Euler Bernoulli Nanobeams Research Articles

Hygro-Thermal Vibrations of Porous FG Nano-Beams Based on Local/Nonlocal Stress Gradient Theory of Elasticity.

In this manuscript the dynamic response of porous functionally-graded (FG) Bernoulli–Euler nano-beams subjected to hygro-thermal environments is investigated by the local/nonlocal stress gradient theory of elasticity. In particular, the influence of several parameters on both the thermo-elastic material properties and the structural response of the FG nano-beams, such as material gradient index, porosity volume fraction, nonlocal parameter, gradient length parameter, and mixture parameter is examined. It is shown how the proposed approach is able to capture the dynamic behavior of porous functionally graded Bernoulli–Euler nano-beams under hygro-thermal loads and leads to well-posed structural problems of nano-mechanics.

Geometrically Nonlinear Electromechanical Instability of FG Nanobeams by Nonlocal Strain Gradient Theory

This paper is concerned with studying the size-dependent nonlinear dynamic pull-in instability and vibration of functionally graded Euler–Bernoulli nanobeams (FG-EBNs) with the von Kármán hypothesis based on the nonlocal strain gradient theory (NLSGT). To this end, the partial differential equation (PDE) is developed by Hamilton’s principle considering the intermolecular, fringing field and electrostatic nonlinear forces. Then, the Galerkin method (GM) is utilized to acquire the ordinary differential equation (ODE) and the results are obtained with the help of an analytical approach called the homotopy analysis method (HAM). To verify the outcome of this study, the nonlinear and linear frequencies obtained are compared with those of the literature. Consequently, the pull-in voltage of the FG nanobeam is obtained and the variations of nonlinear and linear frequencies are discussed in detail. Also, the effects of initial amplitude, electrostatic force, length scale, nonlocal parameter, material gradient index and boundary condition (BC) on the electromechanical behavior of FG-EBNs are analyzed with the results commented.

Hygro-thermal bending behavior of porous FG nano-beams via local/nonlocal strain and stress gradient theories of elasticity

This work studies the bending response of porous functionally graded Bernoulli-Euler nano-beams under hygro-thermo-mechanical loadings. The governing equations of the elastostatic problems associated with both local/nonlocal stress- and strain-driven gradient models of elasticity were derived by using the virtual work principle. A Wolfram language code in Mathematica was then written to carry out a numerical investigation for different boundary conditions including cantilever and simply-simply conditions. The effects of the different parameters, such as porosity volume fraction, gradient index, nonlocal parameter, gradient length parameter and mixture parameter are presented. It is shown how the proposed approach is able to capture the structural behavior of porous functionally graded Bernoulli–Euler nano-beams under a hygro-thermal environment.

Adaptive prescribed‐time disturbance observer using nonsingular terminal sliding mode control: Extended Kalman filter and particle swarm optimization

In this study, adaptive prescribed finite-time stabilisation of uncertain single-input and single-output non-linear systems is considered in the presence of unknown states, unknown parameters, external load disturbance, and non-symmetric input saturation. A prescribed finite time disturbance observer is designed to approximate the unmeasured external disturbance. Also, a non-singular prescribed finite time terminal sliding mode control is proposed for the closed-loop control of the system with the non-symmetric input saturation. Extended Kalman filter algorithm is employed for the real-time estimations of the states and unknown parameters of the system. Moreover, a particle swarm optimisation algorithm is used to obtain the design parameters of the proposed disturbance observer and controller. To show the performance of designed control scheme, the proposed approach is employed to guarantee prescribed finite time stabilisation of non-linear vibration of a non-local strain gradient nanobeam. The Galerkin projection method is used to reduce the non-dimensional form of the governing non-linear partial differential equation of Euler–Bernoulli nanobeam to the ordinary differential equation. Finally, numerical simulations are performed to illustrate the effectiveness and performance of the developed adaptive control scheme for the vibration control of nanobeam in comparison with the conventional sliding mode control.

Stability analysis of nanobeams placed in electromagnetic field using a finite element method

In this work, the buckling analysis of the nanobeams placed in electromagnetic field is presented via a nonlocal finite element method based on Eringen’s nonlocal elasticity theory. The governing differential equation is derived by implementing minimum total potential energy principle. A finite element method is proposed for solution of nonlocal buckling of nanobeam placed in electromagnetic field. The contribution of this article is the use of interpolation functions and the nonlocal elasticity theory to form the stiffness matrices and geometric stiffness matrices of the electromagnetic nanobeam for buckling analysis. A detailed study is performed to indicate the influences of some parameters such as Hartmann parameter (Ha), mode number (n), nonlocal parameter (e0a), length of nanobeam (L), and boundary conditions on the buckling loads of Euler-Bernoulli nanobeams. The values of buckling load of electromagnetic nanobeams are obtained via a finite element solution, examined through several numerical examples, and demonstrated by tables and graphs.

Nonlinear Dynamic Behavior of Porous and Imperfect Bernoulli-Euler Functionally Graded Nanobeams Resting on Winkler Elastic Foundation

Nonlinear free vibrations of functionally graded porous Bernoulli–Euler nano-beams resting on an elastic foundation through a stress-driven nonlocal elasticity model are studied taking into account von Kármán type nonlinearity and initial geometric imperfection. By using the Galerkin method, the governing equations are reduced to a nonlinear ordinary differential equation. The closed form analytical solution of the nonlinear natural flexural frequency is then established using the Hamiltonian approach to nonlinear oscillators. Several comparisons with existing models in the literature are performed to validate the accuracy and reliability of the proposed approach. Finally, a numerical investigation is developed in order to analyze the effects of the gradient index coefficient, porosity volume fraction, initial geometric imperfection, and the Winkler elastic foundation coefficient, on the nonlinear flexural vibrations of metal–ceramic FG porous Bernoulli–Euler nano-beams.

Local gradient Bernoulli–Euler beam model for dielectrics: effect of local mass displacement on coupled fields

The size-dependent behaviour of a Bernoulli–Euler nanobeam based on the local gradient theory of dielectrics is investigated. By using the variational principle, the linear stationary governing equations of the local gradient beam model and corresponding boundary conditions are derived. In this set of equations the coupling between the strain, the electric field and the local mass displacement is taken into account. Within the presented theory, the process of local mass displacement is associated with the non-diffusive and non-convective mass flux related to the changes in the material microstructure. The solution to the static problem of an elastic cantilever piezoelectric beam subjected to end-point loading is used to investigate the effect of the local mass displacement on the coupled electromechanical fields. The obtained solution is compared to the corresponding ones provided by the classical theory and strain gradient theory. It is shown that the beam deflection predicted by the local gradient theory is smaller than that by the classical Bernoulli–Euler beam theory when the beam thickness is comparable to the material length-scale parameter. The obtained results also indicate that the piezoelectricity has a significant influence on the electromechanical response in a dielectric nanobeam. The presented mathematical model of the dielectric beam may be useful for the study of electromechanical coupling in small-scale piezoelectric structures.

Buckling Analysis of a Bi-Directional Strain-Gradient Euler–Bernoulli Nano-Beams

Investigated herein is the buckling of Euler–Bernoulli nano-beams made of bi-directional functionally graded material with the method of initial values in the frame of gradient elasticity. Since the transport matrix cannot be calculated analytically, the problem was examined with the help of an approximate transport matrix (matricant). This method can be easily applied with buckling analysis of arbitrary two-directional functionally graded Euler–Bernoulli nano-beams based on gradient elasticity theory. Basic equations and boundary conditions are derived by using the principle of minimum potential energy. The diagrams and tables of the solutions for different end conditions and various values of the parameters are given and the results are discussed.

Buckling and Nonlinear Vibration of Size-Dependent Nanobeam based on the Non-Local Strain Gradient Theory

Based on the nonlocal strain gradient theory, a Euler-Bernoulli nanobeam model subjected to the compressive axial force and resting on the Winkler-Pasternak layer is developed to study buckling and free nonlinear vibration problems. Critical buckling force and nonlinear frequency of simply supported nanobeam are analytically derived. Comparison of obtained analytical solutions with published and numerical ones shows accuracy of the present solutions. Effects of the scale factor, the aspect ratio, the Winkler parameter and the Pasternak parameter on the critical buckling force ratio and the vibration response of the nanobeam are studied in this work.

An investigation of static bending of a bi-directional strain-gradient Euler–Bernoulli nano-beams with the method of initial values

Investigated herein is the static bending of Euler–Bernoulli nano-beams made of bi-directional functionally graded material with the method of initial values in the frame of gradient elasticity. To the best of the researchers’ knowledge, in the literature, there is no study carried out into gradient elasticity theory for bending analysis of bi-directional strain-gradient Euler–Bernoulli (BDSGEB) nanostructures with arbitrary functions. Basic equations and boundary conditions are derived by using the principle of minimum potential energy. The transfer matrix for beams is given analytically. For an initial value problem, the transport matrix is unique. The diagrams of the solutions for different end conditions and various values of the parameters are given and the results are discussed.

Size-dependent buckling analysis of Euler–Bernoulli nanobeam under non-uniform concentration

Nano-sized batteries composed of nanostructured electrode materials stand as one of the most promising candidates for next-generation rechargeable charging devices which have been widely used in the energy storage systems for advanced power applications. Buckling analysis of nanobeam under non-uniform concentration is significantly important for the design of nano-sized batteries under the rapid charging mode. In this work, such issue is investigated in the framework of the size-dependent mechanical–diffusion model, and size effect of mass transfer on buckling property is considered for the first time. By using the eigenvalue method, the critical buckling loads of Euler–Bernoulli nanobeam under the conditions of clamped–clamped, clamped–free, simply supported–simply supported and clamped–simply supported are analytically obtained. The derived results are compared with those of non-gradient nonlocal elastic stress theory, classical elasticity theory and classical theory of mass transfer. It is also found that the value of critical buckling load will be reduced if diffusive nonlocal parameter becomes larger.

Effects of porosity and flexoelectricity on static bending and free vibration of AFG piezoelectric nanobeams

Abstract In this paper, based on the strain gradient theory, a size-dependent porous axially functional gradient (AFG) flexoelectric Euler-Bernoulli nanobeam model is developed. A modified power-law formula incorporating porosity volume fraction is presented to describe material properties of porous AFG nanobeam, and two typical porosity distributions patterns are considered. The generalized differential quadrature method is employed to discretize governing equations into a series of linear algebraic equations, so that the static bending deflections and free vibration frequencies are calculated conveniently for various boundary conditions. The credibility of the present mathematical formulation and the associated numerical solution are validated by comparing the results in previous literatures. Parametric studies are performed to illustrate the effects of the flexoelectricity, material length scale parameters, functionally graded index, porosity volume fraction, porosity distribution patterns on the static bending and free vibration behaviors of porous AFG flexoelectric nanobeam. The numerical results may provide support for the application of porous AFG flexoelectric nanobeam in Nano-electro-mechanical system.

A comparison of the Bolotin and incremental harmonic balance methods in the dynamic stability analysis of an Euler–Bernoulli nanobeam based on the nonlocal strain gradient theory and surface effects

This study addresses the dynamic stability of an Euler–Bernoulli nanobeam under time-dependent axial loading based on the nonlocal strain gradient theory (NSGT) and considering the surface stress effects. The studied nanobeam cross-section was rectangular, and simply-supported boundary conditions were assumed. Moreover, a uniform thermal gradient was applied to the nanobeam. The elastic medium was modeled based on the Pasternak theory. The strain–displacement relations were derived using the Von Kármán equations. The governing equations were obtained by the energy method and applying the Hamilton's principle. Furthermore, the Bolotin and Incremental Harmonic Balance (IHB) methods were used to solve the differential equations. This study investigates the impact of such parameters as the small-scale parameter, the material length scale, surface effects, elastic medium parameters, temperature variations, geometry, and the static loading factor on the Dynamic Instability Region (DIR). The results are suggestive of the shift of the DIR to lower frequency zone by increasing the small-scale Eringen's nonlocal theory parameter, whereas an increase in the material length scale from the strain gradient theory moves the region to higher frequencies. In case the said parameters are equal, the result conforms to the classical beam theory. In addition, assuming a Pasternak medium and taking into account the effects of surface stress (Young's modulus and the residual stress of the surface) shifts the DIR to higher frequencies, whereas applying a compressive static load moves the region to lower frequencies. Moreover, depending on the thermal expansion coefficient of the medium, temperature variations can also displace the DIR.

Vibration analysis of two-phase local/nonlocal viscoelastic nanobeams with surface effects

According to defects of the differential form of pure nonlocal elasticity, two-phase nonlocal elasticity has recently attracted the attention of researchers for studying the size-dependent mechanical behaviors of nanostructures. Given this, in present work, damping vibration behavior of two-phase local/nonlocal viscoelastic nanobeams in conjunction with surface effects is studied. The governing equation of Euler–Bernoulli nanobeam and corresponding constitutive boundary conditions are presented. Using analytical solution, the influences of viscoelastic parameter, surface effects, local phase fraction and nonlocal parameter on the size-dependent damping vibration behavior of nanobeams are investigated. From the results, it can be observed in all boundary conditions that not only the real part but also the imaginary part of the complex frequencies of nanobeams decreases, while the impact of nonlocal elasticity is raised by increasing the nonlocal parameter ratio or decreasing the local phase fraction. Also, the variation of frequency ratios of nanobeams with different dimensions reveals that the influence of surface elasticity on the both parts of complex frequencies depends on the size of cross section and length of nanobeam.

Size-dependent Nonlinear Forced Vibration Analysis of Viscoelastic/Piezoelectric Nano-beam

In this paper, the nonlinear forced vibration of isotropic viscoelastic/ piezoelectric Euler-Bernoulli nano-beam is investigated. For this purpose, the consistent couple stress theory is utilized for modeling the viscoelastic/piezoelectric nano-beam. Hamilton’s principle is also employed to obtain the governing equations of motion. Further, the Galerkin method is used in order to convert the governing partial differential equations to a nonlinear second-order ordinary differential one, and then multiple scale method is used to solve motion equation.

Contact interaction of a two-layer package of nanobeams package of Bernoulli-Euler nanobeams with gap between them

In this work, mathematical model of contact interaction of two parallel Bernoulli-Euler nanobeams with a small gap between them is built on the basis of a modified couple stress theory. Contact interaction is considered in accordance with B.Ya. Cantor’s theory. The influence of size-dependent coefficient on contact interaction and the nature of the oscillations have been studied. Wavelet analysis, methods of the qualitative theory of differential equations, methods for analyzing the sign of the largest Lyapunov’s exponent are used to solve and analyze.

Mechanical analysis of cutout piezoelectric nonlocal nanobeam including surface energy effects

This manuscript tends to investigate influences of nanoscale and surface energy on a static bending and free vibration of piezoelectric perforated nanobeam structural element, for the first time. Nonlocal differential elasticity theory of Eringen is manipulated to depict the long–range atoms interactions, by imposing length scale parameter. Surface energy dominated in nanoscale structure, is included in the proposed model by using Gurtin–Murdoch model. The coupling effect between nonlocal elasticity and surface energy is included in the proposed model. Constitutive and governing equations of nonlocal-surface perforated Euler–Bernoulli nanobeam are derived by Hamilton’s principle. The distribution of electric potential for the piezoelectric nanobeam model is assumed to vary as a combination of a cosine and linear variation, which satisfies the Maxwell’s equation. The proposed model is solved numerically by using the finite-element method (FEM). The present model is validated by comparing the obtained results with previously published works. The detailed parametric study is presented to examine effects of the number of holes, perforation size, nonlocal parameter, surface energy, boundary conditions, and external electric voltage on the electro-mechanical behaviors of piezoelectric perforated nanobeams. It is found that the effect of surface stresses becomes more significant as the thickness decreases in the range of nanometers. The effect of number of holes becomes significant in the region 0.2≤ɑ ≤0.8. The current model can be used in design of perforated nano-electro-mechanical systems (PNEMS).

Propagation of uncertainty in free vibration of Euler–Bernoulli nanobeam

In this paper, Euler–Bernoulli nanobeam based on the framework of Eringen’s nonlocal theory is modeled with material uncertainties where the uncertainties are associated with mass density and Young’s modulus in terms of fuzzy numbers. A particular type of imprecisely defined number, namely triangular fuzzy number, is taken into consideration. In this regard, double parametric-based Rayleigh–Ritz method has been developed to handle the uncertainties. Vibration characteristics have been investigated, and the propagation of uncertainties in frequency parameters is analyzed. Material uncertainties are considered with respect to three cases, viz. (1) Young’s modulus (2) mass density and (3) both Young’s modulus and mass density, as imprecisely defined. Frequency parameters and mode shapes are computed and presented for Pined–Pined (P–P) and Clamped–Clamped (C–C) boundary conditions. Accuracy and efficiency of the models are verified by conducting the convergence study for all the three cases. Lower and upper bounds of frequency parameters are computed with the help of the double parameter, and graphical results are plotted as the triangular fuzzy number showing the sensitivity of the models. Obtained results for frequency parameters are compared with other well-known results found in previously published literature(s) in special cases (crisp cases) witnessing robust agreement. The uncertainty modeling and the bounds of frequency parameters may serve as an effective tool for the designing and optimal quality enhancement of engineering structures.

Buckling Behavior of Nanobeams Placed in Electromagnetic Field Using Shifted Chebyshev Polynomials-Based Rayleigh-Ritz Method.

In the present investigation, the buckling behavior of Euler–Bernoulli nanobeam, which is placed in an electro-magnetic field, is investigated in the framework of Eringen’s nonlocal theory. Critical buckling load for all the classical boundary conditions such as “Pined–Pined (P-P), Clamped–Pined (C-P), Clamped–Clamped (C-C), and Clamped-Free (C-F)” are obtained using shifted Chebyshev polynomials-based Rayleigh-Ritz method. The main advantage of the shifted Chebyshev polynomials is that it does not make the system ill-conditioning with the higher number of terms in the approximation due to the orthogonality of the functions. Validation and convergence studies of the model have been carried out for different cases. Also, a closed-form solution has been obtained for the “Pined–Pined (P-P)” boundary condition using Navier’s technique, and the numerical results obtained for the “Pined–Pined (P-P)” boundary condition are validated with a closed-form solution. Further, the effects of various scaling parameters on the critical buckling load have been explored, and new results are presented as Figures and Tables. Finally, buckling mode shapes are also plotted to show the sensitiveness of the critical buckling load.

Nonlinear vibration and dynamic instability analysis nanobeams under thermo-magneto-mechanical loads: a parametric excitation study

The nonlinear vibration behavior and dynamic instability of Euler–Bernoulli nanobeams under thermo-magneto-mechanical loads is the main objective of the present paper. Firstly, a short Euler–Bernoulli nanobeam is modeled and exposed to an external parametric excitation. Based on the nonlocal continuum theory and nonlinear von Karman beam theory, the nonlinear governing differential equation of motion is derived. Secondly, to transport the partial differential equation to the ordinary differential equation, Galerkin method is applied. Then, multiple scales method, as an analytical approach, is used to solve the equation. At the end, modulation equation of Euler–Bernoulli nanobeams is obtained. Then, to evaluate the dynamic instability of the system, trivial and nontrivial steady-state solutions are discussed. Emphasizing the effect of parametric excitation, for considering the instability regions, bifurcation points are studied and investigated. As a result, it can be observed that the damping coefficient plays an effective role as well as parametric excitation in stability and frequency response of the system.