Sharif Digital Repository

Carbon nanotubes are regarded as ideal fillers for polymeric materials due to their excellent mechanical properties. Mechanical analysis without consideration of nanotube–matrix interphase, may not give precise predictions. In this work, the impacts of interphase on the behavior of polymer-based nanocomposites are studied. For this purpose, a closed-form micromechanical interphase model considering the diameter of nanotube, the thickness of interphase, and mechanical properties of nanotube and polymer is proposed to estimate the overall mechanical properties of nanotube-reinforced polymer nanocomposites. Furthermore, the effective elastic constants of the nanocomposites for a wide range of... 

In the present study, the mechanical properties of vertically aligned carbon nanotube (VACNT) arrays in the most general case of anisotropic elasticity is studied. To quantify the elastic stiffness coefficients, continuum mechanics is employed, in which the constitutive relation is formulized in terms of the interatomic potential obtained via molecular dynamics (MDs) simulations. Detailed investigations into elastic stiffness coefficients with different geometrical parameters are performed and, consequently, their sensitivity on length and radius parameters is hereby studied. With such study it would be possible to tune the mechanical properties of VACNTs. © 2019, Società Italiana di Fisica... 

In the current work, the effect of interphase region on the mechanical properties of polymer nanocomposites reinforced with nanoparticles is studied. For this purpose, a closed-form interphase model as a function of radial distance based on finite-size representative volume element is suggested to estimate the mechanical properties of particle-reinforced nanocomposites. The effective Young’s and shear moduli of thermoplastic polycarbonate-based nanocomposites for a wide range of sizes and volume fractions of silicon carbide nanoparticles are investigated using the proposed interphase model and molecular dynamics simulations. In order to investigate the effect of particle size, several unit... 

Carbon nanotubes are regarded as ideal fillers for polymeric materials due to their excellent mechanical properties. Mechanical analysis without consideration of nanotube–matrix interphase, may not give precise predictions. In this work, the impacts of interphase on the behavior of polymer-based nanocomposites are studied. For this purpose, a closed-form micromechanical interphase model considering the diameter of nanotube, the thickness of interphase, and mechanical properties of nanotube and polymer is proposed to estimate the overall mechanical properties of nanotube-reinforced polymer nanocomposites. Furthermore, the effective elastic constants of the nanocomposites for a wide range of... 

This paper aims to revisit the effect of sloshing on the flutter characteristics of a partially liquid-filled cylinder. A computational fluid-structure interaction model within the framework of the finite element method is developed to capture fluid-structure interactions arising from the sloshing of the internal fluid and the flexibility of its containing structure exposed to an external supersonic airflow. The internal liquid sloshing is represented by a more sophisticated model, referred to as the liquid sloshing model, and the shell structure is modeled by Sanders' shell theory. The aerodynamic pressure loading is approximated by the first-order piston theory. The initial geometric... 

A general reduced-order aeroelastic model for 3-D complex geometries in subsonic incompressible flow regimes in the continuous-time domain was developed. A boundary element method (BEM) based fluid eigenanalysis solver was integrated with a finite element method (FEM) based modal technique of structural modeling. A body assumed to be a closed surface with known solid boundaries submerged in a potential flow is considered. The wake is considered to be thin and no aerodynamic loads will be supported by it. domain. The modal formulation of the aerodynamic system must be modified with a static correction method to include at least the quasi-static contribution of the higher truncated modes. The... 

This work studies the nonlinear oscillations of an elastic rotating shaft with acceleration to pass through the critical speeds. A mathematical model incorporating the Von-Karman higher-order deformations in bending is developed and analyzed to investigate the nonlinear dynamics of rotors. A flexible shaft on flexible bearings with springs and dampers is considered as rotor system for the present work. The shaft is modeled as a beam with a circular cross-section and the Euler Bernoulli beam theory is applied. The kinetic and strain energies of the rotor system are derived and Lagrange method is then applied to obtain the coupled nonlinear differential equations of motion for 6° of freedom.... 

This work studies the nonlinear oscillations of an elastic rotating shaft with acceleration to pass through the critical speeds. A mathematical model incorporating the Von-Karman higher-order deformations in bending is developed and analyzed to investigate the nonlinear dynamics of rotors. A flexible shaft on flexible bearings with springs and dampers is considered as rotor system for the present work. The shaft is modeled as a beam with a circular cross-section and the Euler Bernoulli beam theory is applied. The kinetic and strain energies of the rotor system are derived and Lagrange method is then applied to obtain the coupled nonlinear differential equations of motion for 6° of freedom.... 

This work studies the nonlinear oscillations of an elastic rotating shaft with acceleration to pass through the critical speeds. A mathematical model incorporating the Von-Karman higher-order deformations in bending is developed to investigate the nonlinear dynamics of rotors. A flexible shaft on flexible bearings with springs and dampers is considered as rotor system for this work. The shaft is modeled as a beam and the Euler-Bernoulli beam theory is applied. The kinetic and strain energies of the rotor system are derived and Lagrange method is then applied to obtain the coupled nonlinear differential equations of motion for 6 degrees of freedom. In order to solve these equations... 

In the present study, free vibrations of single walled carbon nanotubes (SWCNT) on an elastic foundation is investigated by nonlocal theory of elasticity with both beam and shell models. The nonlocal boundary conditions are derived explicitly and effectiveness of nonlocal parameter appearing in nonlocal boundary conditions is studied. Also it is demonstrated that the beam model is comparatively incapable of capturing size effects while shell model captures size effects more precisely. Moreover, the effects of some parameters such as mechanical properties, foundation stiffness, length and radius ratios on the natural frequencies are studied and some conclusions are drawn  

In the present study, dynamic stability of a viscoelastic cantilevered pipe conveying fluid which fluctuates harmonically about a mean flow velocity is considered; while the fluid flow is exhausted through an inclined end nozzle. The Euler-Bernoulli beam theory is used to model the pipe and fluid flow effects are modelled as a distributed load along the pipe which contains the inertia, Coriolis, centrifugal and induced pulsating fluid flow forces. Moreover, the end nozzle is modelled as a follower force which couples bending vibrations with torsional ones. The extended Hamilton's principle and the Galerkin method are used to derive the bending-torsional equations of motion. The coupled... 

This paper investigates the influence of residual bow on the stability of a rotating system consisting of an unbalanced Jeffcott rotor with anisotropy and two nonlinear journal bearing supports. The motion equations of the rotor system are formulated and analyzed considering most common faults and features including coupling effects of unbalance, anisotropy and residual shaft bow, by applying Lagrangian dynamics and Floquet theory. Time varying system properties of stiffness and damping are introduced into the equations of motion affecting the rotor behavior, and the influence is studied with respect to the extent of the bearing nonlinearity and the rotor anisotropy. Increasing area of...