服役环境下四代机透明件的失效分析与寿命评估模型研究

Highly economical and safe aircraft (e.g. F-22) is closely concerned with design and use of environmentally friendly and long-life materials and structures with high reliability, especially transparent parts which subject to ambient environmental and mechanical loadings (e.g. high temperature, frequency and humidity). The understanding of failure property is most elementary. By investigating failure mechanisms of transparent parts (PMMA-based on polymeric materials) in the 4th aircraft under service environments, this proposal will clarify the failure mechanism of craze density nucleation, and explore a fast and in situ strategy of obtaining the (residual) lifetime with the ultimate goal of building a theoretical model for predicting their lifetime. Theoretical, molecular dynamics and experimental approaches will be employed to identify the core principles (e.g. craze density) that link the fundamental molecular-scale material structures (representative molecular chain structure) to failure property (lifetime model). First, through the representative molecular chain structures of PMMA, the mechanism of craze nucleation will be elucidated by using the molecular dynamics (MD) simulation. Second, experiment will be carried out to identify craze damage nucleation and build craze density model. In this step, a design rule of temperature-humidity-loading-time paradigm will also be established. Third, from the damage mechanics theory point of view, we will build the qualitative relationship between craze density and lifetime under service loading conditions. Finally, serials of experiments on samples directly cut from service aircraft will be carried out to verify above findings and theory.

针对四代机透明件，研究服役环境下（温度、湿度、高频载荷等）透明件失效微观机理，建立工作载荷谱下剩余寿命的评估模型，提出一种快速、无损、可靠的银纹密度评估透明件剩余寿命的方法。选取合适的势函数，合理简化分子链，采用分子动力学方法模拟透明件材料银纹化过程,揭示透明件银纹化的微观机理；以银纹损伤为核心，实验研究银纹萌生"温度-湿度-载荷-时间"的准则，提出银纹密度增长模型；基于损伤力学理论，建立工作载荷谱下透明件材料失效的寿命模型；以时间为中间量，寻找银纹密度与透明件剩余寿命间的定量关系，提出用银纹密度评估透明件剩余寿命的模型。并开展校核实验，评估方法的可靠性和可行性。该项目可为飞机透明件的失效寿命预测提供试验测试方法和理论分析基础，具有重要的科学意义和广泛的应用前景。

四代机具有超高速、高机动性能及隐身能力等特点，给透明件座舱盖寿命设计带来新的要求。超高速持久巡航过程中会使透明件的温度发生变化，高机动性能带来结构的高频疲劳，地域的改变引起湿度的变化，这些因素都会对透明件的寿命进行影响。因此，本项目以透明件材料为研究对象，开展服役温度、湿度及工作载荷谱下透明件结构的失效分析，提出一种快速、便捷、无损的剩余寿命评估模型。飞机透明件为高分子材料，因此，采用基于粗粒簧链模型的分子动力学方法，选取合适的势函数，合理简化分子链，采用分子动力学方法模拟透明件材料银纹化过程，揭示透明件银纹化微观机理；以银纹损伤为核心，提出银纹密度增长模型；基于损伤力学的理论，建立工作载荷谱下透明件材料失效分析的寿命模型；以时间为中间量，寻找银纹密度与透明件剩余寿命间的定量关系，提出银纹密度评估透明件剩余寿命的模型。并开展校核实验，评估方法的可靠性和可行性。