炭纤维的压缩特性

本文采用单丝反弹测试及扫描电镜观察(SEM)的方法研究了聚丙烯腈(PAN)基和中间相沥青基(MP)炭纤维的压缩特性,PAN—CF与MP—CF相比具有更高的压缩强度。本文从两相结构观点分析讨论了一些PAN—CF的优异抗拉和抗压强度,其中一相是标准的层面结构,另一相是无序碳结构。分析认为,MP—CF抗压强度较低是由于其结构的高度有序性(石墨化)及其固有的片状结构。受压缩CF的SEM显微照片表明纤维断裂的类型取决于纤维的种类。从而提出了两种不同的形变机制,即对PAN—CF来说是与扭曲有关的多弯曲带的形成机制以及对大多数MP—CF来说是与传统的剪切破坏有关的单一弯曲带的形成机制。

THE STRUCTURES OF SOME MESOPHASE PITCH-BASED CARBON FIBRES

The macro-and micro-structure of two groups(high modulus and high thermalconductivity)of MP-based carbon fibres were studied using X-ray diffraction,and both scanningand transmission electron microscopy.The dominant macrostructure in cross section is of foldedpseudo-radial layers which have a tendency to form a quasi-uniform domain as the fibre modulusincreases.It is found that high thermal conductivity fibres have both missimg sector and circularcross sections(possessed predominantly by the high modulus fibre group).The microstructuralstudy indicates that apart from the fibre C700,which has a three-dimensional graphite structure,these two groups of carbon fibres all exhibit a turbostratic stacking order.Furthermore it is foundthat the turbostratic stacking thickness as determined from dark-field measurement is much largerthan the classical crystallite thickness L_c as measured from X-ray diffraction.