• 한국신뢰성학회지:신뢰성응용연구
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• 제7권1호
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• pp.31-43
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• 2007

The function of O-ring seals is to prevent leakage during the service life of the components in which they are installed. The life prediction of O-ring is very important at various industry fields. Generally, to evaluated the long-term performance of O-ring in severe environments has applied a life prediction technique based on accelerated life test (ALT). In this work, Accelerated thermal aging test(l20, 130, 140, $150^{\circ}C$) of O-ring was applied for life prediction of O-ring. The property changes after thermal aging test was measured using TGA, DSC, FT - IR, Video Microscope and SEM. Shape parameter and life prediction were obtained using MINITAB program.

• Corrosion Science and Technology
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• 제23권2호
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• pp.145-153
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• 2024

In the automotive industry, the hole expanding test is widely used to assess the formability of punched holes in sheets. This test provides a good representation of formability within the framework defined by the ISO 16630 standard. During hole expanding tests on galvanized high strength steels, a negative effect was observed when there was a delay between hole punching and expansion, as compared to performing both operations directly. This effect is believed to be caused by hydrogen aging, which occurs when hydrogen diffuses towards highly-work hardened edges. Therefore, the aim of this study is to demonstrate the migration of hydrogen towards work-hardened edges in high strength Zn-coated steel sheets using a novel Thermal Desorption Analyzer (TDA) designed for small samples. This newly-developed TDA setup allows for the quantification of local diffusible hydrogen near cut edges. With its induction heating and ability to analyze Zn-coated samples while reducing artifacts, this setup offers flexible heat cycles. Through this method, a hydrogen gradient is observed over short distances in shear-cut galvanized steel sheets after a certain period of time following punching.

• The Journal of Advanced Prosthodontics
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• 제7권2호
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• pp.108-114
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• 2015

PURPOSE. The aim of this study was to evaluate effect of different surface treatment methods on the bond strength between aged composite-resin core and luting agent. MATERIALS AND METHODS. Seventy-five resin composites and also seventy-five zirconia ceramic discs were prepared. 60 composite samples were exposed to thermal aging (10,000 cycles, 5 to $55^{\circ}C$) and different surface treatment. All specimens were separated into 5 groups (n=15): 1) Intact specimens 2) Thermal aging-air polishing 3) Thermal aging- Er:YAG laser irradiation 4) Thermal aging- acid etching 5) Thermal-aging. All specimens were bonded to the zirconia discs with resin cement and fixed to universal testing machine and bond strength testing loaded to failure with a crosshead speed of 0.5 mm/min. The fractured surface was classified as adhesive failure, cohesive failure and adhesive-cohesive failure. The bond strength data was statistically compared by the Kruskal-Wallis method complemented by the Bonferroni correction Mann-Whitney U test. The probability level for statistical significance was set at ${\alpha}$=.05. RESULTS. Thermal aging and different surface treatment methods have significant effect on the bond strength between composite-resin cores and luting-agent (P<.05). The mean baseline bond strength values ranged between $7.07{\pm}2.11$ and $26.05{\pm}6.53$ N. The highest bond strength of $26.05{\pm}6.53$ N was obtained with Group 3. Group 5 showed the lowest value of bond strength. CONCLUSION. Appropriate surface treatment method should be applied to aged composite resin cores or aged-composites restorations should be replaced for the optimal bond strength and the clinical success.

• Elastomers and Composites
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• 제54권4호
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• pp.351-358
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• 2019

To evaluate the aging of a rubber pad in power window switch which is the part of a vehicle, the accelerated thermal aging test of rubber pad material is performed. Finite element analysis was performed using the nonlinear material constants of the rubber pad to calculate the operating force, and the Arrhenius relationship was derived from the aging temperature and time. The aging test was performed at 150, 180, 210, or 240 ℃ for 1 to 60 days. When the operating force of the rubber pad is changed by 10% from the initial value, the service life is expected to be 113 years, which is much longer than the life of the vehicle. This indicates that the aging life of the rubber pad is sufficiently safe and the operating force of the rubber pad during the life of the vehicle (20 years) was decreased by approximately 8.4%. By examining the correlation between the shear elastic modulus and operating force calculated from finite element analysis under each aging test condition, the changes in the operating force of the rubber pad and the shear elastic modulus showed good linear relationship. The aging life could be predicted by the change in shear elastic modulus and a process for predicting the aging life of automotive power window switch rubber pad parts is described herein.

• 대한기계학회논문집A
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• 제31권9호
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• pp.915-923
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• 2007

Rubber hoses for automobile radiators are apt to be degraded and thus failed due to the influence of contacting stresses of air and coolant liquid under thermal and mechanical loadings. The aging behaviors of the skin part of the hoses due to thermo-oxidative and electro-chemical stresses were experimentally analyzed. Through the thermo-oxidative aging test, it was shown that the surface hardness IRHD(International Rubber Hardness Degrees) of the rubber increased with a considerable reduction of failure strain as the aging time and temperature increased. On account of the penetration of coolant liquid into the skin part influenced by the electro-chemical degradation(ECD) test the weight of the rubber hose increased, whereas their failure strain and IRHD hardness decreased. The hardness of the hose in the side of the negative pole was the most deteriorated at the test site of the hose skin just below the coolant surface.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.1151-1152
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• 2006

In this paper, we examined 10 domestic samples of three different model using thermal, humidity freeze, thermal-endurance and damp heat test under IEC61215 photovoltaic module environmental endurance test condition. Three was almost no changes on power generation. Insulation resistance capacity was much higher than judgement standard but, showed unstable results depending on environmental test items. On external appearance test, there were two models which showed bubble, humidity penetration, seal melted frame phenomenon. From this results, the degree of aging under the external environment is a main cause that shortens photovoltaic module life time. So it is considered that the efforts for finding optimum condition of manufacturing process should be needed.

• 한국정밀공학회지
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• 제31권12호
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• pp.1155-1159
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• 2014

Thermal barrier coating (TBC) which is used to protect the substrate of gas turbine is exposed to high temperature environment. Because of high temperature environment, thermally grown oxide (TGO) is grown at the interface of thermal barrier coating in operation of gas turbine. The growth of TGO critically affects to durability of TBC, so the evaluation about durability of TBC with TGOs of various thickness is needed. In this research, TGO was inserted by aging of TBC specimen to evaluate the effect of the TGO growth. Then thickness of TGO was defined by microstructure analysis, and thermal fatigue test was performed with these aging specimens. Finally, the relation between thermal fatigue life and the TGO growth according to aging time was obtained.

• 한국신뢰성학회지:신뢰성응용연구
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• 제12권3호
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• pp.177-186
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• 2012

This paper presents a comparison of the failure mechanism for high power converted white LEDs(3W) with the commercially available YAG:Ce and silicate phosphor. We carry out the normal aging life test for 10,000 hours, the high temperature aging test for 8,000 hours, the high temperature and humidity aging test for 8,000 hours and the current aging testing for 5,000 hours. The optical and electrical parameters of LEDs were monitored, such as lumen, correlated color temperature (CCT), chromaticity coordinates(x, y), thermal resistance, I -V curve and spectrum intensity. The stress induced a luminous flux decay on LED in all experiments and causes a failure. So we try to find out what's a main failure mechanism for a high power LED.

• 한국항공우주학회지
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• 제31권10호
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• pp.21-26
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• 2003

본 논문에서는 광섬유 센서를 사용하여 우주환경하에 노출된 그래파이트/에폭시 복합재 적층판의 열팽창계수의 변화를 측정하였다. 열변형률과 온도를 동시에 측정하기 위해서 두개의 FBG 센서를 사용하였다. 또한 열-진공 챔버를 사용하여 고진공, 자외선, 열적 사이클 등의 인자를 가지는 저궤도(LEO) 우주환경을 모사하였다. 예비실험으로써, 본 실험에서 사용되는 온도범위에 대해 FBG 온도센서를 기준온도계로부터 보정하였고 알루미늄 시편에 부착된 FBG 변형률 센서와 변형률 게이지(ESG)의 비교실험을 통해 FBG 변형률 센서의 사용가능성을 검증하였다. 검증된 FBG센서가 삽입된 그래파이트/에폭시 복합재 평판을 모사된 우주환경에 노출하여 일정한 노화간격마다 열팽창계수 변화를 실시간으로 측정하였다. 실험결과 1000 사이클 노화후의 열팽창계수는 노화전에 비해 대체적으로 큰 변화는 없었지만 전 온도구간에서 약간 감소하는 경향을 보였다. 이러한 현상은 가스방출(outgassing), 수분방출, 모재균열 등에 기인한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 추계학술대회 논문집 학회본부
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• pp.241-245
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• 1988

This paper reports the experiments regarding to diagnosis techniques for power transformers by measuring dissipation factor and moisture contents of mineral oils. Thermal aging environments of mineral oils were varied by the specially designed systems. Thermal aging of elevated temperature of $90^{\circ}C$ was performed for about 240 and 460 hours, respectively. Dissipation factor, permittivity, and water content were measured. Our test samples were not exposed to air. Dissipation factor increased while permittivity did not change. The level of dissipation factor determining the insulating quality of mineral oil was compared with the previous results of resistivity and several correction factor.