• Journal of the Korean Society for Railway
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• v.8 no.2
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• pp.188-194
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• 2005

Aging characteristics of glass fabric/phenolic composites for tilting train subjected to combined environmental aging factors were investigated. A 2.5KW accelerated aging tester with a xenon-arc lamp was used to provide environmental aging factors such as temperature, moisture, and ultraviolet. A series of aging tests were conducted up to 3000 hours and several types of specimens were prepared along the warp direction and the fill direction. Mechanical degradations for tensile, flexural, and shear properties were evaluated as a function of exposure times through a material testing system. Thermal analysis properties such as storage shear modulus, loss shear modulus, and tan 3 were measured through a dynamic mechanical analyzer. Finally exposed surfaces of the composites were examined using a scanning electron microscope. According to the experimental results, mechanical properties and thermal analysis properties of glass fabric/phenolic composites were found to be slightly degraded as a function of exposure times due to combined environmental effects.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.20-25
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• 2013

Ultrasonic methods are widely used to degradation assessment. Remaining-life cycle of metal can be estimated by ultrasonic parameters because ultrasonic velocity and attenuation are affected by change of material properties with accumulated fatigue in the metal. Therefore, in this study, we will estimate overall change of material properties by 2D C-scan image. Fatigued aluminum alloy 6061-T6 samples from 0 to 85% were prepared for evaluating fatigue life cycle. Also, degraded image of materials using attenuation is proposed to estimate degree of material degradation for determining degraded area of fatigued samples. Finally, we will predicts process pf degradation with measured attenuation of fatigued aluminum alloy 6061-T6 samples.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.852-858
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• 2007

The durability of carbon/epoxy composites under salt water environment was investigated through salt water spray tester. Salt water environment was obtained through salt spray and salt immersion. 5% NaCl solution was used for salt water as natural salt water. Mechanical test was performed to obtain tensile properties, flexural properties, and shear properties of carbon/epoxy composite over 12 months under salt water environment. Dynamic mechanical analyzer was used to investigate thermal analysis properties such storage modulus, loss modulus, and tan ${\delta}$. Also FT/IR test was conducted to investigate a change in chemical structure. According to the results, mechanical properties were found to be slowly degraded as a function of exposure times. Regarding to thermal analysis properties, storage modulus was insensitive to exposure times, but loss modulus was shown to be slightly decreased. Although the shape and location of peak in FT/IR were not much changed, the intensity of peak in FT/IR was affected on exposure times. We also found that salt water immersion was more severe to the durability of carbon/epoxy composite rather than salt water spray.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.4
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• pp.619-625
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• 1997

$Si_3N_4$ powder with 2 wt% $Al_2O_3$ and 6 wt% $Y_2O_3$additives was gas pressure sintered (GPS). Characterization of the mechanical properties was compared with sintering conditions (temperature, pressure, time). Based on experimental result , the optimal condition of gas pressure sintering was found at $1900^{\circ}C$, 3 MPa for 1 hour. It is assumed that mechanical properties were degraded due to the grain coasening effects with increasing temperature or holding time. However, the grain size was decreased with increasing pressure, resulted in better strength, but lower fracture toughness. Present results suggested that optimization of processing parameters was impotant for better mechanical properties of $Si_3N_4$.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.143-148
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• 2001

This research was undertaken to clarify effects of thermal aging on electrochemical and mechanical properties of superaustenitic stainless steel. The steel was artificially aged at $300{\sim}650^{\circ}C$ for $240{\sim}10,000hrs$. and investigated at $-196{\sim}650^{\circ}C$ using small punch(SP) test. Also, the change in electrochemical properties caused by effects of thermal aging was investigated using electrochemical anodic polarization test in a KOH electrolyte. Carbides and ${\eta}-phase(Fe_2Mo)$ precipitated in the grain bounderies seem to deteriorate the mechanical properties by decreasing cohesive strength in the grain bounderies and promote the current density observed in electrochemical polarization curves. The electrochemical and mechanical properties of superaustenitic stainless steel was drastically decreased in the specimen aged at $650^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.12
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• pp.2116-2124
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• 2001

It's required mechanical properties of in-service facilities to maintain safety operation in power plants as well as chemical plants. In this studdy the four classes of the thermally aged 1Cr-lMo-0.25V specimens were prepared using an artificially accelerated aging method at 630$\^{C}$. Ultrasonic tests, tensile tests, K$\_$IC/ tests and hardness tests were performed in order to evaluate the degree of degradation of the material. The mechanical properties were decreased as degraded, but the attenuation coefficient and the harmonic generation level of a ultrasonic signal were increased. Expecially the nonlinear parameter derived from the harmonic generation level is sensitive and will be a good parameter to evaluate the material degradation.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.129-136
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• 2001

The remaining life estimation for the aged components in power plants as well as chemical plants are very important beacuse mechanical properties of the components are degraded with time of service exposure in high temperature. Since it is difficult to take specimens from the operating components to evaluate mechanical properties of components, nondestructive techniques are needed to estimate the degradation. In this study, test materials with 4 different degradation levels were prepared by isothermal aging heat treatment at $630^{\circ}C$. And the DC potential drop method and destructive methods such as tensile, $K_{IC}$ and hardness tests were used in order to evaluate the degradation of 1Cr-1Mo-0.25V steels. The objective of this study is to investigate the possibility of the application of DCPD method to estimate the material degradation, and to analyse the relationship between the electrical resistivity and the degree of material degradation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.9
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• pp.662-668
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• 2013

Reported here are results of the mechanical and electrical properties of both of intact and thermally degraded epoxy-coated copper busducts that are made by fluidized bed process. To elucidate and compare the properties mentioned above, electrical breakdown by thermal and water aging, v-t characteristic, bending test, impact test and cross cut test are carried out. Although the performance of electrical and mechanical properties are gradually decreased in increasing the severe conditions such as temperature, aging time, and so forth, sample C has a better performance in both mechanical and electrical properties.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.266-271
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• 2001

Spherical indentation technique was developed to evaluate the flow properties of metallic materials in carbon steel, stainless steel and alloys, etc. Through the spherical indentation test, differently degraded 1Cr-1Mo-0.25V steel's mechanical properties were observed and compared with conventional standard test data. The flow properties of 1Cr-1Mo-0.25V steels were estimated by analyzing the indentation load-depth curve. To characterize the flow property, we used material yield slope and constraint factor index rather than strain-hardening exponent because the variation of strain-hardening exponent was very little and the data showed irregularly. And the constraint factor's effect was small when the material yield slope was taken into account.

• Journal of the Semiconductor & Display Technology
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• v.21 no.2
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• pp.11-14
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• 2022

In this work, we evaluated the Al₂O₃ film, which was deposited by atomic layer deposition, degraded by exposure to harsh environments. The Al₂O₃ films deposited by atomic layer deposition have long been used as a gas diffusion barrier that satisfies barrier requirements for device reliability. To investigate the barrier and mechanical performance of the Al₂O₃ film with increasing temperature and relative humidity, the properties of the degraded Al₂O₃ film exposed to the harsh environment were evaluated using electrical calcium test and tensile test. As a result, the water vapor transmission rate of Al₂O₃ films stored in harsh environments has fallen to a level that is difficult to utilize as a barrier film. Through water vapor transmission rate measurements, it can be seen that the water vapor transmission rate changes can be significant, and the environment-induced degradation is fatal to the Al₂O₃ thin films. In addition, the surface roughness and porosity of the degraded Al₂O₃ are significantly increased as the environment becomes severer. the degradation of elongation is caused by the stress concentration at valleys of rough surface and pores generated by the harsh environment. Becaused the harsh envronment-induced degradation convert amorphous Al₂O₃ to crystalline structure, these encapsulation properties of the Al₂O₃ film was easily degraded.