Computations and Simulations in Mechanical Science
Volume:1 Issue: 1, Winter and Spring 2018

In this paper, dynamic behavior of long metallic bars subjected to axial impact is investigated experimentally and numerically. Bars made of steel without and with attached mass are impacted against a rigid wall. Experimental tests are performed by gas gun and numerical results are obtained using FE simulation. Results of shortening, axial force and buckling shape of two mentioned bars are presented. Obtained results for bar without and with attached mass with the same impact energy are compared. It is found that at the same impact energy, shortening and axial force of empty bar and bar together with attached mass is identical, approximately. Also, the deformation mechanism of empty bar and bar together with attached mass is different in which the radial deflections of bar with attached mass is higher than bar without attached mass. Comparing experimental and numerical results shows a good agreement between them.

In the present work, a fuzzy logic approach was used in order to determine the effect of thermal aging on the surface hardness of phenolic resin reinforced by woven carbon fibers (CFP). For this purpose, the specimens made from CFP composites with different fiber volume fraction (20%, 30%, 40%, and 50%) were exposed to different thermal aging fashions (refrigerated at -30 ºC, room temperature at 25 ºC, and thermally aged at 50 ºC).The surface hardness values of both the pristine and aged specimens were then experimentally determined using Barcol hardness testing machine. The hardness values for CFP composites were also predicted by two types of fuzzy inference systems (FIS), i.e. Mamdani and Sugeno methods. Results of the developed fuzzy logic models were compared with the experimental results and it was found that the Sugeno method performed better than Mamdani method.

In this paper, using molecular dynamics simulations, the thermal properties of the nitrogen-doped graphene sheets are investigated. For this purpose, the LAMMPS software is employed. To study the effect of the atomic structure on the thermal conductivity coefficient of the nitrogen-doped graphene, armchair and zigzag nanosheets are modelled. The thermal conductivity coefficients of the N-doped graphene with the nitrogen percentages between 0%-15% are computed. Finally, applying the uniaxial strains in the range of 0-10%, the effect of strain on the thermal conductivity coefficient of the N-doped graphene is evaluated. It is observed that zigzag N-doped graphene sheets have larger thermal conductivity coefficients than the armchair nanosheets with the same sizes and N-doping percentages. Increasing the N-percentage leads to decreasing the thermal conductivity coefficient of the armchair and zigzag graphene sheets. Furthermore, applying the uniaxial strain results in increasing the thermal conductivity coefficient of the N-doped graphene sheets.

The elastoplastic dynamic buckling of a thin rectangular plate with different boundary conditions subjected to uni- and biaxial compression sinusoidal pulse functions is investigated employing Galerkin method on the basis of trigonometric mode shape functions. The equilibrium, stability and dynamic elastoplastic buckling equations are derived based on two theories of plasticity: deformation theory of plasticity (DT) with Hencky constitutive relations and incremental theory of plasticity (IT) with Prandtl-Reuss constitutive relations. Ramberg-Osgood stress-strain model is used to describe the elastoplastic material property of plate. The effects of boundary conditions, force pulse amplitude, loading ratio and type of plasticity theory on the velocity and deflection histories of plate are investigated. According to the dynamic response of plate, the results obtained from DT are lower than those predicted through IT and the boundary conditions of rectangular plate subjected to impulsive load have a significant influence on the dynamic response of palte. The resistance against deformation for corresponding to plates with clamped boundary condition is more than those plates with simply supported boundary condition.

This paper aims to develop a new semi-analytical method based on the continuum approximation and Lennard-Jones (LJ) potential function to investigate the potential energy and van der Waals (vdW) interaction force between sectors of nanotorus and carbon nanotori molecule. Following the present method, a semi-analytical formulation is achieved in terms of double integrals which can be readily employed to obtain the interactions. A semi-analytical expression is also presented to determine the oscillation frequency. The sector is assumed to be orbiting inside the carbon nanotori and is free to choose its perfect position inside this nanostructure. The effects of geometrical parameters such as tube and ring radii of nanotori as well as angle of nanosector on the variation of potential energy, vdW interaction force and frequency are examined. As a significant finding, it is shown that the oscillation frequency, which is in the gigahertz (GHz) range, is independent of the sector angle. Results of this study are shown to be consistent with the existing data and can be beneficial for the future studies on the GHz oscillators.

The prime aim of the current study is to predict the nonlinear buckling and postbuckling behavior of cylindrical nanoshells subjected to two different radial compressive loads including lateral pressure and hydrostatic pressure with the presence of surface stress effects. The Gurtin-Murdoch elasticity theory in conjunction with von Karman geometrical nonlinearity relations is implemented into the classical shell theory to develop size-dependent shell model incorporating the effects of surface stress. Consequently, to satisfy the balance conditions on the free surfaces of nanoshell, a linear variation through the thickness is considered for the normal stress component of the bulk in such a way that it diminishes on mid-plane and is equal to shear surface stress components on the free surfaces. Afterwards, a boundary layer theory is employed which considers both nonlinear prebuckling deformations and large deflections in the postbuckling domain. Finally, a singular perturbation technique is utilized to obtain the critical buckling loads and the postbuckling equilibrium paths of nanoshells including surface stress effects and corresponding to both loading cases. It is revealed that surface stress effect has a more significant influence on the postbuckling behavior of nanoshells with lower thicknesses. Also, it is found that this pattern is some deal more considerable for the hydrostatic pressure loading case compared to the lateral pressure one.