Influence Of Surface Effects Research Articles

Characteristics of wave propagation in pre-stressed viscoelastic Timoshenko nanobeams with surface stress and magnetic field influences

The current investigation explores the behavior of pre-stressed viscoelastic Timoshenko nanobeams under the influence of surface effects and a longitudinal magnetic field. Utilizing a modified version of non-local strain gradient theory through the Kelvin–Voigt viscoelastic model, a closed-form dispersion relation using a suitable analytical approach has been derived. To account for surface stresses, Gurtin–Murdouch surface elasticity theory has been employed. Additionally, the study delves into the impact of a longitudinal magnetic field on a single-walled carbon nanotube, considering Lorentz magnetic forces. The validity of the findings is established by deriving results in the absence of surface effects and magnetic fields, aligning well with existing literature. The investigation indicates that pre-stress has marginal effects on flexural and shear waves, while surface effects, magnetic fields, non-locality, characteristic length, and nanotube diameter significantly influence the phase velocity. Additionally, the threshold velocity and blocking diameter are discussed for the model.

Mechanical behavior of nanocircular plates under coupled surface and nonlocal effects by using molecular dynamics simulations

The equations of control for a circular thin plate under simple support are obtained by coupling the surface effect and non-local effect using the equilibrium method. Molecular dynamics simulations were used to calculate the residual surface strain energies at different crystal orientations. Different crystal orientations of the same material would affect its surface energy and thus result in different mechanical behaviors. The effects of residual surface strain energy and non-local parameters on the mechanical behavior of circular thin plates were analyzed. The analysis reveals that the surface effect and non-local effect on the deflection of the nanoplates are significant. The surface effect parameter of tensile stress increases the deflection, while the opposite is true for the surface effect parameter of compressive stress, and the non-local parameter decreases the deflection. The influence of surface effect and non-local effect is significant for smaller thicknesses and weakens for larger thicknesses.

Surface Effect of Thickness-Dependent Polarization and Domain Evolution in BiFeO3 Epitaxial Ultrathin Films.

With the trend of device miniaturization, ultrathin ferroelectric films are gaining more and more attention. However, understanding ferroelectricity in this nanoscale context remains a formidable challenge, primarily due to the heightened relevance of surface effects, which often leads to the loss of net polarization. Here, the influence of surface effects on the polarization as a function of thickness in ultrathin BiFeO3 films is investigated using phase-field simulations. The findings reveal a notable increase in ferroelectric polarization with increasing thickness, with a particularly discernible change occurring below the 10 nm threshold. Upon accounting for surface effects, the polarization is marginally lower than the case without such considerations, with the disparity becoming more pronounced at smaller thicknesses. Moreover, the hysteresis loop and butterfly loop of the ultrathin film were simulated, demonstrating that the ferroelectric properties of films remain robust even down to a thickness of 5 nm. Our investigations provide valuable insights into the significance of ferroelectric thin films in device miniaturization.

The influence of surface effects on axisymmetric vibration of graded porous Mindlin circular nanoplate in a temperature field

AbstractThe surface effect significantly affects the mechanical response of nanoscale materials. In this work, we introduce Gurtin‐Murdoch surface elasticity theory into Mindlin plate theory to study the axisymmetric vibration characteristic of graded porous circular nanoplate in a temperature field. The main structure is a porous graded material with uniform or non‐uniform porosity distribution in its thickness. The numerical shooting technique was applied to solve the governing differential equations derived from Hamilton's principle. Responses for the vibration characteristic of the graded porous nanoplate for both clamped and simply supported boundary conditions were obtained. The numerical results show that when the surface effect is removed, the classical results of Mindlin circular plate will be obtained. Natural frequencies and mode shapes varying with thermal and porosity coefficients were present graphically. And then the effects of surface material properties on the axisymmetric vibration characteristic of the nanoplates were discussed in detail. The parametric study examined the influence of porosity coefficient, porosity distribution mode, surface elastic parameters, and residual surface stress on the vibration characteristics of porous circular nanoplates.

Influence of surface effect on post-buckling behavior of piezoelectric nanobeams

Piezoelectric nanobeams with excellent mechanical, thermal and electrical properties are important components in micro-nano electromechanical systems, which are widely used as sensors, brakes and resonators. Based on the Euler–Bernoulli beam model, the influence of surface effect on the post-buckling behaviour of piezoelectric nanobeams is analysed. According to the surface elasticity theory and the ‘core–shell’ model, the surface energy model is used to introduce the influence of surface effect. The governing equations and boundary conditions of the post-buckling of piezoelectric nanobeams under the influence of surface effect are derived by the principle of minimum potential energy. The analytical solution of post-buckling is obtained by the eigenvalue method. The influence of surface effect on the post-buckling configuration, post-buckling path, amount of induced charge and critical load of piezoelectric nanobeams with different external constraints and cross-sectional dimensions are discussed. The results show that surface effect has a significant influence on the post-buckling of piezoelectric nanobeams. Considering surface effect, the effective elastic modulus and critical load of piezoelectric nanobeams are increased, and the post-buckling configuration, post-buckling path and amount of induced charge are reduced. These findings contribute to the study of micro-nano electromechanical systems based on nanobeam structures and provide a theoretical basis for the design and manufacture of nanodevices.

Influence of surface effect on post-buckling behavior of graded porous nanobeam subjected to follower force

Influence of surface effect on post-buckling behavior of graded porous nanobeam subjected to follower force

Propagation characteristics of shear horizontal waves in piezoelectric semiconductor nanoplates incorporating surface effect

Elastic wave-based devices made of piezoelectric semiconductors (PSs) find wide applications in modern scientific and technological fields. Elastic waves propagating in PS nanostructures have a rich variety of propagation characteristics due to the interaction between deformation, polarization, and charge carrier, as well as the influence of surface effect. Based on the Gurtin-Murdoch surface model, we conduct an analysis of horizontally polarized shear (SH) waves propagating in an infinite n-type PS plate with nano-thickness in this paper. For the open-circuit and electrically isolated boundary conditions, the analytical frequency and phase velocity spectrum relations and cut-off frequencies of SH waves with anti-symmetric and symmetric modes are presented. The influence of the surface effect, initial electron concentration, and thickness of the PS plate on the propagation characteristics of SH waves, such as frequency spectrum, phase velocity, and cut-off frequency, are elaborated in detail. Numerical results show that propagation characteristics of SH waves are size-dependent, and the macroscopic effective shear rigidity is softened at the nanoscale due to surface effect, which thus leads to the reduction of the frequency and phase velocity of SH waves. Moreover, the propagation characteristics of SH waves can be manipulated by changing the initial electron concentration.

Analytical solutions of bending analysis and vibration of rectangular nano laminates with surface effects

In this paper, a novel continuum mechanics model is developed to investigate the influence of surface effects on the bending and free vibration behaviors of Kirchhoff rectangular nano laminates. The governing equations are established based on the Gurtin–Murdoch theory and the analysis of the equilibrium of forces. Analytical solutions for bending deflections and natural frequencies are presented for selected boundary conditions. Numerical results show that the influences of surface effects on bending deflections and natural frequencies are related to the aspect ratio of the nano laminates and the value of residual surface stress. Moreover, the influence of surface effects can be ignored when the thickness of the nano laminate is large enough.

Modulation of thermometric performance of single-band-ratiometric luminescent thermometers based on luminescence of Nd3+ activated tetrafluorides by size modification

Due to a number of its advantages, luminescence thermometry has been a strongly developed strand of temperature metrology over a period of time. Although there are several different types of luminescent thermometers, recently attention has been focused on a new single-band ratiometric approach, which is based on the excited state absorption phenomenon. Nevertheless, since this process is nontrivial and has not been studied extensively in the context of thermometry to date, a number of studies are necessary to enable the intentional development of highly sensitive thermometers based on this method. One of the important aspects is to investigate the influence of material size and the associated occurrence of surface effects, which is considered in this work. In addition, the research in this paper has been extended to explore the aspect of host material composition. Accordingly, nanocrystals and microcrystals of β-NaYF4:2%Nd3+, β-NaGdF4:2%Nd3+, and LiGdF4:2%Nd3+ were investigated in this work. The influence of surface effects on thermometric parameters was proved, with special emphasis on the useful temperature range. Thus, by increasing the particle size, it was possible to intentionally extend the useful range by even more than 100 K.

First principles study of the structural, electronic, magnetic and optical properties of the Fe doped CoS2 thin films

The structural stability, electronic, magnetic and optical properties of the Fe doped CoS2 bulk alloy and the thin films with different terminations are studied by the first-principle calculations. The bulk Co0.75Fe0.25S2 alloy is 100% spin polarized, and there are new impurity valence bands near Fermi level in both the spin-up and spin-down channels of the band structures. The fracture of Co-S or Fe-S chemical bonds and the change of S-S dimer bonds are the key factors affecting the properties of the films. The surface energy of SS-SS-CoCo termination film under the S-rich and Co-rich boundary conditions is the lowest, and spin polarization maintains -100%. Although the spin polarization of CoFe terminated film is high (-90.2%), but its surface energy is high which lead to the unstable feature. The magnetic moment of the thin film is mainly contributed by the spin magnetic moment of the Co and Fe atoms. The magnetic moments of the atoms at outer layer differ significantly from those at the central layer due to the change of crystal field and the influence of surface effect. Fe doping and termination selection can modulate the optical properties of CoS2 effectively.

Surface effects on buckling of nanowire electrode

Nanowire-based electrodes have attracted much attention due to their high surface energy, short distance for lithium insertion, and the ability to accommodate the enormous strain. However, the buckling behavior may occur during lithiation for such wire-like electrodes, which would lead the battery performance to deteriorate. Therefore, it is vital to quantitatively understand the mechanism about the bucking behavior of the nanowire-based electrodes. Although the buckling behavior of wire-like electrode has been extensively studied in the past few decades, the influence of surface effect on it has not yet been thoroughly explored. For this purpose, a theoretical model of surface effects on buckling of nanowire electrode is presented by taking into account the lithium diffusion, stress, and concentration-dependent elastic properties. Based on the established model, the effects of the residual surface tension and elastic hardening/softening coefficients on buckling are investigated. The results show that surface effects can improve the mechanical reliability, thus delaying the critical buckling time of nanowire electrode. In addition, it is indicated that the surface effects depend on the radius size and slenderness ratio of the nanowire electrode, specifically, the smaller the radius size and the larger the slenderness ratio, the greater the influence of the surface effect is. Furthermore, compared with elastic hardening, with the participation of surface effects, the larger the elastic softening coefficient, the longer it takes for the nanowire electrode to reach the buckled state, and the better the stability of the electrode is. The novelty of this work is that the proposed models highlight the importance of surface effects on buckling of nanowire electrode. These findings provide a prospective insight into the designing of higher structural reliability of electrode.

Dynamic Analysis of Nanosized Arbitrary Shape Inclusion under SH Waves

The scattering of shear waves (SH waves) by nano-scale arbitrary shape inclusion in infinite plane is studied by complex variable function theory. Firstly, the governing equation and the relationships between stress and displacement are given by classical elastic theory. Secondly, the arbitrary shape inclusion in the two-dimensional plane is transformed into a unit circle domain by conformal mapping, the incident wave field and the scattered wave field are presented. Next, the stress and displacement boundary conditions are established by considering surface elasticity theory, The infinite algebraic equations for solving the unknown coefficients of the scattered and standing waves are obtained. Finally, the influence of surface effect, non-dimensional wave number, Shear modulus and hole curvature on the dynamic stress concentration factor are analyzed by some examples, the numerical results show that the surface effect weakens the dynamic stress concentration. With the increase of wave number, the dynamic stress concentration factor (DSCF) decreases. Shear modulus and hole curvature have significant effects on DSCF.

Vibration and Buckling Analysis of Piezoelectric Nanowires Based on Surface Energy Density

In this paper, the influences of surface effects on free transverse vibration and buckling of piezoelectric nanowires are investigated by surface energy density elasticity theory. Analytical relations are given for the natural frequencies of nanowires by taking into account the effects of surface energy density and surface relaxation parameter. By implementing this theory with consideration of surface effects under clamped–clamped boundary conditions, the natural frequencies of nanowires are calculated. It is shown that the natural frequency depends on both the surface effects and piezoelectricity. A closed-form solution is also obtained to calculate the critical buckling voltage. This study is expected to provide useful insights for the design of piezoelectric nanowire-based nanodevices.

Dynamic analysis of bi-directional functionally graded Timoshenko nanobeam on the basis of Eringen's nonlocal theory incorporating the surface effect

In this article, a nonlocal model based on the Timoshenko beam theory has been introduced for vibration response of bi-directional functionally graded moderately thick nanobeam under the influence of surface effect. Surface and nonlocal effects have been accounted using the Gurtin-Murdoch surface elasticity theory and Eringen's nonlocal theory, respectively. The material properties of the beam are changing according to the power-law distribution in both the thickness and length directions. Employing Hamilton's energy principle, the governing equations of motion and corresponding boundary conditions have been extracted. The numerical results for frequency parameter have been obtained using the differential quadrature method for three different combinations of clamped and simply supported edge conditions. The study reveals that the consideration of surface and nonlocal effects in predicting the vibration characteristics of bi-directional functionally graded shear deformable nanobeam plays an important role and can't be ignored in the analysis. The results are validated by comparing with those available in the literature.

The influence of surface effects in the problem of theory of elasticity for a circular hole in a half-plane

Surface effects are important for modeling structures, such as nanofilms, nanoporous materials, and other nanoscale constructions. In the current study, we consider the problem of the theory of elasticity - the problem of a half-plane containing a circular hole, stretched by constant stresses applied at infinity, and take into account surface effects such as surface elasticity and surface stresses. The problem solution has been obtained by expanding the Fourier series with the variables written in the bipolar coordinate system (which simplifies the problem solution because one of the coordinates becomes a constant on the hole contour), where the stress components are expressed through a bi-harmonic stress function. The parametric coefficients involved in the solution, namely in the Fourier series, are determined in order to satisfy the boundary conditions on the hole contour. To solve the problem, in addition to the equations of the theory of elasticity, the equations of surface elasticity were used, in particular, by applying the generalized Young-Laplace’s law and the Shuttleworth’s law; the surface stress on the hole contour has been calculated directly. Using recurrence relations for the stress components at the boundary, stress concentration values have been obtained. The resulting expressions can be considered as a generalized solution of the problem in case of the classical elasticity. The stress concentrations are compared for the cases with and without taking into account surface effects at various points on the hole contour. The contribution caused by the surface effects depending on the relative distance between the hole and the half-plane boundary is studied. It is shown that despite a quite simple geometry, owing to the fairly small distance between the hole and the half-plane boundary, the stress concentration with and without taking into account the surface stress are significantly different from each other, due to the significant contribution of surface effects.

Modeling the Unfrozen Water Content of Frozen Soil Based on the Absorption Effects of Clay Surfaces

AbstractUnfrozen water content significantly affects the thermal‐hydro‐mechanical characteristics of frozen soil. Currently, theoretical explanations for the presence of unfrozen water include capillary action, surface effects, adsorption forces, and the electrical double layer. However, the relationships between unfrozen water and these actions are not well explained, except for capillary forces. In addition, although frost heave experiments indicate that the electrical double‐layer solution on a clay particle contains the main portion of unfrozen water, the electrical double‐layer theory which produces a cation solution has not previously been used to calculate unfrozen water content. In this paper, it is assumed that the residual unfrozen water at very low temperatures (below −18°C) is held within the adsorption‐layer solution and that the remaining unfrozen water within the influence of surface effects is the cationic solution in the diffuse layer. Based on these assumptions, a theoretical model of unfrozen water is established with independent variables of temperature, specific surface area, and electrical double‐layer parameters. While the input parameters of the theoretical model are numerous and difficult to obtain, the theoretical model is simplified as a parametric model. Results of the parametric model are strongly consistent with experimental data within a certain temperature range, supporting the hypothetical conditions. The similarity in the underlying mathematical structure of the derived theoretical and parametric models to current semi‐empirical models further suggests that the surface effects of clay are the main causes of unfrozen water in frozen soil.

Anti-plane problem of nano-cracks emanating from a regular hexagonal nano-hole in one-dimensional hexagonal piezoelectric quasicrystals**Project supported by the National Key R&D Program of China (Grant No. 2017YFC1405605), the Innovation Youth Fund of the Ocean Telemetry Technology Innovation Center of the Ministry of Natural Resources, China (Grant No. 21k20190088), the Natural Science Foundation of Inner Mongolia, China (Grant No. 2018MS01005), and

By constructing a new conformal mapping function, we study the surface effects on six edge nano-cracks emanating from a regular hexagonal nano-hole in one-dimensional (1D) hexagonal piezoelectric quasicrystals under anti-plane shear. Based on the Gurtin–Murdoch surface/interface model and complex potential theory, the exact solutions of phonon field, phason field and electric field are obtained. The analytical solutions of the stress intensity factor of the phonon field, the stress intensity factor of the phason field, the electric displacement intensity factor and the energy release rate are given. The interaction effects of the nano-cracks and nano-hole on the stress intensity factor of the phonon field, the stress intensity factor of the phason field and the electric displacement intensity factor are discussed in numerical examples. It can be seen that the surface effect leads to the coupling of phonon field, phason field and electric field. With the decrease of cavity size, the influence of surface effect is more obvious.

Influence of surface effects on neutron skin in atomic nuclei

The influence of the diffuse surface layer of a finite nucleus on the mean square radii and their isotopic shift is investigated. We present the calculations within the Gibbs - Tolman approach using the experimental values of the nucleon separation energies. Results are compared with that obtained by means of a direct variational method based on Fermi-like trial functions.

Quality factor of circular microdiaphragm with surface effects in contact with liquids

This paper reports an investigation of the influences of surface effects and residual stress on the quality factor of a circular microdiaphragm in contact with liquids on one side. Acoustic radiation, as the main source of energy dissipation, can decrease the quality factor of a circular microdiaphragm. An approximate solution for the natural frequency can be obtained based on the Rayleigh–Ritz energy method. The results show that the influence of surface effects on the quality factor is obvious, in particular for thinner microdiaphragms. A stiffened surface decreases the quality factor, while a softened surface increases it. Furthermore, the quality factor increases with increases in the normalized tension parameter k for both stiffened and softened surfaces. If k is greater than 30, the influence of the surface effects on the quality factor must be considered. The results can provide effective guidance for the determination of dimensions and selection of material parameters in designing microdiaphragm resonant sensors.

The Frequency Spectrum of a Wire Micro- and Nanoresonator

The eigenfrequencies of bending vibrations are determined for wire with micro- and nanosize cross sections. The surface effects associated with an increase in the specific surface when reducing the cross-section area are taken into account. The first effect is induced by the difference in the elastic characteristics of the material of the surface layer and the bulk. The second effect is associated with the interaction between the excess pressure on the wire surface and the difference in the areas of convex and concave surfaces formed by the bending. The case of the wire hinged fastening at both ends is considered. The eigenfrequencies are determined in the linear and nonlinear formulations. The influence of surface effects and other input data on the eigenfrequencies is analyzed.