Physical Mesomechanics最新文献

Single-walled carbon nanotubes (SWCNTs) in an elastic medium under a longitudinal magnetic field have piqued the interest of researchers as elements utilized in nanoelectro-magneto-mechanical systems (NEMMS). This work presents the vibration analysis of embedded SWCNTs using the nonlocal second-order strain gradient elasticity theory. Considering the surface effect, the characteristic equation of motion for a SWCNT embedded in a polymer matrix under a longitudinal magnetic field is formulated and derived. The dependence of the distinct natural frequency of SWCNTs on the nanotube chiral angle and diameter is clarified. The effects of various parameters on the vibration characteristics of SWCNTs are examined and discussed, including the longitudinal magnetic field, surface effect, chiral index, chiral angle, chirality of SWCNTs, vibrational mode number, aspect ratio (length-to-diameter ratio), nonlocal and material length scale parameters. The numerical findings of this work might be helpful in the study and implementation of embedded SWCNTs as NEMMS devices.

The present work is aimed at analyzing free longitudinal vibrations of nanorods composed of a functionally graded (FG) material with deformable boundaries within a hardening nonlocal elasticity approach. For this purpose, a FG nanorod composed of the ceramic and metal constituents is considered to be elastically supported by means of axial springs at both ends. Then the analytical method based on the association of the Fourier sine series and the Stokes transformation is developed to solve the free axial vibration problem of a FG nanorod with both deformable and nondeformable boundaries. Free axial vibration of a restrained FG nanorod is first studied within hardening nonlocal elasticity. To show the validity and profitability of the proposed analytical method, the presented Fourier series method with the Stokes transformation is used for the analysis of axial vibration of a rigidly supported homogeneous nanorod by setting the appropriate spring stiffness values. The main superiority of this new approach is in its power of dealing with numerous boundary conditions to determine longitudinal vibration frequencies of FG nanorods. Using the present solution method, various numerical applications are given for different small-scale parameters, gradient index, and nanorod length.

This research is devoted to the study of the flexural response and buckling analysis (thermal and mechanical) of functionally graded (FG) nanoscale plates integrated in an elastic medium. The structure is modeled on the basis of a refined integral plate theory with four unknowns incorporated into Eringen’s nonlocal elasticity theory. The material properties of the plate are considered to be graded continuously over the entire thickness of the nanoplate. The elastic medium is simulated like Pasternak’s two-parameter elastic foundations. The equilibrium equations are determined from the principle of virtual displacements. The results for simply supported FG nanoscale plates are deduced and compared with those available in the literature. Parametric studies are carried out to demonstrate the impacts of the inhomogeneity parameter, nonlocal parameter, elastic medium stiffness, and plate geometric ratios on the behavior of FG nanoscale plates.

A numerical study is conducted on the influence of the polycrystalline structure, strain rate, and constrained boundary conditions on the plastic strain localization and fracture of 6061-T6 aluminum alloy under dynamic loading. The investigation is carried out on a three-dimensional polycrystalline structure generated by the step-by-step packing method. The deformation behavior of 6061-T6 aluminum alloy under different strain rates and temperatures is described using a relaxation constitutive equation. The initiation and growth of cracks are taken into account using a strain criterion. The developed models and polycrystalline structure are implemented into the ABAQUS/Explicit finite element package to simulate tension of the aluminum samples. It is shown that taking into account the polycrystalline structure leads to lower values of the macroscopic yield stress in comparison with a homogeneous sample. The strain rate and constrained boundary conditions are shown to affect the crack initiation site and fracture patterns.

This paper presents the analysis of wave propagation in functionally-graded (FG) nanoplates on a Winkler–Pasternak foundation. The investigation is carried out in the framework of nonlocal elasticity theory and a new four-unknown higher-order displacement theory including indeterminate integral terms. Hamilton’s principle and Navier’s method are used to obtain the frequency relations of FG nanoplates for different conditions by solving an eigenvalue problem. The obtained results for the frequency and phase velocity of wave propagation in an FG nanoplate are compared with recent outcomes of similar research.

In this paper, both 2D and quasi-3D hyperbolic integral shear deformation theories are employed for buckling analysis of functionally graded (FG) plates. The simplicity of the developed theory is due to the reduced number of the unknowns used in the field of displacement. The proposed model takes into account the effect of both normal and transverse shear deformations and ensures the nullity of transverse shear stresses at the top and bottom surfaces of the studied structure without including any shear correction factors. Properties of the material are microscopically inhomogeneous and change continuously according to a power law model in the z direction. The Navier method is utilized to study the mechanical buckling response of a simply supported FG plate under both uniaxial and biaxial compressive loading. The numerical study is validated by comparing the obtained results with the literature data. The influence of thickness stretching, geometric parameters, material index, and different loading cases on the critical buckling load is examined.

The dynamics of micro/nanoelectromechanical systems (M/NEMS) is a core research area in micromechanics. Due to the nonlinearities and the singular nature of actuation forces that emerge in these systems, it has become a promising and challenging research area. The foremost objective of this manuscript is to examine the dynamics of M/NEMS by approximating rational terms involved in M/NEMS structures. An M/NEMS switch under electromagnetic force is adopted to reveal the effectiveness of the expansion of rational terms. Taylor series is employed to approximate the rational function into the summation of simple terms. The well-known variational iteration method is engaged to obtain the dynamic pull-in threshold value, the nonlinear frequency, and the analytical solution of the objective system. The solution obtained from the proposed strategy exhibits good agreement with observations obtained numerically. As opposed to the existing approaches, the suggested scheme achieves a high level of accuracy.

In this work, the propagation of planar waves in a homogeneous micropolar thermoelastic medium is studied while the entire body rotates with a uniform angular speed. The coordinate system of the rotating medium is assumed to be stationary, and therefore the kinematic equations have two additional terms, namely, the gravitational and the Coriolis accelerations. The problem is addressed based on the two-temperature thermoelastic model with higher-order time derivatives and dual-phase lag, which can explain the effect of microscopic features in nonsimple materials. With certain boundary conditions and the normal mode approach, the variations in temperature, displacement, microrotation, and thermal stresses induced by heating are derived. In the absence of rotation and two-temperature factor, comparison is made with the results of classical thermoelastic models.

The paper proposes a microstructural model of tetragonal single-crystalline barium titanate for analyzing how the state of its domain structure can influence the simulation accuracy of dielectric hysteresis curves with regard for domain interactions and for stress and electric field inhomogeneities in the single crystal. Hysteresis curves based on finite element homogenization are presented for all eight types of second-rank laminate domain patterns satisfying the compatibility conditions. It is shown that the properties of domain structures are substantially anisotropic under loading in different directions and that the dielectric hysteresis for different domain patterns differs greatly. The proposed model allows one to describe the effects of domain hardening and unloading nonlinearity. The results of calculations using the model agree well with experimental data at different cyclic load amplitudes.

Electron beam additive manufacturing with simultaneous feeding of two dissimilar metal wires was used to obtain Ti-6Al-4V specimens successively alloyed with 0.6, 1.6, 6.0 and 9.7 wt % Cu. The specimens were characterized for microstructure, phases, and mechanical properties. Increasing the copper content in the alloy from 0.6 to 9.7 wt % resulted in the refinement of primary β-Ti grains and the columnar-to-equiaxed grain transformation owing to the effect of constitutional undercooling on grain nucleation and growth. The grain growth restriction factor was calculated to substantiate the microstructural evolution from columnar to equiaxed grains. Admixing with up to 6.0 wt % Cu resulted in the formation of ultrathin α-Ti platelets, while increasing the copper content to 9.7 wt % Cu led not only to further thinning of α-Ti platelets but also to the formation of refined α′-Ti and α″-Ti phases. Intermetallic Ti₂Cu particles were precipitated due to the β → Ti₂Cu + α eutectoid decomposition of primary β-Ti grains and then plausibly induced heterogeneous nucleation of α-Ti platelets. A combined effect of solid solution hardening, precipitation hardening, and grain boundary hardening was achieved and allowed increasing the microhardness, ultimate tensile stress, tensile yield stress, and compression yield stress of Ti-6Al-4V/Сu specimens.