Coupling Effect Of Materials Research Articles

Bipolar Rashba Semiconductors: A Class of Nonmagnetic Materials for Electrical Spin Manipulation.

The realization of the electrical control of spin is highly desirable. One promising approach is by regulating the Rashba spin-orbit coupling effect of materials through external electric fields. However, this method requires materials to possess either a high electric field response and a large Rashba constant or the simultaneous presence of Rashba splitting and ferroelectric polarization. These stringent requirements result in a scarcity of suitable materials. In order to surpass these limitations and exploit a new prospect for spin manipulation via the Rashba effect, a conceptual class of materials named bipolar Rashba semiconductors (BRS) is proposed, whose valence band and conduction band possess opposite spin texture directions when approaching the Fermi level. The unique electronic structure of BRS makes it feasible to reverse the spin precession by simply applying a gate voltage. The existence of BRS is confirmed through first-principles calculations on the two-dimensional (2D) material AlBiS3.

Improving the comprehensive energy storage performance of composite materials through the coupling effect of AgNbO3/PVDF nanocomposite

AbstractCeramic‐polymer nanocomposites with high energy storage density can achieve excellent energy storage performance and have a wide range of application prospects. Currently, it has been shown that the coupling effects have a great impact on improving the performance of dielectric composites, but increasing the breakdown strength of polymer nanocomposite is still a tremendous challenge to the achievement of high energy density under high voltages. The aim of this paper is to further investigate this problem and obtain AgNbO3/PVDF flexible composites by introducing a small amount of AgNbO3 ultrafine powder prepared by hydrothermal method into poly(vinylidene fluoride) (PVDF). The interfacial coupling effect within this nanocomposite with the coupling effects of nonlinear dielectric materials improves its energy storage capacity and electrical strength resistance. The energy density of the 2 wt% AgNbO3/PVDF composite film was raised to 16.5 J/cm3 at the electric breakdown strength of 391.7 MV/m, and its energy storage capacity is two to three times that of AgNbO3 lead‐free antiferroelectric ceramics. Finite element simulations showed the further enhancement of breakdown strength was ascribed to the local electric field and to the AgNbO3 ultrafine powder which blocked the breakdown path in the nanocomposites and coupling effects occurred with PVDF. Hence, the AgNbO3 ultrafine powder has a positive effect on improving the energy storage performance of flexible composites. The effects of nonlinear dielectric material coupling effects and interfacial coupling effects on the dielectric properties of composite dielectric materials are further investigated, which are important for the development of flexible high energy storage capacitors.

Surface Damage Coupling Mechanism of Plain Weave Art Ceramic Matrix Composites

In order to solve the problem of the surface damage coupling mechanism of ceramic matrix composites, a method oriented to the damage coupling mechanism of the plain weave art ceramic matrix is proposed by the author. First, the author uses the composite material prepared by a chemical vapor infiltration process as the research object, and the damage mechanical behavior of materials under simple and complex plane stress states is studied. Second, the calculation of the mechanical property parameters of the material components and the research on the mechanical behavior of the material in-plane shear mesodamage are studied; Finally, the research on the damage coupling effect of materials under complex stress state is conducted, as well as the decoupling test research of the damage coupling effect. It is demonstrated that based on 0 and 45° off-axis tensile stress-strain behavior, a prediction model of off-axis tensile stress-strain behavior of the material was established, and the prediction results were in good agreement with the experimental results.

Energy-based collapse assessment of concrete structures subjected to random damage evolutions

The assessment of structural capacity against collapse is conducive to the optimal design of new structures as well as checking the safety of existing structures. However, the evaluation cannot be typically carried out by means of destructive tests on prototype or reduced scale structures. In this regard, the numerical models that adequately represent the prototype structures can be alternatively used. Specifically, both the nonlinearities and randomness as well as their coupling effect of materials need to be represented in a unified manner in structural analysis. The present paper aims at providing an effective approach to incorporate the stochastic nature of damage constitutive relationships in collapse analysis and assessment of concrete structures subjected to earthquake ground motions. Within the framework of stochastic damage mechanics, the spatial variability of concrete is represented by a two-scale stationary random fields. The concept of covariance constraint is introduced to bridge the two-scale random fields such that the scale-of-fluctuation of the random material property is satisfied at both scales. Random damage evolution induced structural collapse analysis is achieved via the nonlinear stochastic finite element method. To address the randomness propagation across scales, the probability density evolution method is employed. By exerting the absorbing boundary condition associated with an energy-based collapse criterion on the generalized probability density evolution equation, the anti-collapse reliability of concrete structures can be evaluated with fair accuracy and efficiency. Numerical investigation regarding an actual high-rise reinforced concrete frame-shear wall structure indicates that the random damage evolution of concrete dramatically affects the structural nonlinear behaviors and even leads to entirely different collapse modes. The proposed method provides a systematic treatment of both uncertainties and nonlinearities in collapse assessment of complex concrete structures.

Analytical Electromechanical Modeling of Nanoscale Flexoelectric Energy Harvesting

With the attention focused on harvesting energy from the ambient environment for nanoscale electronic devices, electromechanical coupling effects in materials have been studied for many potential applications. Flexoelectricity can be observed in all dielectric materials, coupling the strain gradients and polarization, and may lead to strong size-dependent effects at the nanoscale. This paper investigates the flexoelectric energy harvesting under the harmonic mechanical excitation, based on a model similar to the classical Euler–Bernoulli beam theory. The electric Gibbs free energy and the generalized Hamilton’s variational principle for a flexoelectric body are used to derive the coupled governing equations for flexoelectric beams. The closed-form electromechanical expressions are obtained for the steady-state response to the harmonic mechanical excitation in the flexoelectric cantilever beams. The results show that the voltage output, power density, and mechanical vibration response exhibit significant scale effects at the nanoscale. Especially, the output power density for energy harvesting has an optimal value at an intrinsic length scale. This intrinsic length is proportional to the material flexoelectric coefficient. Moreover, it is found that the optimal load resistance for peak power density depends on the beam thickness at the small scale with a critical thickness. Our research indicates that flexoelectric energy harvesting could be a valid alternative to piezoelectric energy harvesting at micro- or nanoscales.

Experimental identification of smart material coupling effects in composite structures

Smart composite structures have an enormous potential for industrial applications, in terms of mass reduction, high material resistance and flexibility. The correct characterization of these complex structures is essential for active vibration control or structural health monitoring applications. The identification process generally calls for the determination of a generalized electromechanical coupling coefficient. As this process can in practice be difficult to implement, an original approach, presented in this paper, has been developed for the identification of the coupling effects of a smart material used in a composite curved beam. The accuracy of the proposed identification technique is tested by applying active modal control to the beam, using a reduced model based on this identification. The studied structure was as close to reality as possible, and made use of integrated transducers, low-cost sensors, clamped boundary conditions and substantial, complex excitation sources. PVDF (polyvinylidene fluoride) and MFC (macrofiber composite) transducers were integrated into the composite structure, to ensure their protection from environmental damage. The experimental identification described here was based on a curve fitting approach combined with the reduced model. It allowed a reliable, powerful modal control system to be built, controlling two modes of the structure. A linear quadratic Gaussian algorithm was used to determine the modal controller–observer gains. The selected modes were found to have an attenuation as strong as −13 dB in experiments, revealing the effectiveness of this method. In this study a generalized approach is proposed, which can be extended to most complex or composite industrial structures when they are subjected to vibration.

Transverse vibration analysis of generally laminated two-segment composite shafts with a lumped mass using generalized differential quadrature

The use of composite materials for weight reduction of shaft drivelines has positive impacts in different applications. The driveshafts design is mostly dictated by its natural frequencies. In order to maximize the natural frequencies, shafts are built in one, two or more segments. Analysis of such components has complexities in dealing with two-segments, shear deformation, and material coupling effects. This paper presents a theory that includes shear deformation and rotary inertia along with coupling effects to analyze transverse vibration behavior of generally laminated shafts with intermediate joints. Equivalent modulus of elasticity is used instead of traditional stiffness terms to account for material coupling. The equations of motion are solved using generalized differential quadrature. Results were compared with those published in the literature and finite element simulations, and it has been shown that the present method can accurately predict transverse vibration behaviors of generally laminated two-segment shafts with a lumped mass.

Prediction of material coupling effect on structural damping of composite beams and blades

The present paper investigates the effect of material coupling on static and modal characteristics of composite structures. Incorporation of stiffness and damping coupling terms into a beam formulation yields equivalent section stiffness and damping properties. Building upon the damping mechanics, an extended beam finite element is developed capable of providing the stiffness and damping matrices of the structure. Validation cases on beams and blades demonstrate the importance of all stiffness and damping terms. Numerical results validate the predicted effect of material coupling on static characteristics of composite box-section beams. The effect of the full coupling damping matrices on modal frequencies and structural modal damping of composite beams is investigated. Box-section beams and small blade models with various ply angle laminations at the girder segments are considered. Finally, the developed finite element is applied to the prediction of the modal characteristics of a 19m realistic wind-turbine model blade.

GBT formulation to analyse the buckling behaviour of FRP composite open-section thin-walled columns

Abstract This paper presents a Generalised Beam Theory (GBT) formulation to analyse the local and global buckling behaviour of FRP (fibre-reinforced polymer) composite thin-walled columns with arbitrary open cross-sections, which takes into account both shear deformation and cross-section deformation effects. After describing the steps and procedures involved in performing the GBT cross-section analysis of an arbitrarily branched composite (laminate plate) thin-walled member, the paper addresses the numerical implementation of the proposed GBT formulation, carried out by means of the finite element method (GBT-based beam element) – particular attention is devoted to the derivation of the element linear and geometric stiffness matrices, which incorporate all the material coupling effects. In order to illustrate the application and capabilities of the proposed formulation and implementation, several numerical results are presented and discussed, dealing with the local and global buckling behaviour of FRP composite I-section columns with different ply orientations and stacking sequences. Taking advantage of the GBT modal features, deep insight is acquired on the complex composite member buckling mechanics, namely those involving bending–torsion or global–local coupling effects. In particular, one investigates the influence of (i) the constitutive assumption regarding the transverse extension occurring in the cross-section composite walls and (ii) the distribution of pre-buckling normal stresses (due to axial compression) on the buckling behaviour of I-section columns. For validation purposes, the above results are compared with values recently reported in the literature and estimates obtained from shell finite element analyses.

Damped structural dynamics models of large wind-turbine blades including material and structural damping

The paper presents a brief description of composite damping mechanics for blade sections of arbitrary lamination and geometry. A damped 3-D shear beam element is presented enabling the assembly of damped structural dynamic models of blades with hollow multi-cell tubular laminated sections. Emphasis is placed to the inclusion of composite material coupling effects, first in the blade section stiffness and damping matrices and finally into the stiffness and damping matrices of the finite element. Evaluations of the beam element are presented, to quantify the material coupling effect on composite beams of simple box sections. Correlations between predicted and measured modal frequencies and damping values in small model Glass/Epoxy are also shown. Finally, the damped modal characteristics of a 35m realistic wind-turbine blade model design, are predicted.

Effect of material coupling on wave vibration of composite Euler–Bernoulli beam structures

Fiber-reinforced composite materials are an important development in the continuing search for lightweight materials for great strength and stiffness. Lighter structures are usually more prone to vibrations. Furthermore, due to material coupling, composite beams normally vibrate with coupled vibration modes, which complicates vibration analysis. This paper presents the effect of coupling between bending and torsional deformations on vibrations of composite Euler–Bernoulli beams from a wave vibration standpoint. In the study, it is found that the torsional mode is only unaffected by the material coupling at low frequencies. The flexural modes are found affected over the entire frequency band. Unlike their uncoupled metallic counterparts, the wavenumbers for propagating and decaying wave components are no longer the same due to material coupling. Free vibration analysis is performed from a wave standpoint. Free vibration of composite beam with the coupling effect taken into account is of great importance. This is because the free vibration characteristics can be designed favorably by suitable choice of ply orientations and stacking sequence—one of the unique features of composite structures. Numerical examples for which comparative results are available in the literature are presented.

Effect of Material Coupling on Wave Vibration of Composite Timoshenko Beams

This paper presents the effect of coupling between bending and torsional deformations on vibrations of composite Timoshenko beams from the wave standpoint. The dispersion characteristics and the modes of vibrations are in general affected by material coupling, except those of the torsional modes at low frequencies; and higher-frequency modes are normally more sensitive to material coupling. The wave mode transition phenomenon is also investigated. It is found that like their metallic counterparts, composite Timoshenko beams also exhibit wave mode transition. Furthermore, the transition frequency is found to be unaffected by material coupling. Numerical examples for which comparative results are available in the literature are presented.

Explicit Modal Analysis of Axially Loaded Composite Timoshenko Beams Using Symbolic Computation

Introduction I NVESTIGATIONS into the free vibration analysis of composite beams have been well documented.1i4 A principal Ž nding of this research shows that the effect of material coupling arising from ply orientation on the free vibration behavior of composite beams can be important from the point of view of aeroelastic tailoring.5 Generally, solutions of vibration problems of composite beams are numerically based because of the huge difŽ culties involved in seeking closed-formanalytical solutions.However, the recent advancement in symbolic computation6 has made it possible to solve engineering problems by algebra rather than by numerical means. This has motivated investigations in recent years to derive explicit expressions for the frequency equations and mode shapes of simple composite beams and composite Timoshenko beams. The purpose of the present study is to extend these earlier works and derive the frequency equation and mode shape of a cantilever composite Timoshenko beam by taking into account the important effect of an axial load. The proposed theory can be extended to other end conditions of axially loaded composite Timoshenko beams, and it offers prospects for aeroelastic optimization.

Explicit analytical expressions for frequency equation and mode shapes of composite beams

A systematic procedure for the derivation of exact expressions for the frequency equation and mode shapes of composite beams undergoing free vibration is presented by using the symbolic computing package reduce. The effect of material coupling between the bending and torsional modes of deformation, which usually exists in composite beams due to ply orientation, is taken into account while developing the theory. The governing differential equations of motion of the bending–torsion coupled composite beam are solved analytically for bending displacements and torsional rotations in free vibration. For subsequent developments, the important case of the cantilever beam is chosen because of its application to aircraft wings. The boundary conditions for displacements and forces for the cantilever are imposed and the frequency equation is obtained, but first in the form of a determinant, and then, in the form of an explicit algebraic expression. The expressions for the mode shapes are also derived in explicit analytical form. The method is demonstrated by an illustrative example of a composite beam for which some comparative results are available in the literature. The future potential of this method, particularly in the context of aeroelastic optimisation of composite wings, is considerable because it is very accurate, computationally efficient and importantly, free from ill-conditioning problems usually associated with numerical matrix manipulation.

Frequency equation and mode shape formulae for composite Timoshenko beams

Exact expressions for the frequency equation and mode shapes of composite Timoshenko beams with cantilever end conditions are derived in explicit analytical form by using symbolic computation. The effect of material coupling between the bending and torsional modes of deformation together with the effects of shear deformation and rotatory inertia is taken into account when formulating the theory (and thus it applies to a composite Timoshenko beam). The governing differential equations for the composite Timoshenko beam in free vibration are solved analytically for bending displacements, bending rotation and torsional rotations. The application of boundary conditions for displacement and forces for cantilever end condition of the beam yields the frequency equation in determinantal form. The determinant is expanded algebraically, and simplified in an explicit form by extensive use of symbolic computation. The expressions for the mode shapes are also derived in explicit form using symbolic computation. The method is demonstrated by an illustrative example of a composite Timoshenko beam for which some published results are available.

Transient coupled-thermoelastic problem of heat conduction in a multilayered composite plate

The authors give a step-by-step algorithm for computations of the transient response, which occurs in a one-dimensional multilayered composite plate, subjected to a sudden heating or cooling from the surrounding atmosphere. In each layer, the materials are assumed as homogeneous and isotropic; the thermo-elastic coupling effect of materials is taken into account, but their inertia effect is neglected. The method of Laplace transform is used to give the solutions in each layer of the plate, under the boundary conditions at the outer surfaces and the interfaces between layers. The numerical computations are carried out for one-, two-, and three-layered plates to display the variations of the stress and temperature fields.

Buckling of Antisymmetrically Laminate Cross-Ply and Angle-Ply Rectangular Plates

An exact method based on a displacement approach is developed and applied to obtain the buckling response of antisymmetrically laminated cross-ply and angle-ply rectangular plates resting on Winkler-Pasternak foundation. Two opposite loaded edges are assumed to be simply supported and various other boundary conditions on the remaining two edges are considered. Typical results for a number of different plate lay-ups and Winkler-Pasternak values are presented in dimensionless graphical form. The effect of material coupling and foundation stiffnesses on the buckling response of plates are considered.