Modelling of the chemo-thermomechanical ageing of elastomers based on experimental investigations

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Polymers and polymer components are highly important in industrial applications such as bearings, seals, bonds and coatings.Since these components are used in various areas of engineering, it is obvious that they are exposed to different environmental influences such as mechanical stresses, temperature profiles and chemical or biological substances. Therefore, their properties change over time leading to a limited lifetime. In order to estimate their lifetime, there is a great interest in simulation methods that are able to consider complex long-term processes. This is the point where the proposed project attaches.The aim of this project is the modelling of chemo-thermomechanical ageing of elastomers in a liquid environment which is an irreversible process. The environmental medium diffuses into the solid and triggers a chemical reaction after the so called initialisation time. Taking into account components of finite thickness, this process is inhomogeneous and thermally activated, which means that an increase of temperature results in an acceleration of the ageing process.In order to characterise the material behaviour, ageing experiments on nitrile rubber (NBR) are per-formed. Since this material is often used for seals in hydraulic systems, it is suitable to use mineral oils at different constant temperatures as environmental medium. The experimental data base consists of investigations of samples at the laboratory scale as well as tests with specimens of finite thickness in order to detect non-uniform diffusion-reaction processes. Therefore, the NBR is subjected to a number of mechanical, calorimetric, chemoanalytical and spectroscopic studies using different constant tempe-ratures. The obtained dataset is used to establish and adapt a coupled chemo-mechanical material mo-del, which is on the one hand able to predict the typical viscoelastic material properties of elastomers. In addition, the diffusion-reaction process with the surrounding medium is considered as well as swelling and the degradation and reformation process of the polymeric network.As validation, a typical ageing process of an established polymer component will be simulated with the identified model.