• Composites Research
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• v.22 no.6
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• pp.39-44
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• 2009

The effect of exposure times on the aging characteristics of carbon fiber/epoxy composite ring specimen was evaluated using an accelerating aging tester. Combined exposure conditions, such as temperature, moisture, and ultraviolet, were applied up to 3000 hours. Tensile properties and flexural properties including the effect of curvature were evaluated on the specimens subject to various exposure times through a material testing system. Their aging surfaces were observed through a scanning electron microscope. According to the results, tensile modulus was little affected by the exposure times. However, tensile strength, at the early stage of the exposure times, increased due to physical aging and curing reaction, but tensile strength slightly decreased due to degradation as the exposure times increased. The flexural modulus and flexural strength increased at the early stage of the exposure times, but slightly decreased as the exposure times increased. Aging surfaces of the specimens examined using the scanning electron microscope revealed a different morphology in various exposure times and provided useful information for identifying the degradation in mechanical properties of the composite subject to various exposure times.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.5A
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• pp.417-424
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• 2010

The dynamic properties of laminated rubber bearings used as isolators in structures could be significantly deteriorated because of the change of microstructure in rubber caused by thermal aging. As a result, a catastrophic failure of bridges and buildings unexpectedly occurs when they are subjected to earthquake attack. Here, the dynamic properties of laminated rubber bearings before and after different of compression-shear loading and repeated cycles loadings, ultimated failure test with thermal aging were first measured and compared to each other. The experimental results, the effects of thermal aging on the shear stiffness, energy absorption, and equivalent damping coefficient of laminated rubber bearings are investigated. It is found that the deterioration of dynamic properties of laminated rubber bearings caused by thermal aging is significant and should be taken into account in designing rubber bearings.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.855-864
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• 2013

The dynamic characteristics of natural rubber bearings, which are used as isolator, are dependent on the main rubber's dynamic behaviors and nonlinear properties. Rubber materials tend to undergo an aging process under the influence of mechanical or environmental factors, so they inevitably end up facing damage. A main cause of aging like this is known to be oxidization, which occurs through the heat of reaction at high temperatures. Accordingly, in this study an accelerated thermal aging test was carried out in order to compare the characteristic values of the bearings before and after thermal aging occurs. As a result of this experiment, it was found that a thermal aging phenomenon could have some effects on shear stiffness, energy absorption, and equivalent damping coefficients of the bearings. Furthermore, a deterioration in the dynamic properties of the natural rubber bearings caused by the thermal aging was applied to an actual bridge and then the effects of such thermal aging on the seismic performance of the bridge were also compared and analyzed based on numerical analysis. As a result of this analysis, it was found that the changes in the basic properties of the natural rubber bearings caused by the thermal aging bring only a minor effect on the seismic performance of bridges.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2A
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• pp.109-116
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• 2012

The dynamic properties of lead rubber bearings, which are used as isolator, are dependent on the main rubber's dynamic behaviors and nonlinear qualities. Rubber materials tend to undergo an aging process under the influence of mechanical or environmental factors, so they can end up inevitably facing damage. A main cause of such aging is known to be oxidization, which occurs through the heat of reaction at high temperatures. Accordingly, in this study an accelerated thermal aging test was carried out in order to compare the characteristic values of the bearings with each other before and after thermal aging occurs. As a result of this experiment, it was found that a thermal aging phenomenon could have an effect on shear stiffness, energy absorption, and equivalent damping coefficients. Furthermore, a decline in the dynamic properties of the lead rubber bearings by means of the thermal aging process was applied to an actual bridge and the effects of such thermal aging on the seismic performance of the bridge were also compared and analyzed based on numerical analysis. As a result of this analysis, it was found that the changes in the basic properties of the lead rubber bearings have a minor effect on the seismic performance of bridges.

• Journal of Korean Society of Archives and Records Management
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• v.3 no.2
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• pp.143-155
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• 2003

As archives, photograph is the evident records of historical facts and experiences. Thus, it is worth preserving. Unlike other documents silver halide photographic films and prints are quite sensitive to environmental factors such as light, temperature and humidity, which demands careful treatment in preservation. This study was carried out to select popular photographic films and papers on the market, to examine their photographic speeds (or sensitivities) and to compare and analyze their preservative features after keeping them some time in a weather-o-meter. Consequently, B/W materials were superior to color ones in preservation. And films were better than papers in the same manner. But we were not able to observe remarkable differences among material's manufacturers.

• 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.

• Composites Research
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• v.22 no.5
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• pp.37-42
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• 2009

Thermal analysis properties and chemical structure of carbon fiber/epoxy composites under environmental exposure were examined using an accelerated aging tester which can simulate real weather conditions such as temperature, moisture and ultraviolet. The composite specimens were exposed to combined environmental factors up to 3000 hours. Thermal analysis properties and chemical structure of the composites were evaluated with various exposure times through Modulated DSC and FTIR. According to the results of Modulated DSC, the glass transition temperature increased as exposure time increased due to the formation of network structures in the composites. Also endotherm peaks of enthalpy relaxation related to physical aging that can affect the properties of the composites were observed as exposure time increased. From the results of FTIR, it was found that the location of the peaks was little affected by exposure time, but the intensity of the peaks slightly decreased as exposure time increased due to the curing reaction in the epoxy group.

• Journal of Drive and Control
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• v.18 no.2
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• pp.32-37
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• 2021

The piston reservoir is mainly used in hydraulic blow-down system for aerospace engineering. The reservoir is heavy due to both hydraulic cylinder and piston in pressurization. The positive expulsion tank with rubber diaphragm has been mostly applied propellant and fuel tank at low pressure to satellites. To reduce weight, the reservoir that can be used at high pressure with rubber diaphragm was developed. In this research, the prediction of life-time for the rubber diaphragm was implemented through an accelerated life test, as a part of development of new reservoir. Also, the diaphragm was stored in an temperature chamber at the same condition as and operation with hydraulic oil. As a result, the life-time for a rubber diaphragm was successfully evaluated via Arrhenius law and Time-Temperature Superposition based on failure times over temperatures in the accelerated test.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1416-1425
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• 2002

In this study, the effects of combined environmental factors on mechanical and thermal analysis properties of graphite/epoxy composites were evaluated by the use of an accelerated aging test. Environmental factors such as temperature, moisture. and ultraviolet were considered. A xenon-arc lamp was utilized for ultraviolet light. and exposure times of up to 3000 hours were applied. Several types of specimens - tensile. bending, and shear specimens those are transverse to the fiber direction, and bending specimens those are parallel to the tiber direction - were used to investigate the effects of environmental factors on mechanical properties of the composites. Also, glass transition temperature, storage shear modulus, loss shear modulus, and tan ${\delta}$ were measured as a function of exposure times through a dynamic mechanical analyzer. In addition. a suitable testing method for determining the effect of environmental factors on mechanical properties is suggested by comparing the results from using two different types of strain measuring sensors. Finally, composite surfaces exposed to environmental factors were examined using a scanning electron microscope.