• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.11b
• /
• pp.258-261
• /
• 2001

In this paper, aging characteristics of silicone rubber used for outdoor insulation have been investigated with regards to salt fog condition and heat aging effect. We look over the change of properties of silicone rubber in salt fog chamber with average leakage current monitoring for observing the transformation of surface degradation properties of silicone rubber with different ATH(alumina trihydrate, $Al_2O_3{\cdot}3H_2O$) filler contents. Surface resistivity, SEM(Scanning Electro Microscope) were measured.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.11a
• /
• pp.258-261
• /
• 2001

In this paper, aging characteristics of silicone rubber used for outdoor insulation have been investigated with regards to salt fog condition and heat aging effect. We look over the change of properties of silicone rubber in salt fog chamber with average leakage current monitoring for observing the transformation of surface degradation properties of silicone rubber with different ATH(alumina trihydrate, Al$_2$O$_3$$.$3H$_2$O) filler contents. Surface resistivity, SEM(Scanning Electro Microscope) were measured.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.4
• /
• pp.333-342
• /
• 2004

Tensile and low cycle fatigue (LCF) tests on prior cold worked 316L stainless steel were carried out at various temperatures from room temperature to 650$^{\circ}C$. At all test temperatures, cold worked material showed the tendency of higher strength and lower ductility compared with those of solution treated material. The embrittlement of material occurred in the temperature region from 300$^{\circ}C$ to 600$^{\circ}C$ due to dynamic strain aging. Following initial cyclic hardening for a few cycles, cycling softening was observed to dominate until failure occurred during LCF deformation, and the cyclic softening behavior strongly depended on temperature and strain amplitude. Non-Masing behavior was observed at all test temperatures and hysteresis energy curve method was employed to describe the stress-strain hysteresis loops at half$.$life. The prediction shows a good agreement with the experimental results.

• Journal of the Korean Electrochemical Society
• /
• v.11 no.3
• /
• pp.184-189
• /
• 2008

Inhibitive effects of chromate, phosphate, sulfate, and borate on chloride pitting corrosion of Al have been investigated using cyclic voltammetry. During the anodic oxide growth, the critical concentration of chloride for pit initiation decreased in the order: chromate > phosphate > sulfate > borate, and the maximum pitting current density increases in the reverse order: chromate < phosphate < sulfate < borate. The decreasing pitting current density was observed in the successive polarization cycles, which was attributed to the aging of Al oxides and field relaxation at oxide/solution interface.

• Proceedings of the KIEE Conference
• /
• 2008.05a
• /
• pp.131-132
• /
• 2008

This paper describes a method to estimate the thermal lifetime of coil used in the dry-type molded transformer which is widely used in the domestic distribution system. In order to reduce the testing time, temperature accelerated aging test is planned. Finally, the thermal lifetime estimation method is composed of a temperature aging test and a cyclic test of temperature, humidly and lightning impulse voltage withstand test.

• Proceedings of the KIEE Conference
• /
• 2002.11a
• /
• pp.179-182
• /
• 2002

XLPE compound have used for insulation of 22.9(kV) power cable. But tree retardant power cable has developed and is going to br used commonly. TR XLPE compound retard production and growth of water tree. In this paper, tensile strength, elongation at break, degree of crosslinking, lightning impulse test, AC breakdown test, cyclic aging for 14days and accelerated water treeing test of TR XLPE insulated power cable were examined according to the KEPCO buying spec. & AEIC CS 5-94 standards. before and after As the result, tensile strength, elongation at break and degree of crosslinking test results of TR XLPE insulation were higher than requirement values. After accelerated water treeing test for 120 days, 240 days and 360 days, AC breakdown voltages were not decreased for accelerated water treeing aging duration

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.9 s.180
• /
• pp.2183-2190
• /
• 2000

A thermal aging is observed in a primary reactor cooling system(RCS) made of a casting stainless steel when the RCS is exposed for long period at the reactor operating temperature, 290~3300C An investigation of effects of thermal aging on a low cycle fatigue characteristics included a stress variations caused by a reactor operation and trip, is required. The purpose of the present investigation is to find an effect of a thermal aging of the CF8M on a low cycle fatigue life. The specimen of CF8M are prepared by an artificially accelerated aging technique holding 300 and 1800hr at 4300C respectively. The low cycle fatigue tests for the virgin and two aged specimens are performed at the room temperature for various strain amplitudes($\varepsilon$ta), 0.3, 0.5, 0.8, 1.0, 1.2 and 1.5% strain. Through the experiment, it is found that the fatigue life is rapidly reduced with an creasing of the aging time. The experimental fatigue life estimation formulas between the virgin and two aged specimen are obtained and are proposed to a analysis purpose.

• Journal of Advanced Marine Engineering and Technology
• /
• v.24 no.6
• /
• pp.70-77
• /
• 2000

In this paper, the effect of solution and age heat treatment to the corrosion behavior for the Ti-6Al-4V alloy were studied by cyclic polarization methods. Ti-6Al-4V was solution heat treated at $1,066^{\circ}C$ and $966^{\circ}C$ for 5 hours, and followed by age heat treated at $650^{\circ}C$, $600^{\circ}C$ and $550^{\circ}C$ with 1, 2, 4, 8 and 16 hours under vacuum environment. Test solution was 3.5% NaCl with temperature $25^{\circ}C$. The obtained results were as follows: 1. Base metal was exhibited higher electrical charge than that of solution and aged material. With decrease of solution-treatment temperature from 1066 to $966^{\circ}C$, the electrical charge was increased due to softening of micro structure. 2. The corrosion resistance of specimen that solution treated at $966^{\circ}C$ for 5 hours and age heat treated at 650, 660 and $550^{\circ}C$ were increased with increase of aging time to 4, 8 and 16 hours respectively, and then decreased. 3. In case of 316L stainless steel, measured charge and corrosion potential was 0.0627 coulomb and -614 mV respectively. Corrosion resistance of Ti-6Al-4V was higher than that of 316L.

• Journal of the Korean Geotechnical Society
• /
• v.32 no.9
• /
• pp.29-36
• /
• 2016

Backfill materials of rail abutment were commonly composed with cement treated aggregate, general aggregate and soil. The friction angle of cement treated aggregate increased up to $40^{\circ}$ or more due to strength enhancement. However, $30^{\circ}{\sim}35^{\circ}$ of friction angle was typically applied for in-situ condition. This phenomenon could cause over-designing, therefore, it is essential to determine reasonable material properties of cemented treated aggregate. In this study, a series of CBR tests and circular model tests have been conducted for cement treated aggregate, while changing cement mixing ratio. Based on test results, characteristics of settlement and strength have been analyzed quantitatively. The settlement of cement treated aggregate decreased with the number of cyclic loading and aging period. In addition, The strength increment ratio in CBR test increased up to 13~16 times at 28 days aging.

• Journal of Korea Foundry Society
• /
• v.32 no.1
• /
• pp.32-37
• /
• 2012

In this study, microstructural evaluation was carried out on secondary hardening type ultrahigh strength steel, Fe-Co-Ni composition. This paper as a first part of whole research presented the microstructural behavior by cyclic heat treatment. The cyclic heat treatment method includes normalizing, stress relieving, solution treatment and aging. Especially, solution treatments performed triple times to get maximized solution hardening. Phase transformation and microstructure were observed by using optical microscope (OM), Electron back-scattered diffraction (EBSD) and X-ray stress analyzer. During the triple solution treatment, size of grain boundary was dramatically decreased by generating a packet from the martensite transformation of residual austenite in the inner part of grain, whereas the hardness increase was not significant.