• Elastomers and Composites
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• v.56 no.3
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• pp.124-135
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• 2021

Evaluating service lives of rubber materials at certain temperatures requires a destructive method (typically using elongation at break). In this study, a non-destructive method based on hardness change rate was proposed for evaluating the service life of chloroprene rubber (CR). Compared to the destructive method, this non-destructive method ensures homogeneity of CR specimens and requires a small number of samples. Thermal accelerated degradation test was conducted on the CR specimens at 55, 70, 85, 100, and 125℃, and the tensile strength, elongation at break, and hardness were measured. The results of the experiment were compared to those of the accelerated life evaluation method proposed in this study. Comparing the analyzed lives in the high temperature region (70, 85, 100, and 125℃), the difference between the service lives for the destructive method (using the elongation at break) and non-destructive method (using the hardness) was approximately 0.1 year. Therefore, it was confirmed that the proposed non-destructive evaluation method based on hardness changes can evaluate the actual life of CR under thermally accelerated degradation conditions.

• Journal of Drive and Control
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• v.21 no.1
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• pp.16-21
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• 2024

The yaw gearbox is a key device in a wind power generator that improves power generation efficiency by rotating hundreds of tons (400 to 600 tons) of nacelle so that the blade reaches 90 degrees in the wind direction. Recently, installation sites have been advancing from land to sea as they have become super-large at (8-12) MW to increase the economic feasibility of wind power generators and utilize excellent wind resources, and the target life of large wind power generators is 25 to 30 years. The yaw gearbox of 6 to 12 sets is installed in a very complex place inside the nacelle on the tower with parallels, and it is important to secure the reliability of the yaw gearbox because if a failure occurs after installation, it costs tens to hundreds of times the price of a new product to restore. In this study, equivalent loads were calculated by analyzing failure mode and field data, accelerated life test conditions were established, and a test device was constructed to perform the accelerated life tests and performance tests to ensure the reliability of the gearbox.

• Nuclear Engineering and Technology
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• v.56 no.4
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• pp.1244-1249
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• 2024

A combination of flow-accelerated corrosion (FAC) tests and corresponding computational fluid dynamics (CFD) tests were performed to determine the hydrodynamic parameters that could help predict the highly susceptible location to FAC in the elbow section. The accelerated FAC tests were performed on a specimen containing elbow sections fabricated using commercial 2-inch carbon steel pipe. The tests were conducted at flow rates of 9 m/s under the following conditions: water temperature of 150 ℃, dissolved oxygen <5 ppb, and pH 7. Thickness reduction of the specimen pipe due to FAC was measured using ultrasonic testing. CFD was conducted on the FAC test specimen, and the turbulence intensity, and shear stress were analyzed. Notably, the location of the maximum hydrodynamic parameters, that is, the wall shear stress and turbulent intensity, is also the same location with maximum FAC rate. Therefore, the shear stress and turbulence intensity can be used as hydrodynamic parameters that help predict the FAC-induced wall-thinning rate. The results provide a method to identify locations susceptible to FAC and can be useful for determining inspection priority in piping systems.

• Journal of the Korean Society of Safety
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• v.31 no.1
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• pp.19-24
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• 2016

Rubber parts are widely used in many applications such as dampers, shock absorbers, and seals used in railway and automotive industries. Much research has thus far been conducted on property estimation and life prediction of rubber parts. To predict the service life of rubber parts at room temperature, most prior work adopts the well-known Arrhenius model that needs the accelerated life test in high-temperature conditions. However, they may not reflect the actual conditions of use that rubber parts are usually used under a specific strain condition during long period of time. In this context, we propose a method for the life prediction of rubber parts in actual conditions of use. The proposed method is based on the accelerated life test using stress relaxation during which three relatively high elongation percentages (100%, 200%, and 300%) are applied to the rubber specimens. Rubber specimens were prepared in accordance with KS M 6518 standard and three stress relaxation testers were fabricated for actual experiments. Finally, a inverse power model for life prediction was derived from experimental results. The predicted life was compared with the actual test life for validation.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.53-60
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• 1999

As the flying height decreased, it is essential that hard disk drives perform reliable under various environmental conditions. In this paper the tribological characteristics of a head/disk interface are investigated under various temperature, relative humidity, altitude and outgas conditions. Specially, Contact-Start-Stop(CSS) tests were performed to assess the stiction, acoustic emission, slider take-off behavior, and track average amplitude(TAA). It is shown that the surface damage and head failure are accelerated by high temperature and humidity as well as low ambient pressure.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.10a
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• pp.131-138
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• 1998

It is essential that hard disk drives perform reliable under various temperature, humidity, and ambient pressure conditions. In this paper the tribological characteristics of a head/disk interface are investigated under various environmental conditions. Specially, Contact-Start-Stop(CSS) tests were performed to assess the stiction and slider take-off behavior. It is shown that the surface damage is accelerated by high temperature and humidity as well as low ambient pressure.

• The Korean Journal of Pesticide Science
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• v.8 no.2
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• pp.103-106
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• 2004

To confirm physico-chemical stability of formulated products, this study was conducted under different storage conditions; room temperature and accelerated temperature of $54^{\circ}C$. The tested pesticide formulations were dichlorvos 50% EC, acephate 50% WP, hymexazol 4% DP, thiram 80% WP and isoprothiolane 12% GR. The selected formulations were stored for 10 weeks and 5 years under the given temperature in maximum and contents of active ingredients were also analyzed by GLC or HPLC after each time of storage. The degradation rates of 5 active ingredients under the two conditions showed a similar trend except acephate. Acephate was rapidly decomposed at $54^{\circ}C$ but slowly decomposed at room temperature, and the degradation rate under the accelerated condition was 2.4 to 5-fold higher than that under the room temperature. Consequently, the stability test on active ingredients in pesticide formulations was able to recommend to be carried out under the accelerated condition except acephate. And the physical properties of all formulations tested under two storage conditions were good.

• The Plant Pathology Journal
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• v.26 no.2
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• pp.178-184
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• 2010

Four major diseases of chili pepper including two fungal diseases, anthracnose (Colletotrichum acutatum) and Phytophthora blight (Phytophthora capsici), and two bacterial diseases, bacterial wilt (Ralstonia solanacearum) and bacterial spot (Xanthomonas campestris pv. vesicatoria), were investigated under future climate-change condition treatments in growth chambers. Treatments with elevated $CO_2$ and temperature were maintained at $720ppm{\pm}20ppm$ $CO_2$ and $30^{\circ}C{\pm}0.5^{\circ}C$, whereas ambient conditions were maintained at $420ppm{\pm}20ppm$ $CO_2$ and $25^{\circ}C{\pm}0.5^{\circ}C$. Pepper seedlings or fruits were infected with each pathogen, and then the disease progress was evaluated in the growth chambers. According to paired t-test analyses, bacterial wilt and spot diseases significantly increased by 24% (p=0.008) and 25% (p=0.016), respectively, with elevated $CO_2$ and temperature conditions. On the other hand, neither Phytophthora blight (p=0.906) nor anthracnose (p=0.125) was statistically significant. The elevated $CO_2$ and temperature accelerated the progress of bacterial wilt by two days and bacterial spot by one day compared to the ambient treatment. Temperature regime studies of the diseases without changes in $CO_2$ confirmed that the accelerated bacterial disease progress was mainly due to the increased temperature rather than the elevated $CO_2$ conditions.

• Journal of Pharmaceutical Investigation
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• v.8 no.4
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• pp.23-36
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• 1978

Since the active center of digestive enzymetic preparations, while under storage, lose their activity and potency by the exposure to moisture, colorization, solidifying and other physical changes. It is more important than beautiful package form that protected packaging form from moisture to get a pharmaceutical safety preparations and to maintain a definite potency. Then, in order to get a desirable conditions of storage and packaging, we used shellac and $AEA^{\circledR}$ as a coating base, and blister package, foil and bottle container as a packaging material. Temperature were set on room temperature and $37^{\circ}C$, moisture was adjusted to 40% RH and 80 % RH as a accelerated conditions. Accelerated test was carried out 6 times. The results are as follows: 1) The effect of packaging conditions give great influence on the maintenace of the stable potency. 2) Best result was produced with bottle container package. 3) $AEA^{\circledR}$ is more useful than shellac as a coating base of prevention from moisture. 4) Absorption of moisture gave considerable effects on potency and it has a limited point. 5) Difference in potency between optimal and worst condition is 472 u/2T, and difference in effective period is about 44 months.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.443-446
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• 2009

In this study, a series of degradation test for structural adhesives was performed to investigate the possibility of replacement of the alternative adhesives to the conventional adhesives. Four types of the adhesives were exposed to combined environmental conditions over 1000 hours at an accelerated aging tester, which can simulate natural weather conditions such temperature, moisture and ultraviolet. Mechanical and chemical properties of the adhesives were evaluated through material testing system and FT/IR spectrometer. According to the results, the conventional adhesives can be replaced by the alternative adhesives because the alternative adhesives were more stable to environmental conditions rather than the conventional adhesives.