标题： 火焰攻击下碳纤维的损伤演化及其杂质的作用 显示英文标题

标题： Carbon fiber damage evolution under flame attack and the role of impurities

摘要： 碳纤维（CFs）在火焰攻击下容易发生大量氧化，例如在飞机火灾场景中。 本研究探讨了暴露于明火下的不同微观结构聚丙烯腈（PAN）基碳纤维所观察到的损伤机制。 开发了一种定点技术，通过时间控制将单根碳纤维插入预混甲烷/空气火焰中，随后通过扫描电子显微镜（SEM）和能量色散X射线光谱（EDS）分析来追踪。 除了直径减小外，在杂质存在的情况下还辨别出三种局部损伤机制，并通过中子活化分析（NAA）进行了量化。 严重的点蚀归因于主要由碱金属和碱土金属引起的催化氧化。 在杂质与碳表面之间的催化反应占主导地位的初始阶段之后，火焰的化学计量学控制了碳纤维的气化过程，贫燃火焰比富燃火焰更具侵蚀性。 第二种机制，通道效应，是由可移动的金属杂质引起的。 一些杂质表现出相反的效果，降低反应性从而阻止进一步的催化作用。 认为非晶态损伤伴随剥落效应是由于高浓度局部杂质和微观结构变化的结果。 讨论了杂质之间的阻碍或协同效应。 最后，确定了明显的轴向点蚀生长速率并与其它碳质材料进行了比较，揭示了杂质和火焰反应气氛对碳纤维氧化的强烈影响。 显示英文摘要

摘要： Carbon fibers (CFs) are prone to extensive oxidation under fire attack, for instance, in an aircraft fire scenario. This work addresses the damage mechanisms observed on polyacrylonitrile (PAN)-based CFs with different microstructure exposed to open flames. A fixed-point technique was developed to follow up individual CFs by means of time-controlled insertion into premixed methane/air flames, followed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses. Besides diameter reduction, three localized damage mechanisms were discerned in presence of impurities, which were quantified by neutron activation analysis (NAA). Severe pitting was ascribed to catalytic oxidation mainly caused by alkali and alkaline earth metals. After an initial period where catalytic reactions between impurities and the carbon surface dominate, the flame stoichiometry governed the CF gasification process, with lean flames being much more aggressive than rich ones. A second mechanism, channelling, was caused by mobile metallic impurities. Some impurities showed an opposite effect, lowering reactivity and thus preventing further catalysis. Amorphous damage with a skin-peeling effect is believed to be the result of localized impurities at high concentrations and microstructural variations. Hindrance or synergistic effects between impurities are discussed. Finally, apparent axial pit growth rates were determined and compared with other carbonaceous materials, revealing a strong influence of impurities and the flame reactive atmosphere on CF oxidation.