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

聚合物和聚合物组件在工业应用中非常重要，如轴承、密封件、粘合剂和涂层。由于这些组件用于各种工程领域，因此它们显然会受到不同的环境影响，如机械应力、温度曲线和化学或生物物质。因此，它们的性质随着时间的推移而变化，导致寿命有限。为了估计它们的寿命，人们对能够考虑复杂长期过程的模拟方法非常感兴趣。该项目的目的是模拟液体环境中弹性体的化学热机械老化，这是一个不可逆的过程。在所谓的初始化时间之后，环境介质扩散到固体中并触发化学反应。考虑到有限厚度的部件，该过程是不均匀的和热激活的，这意味着温度的升高导致老化过程加速。为了验证材料的行为，对丁腈橡胶（NBR）进行了老化实验。由于这种材料经常用于液压系统中的密封件，因此适合使用不同恒温的矿物油作为环境介质。实验数据库包括在实验室规模的样品的调查，以及有限厚度的试样，以检测非均匀的扩散反应过程的测试。因此，使用不同的恒定温度对NBR进行许多机械、量热、化学分析和光谱研究。所获得的数据集被用来建立和调整一个耦合的化学-力学材料模型，这是一方面能够预测弹性体的典型粘弹性材料的属性。此外，考虑了与周围介质的扩散-反应过程以及聚合物网络的溶胀和降解和重组过程。作为验证，将用所识别的模型模拟所建立的聚合物组件的典型老化过程。

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.