Long-term creep properties and the effect of water are important for fiber reinforced polymer (FRP) composite materials used in offshore applications. Epoxies are often used as a matrix material in such composites. A typical design lifetime of offshore FRP structures is 25 or more years in direct contact with water leading to some deterioration of the material properties. Knowing and predicting the extent of the material property deterioration in water is of great interest for designers and users of the offshore FRP structures. It has been established that the time–temperature superposition principle (TTSP) is a useful tool for estimating changes in properties of polymer materials at long times or extreme temperatures. In this work, a time–temperature–plasticization superposition principle (TTPSP) is described and used for predicting the long-term creep behavior of an epoxy compound. The studied epoxy does not degrade chemically via hydrolysis or chain scission but is negatively affected by plasticization with water. The methodology enables prediction of the long-term viscoelastic behavior of amorphous polymers at temperatures below the glass transition (Tg) using short-term creep experimental data. The results also indicate that it is possible to estimate the creep behavior of the plasticized polymer based on the short-term creep data of the respective dry material and the difference between Tg values of dry polymer and plasticized polymer. The methodology is useful for accelerated testing and for predicting the time-dependent mechanical properties of a plasticized polymer below the glass transition temperature.

Rubber compounds for pressure sealing application typically have inferior dimensional stability with temperature fluctuations compared with their steel counterparts. This effect may result in seal leakage failures when subjected to decreases in temperature. and compression set of these materials is also discussed.

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Elastic recovery after compression or compression set is one of the key indicators of elastomer performance in sealing applications, such as O-rings in flange joints. In this work, findings of a study of the compression set property of a hydrogenated nitrile butadiene rubber (HNBR) at temperatures above and below the glass transition temperature T g are presented. The compression set in the elastomer is found to increase with cooling up to 100 % at the glass transition temperature and decrease with time after unloading even at temperatures below T g . The effects of reinforcing filler (carbon black) and the initial compression time are also considered. Equivalence of time and temperature effects on the compression set of the elastomers is then demonstrated. A viscoelastic model describing the time-temperature variation of the compression set is proposed and verified by finite element analysis (FEA) and experimental results. It is shown that modelling captures well the experimental behaviour of the elastic recovery of the studied HNBR at ambient and low temperatures.

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