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In this paper, the size dependent vibration behavior of doubly clamped single-walled coiled carbon nanotubes (CCNTs) is investigated using nonlocal helical beam model. This model is based on Washizu's beam theory so that all displacement components of CCNT in the equations of motion are defined at the centroidal principal axis and transverse shear deformations are considered. After deriving the nonlocal free vibration equations, they are solved by the generalized differential quadrature method (GDQM). Then, the natural frequencies and corresponding mode shapes are determined for the clamped-clamped boundary conditions (BCs). After that, a parametric study on the effect of different parameters, including the helix cylinder to the tube diameters ratio (D/d), the number of pitches, the helix pitch angle, and the nonlocal parameter on the natural frequencies is conducted. It is worth noting that the results of the proposed method would be useful in the practical applications of CCNTs such as using in nanoelectromechanical systems. [ABSTRACT FROM AUTHOR]

In this paper, fracture mechanics in orthotropic plates, stress and displacement distributions around the crack tip in an anisotropic material are considered. Classical displacement based finite elements, elements with penalized equilibrium and elements with drilling degrees of freedom are employed. The path independent integrals J and I* are applied to orthotropic fracture mechanics problems to determine the stress intensity factor at the crack tip. Again, convergence studies are done, and the path independence of J and I* are investigated for orthotropic problems. Numerical results for typical fracture specimens are presented and discussed. The effect of the degree of anisotropy and fiber orientation on the stress intensity factor is also demonstrated.

In this paper, bending of cylindrical sandwich pipes based on the high-order theory of sandwich structures with flexible core is investigated. The cylindrical sandwich pipe is composed of a flexible core and two composite face sheets. Behavior of the cylindrical sandwich pipe is described by a high-order sandwich shell theory, which explains nonlinear distortions of cross-sectional plane of the flexible core as well as changes in its height. The theory based on variational principles and using an extremely thorough systematic closed-form approach is formulated. In this model, no assumption has been considered for displacement distribution of core components. In this study, stress and displacement of the flexible core are obtained through a three-dimensional elasticity solution and the face sheets are modeled using classical shell theory. Also, a comparison is made in order to verify high-order solution results between a closed-form solution, which is expanded for simply supported boundary conditions and results that are obtained from the commercial finite element method. Finally, influences of physical and geometrical parameters on behavior of the cylindrical sandwich pipe are investigated. [ABSTRACT FROM AUTHOR]

This paper presents a nonlinear analysis of impact response of nanocomposites cylindrical shells reinforced by single‐walled carbon nanotubes (SWCNTs) in thermal environments. The nanotube reinforcement distributions are either uniform or functionally graded in the shell thickness direction. Micromechanical models are employed to estimate the material properties of nanotube reinforced composites. A higher‐order shear deformation theory with a von Kármán‐type of kinematic nonlinearity yields the equations of motion. By considering the nanotube reinforced composites as temperature‐dependent, the thermal effects are included. A two‐step perturbation technique is used to solve the equations of motion. A parametric study is carried out, and the effects of nanotube distribution and its volume fraction, impactor initial velocity, temperature change, geometric parameter of shell, and edge boundary condition on the impact response of the shell are discussed. The numerical results show that the central deflection of the shell subjected to impact is sinusoidal. It is found that the nanotube distribution through the thickness can alter the amplitude and the frequency of the central deflection and also the energy absorption significantly. POLYM. COMPOS., 39:730–745, 2018. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

In the present study, the surface effect on the forced vibration of a double, single-walled carbon nanotube system (DSWNTS) under excitation of a moving nanoparticle is analyzed based on the modified nonlocal elasticity theory. The nanotube surroundings are modeled by an elastic medium and it is assumed that two nanotubes are connected to each other continuously, using elastic springs. In a parametric study, influences of the nonlocal parameter, velocity of the moving nanoparticle, the elastic layer between the nanotubes, and the order of derivative on dynamic responses of the DSWNTS are investigated in detail. The results demonstrate that the variation of order of derivative affects dynamic deflection and frequency of DSWNTS considerably. In this study, the influences of additional terms in nonlocal theory and improving the accuracy of results by presenting a modified version of nonlocal elasticity theory is investigated. As the results have presented, there is a noticeable difference in comparison with a previous case and this issue certifies the importance of the presented work. Also, a general and exact validation has been performed on the results, differences percentages have been observed, and effective factors on these differences have been reported. [ABSTRACT FROM PUBLISHER]

Small scale effects in the functionally graded beam are investigated by using various nonlocal higher-order shear deformation beam theories. The material properties of a beam are supposed to vary according to power law distribution of the volume fraction of the constituents. The nonlocal equilibrium equations are obtained and an exact solution is presented for vibration analysis of functionally graded (FG) nanobeams. The accuracy of the present model is discussed by comparing the results with previous studies and a parametric investigation is presented to study the effects of power law index, small-scale parameter, and aspect ratio on the vibrational behavior of FG nanostructures. [ABSTRACT FROM PUBLISHER]