Molecular dynamics simulations of carbon nanotube (CNT) composites, in which the CNTs are continuous across the periodic boundary, overestimate the experimentally measured mechanical properties of CNT composites along the fiber direction. Since the CNTs in these composites are much shorter than the composite dimensions, load must be transferred either directly between CNTs or through the matrix, a mechanism that is absent in simulations of effectively continuous CNTs. In this study, the elastic and fracture properties of high volume fraction discontinuous carbon nanotube/amorphous carbon composite systems were compared to those of otherwise equivalent continuous CNT composites using ReaxFF reactive molecular dynamics simulations. These simulations were used to show how the number of nanotube-matrix interfacial covalent bonds affect composite mechanical properties. Furthermore, the mechanical impact of interfacial bonding was decomposed to reveal its effect on the properties of the CNTs, the interfacial layer of matrix, and the bulk matrix. For the composites with continuous reinforcement, it was found that any degree of interfacial bonding has a negative impact on axial tensile strength and stiffness. This is due to disruption of the structure of the CNTs and interfacial matrix layer by the interfacial bonds. For the discontinuous composites, the modulus was maximized between 4%-7% interfacial bonding and the strength continues to increase up to the highest levels of interfacial bonding studied. Areas of low stress and voids were observed in the simulated discontinuous composites at the ends of the tubes, from which fracture was observed to initiate. Experimental carbon nanotube yarn composites were fabricated and tested. The results were used to illustrate knockdown factors relative to the mechanical performance of the tubes themselves.

中文翻译：

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模拟碳纳米管连续性和界面结合对复合材料强度和刚度的影响

碳纳米管 (CNT) 复合材料的分子动力学模拟，其中 CNT 在周期性边界上是连续的，高估了实验测量的 CNT 复合材料沿纤维方向的机械性能。由于这些复合材料中的碳纳米管比复合材料的尺寸短得多，负载必须直接在碳纳米管之间或通过基体转移，这种机制在有效连续碳纳米管的模拟中是不存在的。在这项研究中，使用 ReaxFF 反应分子动力学模拟将高体积分数不连续碳纳米管/无定形碳复合材料系统的弹性和断裂性能与其他等效的连续 CNT 复合材料的弹性和断裂性能进行了比较。这些模拟用于显示纳米管-基质界面共价键的数量如何影响复合材料的机械性能。此外，分解了界面键合的机械影响，以揭示其对碳纳米管、基质界面层和体基质性能的影响。对于具有连续增强功能的复合材料，发现任何程度的界面结合都会对轴向拉伸强度和刚度产生负面影响。这是由于界面键破坏了碳纳米管和界面基质层的结构。对于不连续复合材料，模量在 4%-7% 的界面结合之间达到最大，并且强度继续增加到所研究的最高界面结合水平。在管端的模拟不连续复合材料中观察到低应力和空隙区域，观察到从该处开始破裂。制造并测试了实验性碳纳米管纱线复合材料。结果用于说明与管本身机械性能相关的击倒因素。