International Journal of Computational Materials Science and Engineering

Possessing exceptional properties, graphene has garnered immense interest in the research community for a wide array of potential applications. The mechanical properties play an important role in the success of the potential applications and thus a thorough understanding is cardinal. Computational modeling and simulation is an important tool in the design process due to the low costs compared to the experimental means. This review aims to consolidate the findings of works of computational modeling and simulation of graphene, with focus on models at the continuum and molecular levels. The review shows intrinsic differences in focus of the applications and types of graphene investigated by the different scale models, thus highlighting the advantages and shortcomings of each type of modeling approach.

Optimum waviness of carbon nanotubes (CNTs) inside a matrix composite beam and composite bridge is endeavor to obtain its utmost natural frequencies considering a volume fraction of CNTs. 3D FE model of the beam is generated via ABAQUS along with Python programming and thereafter to calculate an optimal waviness under encastre boundary conditions and different vibration modes. The effect of waviness and the number of waves on mode shapes, natural frequency, and corresponding stiffness of a beam are examined, and the outcomes are compared to those of a pure polymer beam, straight CNT-based composite beam and nanobridge value. It was decided to conduct a convergence analysis and the optimum value of the number of elements and nodes was studied and found that 19666 nodes are reliable to give correct results. The FE analysis results reveal that the waviness effect of CNTs significantly depends on mode shapes. The fundamental natural frequency, as well as other related vibrational properties, is observed to be enhanced. By decreasing the waviness from 50 to 25, there is an increment in natural frequency in the 3rd mode by 68.68, 5th mode by 44.6 and 6th mode by 62.4, but in other modes, there is negligible difference. When single-wave CNTs were compared, the sine wave produced more frequency in the third mode by 206.03, 4th mode by 199.8 and 6th mode by 478.6 Hz. After comparing the results of different waviness types, single sine waviness, multi-waved CNTs, straight CNTs and neat matrix, it is found that for the highest value of waviness of CNT fiber-based nanocomposites, the natural frequency of CNT-reinforced nanocomposite reaches the frequency of the neat matrix and further adding of CNTs does not increase the value of frequency. The result showed that the finite element model (FEM) is a good simulation of the vibratory system.

Polymer-derived ceramics’ (PDCs) route, which converts preceramic polymers to ceramics through heat treatment, presents a flexible and energy-efficient approach to fabricate ceramic composites with arbitrary geometries and tailorable properties. Due to the huge gaps of thermal and mechanical properties of polymers and ceramics, the current state phase composition and phase distribution largely affect the heat transfer behavior and temperature field evolution that ultimately determine the subsequent polymer decomposition and phase redistribution. In this paper, a computational framework is developed to predict the continuum-level phase transition and its effect on mechanical properties. Molecular dynamics (MD) simulations are carried out first to track the atomic structure evolution and mass loss associated with gas generation. It is found that pyrolysis temperature primarily determines the amount of gases that can be generated. Gas diffusion is triggered as a result of the non-uniform temperature field. Ceramic phase formation depends on the interplay between gas generation and gas diffusion. This computational framework allows real-time temperature field and phase composition map to be explicitly extracted. The phase composition map is incorporated into a finite element model for compression simulation. The effects of heating rate, pyrolysis temperature and pyrolysis time on mechanical response are systematically studied. Conclusions from this study can provide direct guidance for fabricating PDCs with tailored properties.

Carbon nanotubes (CNTs) have benefits in various fields, they are disadvantageous due to their tendency to form aggregates and poorly controlled alignment of the CNT molecules (characterized by order parameters). These deficiencies can be overcome by dispersing the CNTs in nematic liquid crystal (LC) and placing the mixture under the influence of an electric field. In this study, Doi and Landau–de Gennes free energy density equations are used to analytically confirm that an electric field increases the order parameters of CNTs and LCs in a dispersion mixture. The anchoring strength of the nematic LC is also found to affect the order parameters of the CNTs and LC. Further, increasing the length-to-diameter ratio of the CNTs increases their alignment without affecting the LC alignment. These findings indicate that CNT molecular alignment can be controlled by adjusting the CNT length-to-diameter ratio, anchoring the LCs, and adjusting the electric field strength.

Inside a greenhouse, during the day, the temperature rises very quickly, while the plants have to face temperatures that rise to more than 35${}^{\circ }$C. The plant closes its pores to limit sweating and stops growing. As soon as it gets hot, it is therefore necessary to ventilate the greenhouse. In this context, this research aims to investigate the behavior of the natural ventilation on the internal climate of the tunnel greenhouse, which contains two openings in the roof. The effect of the position of the openings on heat transfer is considered, thus promoting photosynthesis and plant growth. The vorticity transport equation, the Poisson equation and the energy equation are discretized by using the finite volume method. Two-dimensional simulations that described laminar flows in a steady state were carried out. Flows are studied for a range of parameters: the Rayleigh number, Ra, $10^3\le \mathrm{\text{Ra}}\le 10^6$, and three positions of opening ventilation. The results reveal that the ventilation through the top opening position allows the best creation of heat exchanges between the air inside the greenhouse and its atmosphere, which serves to conserve the plant under a favorable climate that allows its growth.

The electronic and transport properties of hybrid armchair–zigzag nanostructures, which include right-angles-shaped GNRs, U-shaped GNRs, and patterned nanopores structured GRNs, were studied by the combination of density functional theory and nonequilibrium Green’s function method. The density of state, electron transmission spectra, and molecular orbitals were analyzed. The obtained results show that right-angles-shaped GNRs junctions tend to open a transport gap when the numbers of right-angles are greater than or equal to 4. The gap increases insignificantly as the numbers of right-angles are greater than 4. It implies that the U-shaped GNR junction, corresponding to 4 right-angles structure, is a potential structure for controlling transport gap of GRNs. The transport gap of the U-shaped GNRs decreases as the length of horizontal edge increases. In contrast, the transport gap increases as the high of vertical edge increases. In addition, the patterned nanopore had an enormous influence on the electronic and transport properties though the armchair GNRs junctions, depending on the shape and size of nanopore. This research suggests that designed tailored GNRs based on hybrid armchair–zigzag nanostructures can be used to control the transport gap of graphene. The formation of quasi-bound states at zigzag edges of the hybrid nanostructures plays a key role.