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C Q Ru - One of the best experts on this subject based on the ideXlab platform.

  • Curvature effects on axially compressed Buckling of a small-diameter double-walled carbon nanotube
    International Journal of Solids and Structures, 2005
    Co-Authors: H. Qian, K. Y. Xu, C Q Ru
    Abstract:

    Abstract The curvature effects of interlayer van der Waals (vdW) forces on axially compressed Buckling of a double-walled carbon nanotube (DWNT) of diameter down to 0.7 nm are studied. Unlike most existing models which assume that the interlayer vdW pressure at a point between the inner and outer tubes depends merely on the change of the interlayer spacing at that point, the present model considers the dependence of the interlayer vdW pressure on the change of the curvatures of the inner and outer tubes at that point. A simple expression is derived for the curvature-dependence of the interlayer vdW pressure in which the curvature coefficient is determined. Based on this model, an explicit formula is obtained for the axial Buckling Strain. It is shown that neglecting the curvature effect alone leads to an under-estimate of the critical Buckling Strain with a relative error up to −7%, while taking the average radius of two tubes as the representative radius and the curvature effect leads to an over-estimate of the critical Buckling Strain with a relative error up to 20% when the inner radius downs to 0.35 nm. Therefore, the curvature effects play a significant role in axially compressed Buckling problems only for DWNTs of very small radii. In addition, our results show that the effect of the vdW interaction pressure prior to Buckling of DWNTs under pure axial stress is small enough and can be negligible whether the vdW interaction curvature effects are neglected or not.

  • degraded axial Buckling Strain of multiwalled carbon nanotubes due to interlayer slips
    Journal of Applied Physics, 2001
    Co-Authors: C Q Ru
    Abstract:

    A multiple-shell model is presented for infinitesimal axially compressed Buckling of a multiwalled carbon nanotube embedded within an elastic matrix. In contrast to an existing single-shell model which treats the entire multiwalled nanotube as a singlelayer elastic shell, the present model assumes that each of the nested concentric tubes is an individual elastic shell and the deflections of all shells are coupled through the van der Waals interaction between adjacent nanotubes. By examining a doublewalled carbon nanotube, it is found that the change in interlayer spacing has a negligible effect on the axial Buckling Strain provided that the innermost radius is at least a few nanometers. Under this condition, a single equation is derived which determines the deflection of the multiwalled carbon nanotube, and it is shown that infinitesimal axial Buckling of a N-walled carbon nanotubes is equivalent to that of a single layer elastic shell whose bending stiffness is approximately N times the effective bending...

Otto Zhou - One of the best experts on this subject based on the ideXlab platform.

Quan Wang - One of the best experts on this subject based on the ideXlab platform.

  • Buckling and Vibration of Carbon Nanotubes Embedded in Polyethylene Polymers
    Applied Mechanics and Materials, 2011
    Co-Authors: Quan Wang
    Abstract:

    The discovery of Buckling instability and vibration of polyethylene/ carbon nanotube matrices is reported by molecular mechanics simulations. The research is aimed to acquire a high strength design of PE-CNT matrix with proper PE/CNT ratio as well as discovering the dynamic characteristics of the PE-CNT composites. The Buckling Strains and the resonance frequencies are found to decrease with an increase in the number of polyethylene chains in the polyethylene/carbon nanotube matrices. Van der Waals forces are collected to explain the relation of the PE chains to the Buckling Strain and the resonance frequency of the composites.

  • Compressive Buckling of carbon nanotubes containing polyethylene molecules
    Carbon, 2011
    Co-Authors: Quan Wang
    Abstract:

    The instability of a carbon nanotube containing a polyethylene molecule subjected to compression is investigated using molecular dynamics. A decrease up to 35% in the Buckling Strain of the (6,6) and (10,10) carbon nanotube/polymer structures due to the attractive van der Waals interaction between the tube wall and the polymer molecule is reported. In particular, the decrease in the Buckling Strain of the (6,6) carbon nanotube/polymer structure is attributed to the initiation of two flattenings on the tube wall. Simulations show that the Buckling Strain of the structure is insensitive to the number of units of the polymer molecule.

  • Buckling of carbon nanotubes wrapped by polyethylene molecules
    Physics Letters A, 2011
    Co-Authors: Quan Wang
    Abstract:

    Abstract The discovery of a Buckling instability of a single-walled carbon nanotube wrapped by a polyethylene molecule subjected to compression is reported through molecular mechanics simulations. A decrease up to 44% in the Buckling Strain of the nano-structure owing to the van der Waals interaction between the two molecules is uncovered. A continuum model is developed to calculate both the interaction between the tube and the polymer and the decreased Buckling Strain of the structure by fitting the molecular mechanics results.

  • Instability analysis of double-walled carbon nanotubes subjected to axial compression
    Journal of Applied Physics, 2008
    Co-Authors: Quan Wang
    Abstract:

    The Buckling of short double-walled carbon nanotubes subjected to compression is investigated through molecular dynamics in the paper. The inner wall is discovered to have helically aligned Buckling mode while the outer wall is reported to have shell Buckling mode with kinks. Such Buckling modes are attributed to the interaction of the two walls via the van der Waals effect. In addition, a Buckling Strain higher than the Buckling Strains of two constituent inner and outer walls is found in the double-walled tube within a certain size range. The causes for such a phenomenon are analyzed and discussed.

  • ON INSTABILITY OF SINGLE-WALLED CARBON NANOTUBES WITH A VACANCY DEFECT
    International Journal of Structural Stability and Dynamics, 2008
    Co-Authors: Quan Wang, Vijay K. Varadan, Yang Xiang
    Abstract:

    This technical note is concerned with the Buckling of single-walled carbon nanotubes with one atomic vacancy. An elastic beam theory is developed to predict the Buckling Strain of defective CNTs, and the Strain prediction via the continuum mechanics model is verified from comparison studies by molecular dynamics simulations. The results demonstrate the effectiveness of the continuum mechanics theory for longer CNTs. In addition, a local kink is revealed in the morphology of the Buckling of shorter defective CNTs via molecular dynamics.

Quanshui Zheng - One of the best experts on this subject based on the ideXlab platform.

  • Anomalous elastic Buckling of layered crystalline materials in the absence of structure slenderness
    Journal of The Mechanics and Physics of Solids, 2016
    Co-Authors: Lifeng Wang, Quanshui Zheng
    Abstract:

    Abstract Layered crystalline materials, such as graphene, boron nitride, tungsten sulfate, phosphorene, etc., have attracted enormous attentions, due to their unique crystal structures and superior mechanical, thermal, and physical properties. Making use of mechanical Buckling is a promising route to control their structural morphology and thus tune their physical properties, giving rise to many novel applications. In this paper, we employ molecular dynamics (MD) simulations and theoretical modeling to study the compressive Buckling of a column made of layered crystalline materials with the crystal layers parallel to the compressive direction. We find that the mechanical Buckling of the layered crystalline materials exhibits two anomalous and counter-intuitive features as approaching the zero slenderness ratio. First, the critical Buckling Strain e cr has a finite value that is much lower than the material's elastic limit Strain. A continuum mechanics model (by homogenizing the layered materials) is proposed for the e cr , which agrees well with the results of MD simulations. We find that the e cr solely depends on elastic constants without any structural dimension, which appears to be an intrinsic material property and thus is defined as intrinsic Buckling Strain (IBS), e cr IBS , in this paper. Second, below a certain nanoscale length, l 0 , in the compressive direction ( e.g. , about 20 nm for graphite), the critical Buckling Strain e cr shows a size effect, i.e. , increasing as the column length L decreases. To account for the size effect, inspired by our recently developed multi-beam shear model ( Liu et al., 2011 ), a bending energy term of individual crystal layer is introduced in our continuum model. The theoretical model of e cr agrees well with the size effects observed in MD simulations. This study could lay a ground for engineering layered crystalline materials in various nano-materials and nano-devices via mechanical Buckling.

  • Mechanical Buckling induced periodic kinking/stripe microstructures in mechanically peeled graphite flakes from HOPG
    Acta Mechanica Sinica, 2015
    Co-Authors: Quanshui Zheng
    Abstract:

    Mechanical exfoliation is a widely used method to isolate high quality graphene layers from bulk graphite. In our recent experiments, some ordered microstructures, consisting of a periodic alternation of kinks and stripes, were observed in thin graphite flakes that were mechanically peeled from highly oriented pyrolytic graphite. In this paper, a theoretical model is presented to attribute the formation of such ordered structures to the alternation of two mechanical processes during the exfoliation: (1) peeling of a graphite flake and (2) mechanical Buckling of the flake being subjected to bending. In this model, the width of the stripes L is determined by thickness h of the flakes, surface energy \(\gamma \), and critical Buckling Strain \(\varepsilon _{\mathrm{cr}}\). Using some appropriate values of \(\gamma \) and \(\varepsilon _{\mathrm{cr}}\) that are within the ranges determined by other independent experiments and simulations, the predicted relations between the stripe width and the flake thickness agree reasonably well with our experimental measurements. Conversely, measuring the L–h relations of the periodic microstructures in thin graphite flakes could help determine the critical mechanical Buckling Strain \(\varepsilon _{\mathrm{cr}}\) and the interface energy \(\gamma \).

  • Anomalous elastic Buckling of hexagonal layered crystalline materials in the absence of structure slenderness
    arXiv: Materials Science, 2014
    Co-Authors: Lifeng Wang, Quanshui Zheng
    Abstract:

    Hexagonal layered crystalline materials, such as graphene, boron nitride, tungsten sulfate, and so on, have attracted enormous attentions, due to their unique combination of atomistic structures and superior thermal, mechanical, and physical properties. Making use of mechanical Buckling is a promising route to control their structural morphology and thus tune their physical properties, giving rise to many novel applications. In this paper, we employ finite element analysis (FEA), molecular dynamic (MD) simulations and continuum modeling to study the mechanical Buckling of a column made of layered crystalline materials with the crystal layers parallel to the longitudinal axis. It is found that the mechanical Buckling exhibits a gradual transition from a bending mode to a shear mode of instability with the reduction of slenderness ratio. As the slenderness ratio approaches to zero, the critical Buckling Strain {\epsilon}cr converges to a finite value that is much smaller than the material's mechanical strength, indicating that it is realizable under appropriate experimental conditions. Such a mechanical Buckling mode is anomalous and counter-intuitive. The critical Buckling Strain {\epsilon}cr predicted by our continuum mechanics model agrees very well with the results from the FEA and MD simulations for a group of typical hexagonal layered crystalline materials. MD simulations on graphite indicate the continuum mechanics model is applicable down to a scale of 20 nm. This theoretical model also reveals that a high degree of elastic anisotropy is the origin for the anomalous mechanical Buckling of a column made of layered crystalline materials in the absence of structural slenderness. This study provides avenues for engineering layered crystalline materials in various nano-materials and nano-devices via mechanical Buckling.

Chien Ming Wang - One of the best experts on this subject based on the ideXlab platform.

  • Buckling BEHAVIOR OF SHORT MULTI-WALLED CARBON NANOTUBES UNDER AXIAL COMPRESSION LOADS
    International Journal of Structural Stability and Dynamics, 2012
    Co-Authors: Asghar Habibnejad Korayem, Wenhui Duan, Xiao Ling Zhao, Chien Ming Wang
    Abstract:

    We investigate the Buckling behaviors of short multi-walled carbon nanotubes (MWCNTs) under axial compression by using molecular mechanics (MM) simulations. The effects of the number of walls, length and chiral angle of MWCNTs on the Buckling behaviors are examined. The results show that the Buckling behaviors of short MWCNTs are rather different from single walled carbon nanotubes (SWCNTs) and slender MWCNTs. Moreover, it is observed that the Buckling Strains of short MWCNTs vary inversely proportional to the number of nanotube walls. For slender MWCNTs, the Buckling Strains fluctuate as the number of walls increase. It increases for beam-like Buckling mode, decreases for shell-like Buckling mode and is approximately constant for the shell-beam-like Buckling mode. The increase in the length of MWCNT has also led to a significant decrease of the Buckling Strain for short MWCNTs. However, chirality does not have a significant effect on the Buckling Strain of MWCNTs nor alter the Buckling mode of short MWCNTs.

  • Mechanical properties and Buckling behaviors of condensed double-walled carbon nanotubes.
    Journal of Nanoscience and Nanotechnology, 2009
    Co-Authors: Yingyan Zhang, Chien Ming Wang
    Abstract:

    Molecular dynamics (MD) simulations are performed on condensed double-walled carbon nanotubes (CDWCNTs) to investigate the effects of compressed interwall spacings on their mechanical properties, in particular their Buckling behavior under axial compression, torsion and bending. In CDWCNTs, the inner and outer nanotubes have diameters that are closer to each other than the nanotubes of conventional double-walled carbon nanotubes (DWCNTs). This leads to a smaller interwall spacing. The mechanical properties of the CDWCNTs, such as Young's modulus, interwall shear modulus, and the Buckling Strain under axial compression, torsion and bending are found to be greatly enhanced when compared with those of conventional DWCNTs. The enhancement is found to be inversely proportional to the interwall spacing. Copyright

  • Examining the effects of wall numbers on Buckling behavior and mechanical properties of multiwalled carbon nanotubes via molecular dynamics simulations
    Journal of Applied Physics, 2008
    Co-Authors: Yingyan Zhang, Chien Ming Wang
    Abstract:

    Molecular dynamics simulations are performed on multiwalled carbon nanotubes (MWCNTs) under axial compression to investigate the effects of the number of walls and their van der Waals (vdW) interaction on the Buckling behaviors and mechanical properties (Young's modulus and Poisson's ratio). The Brenner second-generation reactive empirical bond order and Lennard-Jones 12-6 potential have been adopted to describe the short-range bonding and long-range vdW atomic interaction within the carbon nanotubes, respectively. In the presence of vdW interaction, the Buckling Strain and Young's modulus of MWCNTs increase as the number of tubes is increased while keeping the outermost tube diameter constant, whereas Poisson's ratio was observed to decrease. On the other hand, when the MWCNTs are formed by progressively adding outer tubes while keeping the innermost tube diameter constant, Young's modulus and Buckling Strain were observed to decrease, whereas Poisson's ratio increases. The Buckling load increases with increasing the number of walls due to the larger cross-sectional areas. Individual tubes of MWCNTs with a relatively large difference between the diameters of the inner and outer tubes buckle one at a time as opposed to simultaneously for MWCNTs with a relatively small difference in diameters.

  • Effect of omitting terms involving tube radii difference in shell models on Buckling solutions of DWNTs
    Computational Materials Science, 2006
    Co-Authors: Yingyan Zhang, Chien Ming Wang
    Abstract:

    Continuum cylindrical shell models have been widely applied in the Buckling analysis of carbon nanotubes. An explicit expression for the critical Buckling Strain of double-walled carbon nanotubes (DWNTs) may be obtained based on cylindrical shell models. The expression is usually simplified by neglecting the terms involving outer and inner tube radii difference. In this brief note, we present the critical Buckling Strains of DWNTs with the inclusion of these terms and investigate the quantitative effect of neglecting these terms on the critical Strain. It was found that the omission of the terms related to outer and inner tube radii difference leads to an overprediction of the critical Buckling Strain as well as a possible change in the Buckling mode shape. It is also observed that the effect of the terms is especially significant for DWNTs with small inner radius but is negligible when the inner radius is relatively large.