• Journal of Applied Reliability
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• v.6 no.2
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• pp.135-150
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• 2006

Rubber material properties and lifetime evaluation are very important in design procedure to assure the safety and reliability of the rubber components. This paper discusses the failure mechanism and material tests were carried out to predict the useful lifetime of NBR and EPDM for compression motor, which is used in refrigerator component. The heat-aging process leads not only to mechanical properties change but also to chemical structure change so called degradation. In order to investigate the aging effects on the material properties, the accelerated test were carried out. The stress-strain curves were plotted from the results of the tensile test for virgin and heat-aged rubber specimens. The rubber specimens were heat-aged in an oven at the temperature ranging from $70^{\circ}C\;to\;100^{\circ}C$ for a period ranging from 1 to 180 days. Compression set results changes as the threshold are used for assessment of the useful life and time to threshold value were plotted against reciprocal of absolute temperature to give the Arrhenius plot. By using the compression set test, several useful lifetime prediction equations for rubber material were proposed.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.576-580
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• 2008

Rubber material properties and useful life evaluation are very important in design procedure to assure the safety and reliability of the rubber components. In this paper, the evaluation of characteristics and useful life prediction of rubber component for elevator cabin were experimentally investigated. The material test and accelerated heat-aging test were carried. Rubber material constants were obtained by curve fittings of simple tension, pure shear and bi-axial tension test data. Heat aging test results changes as the threshold are used for assessment of the useful life and time to threshold value were plotted against reciprocal of absolute temperature to give the Arrhenius plot. By using the rubber material and component test several useful life prediction equations for rubber component were proposed. Predicted useful life of rubber component for elevator cabin agreed fairly with the experimental lives.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3A
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• pp.341-347
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• 2008

Among coating systems used for steel bridge coatings on highway such as red lead-pigmented alkyd, chlorinated rubber, waterborne inorganic zinc, inorganic zinc/epoxy/urethane and inorganic zinc/epoxy/fluororesin, evaluation of deterioration degree and prediction of lifetime through regression analysis were carried out for coating systems widely used and grossly degraded. For evaluation of deterioration degree, 75 bridges on highway were selected, and evaluations were carried out according to point offering method regulated by Guideline of maintenance coating for steel bridges used in Korea Expressway Corporation. Lifetime prediction results showed 13.0~13.3 years for the whole nation, 11.8 years for urban and industrial region in the metropolitan area, 13.2 years for rural region except the metropolitan area, 13.5~13.7 years for chlorinated rubber coating systems, and 12.86 years for red lead-pigmented alkyd systems. For prediction of the rest life of coating, we tried to execute parallel translations of standard deterioration curve to current life and deterioration degree for both x and y axes, and it was thought that parallel translation for x axis corresponded to deterioration aspects in actual environment. Maximum and minimum equations were derived from standard deterioration equation by adding and subtracting error values deduced in regression analysis to/from each coefficient in order to establish maintenance coating criteria for overall steel bridges on highway. Whole domain was divided into 8 parts in order to predict the rest life of coating and optimum time of maintenance coating, and maintenance coating criteria for each 8 domains were presented.

• Polymer(Korea)
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• v.26 no.4
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• pp.452-461
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• 2002

In this study, the effect of various concentrations of antioxidants on thermo-oxidative degradation of polyamide 6 was investigated. Unstabilized and stabilized polyamides 6 were subjected to long-term oven aging in ambient atmosphere at 70~$160^{\circ}C$. All of specimens were discolored within 100 hr at temperature range of 70~$160^{\circ}C$. Optimum antioxidant concentration was determined from the data of mechanical properties, yellowness index and relative viscosity. The synergistic effect of each primary and secondary antioxidant concentrations was not observed. Yellowing phenomenon was explained by using NMR, IR and EA. Different carbonyl groups were detected by $^{13}C$/NMR. During thermooxidative degradation, oxygen consumptions were determined by EA. The lifetime after long-term aging was predicted using Arrhenius equation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.2
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• pp.296-303
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• 2001

Kachanov-Rabotnov(K-R) creep damage theory was reviewed, and applied to design a creep curve for type 316LN stainless steel. Seven coefficients used in the theory, i.e., A, B, k, m, λ, r, and q were determined, and their physical meanings were analyzed clearly. In order to quantify a damage parameter ($\omega$), cavity amount was measured in the crept specimen taken from interrupted creep test with time variation, and then the amount was reflected into K-R damage equations. Coefficient λ, which is regarded as a creep tolerance feature of a material, increased with creep strain. Mater curve with λ=2.8 was well coincided with an experimental one to the full lifetime. The relationship between damage parameter and life fraction was matched with the theory at exponent ${\gamma}$=24 value. It is concluded that K-R damage equation was reliable as the modelling equation for type 316LN stainless steel. Coefficient data obtained from type 316LN stainless steel can be utilized for life prediction of operating material.