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本文采用分子动力学计算方法和Tersoff作用势研究了无定型碳(amorphous carbon,a-C)涂层厚度对Si C纳米纤维/Si C纳米复合材料断裂方式及力学性能的影响.分析结果发现,随着涂层厚度的增加,纳米纤维的平均应力集中系数下降,即足够厚度涂层可以同时起到增强和补韧的作用.当a-C涂层厚度t 0.3 nm时,裂纹直接穿透纤维,纳米复合材料表现出典型的脆性断裂方式;t=4.0 nm时,裂纹发生偏转,Si C纳米纤维发生拔出现象,此时纳米复合材料的拉伸强度约为无涂层纳米复合材料的4倍,断裂能则提高一个数量级.计算结果表明,a-C涂层的厚度是Si C纳米纤维/Si C纳米复合材料中产生韧性机理的重要因素,即传统微米级陶瓷基复合材料的增韧理论在纳米复合材料中仍适用.研究结果可望为设计同时具有高强度、高韧性的陶瓷基纳米复合材料提供理论基础.
In this paper, the effects of the thickness of amorphous carbon (aC) coating on the fracture mode and mechanical properties of Si C nanofibers / Si C nanocomposites were investigated by molecular dynamics method and Tersoff potential. When the thickness of aC coating is 0.3 nm, the crack penetrates directly through the fibers and the nanocomposites Which shows the typical brittle fracture mode. At t = 4.0 nm, the cracks are deflected and the Si C nanofibers pull out. At this time, the tensile strength of the nanocomposites is about 4 times that of the uncoated nanocomposites. The fracture energy The results show that the thickness of aC coating is an important factor in the toughness mechanism of Si C nanofibers / Si C nanocomposites, that is, the toughening theory of traditional micrometer-sized ceramic matrix composites in nanocomposites The results are still expected to be applied to provide a theoretical basis for designing ceramic-based nanocomposites with high strength and toughness.