Accelerated polymer aging under thermal oxidative conditions often involves heterogeneous degradation processes due to diffusion limited oxidation (DLO). DLO depends on geometrical shape and size, intrinsic oxidation rate and oxygen permeability of the material and occurs through the competition of simultaneous diffusional transport and reaction of oxygen. Definitions of the many parameters that describe polymer aging under DLO conditions are summarized for several applicable situations, which include the average oxidation rate, the oxidizing material fraction (i.e. fraction of the material oxidizing at a reference oxidation rate), and the depth of a specific flux reduction (i.e. generalized total oxidized layer (TOL)). Analytical and numerical solutions are derived for the prediction of spatially dependent oxidation behavior within a systematic framework for 1D to 3D geometries, multi-material situations and for a range of boundary conditions. Traditional mathematical approaches are expanded to embrace an arbitrary reaction domain through the finite element method (FEM). Concepts are also developed that address time dependent DLO profiles when the underlying oxidation rate or permeability may in itself depend on the evolving oxidation level. Understanding the occurrence of DLO and having the ability to predict spatially resolved oxidation reactions in polymers is critically important to determine when DLO (i.e. non uniform degradation) will interfere as part of accelerated aging studies, or to predict the aging behavior of multi-material polymer components of any geometry. This overview wishes to guide the polymer aging community towards embracing DLO phenomena and share newly developed computational approaches that facilitate comprehensive predictive modeling capabilities.

由于扩散限制氧化（DLO），在热氧化条件下加速的聚合物老化通常涉及非均相降解过程。DLO取决于材料的几何形状和大小，固有氧化速率和氧气渗透性，并且通过同时扩散的输运和氧气的竞争而发生。针对几种适用情况，总结了描述DLO条件下聚合物老化的许多参数的定义，包括平均氧化速率，氧化性物质分数（即，在参考氧化率下氧化的物质分数）以及特定氧化层的深度。减少通量（即广义总氧化层（TOL））。在1D到3D几何形状，多材料情况和一系列边界条件的系统框架内，可以得到用于预测空间相关氧化行为的分析和数值解决方案。传统的数学方法通过有限元方法（FEM）扩展为包含任意反应域。当潜在的氧化速率或渗透性本身可能取决于不断发展的氧化水平时，还开发了解决时间依赖的DLO曲线的概念。了解DLO的发生并具有预测聚合物中空间分辨的氧化反应的能力，对于确定DLO（即非均匀降解）何时会作为加速老化研究的一部分而产生干扰至关重要，或预测任何几何形状的多材料聚合物组件的老化行为。本概述希望引导聚合物老化社区接受DLO现象，并分享有助于全面的预测建模功能的最新开发的计算方法。