Graphene is the strongest material but its performance is significantly weakened by vacancy defects. We use molecular dynamics simulations to inves- tigate the tensile behavior of a graphene which contains a single va...Graphene is the strongest material but its performance is significantly weakened by vacancy defects. We use molecular dynamics simulations to inves- tigate the tensile behavior of a graphene which contains a single vacancy defect. Our results suggest that because of the single vacancy, the fracture strength of graphene losses about 17.7%. The stress concentration around the vacancy defect leads to the destruction of nearby six-member rings structure, which forms the initial crack. The propagation direction of this crack in defective graphene is at an angle of 60° to the tensile direction initially, but then becomes perpendicular to the tensile direction.展开更多
In this work the thermal transport properties of graphene nanoribbons with randomly distributed vacancy defects are investigated by the reverse non-equilibrium molecular dynamics method. We find that the thermal condu...In this work the thermal transport properties of graphene nanoribbons with randomly distributed vacancy defects are investigated by the reverse non-equilibrium molecular dynamics method. We find that the thermal conductivity of the graphene nanoribbons decreases as the defect coverage increases and is saturated in a high defect ratio range. Further analysis reveals a strong mismatch in the phonon spectrum between the unsaturated carbon atoms in 2-fold coordination around the defects and the saturated carbon atoms in 3-fold coordination, which induces high interfacial thermal resistance in defective graphene and suppresses the thermal conductivity. The defects induce a complicated bonding transform from sp2 to hybrid sp--sp2 network and trigger vibration mode density redistribution, by which the phonon spectrum conversion and strong phonon scattering at defect sites are explained. These results shed new light on the understanding of the thermal transport behavior of graphene-based nanomaterials with new structural configurations and pave the way for future designs of thermal management phononic devices.展开更多
The Young＇s modulus of graphene with various rectangular and circular vacancy defects is investigated by molecular dynamics simulation. By comparing with the results calculated from an effective spring model, it is d...The Young＇s modulus of graphene with various rectangular and circular vacancy defects is investigated by molecular dynamics simulation. By comparing with the results calculated from an effective spring model, it is demonstrated that the Young＇s modulus of graphene is largely correlated to the size of vacancy defects perpendicular to the stretching direction. And a linear reduction of Young＇s modulus with the increasing concentration of monoatomic-vacancy defects （Le., the slope of =0.03） is also observed. The fracture behavior of graphene, including the fracture strength, crack initiation and propagation are then studied by the molecular dynamics simulation, the effective spring model, and the quantized fracture mechanics. The blunting effect of vacancy edges is demonstrated, and the characterized crack tip radius of 4.44 A is observed.展开更多
The effects of Ni coating on the mechanical behaviors of single graphene sheet and their embedded Almatrix composites under axial tension are investigated using molecular dynamics (MD) simulation method.The resultssho...The effects of Ni coating on the mechanical behaviors of single graphene sheet and their embedded Almatrix composites under axial tension are investigated using molecular dynamics (MD) simulation method.The resultsshow that the Young's moduli and tensile strength of graphene obviously decrease after Ni coating.The results also showthat the mechanical properties of Al matrix can be obviously increased by embedding a single graphene sheet.Fromthe simulation,we also find that the Young's modulus and tensile strength of the Ni-coated graphene/Al composite isobviously larger than those of the uncoated graphene/Al composite.The increased magnitude of the Young's modulusand tensile strength of graphene/A1 composite are 52.27% and 32.32% at 0.01 K,respectively,due to Ni coating.Byexploring the effects of temperature on the mechanical properties of single graphene sheet and their embedded A1 matrixcomposites,it is found that the higher temperature leads to the lower critical strain and tensile strength.展开更多
基金supported by the Open Research Fund Program(2042014kf0002)of Wuhan Universitythe National Natural Science Foundation of China(11372230)the Open Research Fund Program(HBKLWJ-2014F02)of Key Laboratory of Hubei Province for Water Jet Theory&Technology
文摘Graphene is the strongest material but its performance is significantly weakened by vacancy defects. We use molecular dynamics simulations to inves- tigate the tensile behavior of a graphene which contains a single vacancy defect. Our results suggest that because of the single vacancy, the fracture strength of graphene losses about 17.7%. The stress concentration around the vacancy defect leads to the destruction of nearby six-member rings structure, which forms the initial crack. The propagation direction of this crack in defective graphene is at an angle of 60° to the tensile direction initially, but then becomes perpendicular to the tensile direction.
基金Project supported by the National Natural Science Foundation of China(Grant No.51202032)the National Key Project for Basic Research of China(Grant No.2011CBA00200)+1 种基金the Natural Science Foundation of Fujian Province,China(Grant Nos.2012J01004 and 2013J01009)the Funds from the Fujian Provincial Education Bureau,China(Grant No.GA12064)
文摘In this work the thermal transport properties of graphene nanoribbons with randomly distributed vacancy defects are investigated by the reverse non-equilibrium molecular dynamics method. We find that the thermal conductivity of the graphene nanoribbons decreases as the defect coverage increases and is saturated in a high defect ratio range. Further analysis reveals a strong mismatch in the phonon spectrum between the unsaturated carbon atoms in 2-fold coordination around the defects and the saturated carbon atoms in 3-fold coordination, which induces high interfacial thermal resistance in defective graphene and suppresses the thermal conductivity. The defects induce a complicated bonding transform from sp2 to hybrid sp--sp2 network and trigger vibration mode density redistribution, by which the phonon spectrum conversion and strong phonon scattering at defect sites are explained. These results shed new light on the understanding of the thermal transport behavior of graphene-based nanomaterials with new structural configurations and pave the way for future designs of thermal management phononic devices.
文摘The Young＇s modulus of graphene with various rectangular and circular vacancy defects is investigated by molecular dynamics simulation. By comparing with the results calculated from an effective spring model, it is demonstrated that the Young＇s modulus of graphene is largely correlated to the size of vacancy defects perpendicular to the stretching direction. And a linear reduction of Young＇s modulus with the increasing concentration of monoatomic-vacancy defects （Le., the slope of =0.03） is also observed. The fracture behavior of graphene, including the fracture strength, crack initiation and propagation are then studied by the molecular dynamics simulation, the effective spring model, and the quantized fracture mechanics. The blunting effect of vacancy edges is demonstrated, and the characterized crack tip radius of 4.44 A is observed.
基金Supported by National Natural Science Foundation of China under Grant No.10902083the Natural Science Foundation of Shannxi Province under Grant No.2009GM1007
文摘The effects of Ni coating on the mechanical behaviors of single graphene sheet and their embedded Almatrix composites under axial tension are investigated using molecular dynamics (MD) simulation method.The resultsshow that the Young's moduli and tensile strength of graphene obviously decrease after Ni coating.The results also showthat the mechanical properties of Al matrix can be obviously increased by embedding a single graphene sheet.Fromthe simulation,we also find that the Young's modulus and tensile strength of the Ni-coated graphene/Al composite isobviously larger than those of the uncoated graphene/Al composite.The increased magnitude of the Young's modulusand tensile strength of graphene/A1 composite are 52.27% and 32.32% at 0.01 K,respectively,due to Ni coating.Byexploring the effects of temperature on the mechanical properties of single graphene sheet and their embedded A1 matrixcomposites,it is found that the higher temperature leads to the lower critical strain and tensile strength.
文摘采用分子动力学方法,模拟了金属原子存在条件下缺陷石墨烯的自修复过程.模拟采用了 Ni 和 Pt 两种金属原子作为催化剂,通过改变系统温度,得到了多组模拟结果.观察对比了模拟结束时获得的原子构型图,并通过计算修复过程中石墨烯内 5, 6, 7 元环的数量变化,研究了不同金属原子对缺陷石墨烯的催化修复效果,发现在适当的温度(1600 K 和 2000 K)下,与无金属原子条件下的修复结果相比,两种金属原子都表现出了一定的催化修复能力,且 Ni 表现出的催化修复能力要优于 Pt.为了探究其背后的机理,我们模拟了部分典型的结构演变.发现 Ni 和 Pt 原子分别会导致“环内跳出”和“断环”的局部结构转变,并且在不同温度下均表现出不同程度捕获碳链的能力.此外,观察了两种金属原子在平面内外的不同迁移行为,并通过绘制金属原子的迁移路线,计算其迁移量,进一步研究了两种金属原子不同的催化修复机理.研究结果有利于认识不同金属原子具有的不同催化修复效果,理解不同金属原子的催化作用机制,有助于针对缺陷石墨烯的修复选择合适的催化剂.
