Cradle-to-Grave Life Cycle Prediction of Automotive Materials and Systems in Service: Impact of Ageing on Performance

材料老化通常被理解为材料特性随时间的变化。这种物理或化学变化会对材料性能产生有害影响，导致设计功能逐渐丧失，效率损失不可接受或最终失效（在某些情况下，老化可能被视为一种改进，例如发动机性能）。材料系统在正常使用条件下的老化是一个很难处理的问题。许多因素会显著影响其耐久性，例如温度、辐照、湿度、化学品、机械蠕变和疲劳载荷。当几种应力的同时作用导致的老化效应不同于按顺序施加单独应力时观察到的老化效应时，通常会出现整体老化的协同效应。在努力了解老化过程中，第一个任务是确定年龄参数，代表，在宏观尺度上，微观和亚微观特征，潜在的过程，如成核和生长的微观缺陷，和/或物理化学转化。第二项任务包括制定本构方程，可以数学上表示老化。第三个任务显然是实验检查的条件下，导致灾难，如小扰动控制参数导致大的变化的年龄参数。可以引入材料张量“g”作为类似于应力和温度的年龄参数。变分原理的方法，然后可以制定一个本构方程老化。有趣的是，四维材料时空连续体中的“g”的演化将导致非弹性行为，这表现为外部观察者记录的时间依赖性材料特性。对于一个最简单的线性化的情况下，这种方法导致一个半经验的蠕变行为模型。目前，大多数研究都是基于试样级的加速老化试验，需要外推到零件/组件的正常使用条件，导致许多不确定性，导致现场频繁的诊断测试（目视检查，化学测量，物理测量），对成本产生巨大影响。拟议工作的目的是开发一种“年龄感知”的综合仿真工具，用于预测和评估制造，使用和寿命结束期间至关重要的汽车部件和系统。

Material ageing is commonly understood as changes of material properties with time. This physical or chemical alteration has a detrimental effect on the material properties and leads to gradual loss of the design function and unacceptable loss of efficiency or ultimate failure (in some cases ageing may be observed as an improvement, for instance, engine performance). Ageing of a material system under normal service conditions is a difficult case to treat. Many factors can significantly affect its durability, such as temperature, irradiation, moisture, chemicals, mechanical creep and fatigue loading. Synergism in the global ageing often occurs when the simultaneous action of several stresses results in an ageing effect that differs from that which would be observed if the individual stresses were applied sequentially. In an effort to understand the ageing process, the first task is to identify the age parameter that represents, on a macroscopic scale, the micro and sub microscopic features, underlying processes such as nucleation and growth of micro defects, and/or physico-chemical transformations. The second task consists of formulation of a constitutive equation that can mathematically represent ageing. The third task obviously is the experimental examination of the condition that leads to catastrophes such as small perturbation in controlling parameters leading to large variations of the age parameter. A material tensor "g" can be introduced as an age parameter similar to stresses and temperature. A variational principle approach can then be followed to formulate a constitutive equation for ageing. Interestingly, an evolution of "g" in four dimensional material space-time continuum would lead to an inelastic behaviour, which manifests as time dependent material properties recorded by an external observer. For one of the simplest linearized case this approach leads to a semi-empirical creep behaviour model. Currently, most of the studies are based on accelerated ageing test at coupon level and require extrapolation to normal service conditions of the part/component, resulting in many uncertainties, leading to frequent diagnostic tests in the field (visual inspection, chemical measurements, physical measurements), impacting dramatically on cost. The aim of the proposed work is to develop an 'age-aware' comprehensive simulation tool for the prediction and assessment of critically important automotive components and systems during manufacturing, in-service and the end of life.