Service Lifetime Estimation of EPDM Rubber Based on Accelerated Aging Tests
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JMEPEG DOI: 10.1007/s11665-017-2519-8
Service Lifetime Estimation of EPDM Rubber Based on Accelerated Aging Tests Jie Liu, Xiangbo Li, Likun Xu, and Tao He (Submitted April 8, 2016; in revised form August 27, 2016) Service lifetime of ethylene propylene diene monomer (EPDM) rubber at room temperature (25 °C) was estimated based on accelerated aging tests. The study followed sealing stress loss on compressed cylinder samples by compression stress relaxation methods. The results showed that the cylinder samples of EPDM can quickly reach the physical relaxation equilibrium by using the over-compression method. The nonArrhenius behavior occurred at the lowest aging temperature. A significant linear relationship was observed between compression set values and normalized stress decay results, and the relationship was not related to the ambient temperature of aging. It was estimated that the sealing stress loss in view of practical application would occur after around 86.8 years at 25 °C. The estimations at 25 °C based on the nonArrhenius behavior were in agreement with compression set data from storage aging tests in natural environment. Keywords
aging, EPDM, nonlinearity, service lifetime, superposition principle
1. Introduction Since rubber has many beneficial properties such as high air proofness, a high damping characteristic and high elongation, it has widely been applied in wire, hoses, tubes covers, tires, etc. (Ref 1). When rubber is serviced for a long period of time, rubber usually becomes hardened and loses its damping capability. This aging process results mainly from heat due to hysteric loss, and it affects not only the material property but also the service lifetime of rubber (Ref 2). Historically, the socalled Arrhenius approach has been utilized to analyze shorterterm high temperature accelerated aging exposures and then to extrapolate the results to make long-term estimations at the room temperature (25 °C). The approach is based on the assumption that the degradation involves an activated chemical process whose rate is proportional to exp (Ea/RT), where Ea is the Arrhenius activation energy, R is the gas constant, and T is the absolute temperature (Ref 3-5). The approach involves determining the value of Ea at higher temperatures and then using the value to make extrapolated predictions by assuming that Ea remains unchanged at lower temperatures. Given the
Jie Liu and Tao He, College of Chemistry and Chemical Engineering, Yantai University, Yantai 264005, PeopleÕs Republic of China; and Xiangbo Li and Likun Xu, State Key Laboratory for Marine Corrosion and Protection, Luoyang Ship Material Research Institute (LSMRI), Qingdao 266101, PeopleÕs Republic of China. Contact e-mail: [email protected].
Journal of Materials Engineering and Performance
extremely complex set of reactions underlying the degradation of rubber materials, it is presumptuous to expect a single value of Ea to be valid over a large temperature range (Ref 6). Nonetheless, there is a growing literature indicative of nonArrhenius behav
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