Abstract
To improve the predictive capability of long-term stress relaxation of elastomers during thermo-oxidative ageing, a method to separate reversible and irreversible processes was adopted. The separation is performed through the analysis of compression set after tempering. On the basis of this separation, a numerical model for long-term stress relaxation during homogeneous ageing is proposed. The model consists of an additive contribution of physical and chemical relaxation. Computer simulations of compression stress relaxation were performed for long ageing times and the results were validated with the Arrhenius treatment, the kinetic study and the time-temperature superposition technique based on experimental data. For chemical relaxation, two decay functions are introduced each with an activation energy and a degradative process. The first process with the lower activation energy dominates at lower ageing times, while the second one with the higher activation energy at longer ageing times. A degradation-rate based model for the evolution of each process and its contribution to the total system during homogeneous ageing is proposed. The main advantage of the model is the possibility to quickly validate the interpolation at lower temperatures within the range of slower chemical processes without forcing a straight-line extrapolation.
Highlights
IntroductionThe second factor are the environmental conditions to which the elastomer components are exposed during application
Lifetime prediction of elastomer components is a very challenging task due to many factors.The first factor is the variety of fields of application and their requirements ranging from coatings in medical application [1] to isolation bearings in construction [2] or even to special sealing applications such as e.g., in containers designed for transport, storage and/or disposal of radioactive materials.The second factor are the environmental conditions to which the elastomer components are exposed during application
The constitutive model is implemented as a user-defined material behavior in a standard large displacement based large strain finite element code ABAQUS /Standard®
Summary
The second factor are the environmental conditions to which the elastomer components are exposed during application. Environmental conditions are for instance moisture, weathering, oxygen, mechanical loading, radiation (e.g., γ-radiation in nuclear application [3]), contact with chemical (e.g., in vehicle engine exposed to different fuels [4]) or biological media and temperature, which can be encountered separately or in combination. On the other hand, is an irreversible process that leads to oxidation, chain scission, and/or the formation of new cross-links [5]. These irreversible microstructural changes are thermally driven effects and affect the mechanical properties of the material. The change of a chosen mechanical property is evaluated under accelerated ageing conditions, in order to extrapolate it to a suitable lower temperature such
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