• Smart Structures and Systems
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• v.19 no.3
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• pp.335-340
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• 2017

Fiber Bragg grating (FBG) sensors are applied to structural health monitoring (SHM) in many areas due to their unique advantages such as ease of multiplexing and capability of absolute measurement. However, they are exposed to cyclic thermal load, generally in the temperature range of $-20^{\circ}C$ to $60^{\circ}C$, in railways during a long-term SHM and the cyclic thermal load can affect the mechanical strength of FBGs. In this paper, the effects of both cyclic thermal load and the reflectivity of FBGs on the mechanical strength are investigated though tension tests of FBG specimens after they are aged in a thermal chamber with temperature changes in a range from $-20^{\circ}C$ to $60^{\circ}C$ for 300 cycles. Results from tension tests reveal that the mechanical strength of FBGs decreases about 8% as the thermal cycle increases to 100 cycles; the mechanical strength then remains steady until 300 cycles. Otherwise, the mechanical strength of FBGs with reflectivity of 6dB (70%) and 10dB (90%) exhibits degradation values of about 6% and 12%, respectively, compared to that with reflectivity of 3dB (50%) at 300 cycles. SEM photos of the Bragg grating parts also show defects that cause their strength degradation. Consequently, it should be considered that mechanical strength of FBGs can be degraded by both thermal cycles and the reflectivity if the FBGs are exposed to repetitive thermal load during a long-term SHM.

• KEPCO Journal on Electric Power and Energy
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• v.8 no.2
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• pp.143-149
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• 2022

As ESS safety issues increase recently, there is a need to more precisely monitor the temperature of the ESS. In this paper, DTS technology for temperature monitoring of ESS batteries is introduced and the temperature measurement principle is explained. The temperature of the battery module is measured using the DTS system, and the thermal deviation between battery cells inside the battery module is analyzed. In order to analyze how thermal imbalance affects the charging and discharging performance of the battery, an accelerated degradation test was conducted. Cycle life characteristics analysis, battery surface temperature change, and AC impedance characteristics were conducted to analyze how the performance of battery cells differs according to temperature conditions.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1627-1629
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• 1999

In order to analysis the degradation process of epoxy/glass fiber for outdoor condition, FRP laminate was exposed to high temperature and water. Then the degradation process was evaluated by comparing contact angle, surface potential decay, and surface resistivity. For the change of wettability, the contact angle of thermal-treated specimen with the high temperature of $200^{\circ}C$ increased. But that of water-treated specimen decreased. The characteristic of surface potential decay shows the tendency of the remarkable decrease on water-treated specimens, but no difference on thermal-treated specimen compared with untreated one. Also, for the surface resistivity, it shows the same trend compared with the change of contact angle.

• Journal of Applied Reliability
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• v.13 no.2
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• pp.109-116
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• 2013

The solder is any of various fusible alloys, usually tin and lead, used to join metallic parts that provide the contact between the chip package and the printed circuit board. Solder plays an important role of electrical signals to communicate between the two components. In this study, two kinds of Ag-free solder as sample is made to conduct the thermal shock test and the high humidity temperature test. Low resistance is measured to estimate crack size of solder, using daisy chain. The low speed shear test is also performed to analyze strength of solder. The appropriate degradation model is estimated using the result data. Depending on the composition of solder, lifetime estimation is conducted by adopted degradation model. The lifetime estimated two kinds of Ag-free solder is compared with expected lifetime of Sn-Ag-Cu solder. The result is that both Ag-free composition are more reliable than Sn-Ag-Cu solder.

• Plant Journal
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• v.10 no.1
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• pp.40-46
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• 2014

The metallographic examination and hardness measurements were conducted for the rotor of the 500 MW tandem steam turbine of Unit 4 in Dangjin Thermal Power Plants at the locations of steam inlet where the high temperature steams pass; high and intermediate pressure turbines. Creep cavity and degradation levels of optical micrographs of them are observed. The remaining life time of 201,523h for the rotor of the 500 MW tandem steam turbine of Unit 4 in Dangjin Thermal Power Plants was determined by the results of the inspection.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2009.10a
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• pp.335-338
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• 2009

In this study, in order to investigate the thermal and electrical properties of ZnO arrester block against 60[Hz] AC voltage, the changes in leakage current were measured. The temperature distribution appearing on the ZnO arrester blocks was observed using a forward looking infrared camera. In particular, the correlation between the thermal and electrical properties of a ZnO arrester block was analyzed experimentally. From this analysis, the thermal phenomena resulting from the heat generation and dissipation of the ZnO arrester block were interpreted. The degradation and thermal runaway phenomena of ZnO arrester block are closely related to the temperature limit of the ZnO arrester block. The installation of an additional metal electrode has resulted in the decrease of the leakage current due to the heat dissipation.

• Journal of the Korean Ceramic Society
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• v.36 no.6
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• pp.604-610
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• 1999

Silicide layer structures and morphology degradation of the surface and interface of the silicide layers for he Co/refractory metal bilayer sputter-deposited on the P-doped polycrystalline Si substrate and subjected to rapid thermal annealing were investigated and compared with those on the single Si substrate. The CoSi-CoSi2 phase transition temperature is lower an morphology degradation of the silcide layer occurs more severely for the Co/refractorymetal bilayer on the P-doped polycrystalline Si substrate than on the single Si substrate. Also the final layer structure and the morphology of the films after silicidation annealing was found to depend strongly upon the interlayer metal. The layer structure after silicidation annealing of Co/Hf/doped-poly Si is Co-Hf alloy/polycrystalline CoSi2/poly Si substrate while that of Co/Nb is polycrystalline CoSi2/NbSi2/polycrystalline CoSi2/poly Si.

• Elastomers and Composites
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• v.23 no.3
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• pp.213-222
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• 1988

The thermal decomposition of poly(n-butyl methacrylate)(Pn-BMA) was studied using a dynamic and isothermal thermogravimetry in nitrogen gas with 50ml/min at several heating rates from 1 to $20^{\circ}C/min$, and at several heating temperature from 320 to $370^{\circ}C$. The mathematical techniques used for calculation of activation energy were Kissinger, Anderson, Chatterjee-Conrad, Friedman, Fuoss, Ozawa and isolthermal method. The range of activation energies obtained using the several techniques was between 43 and 51Kcal/mol except Chatterjee-Conrad and this range agreed with each other very well. The thermal degradation of Pn-BMA was considered to be carried out by main chain scission.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1572-1574
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• 2000

In this paper, study on the properties of the thermal degradated epoxy resin which is used in cast resin transformer is performed to investigate the problems of the decreasing insulation characteristics and crack in the cast resin transformer. In the test, contact angle, weight loss, surface resistivity and relative dielectric constant are measured. As the results of the above measurements, the epoxy resin has increased to 150$^{\circ}C$ in the contact angle and surface resistivity but at the above 150$^{\circ}C$ the values have decreased. The relative dielectric constants have increased in the thermal treated samples with the degradation temperature. Consequently, the insulation properties of the epoxy resin which is used in cast resin transformer have increased by the 150$^{\circ}C$ but decreased in the above 150$^{\circ}C$.

• Proceedings of the KIEE Conference
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• 2002.06a
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• pp.75-78
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• 2002

In this paper, we investigated the change of wettability, surface potential decay and surface resistivity caused by thermal-treated and plasma-treated FRP respectively for finding out the influence of electrical characteristics on the surface of polymer composites. For the change of wettability, the contact angle of thermal-treated specimen with the high temperature of 200$^{\circ}C$ increased. But that of plasma-treated specimen decreased. The characteristic of surface potential decay shows the tendency of the remarkable decrease on plasma-treated specimens, but no difference on thermal-treated specimen compared with untreated one. Also, for the surface resistivity, it shows the same trend compared with the change of contact angle. We can conclude that the degradation phenomena of epoxy surface are dominated by the induction of hydrophilicity and hydrophobicity.