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

聚合物和聚合物组分在工业应用中非常重要，如轴承、密封件、粘合剂和涂料。由于这些部件用于各种工程领域，很明显，它们会受到不同环境的影响，如机械应力、温度曲线和化学或生物物质。因此，它们的性质会随着时间的推移而改变，从而导致有限的使用寿命。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。这是拟议的项目所附加的一点。这个项目的目的是模拟弹性体在液体环境中的化学-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引发化学反应。考虑到有限厚度的构件，这一过程是不均匀的和热激活的，这意味着温度的升高会导致老化过程的加速。为了表征材料性能，对丁腈橡胶（NBR）进行了老化试验。由于该材料常用于液压系统的密封件，因此适合使用不同恒温的矿物油作为环境介质。实验数据库包括实验室规模的样品调查以及有限厚度样品的测试，以检测非均匀扩散-反应过程。因此，丁腈橡胶在不同的恒温条件下进行了许多力学、量热、化学分析和光谱研究。利用获得的数据集建立并调整了化学-力学耦合材料模型，该模型一方面能够预测弹性体的典型粘弹性材料性能；此外，还考虑了聚合物网络与周围介质的扩散反应过程以及聚合物网络的溶胀、降解和重整过程。作为验证，将用识别的模型模拟已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.