中文摘要：

采用X射线衍射（XRD）、扫描电镜（SEM）、原子力显微镜（AFM）以及力学性能测试等方法对500—1350℃碳化纤维进行表征，研究了碳化温度对纤维结构缺陷和力学性能的影响。结果表明：在500—900℃低温阶段其强度和模量都随着碳化温度的升高呈增加趋势，但二者的增长速率在700℃前后是不同的。应力-应变曲线表明，低于700℃出现应力急剧下降的“之”字形拐点，没有明显屈服：700℃之后先出现屈服，后产生拐点。在1350℃高温阶段，纤维的断裂呈现出典型的脆性材料特征。在500—1350℃，碳化纤维的断裂主要取决于其表面缺陷。700℃和1350℃两种纤维表面都存在沿纤维轴方向的细长裂纹，700℃碳化纤维中的细长裂纹直径约为2nm，长度从几十纳米到几百纳米，1350℃碳化纤维中的细长裂纹直径约为1nm，长度在50—190nm。这些细小的裂纹，可能是导致纤维断裂的主要原因。

英文摘要：

The effects of carbonization temperature on the structural defects and mechanical properties were studied by using X-ray diffraction （XRD）, scanning electron microscope （SEM）, atomic force microscope （AFM） and mechanical properties test. The results show that, in the stage of low temperature, strength and modulus both increase with temperature increasing, but they show different increasing rate lower and higher than that in 700℃. When temperature is lower than 700℃, the stress-strain curves demonstrate there are ＂zigzag＂ inflections due to rapid decreasing of stress without obvious yield. Above 700℃, yield appears prior and then inflection. In the stage of high temperature, the fracture of fiber pres- ents typical characteristics of brittle material .The changes of mechanical properties are related to the changes of structure. The increase of strength is due to the crystallinity of quasi-crystal graphite, while the increase of modulus is mainly depended on the improvement and packing order of the quasi-crystal graphite. The fracture of carbonized fibers in 500-1350℃ mainly depends on the surface defects. The slender cracks along the fiber axis are both on the surface of carbonized fibers in 700℃ and 1350℃. The slender crack diameter of carbonized fiber in 700℃ is about 2 nm, and the length is from dozens of nanometers to hundreds of nanometers. The slender crack diameter of carbonized fiber in 1350℃ is about 1 nm, and the length is in the range of 50-190 rim. These slender cracks may be the main reason for the fracture of the fibers.