Elastic properties of fullerites and diamond-like phases

Diamond‐like structures, that include sp2 and sp3 hybridized carbon atoms, are of considerable interest nowadays. In the present work, various carbon auxetic structures are studied by the combination of molecular dynamics (MD) and analytical approach. Two fullerites based on the fullerene C60 and fullerene‐like molecule C48 are investigated as well as diamond‐like structures based on other fullerene‐like molecules (called fulleranes), carbon nanotubes (called tubulanes) and graphene sheets. MD is used to find the equilibrium states of the structures and calculate compliance and stiffness coefficients for stable configurations. Analytical methods are used to calculate the engineering elastic coefficients (Young's modulus, Poisson's ratio, shear modulus and bulk modulus), and to study their transformation under rotation of the coordinate system. All the considered structures are partial auxetics with the negative value of Poisson's ratio for properly chosen tensile directions. It is shown that some of these structures, in a particular tension direction, have a very high Young's modulus, that is, 1852 GPa for tubulane TA6

ELASTIC DAMPER BASED ON THE CARBON NANOTUBE BUNDLE

Mechanical response of the carbon nanotube bundle to uniaxial and biaxial lateral compression followed by unloading is modeled under plane strain conditions. The chain model with a reduced number of degrees of freedom is employed with high efficiency. During loading, two critical values of strain are detected. Firstly, period doubling is observed as a result of the second order phase transition, and at higher compressive strain, the first order phase transition takes place when carbon nanotubes start to collapse. The loading-unloading stress-strain curves exhibit a hysteresis loop and, upon unloading, the structure returns to its initial form with no residual strain. This behavior of the nanotube bundle can be employed for the design of an elastic damper

Strength and Deformation Behavior of Graphene Aerogel of Different Morphologies

Graphene aerogels are of high interest nowadays since they have ultralow density, rich porosity, high deformability, and good adsorption. In the present work, three different morphologies of graphene aerogels with a honeycomb-like structure are considered. The strength and deformation behavior of these graphene honeycomb structures are studied by molecular dynamics simulation. The effect of structural morphology on the stability of graphene aerogel is discussed. It is shown that structural changes significantly depend on the structural morphology and the loading direction. The deformation of the re-entrant honeycomb is similar to the deformation of a conventional honeycomb due to the opening of the honeycomb cells. At the first deformation stage, no stress increase is observed due to the structural transformation. Further, stress concentration on the junctions of the honeycomb structure and over the walls occurs. The addition of carbon nanotubes and graphene flakes into the cells of graphene aerogel does not result in a strength increase. The mechanisms of weakening are analyzed in detail. The obtained results further contribute to the understanding of the microscopic deformation mechanisms of graphene aerogels and their design for various applications

Metal/Graphene Composites: A Review on the Simulation of Fabrication and Study of Mechanical Properties

Although carbon materials, particularly graphene and carbon nanotubes, are widely used to reinforce metal matrix composites, understanding the fabrication process and connection between morphology and mechanical properties is still not understood well. This review discusses the relevant literature concerning the simulation of graphene/metal composites and their mechanical properties. This review demonstrates the promising role of simulation of composite fabrication and their properties. Further, results from the revised studies suggest that morphology and fabrication techniques play the most crucial roles in property improvements. The presented results can open up the way for developing new nanocomposites based on the combination of metal and graphene components. It is shown that computer simulation is a possible and practical way to understand the effect of the morphology of graphene reinforcement and strengthening mechanisms

Mechanical Properties of Graphene Networks under Compression: A Molecular Dynamics Simulation

Molecular dynamics simulation is used to study and compare the mechanical properties obtained from compression and tension numerical tests of multilayered graphene with an increased interlayer distance. The multilayer graphene with an interlayer distance two-times larger than in graphite is studied first under biaxial compression and then under uniaxial tension along three different axes. The mechanical properties, e.g., the tensile strength and ductility as well as the deformation characteristics due to graphene layer stacking, are studied. The results show that the mechanical properties along different directions are significantly distinguished. Two competitive mechanisms are found both for the compression and tension of multilayer graphene—the crumpling of graphene layers increases the stresses, while the sliding of graphene layers through the surface-to-surface connection lowers it. Multilayer graphene after biaxial compression can sustain high tensile stresses combined with high plasticity. The main outcome of the study of such complex architecture is an important step towards the design of advanced carbon nanomaterials with improved mechanical properties

Strain-induced ripples in graphene nanoribbons with clamped edges

Molecular dynamics is employed to study the mechanical behavior of graphene nanoribbons with clamped edges under in-plane strain. Buckling of nanoribbons results in the appearance of periodic ripples whose orientation, wavelength, and amplitude can be controlled by varying strain components and nanoribbon width. This study shows a way of controlling physical properties of nanoribbons by introducing strain-induced ripples

Discrete breather clusters in strained graphene

Molecular-dynamics simulations based on many-body interatomic potentials are conducted to investigate the clusters of discrete breathers in graphene under in-plane homogeneous strain. It is found that the discrete breather clusters can easily be excited when the gap in the phonon density of states is introduced by the homogeneous strain. Clusters of up to four discrete breathers were studied. We demonstrate that such clusters are robust with respect to small perturbations and can have the lifetime of order of 103 oscillation periods. Partial energy exchange between discrete breathers in the clusters was observed under certain conditions. The possible role of discrete breather clusters in formation of lattice defects is discussed

Bonding of Dissimilar Metals in the Interlayer Region in Al-Based Composites: Molecular Dynamics

The aluminum–matrix composites possess are very important for future applications because they have unique mechanical properties. Here, molecular dynamics is used to analyze the bonding of dissimilar metals on the interface of Al/Mg, Al/Ti, and Al/Cu interfaces during deformation treatment–compression combined with shear at room temperature. The terminal-mechanical treatment used in this simulation is a variant of the experimental technique applied to fabricate Al/Metal composites. It is found that there is a critical value of compressive and shear strain required to obtain the strong mixed Al/Metal interface. The diffusion depth of atoms of both components is dependent on the applied strain: (i) linear relationship for Al/Mg; (ii) logarithmic relationship for Al/Ti and Al/Cu. The mechanical behavior under tension and fracture analysis of the obtained interfaces are discussed in terms of atomic-level structural features which allow an understanding of the interconnection between the mechanical behavior and structure mixture near the interface. One of the important criteria for atomic mixing is the symmetry of the interface. After atomic mixing, Al/Ti composite has the highest ultimate tensile strength, Al/Cu—the average, and Al/Mg—the lowest between the considered interfaces, while the fracture strain of Al/Mg and Al/Ti composites are very close and higher than for Al/Cu. The obtained results are significant for the development of fabrication of Al/Metal interface by high-pressure torsion in practice

The Effects of Dislocation Dipoles on the Failure Strength of Wrinkled Graphene from Atomistic Simulation

This research paper studies the fracture and mechanical properties of rippled graphene containing dislocation dipoles. The atomistic simulation is performed to study the deformation behavior of pristine and defective wrinkled graphene. Graphene wrinkling considerably decreases the ultimate tensile strength of graphene with and without defects but increases the fracture strain. For graphene with the dislocation dipoles, temperature increase slightly affects mechanical properties, in contrast to graphene and graphene with Stone–Wales defect. The extremely similar slopes of the stress-strain curves for graphene with the dislocation dipoles with different arms imply that the distance between dislocations in the dipole does not have noticeable effects on the elastic modulus and strength of graphene. Defects in graphene can also affect its wrinkling; for example, preventing wrinkle formation