured frequency, respectively. As the accelerated thermally aged years and the measured frequency increase, the phase degree of response voltage vs excitation voltage of the CSPE increase but the phase degree of response current vs excitation voltage decrease, respectively. As the accelerated thermally aged years increase, the apparent density, glass transition temperature and the melting temperature of the CSPE increase but the percent elongation and % crystallinity decrease, respectively. The differential temperatures of those are $0.013-0.037^{\circ}C$ and, $0.034-0.061^{\circ}C$ after the AC and DC voltages are applied to CSPE-0y and CSPE-20y, respectively; the differential temperatures of those are $0.011-0.038^{\circ}C$ and $0.002-0.028^{\circ}C$ after the AC and DC voltages are applied to CSPE-60y and CSPE-100y, respectively. The variations in temperature for the AC voltage are higher than those for the DC voltage when an AC voltage is applied to CSPE. It is found that the dielectric loss owing to the dissipation factor($tan{\delta}$) is related to the electric dipole conduction current. It is ascertained that the ionic (electron or hole) leakage current is increased by the partial separation of the branch chain of CSPE polymer as a result of thermal stress due to accelerated thermal ageing.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.43 no.2
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• pp.40-48
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• 2011

To build up the conservativeness of aged paper heritages, the strength reinforcement treatment using various cellulose derivative solutions was considered. Hand-made Hanji prepared by traditional papermaking technique was firstly simulated in order to modify the overall of paper properties like aged paper heritages by accelerated ageing treatment at $150^{\circ}C$ for 24 hours, and then the ageing stability of Hanji was verified through the secondary accelerated ageing at $150^{\circ}C$ for 12 hours. The physical properties of aged Hanji were improved by applying with cellulose derivative solutions. The ageing stability for physical, optical (L, brightness, opacity, yellowness) and chemical (oxidation index, degree of polymerization) properties of aged Hanji treated with all kinds of cellulose derivative solutions was also good compared to those of untreated samples, especially using MC solution. Therefore, it was that a kind of MC solution would be well-suited for the strength reinforcement treatment of aged paper heritages.

• Journal of the Korean Society of Tobacco Science
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• v.17 no.2
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• pp.126-138
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• 1995

To investigate the changes of physicochemical properties of leaf tobacco during storage, cured leaves (both flue-cured(KF109) and burley(Burley 21) : 4 grades of leaves) were stored under the natural warehouse condition(room temperature) and processed leaves(both Rue-cured(NC82) and burly(Burley 21) : 6 grades of leaves) were stored at storerooms in tobacco processing plants(flue-cured Cheongju plant ; 2nd, 4th and 5th floor, burley : Kwangju plant ; 2nd floor, Chonju plant : 3rd and 5th floor). Tobacco leaves were sampled and analyzed every 3 months. Total sugar content of flue-cured leaf decreased slightly and the redness degree of leaf increased after 15 months' storage under the natural warehouse conditions. The pH of cured leaves were lowered both flue-cured and burley, and the decreasing rate of pH was large in flue-cured(0.24) as compared with burley(0.14). There was no significant differences of physicochemical properties of processed leaf among storerooms during 15 months' storage. The decreasing rate of processed leaf pH was somewhat large in flue-cured(0.26) as compared with burly (0.20), and in thick leaves as compared with thin leaves. The redness degree of flue-cured leaf increased slightly, while the degree of lightness and yellowness lowered slightly during storage. The lightness degree of burley leaf lowered slightly, too. The ageing process of cured leaf was similar to that of processed leaf, it is considered that the passing days after curing will be more reasonable than the passing days after processing for the establishment of proper ageing period.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1851-1853
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• 1996

In this paper the criteria for insulating oil condition of pole transformer were suggested by applying the UV-Visible spectrophotometric method. Ageing of insulating oil caused the change in absorbances of oil os well os the deterioration of electrical properties of oil. By comparing the electrical properties such as $tan{\delta}$ and breakdown voltage with the UV-Visible absorbances of oil, criteria for absorbance values determining oil condition were established. This UV-Visible spectrophotometric method might be applied in ageing analysis of oil and be expected to replace the current method.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1541-1543
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• 1996

This paper describes the results of characteristics on the tracking resistance, hydrophobicity and dielectric properties of silicone rubbers used for outdoor insulation with ozone ageing. The tracking and ozone ageing tests for this purpose ware made in according to IEC 587 and ASTM D 1149, respectively. Additionally, we investigated the surface structure of the silicone rubbers with FT-IR and SEM. From the test results, it is proven that the higher the degree of ozon ageing, the worse tracking characteristics.

• Journal of the Korean Geographical Society
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• v.43 no.3
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• pp.337-357
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• 2008

This study examines the characteristics of population ageing and the employment of aged workers in Seoul. Population indexes such as aged/child ratio and longevity degree are analyzed to identify the time-spatial changes and differentiation of population ageing by Gu. Job offerers, job seekers and employees related to the aged workers are also analyzed using data from Center of Job Placement for the Aged in Seoul. The results indicate that population ageing of Seoul has progressed faster than other regions in recent years. In addition, regional differences in tendency of population ageing is obvious even within Seoul. The percentage of unskilled laborer is much higher in Seoul compared with other regions. There is geographical differentiation in employment of aged workers among regions within Seoul. The employment opportunity of the aged is high in core economic areas of Seoul, while low in the outer residential area. This shows geographical mismatch between job offerers and seekers, which means that it is difficult for aged workers to get the jobs near to their residence. Accordingly, governmental support and intervention is needed considering their lower mobility.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.39 no.1 s.119
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• pp.16-24
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• 2007

This study was performed to investigate the reaction between alkylketene dimer(AKD) and cellulose molecules in AKD-sized paper sheet. AKD was added to highly beaten($80{\pm}3^{\circ}SR$) SwBKP(ca. 0.8% on pulp) in order to have much AKD retention in the paper sheet. This AKD-sized paper sheet was aged at different temperatures, $60^{\circ}C,\;80^{\circ}C,\;105^{\circ}C\;and\;125^{\circ}C$. Changes in FT-IR spectra of AKD in paper sheet during the ageing were measured. In addition, sizing degrees of the AKD-sized paper sheet pretreated for 30 sec. at $105^{\circ}C$ were measured by HST size tester during the storage at different temperature. IR spectra of AKD-sized paper sheet preheated at $105^{\circ}C$ for 30 sec. showed unchanged spectra two absorption bands at $1849cm^{-1}\;and\;1722cm^{-1}$ which refer to the typical AKD IR bands. However, these typical AKD bands were gradually reduced with increasing ageing, completely disappeared after 6 hrs. and formed new absorption band at $1706cm^{-1}$, which refers to carbonyl stretching vibration of dialkylktone. Eventually the AKD molecule was hydrolyzed to diakylketone without formation of ${\beta}$-ketoester with cellulose in paper sheet. After 6 days ageing, a little amount of ${\beta}$-ketoester bands was identified in 6 or 7 days ageing, because of the absence of water due to long-term heating. The same tendency was observed at different ageing conditions. At the practical papermaking process, AKD reacts prevailing with water, and mostly seems to be hydrolyzed to dialkylketene. Concerned to the sizing development, AKD-sized paper sheet was shown no sizing development at the initial stage of ageing at $60^{\circ}C$ after heating treatment at $105^{\circ}C$ for 30 sec., and gradually increased the sizing degree with increasing ageing, such as Hercules Sizing Tester (HST) 130 see for 12 hr, HST 300 sec. for 3 days and HST 400 sec. for 5 days. It was concluded that hydrolyzed AKD could contributed to the sizing development of the paper sheet.

• Journal of Oral Medicine and Pain
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• v.18 no.1
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• pp.107-117
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• 1993

The author has taken intraoral standard films by the paralleling technique of 6414 teeth in 838 patients ranged from early twenties to early sixties and analysed the change of pulp cavity in the mandibular posterior teeth by ageing. The obtined results were as follows : 1. There was no significant difference between the right and left teeth. 2. The degree of change of pulp cavity in female was higher than that in male. 3. The change of pulp cavity was increased by ageing. 4. The correlation between the degree of change of pulp cavity inmandibular posterior teeth (X) and age (Y) were : Male 1st premolar Y=13.22X3.37+ r=0.79 2nd premolar Y=12.09X+3.65 r=0.79 1st molar Y=11.90X+1.25 r=0.78 2nd molar Y=10.51X+10.43 r=0.83 Female 1st premolar Y=13.66X-2.49 r=0.86 2nd premolar Y=13.63X-2.42 r=0.86 1st molar Y=12.42X-1.44 r=0.79 2nd molar Y=11.42X+5.91 r=0.84