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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2 nm,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1 nm,长度在50-190 nm。这些细小的裂纹,可能是导致纤维断裂的主要原因。
The carbon fibers of 500-1350 ℃ were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and mechanical properties test. The effects of carbonization temperature on the fiber structure defects and mechanical properties were investigated. The results show that both the strength and modulus increase with the increase of carbonization temperature at 500-900 ℃ during the low temperature stage, but the growth rate of both is different before and after 700 ℃. The stress-strain curve shows that there is no obvious yield point when the stress drops sharply below 700 ℃, and then inflection point appears after 700 ℃. In the high temperature of 1350 ℃, the fracture of the fiber shows typical brittle material characteristics. At 500-1350 ° C, the fracture of the carbonized fiber depends mainly on its surface defects. At 700 ℃ and 1350 ℃, there are elongated cracks in the fiber axis along the fiber axis. The elongated cracks in carbonized fibers at 700 ℃ are about 2 nm in diameter and tens to hundreds of nanometers in length. Carbon fibers at 1350 ℃ The elongated crack is about 1 nm in diameter and 50-190 nm in length. These tiny cracks may be the main cause of fiber breakage.