ABSTRACT
In the majority of applications ageing of elastomers is affected by heterogeneous effects. Probably the most important one is the influence of oxygen from the ambient environment. Oxygen molecules are absorbed by the surface layer and get transported into the interior by diffusion before reactions with the elastomer structure occur. Besides the mechanical properties, thermo-oxidative reactions affect the diffusion process itself and hence the prediction of oxidation is a current challenge when modelling ageing. This work provides a reaction-diffusion approach based on Fick’s second law of diffusion. Diffusivity is described as a function of temperature and ageing to simulate the decreasing permeability by progressing oxidation. In order to describe the reaction rate of oxidation an Arrhenius approach is chosen which considers the available amount of oxygen. The progress of ageing is given by an evolution equation depending on temperature and reaction rate. Since heterogeneous oxidation is influenced by the shape and size of the elastomer sample, the model is solved and visualized in two spatial dimension using Alternating Direction Implicit (ADI) method. This numerical algorithm is able to solve the developed model with unconditional stability and sufficient accuracy. This work illustrates the effect of ageing on diffusivity and is able to simulate Diffusion-Limited-Oxidation (DLO) which is a key factor of heterogeneous oxidation.
