Search

The aim of this work is to study the method of explosive welding to produce niobium-steel composite plate, which is used in nuclear industry equipment material manufacturing. The welding parameters were determined by weldability window, and numerical simulation was used to predict the wave shape of the welding interface. The morphology of the interface wave was observed by scanning electron microscope. Measured element distribution near the interface. The experimental samples were investigated using mechanical tests. The results show that the welding parameters optimized by theory and numerical simulation can be used to obtain a niobium-steel composite plate with better welding quality. It can be proved that the welding quality is better by observing the interface wave and testing the mechanical properties; it can be seen that the melting zone of the welding interface is composed of niobium and steel by the composition analysis instrument. The morphology of the welding interface wave is consistent with the numerical simulation results, and the numerical simulation shows the changes of temperature, strain, and stress during the welding process. [ABSTRACT FROM AUTHOR]

We study interactions between mechanical loads and distributions of charge carriers as well as current densities in the bending of a sandwich plate with a piezoelectric dielectric layer between two nonpiezoelectric semiconductor layers. A set of two-dimensional plate equations is derived from the underlying three-dimensional macroscopic theory of piezoelectric semiconductors when the plate is in bending with shear deformation under transverse mechanical loads. It is shown that the distribution and motion of the mobile charges in the semiconductor layers are sensitive to and can be manipulated by mechanical loads. In particular, local electric potential barriers/wells form when the plate is under local mechanical loads, and the potential barriers/wells affect the distributions of the current densities in the semiconductor layers. Thus the sandwich plate exhibits couplings between mechanical loads and the distribution/motion of mobile charges and can be used for electromechanical semiconductor devices with broad applications in sensing and transduction. [ABSTRACT FROM AUTHOR]

The instability of composite plates subjected to an arbitrary periodic dynamic loading is investigated based on Lo's high-order shear-deformation plate theory. The differential equations of motion of Mathieu-type are formed by Hamilton's principle and employing the Galerkin method. Using Bolotin's method, the excitation frequencies of composite plates are evaluated to determine their dynamic stability region and dynamic instability index. Omitting the high-order terms of Lo's displacement field, the system equations can be simplified to governing equations in the first-order plate theory. The dynamic instability determined by the present theory is compared with results of the first-order plate theory. Results show that high order terms have a significant impact on the dynamic instability of composite plates. [ABSTRACT FROM AUTHOR]

Introduction: Autonomous shape and vibration control of a structure expand its utility, thereby increasing the need for adaptive composites in the field of aerodynamics, civil, space, and mechanical engineering. One way to achieve this is by reinforcing composites with smart materials like shape memory alloy (SMA) wires or ribbons, piezoelectric (PZT) materials, and magnetostrictive materials. Objectives: In this study, the authors optimize the numerically solved bending behavior of SMA fiber-reinforced E-glass fiber-Silicone matrix composite upon thermal actuation. The study is shown for four cases (a) single layer of SMA embedded unimorph, (b) two-layers of SMA embedded bimorph, (c) single layer SMA embedded bimorph with a honeycomb core, and (d) single layer SMA embedded bimorph with an auxetic core. The vibration responses of these cases upon analysis show that the first three eigenmodes of the unimorph and the bimorph SMA composite include bending and torsion modes and the corresponding eigenfrequencies are significantly close in magnitude for the Austenite finish ( A f ) temperature. In other words, the first natural frequency displays complex eigenmodes. A multi-objective optimization approach for SMA hybrid composite plates for de-coupling eigenfrequencies is proposed in this study. Methods: The Non-dominated Sorting Genetic Algorithm (NSGA-II) is used to minimize the eigenfrequency corresponding to the first bending eigenmode and maximize the eigenfrequency corresponding to the first twisting eigenmode, thus increasing the effective difference between the two eigenfrequencies. The authors also simultaneously maximize the deflection of the structures in order to obtain a considerable morphing observation. The present investigations involve determining the best laminate configuration relying on SMA fiber angle orientation and SMA ply thickness as the variables. Results: A complex mode or a combination of two modes at the first eigenfrequency or complex modes can cause failure of the structure, making decoupling an essential requirement. The algorithm proposed can also be used to interchange the eigenmodes of their corresponding eigenfrequencies, thus allowing the first natural frequency to give a twisting or torsional eigenmode and the consecutive natural frequency that of a bending mode. This technique can be used to avoid Phugoid motion-based failure in an aircraft by continuously controlling and interchanging the eigenmodes of its wings. [ABSTRACT FROM AUTHOR]

Mg/Al laminate composites were prepared at 400 ℃ for 15 min through single-pass rolling with reduction ratio from 10 to 27%. The bonding mechanism of the initial bonding stage under low pressure was studied. Two critical statuses (beginning bonding and complete bonding) are found at the reduction ratio of 14.5% and 21.75%. In this article, the coincidence of the ratio of external force (normal stress) and internal force (electronic force) at the two critical points shows that electrons overcome the potential barriers of Mg and Al respectively and make them move freely to form metal bonds. The free movement of electrons between two metal interfaces forms a metallic bond, which bonds the two metals. The formation of metallic bonds overcomes the classical barrier to achieve electron free motion. The ratio of σMg to σAl (σMg/σAl) is 0.7340, and the ratio of fMg to fAl (fMg/fAl) is 0.7988, where it can be found that the former agrees well with the latter. The good agreement between theory and experiment proves that overcoming the potential barrier plays an important role in the early bonding stage of bimetal composite plates. [ABSTRACT FROM AUTHOR]

A size-dependent piezoelectric-piezomagnetic bi-layered composite plate bending model is established based on the modified strain gradient theory and layerwise theory, where the governing equations and corresponding definite solution conditions are firstly derived by the Hamilton variational principle. And then, the meshless collocation method coupled with the method of polynomial particular solutions is tentatively to solve this bending problem. Finally, the influences of size effect, applied coupling loads, structure dimension, and foundation parameters on the bending properties of piezoelectric-piezomagnetic bi-layered composite plates are systematically discussed by some typical numerical examples. Moreover, the bending analyses under different boundary conditions and proportions of component materials are further carried out, and some interesting conclusions are obtained. [ABSTRACT FROM AUTHOR]

In this article, the Lippmann–Schwinger equation for nonlinear elasticity at small-strains is extended by mixed strain/stress gradient loadings. Such problems occur frequently, for instance when validating computational results with three-point bending tests, where the strain in the bending direction varies linearly over the thickness of the sample. To control all components of the effective strain/stress gradient the periodic boundary conditions are combined with constraints that enforce the periodically deformed boundary to approximate the kinematically fully prescribed boundary in an average sense. The resulting fixed point and Fletcher–Reeves algorithms preserve the positive characteristics of existing FFT-algorithms, like low memory consumption and extraordinary computational speed. The accuracy and power of the proposed methods is demonstrated with a series of numerical examples, including continuous fiber reinforced laminate materials. [ABSTRACT FROM AUTHOR]

Low-velocity impact damaging of the composite structural elements is an important problem during machine's operation, especially in the aircraft and aerospace industries. Thus, appropriate nondestructive structural diagnostics methods should be developed in order to identify the damages in possible early stage of their development. The paper deals with the experimental study of impact damage identification of composite structures subjected to the low-velocity impacts by stones. The proposed damage identification algorithm is based on the modal analysis of damaged structures and further wavelet analysis of acquired modal shapes using nonseparable quincunx wavelets. The analysis was performed for the composite structures typical for those used in the aeroplane sheeting impacted with various energies. The application of quincunx wavelets allows for accurate localization of the damages and for avoiding the boundary effect occurred during an application of separable wavelets. Obtained results show the efficiency of the proposed method and could be used in industrial applications as well. [ABSTRACT FROM AUTHOR]

Thick steel/aluminum/aluminum-alloy composite plates are one of the key materials connecting steel structures and aluminum alloy structures and have been widely used in the shipbuilding industry and other fields. However, steel/aluminum/aluminum-alloy composite plates with a total thickness of more than 10 mm and a steel layer thickness of more than 5 mm are prone to problems such as inconsistent deformation of component metals and low bonding strength during the rolling process, and cannot be continuously prepared. To solve this problem, this article proposes a two-pass different temperature rolling process for thick steel/aluminum/aluminum-alloy composite plates and conducts research on Q235B steel, 1060 aluminum, and 5083 aluminum alloy as component metals. The results show that the process is reliable. It can prepare Q235B/1060/5083 composite plates with a thickness of 15.65 mm without oxygen protection measures. Meanwhile, the interfacial shear and pull-off strength of the composite plates obtained under different experimental conditions in this article are higher than the requirements of the US military standards MIL-J-24445A and Chinese ship standard CB20091-2012. The composite plates show good performance in 90° and 137° bending tests without obvious defects. Under the best condition, a 1.48 μm interlocking diffusion layer is formed at the steel/aluminum interface of the composite plates, the interfacial shear strength exceeds 70 MPa, and the interfacial pull-off strength exceeds 110 MPa. Finally, according to the experimental results, the reasons for the feasibility of the two-pass different temperature rolling of thick steel/aluminum/aluminum-alloy composite plates are given. [ABSTRACT FROM AUTHOR]

Free vibrations of shallow sandwich shells resting on elastic foundations are investigated. It is assumed that the shell consists of three layers of defined thickness. The core is made of ceramics or metal, while the upper and lower layers are made of functionally graded material (FGM). The volume fractions of metal and ceramics are described by the power law. Hence, estimation methods for higher accuracy remain a challenge. The elastic foundation is described by two-parameter Pasternak's model. Both higher-order shear deformation shell theory (HSDT), which includes interactions with elastic foundation, and the R-functions theory combined with the variational Ritz method are used to study shells with arbitrary planforms. The numerical study is carried out in the framework of the refined third-order theory. The proposed method and developed numerical techniques have been validated on test problems for FG shell with rectangular planform. Furthermore, new results for shallow shells with a cut-out of the complex form are obtained. The effects of the gradient index, boundary conditions, thickness of core and face sheet layers, as well as elastic foundations on fundamental frequencies, are investigated. In addition, we demonstrate how the divergence of the results varies with the gradient index. The considered studied cases show that the natural frequencies depend on the foundation parameters, the thickness of the layers, boundary conditions, and the thickness arrangement. [ABSTRACT FROM AUTHOR]

In the present article, the vibration analysis of laminated composite plates strengthened with multi-walled carbon nanotubes (MWCNTs) is performed, employing the finite element method. Rule of mixtures and the Halpin–Tsai model are utilized to ascertain the elastic properties of the nanocomposite matrix. The effect of random orientation, the curved state, and the agglomeration of carbon nanotubes in the epoxy resin on mechanical properties is investigated. Classical lamination theory is also implemented to theoretically estimate the natural frequencies for validation purposes. Then, the natural frequencies of the laminated composite plates are determined by the numerical method for various parameters involved in the design process. The effect of MWCNTs' inclusion on the natural frequencies of the carbon nanotube-based laminated plate, taking into account the reformed micromechanical Halpin–Tsai model, is finally investigated. The outcomes of the research are in compliance with experimental values and theoretical evidence available in the bibliography. [ABSTRACT FROM AUTHOR]

The use of advance composite materials is increasing in various industrial applications such as renewable energy, transportation, medical devices, etc. As the demand for stability under high mechanical, thermal, electrical and combined loads is increasing, research is being focused on developing newer types of composites and developing analytical and numerical methods to study composite plates as well. The present work is aimed to provide a comprehensive review of research in the structural analysis of composite plates along-with research trends in the last 15 years. The article first presents the evolution of plate theories comparing their formulations, applicability and discusses some key papers, results and conclusions. Evolution of research from the equivalent shear deformation theories (ESL) such as first order theory and higher order theories based on various shape strain functions e.g., polynomial, trigonometric to layer-wise, zigzag and displacement potential theories is presented. The comparative analysis of various solution approaches is done based on a review of research work in the structural analysis of plates. This is followed by review of meshless analysis methods for composite materials highlighting problem domains where conventional finite element analysis (FEA) approach has limitations. This article also presents a discussion on the new methods of plate analysis such as region-by-region modeling, hierarchic modeling and mixed FE and neural network based modeling. An attempt has been done in this article to focus on research trends in the last 15 years. [ABSTRACT FROM AUTHOR]

The multiple delaminations at different interfaces and their interactions should be described simultaneously in an accurate analysis approach of composite laminates under the multi-physics loading, but it is not studied thoroughly in the existing research works. A thermo-mechanical cohesive zone model is proposed to investigate the thermo-mechanical progressive growth of multiple delaminations in composite laminated plates. The multiple delaminations are simulated by the extended layerwise method (XLWM), and their thermo-mechanical progressive damage characterization is described by a discrete damage zone model (DDZM). A traction–separation law is employed to account for the heat flux transfer and mechanical load transfer across the delamination front. Several numerical examples of double cantilever beams and laminated plates are carried out to verify the proposed model for the contact and degradation problems. The thermo-mechanical progressive growth mechanism is also investigated for the multiple delaminations in composite laminated plates [ABSTRACT FROM AUTHOR]

Laminated and segmented ceramic/polyurea composite plates were fabricated by coating bulk ceramic plate and bonding ceramic tablets with polyurea, respectively. Also, nacre-like ceramic/polyurea composite plates, which mimic the "brick-mortar" structure of nacre, were fabricated by layering segmented ceramic/polyurea composite plates in a staggered way and bonding them with polyurea. Drop-weight impact tests were performed for the composite plates and corresponding bulk ceramic plates of similar size. The failure mode and low velocity impact resistance of the composite plates and the bulk ceramic plates were compared. The effects of polyurea on low velocity impact resistance of ceramic were analyzed. It is found that the laminated composite plate has much higher failure energy than the bulk ceramic plate due to the buffering effect of polyurea coating. The segmented composite plate has better multiple-impact resistance than the bulk ceramic plate, due to the crack arrest effect of polyurea filler between ceramic tablets. The nacre-like composite plate has better multiple-impact resistance compared with the bulk ceramic plate of similar thickness, since it can stop cracks propagating in plane and along thickness. [ABSTRACT FROM AUTHOR]

The nonlinear dynamics of functionally graded graphene nanoplatelets (GPLs) reinforced composite plates are studied based on the first-order shear deformation theory (FSDT). The ordinary differential equation of the plate is derived by Hamilton principle and Galerkin method. The multi-scale method is used to analyze the jump forces. The effects of GPL distribution pattern, weight fraction, total number of layers and plate size on the resonance peak under sweep excitations, the maximal amplitude and attenuation time under impact loads, the jump force under harmonic excitations are quantitatively studied. The highest nonlinearity is found for the plate with uniform GPL distribution. The change of the number of layers has no effect on the nonlinearity but affects the natural frequency. The size of the plate and weight fraction of GPL both influence the natural frequency and nonlinearity, thereby influencing the dynamic characteristics. [ABSTRACT FROM AUTHOR]

We consider a partially hinged composite plate problem and we investigate qualitative properties, e.g. symmetry and monotonicity, of the eigenfunction corresponding to the density minimizing the first eigenvalue. The analysis is performed by showing related properties of the Green function of the operator and by applying polarization with respect to a fixed plane. As a by-product of the study, we obtain a Hopf type boundary lemma for the operator having its own theoretical interest. The statements are complemented by numerical results. [ABSTRACT FROM AUTHOR]

This article performs an analytical study on the damping vibration behavior of metal foam nanocomposite plate reinforced with graphene oxide powders (GOPs) in thermal environment. The GOPs are dispersed through the thickness of the structure according to three functionally graded (FG) and one uniform distribution patterns. The Halpin–Tsai micromechanical model is chosen for estimating the effective material properties of the structure having GOPs as reinforcement phase. Also, different porosity types are taken into account for the metal foam matrix. The plate is resting on a three-parameter viscoelastic medium containing Winkler and Pasternak layers in combination with viscous dampers which can dissipate the oscillation of the structure in some special cases. The Governing differential equations are derived via Hamilton's principle on the basis of refined higher order shear deformation theory and then solved with employing Galerkin solution method to obtain the natural frequencies of the proposed structure. Moreover, various boundary conditions (B.Cs) including simply supported, fully clamped and different combinations of these B.Cs are considered in this study. The influences and confrontation of different significant parameters such as GOPs' weight fraction, foundation parameters, aspect and side-to-thickness ratios, porosity coefficients, thermal environment, and FG patterns are investigated through various graphical and numerical results. Our findings declare that the dynamic behavior of the graphene oxide powder reinforced metal foam (GOPRMF) plate remarkably depends on these parameters. [ABSTRACT FROM AUTHOR]

We consider a family of variational problems on the equilibrium of a composite Kirchhoff–Love plate containing two flat rectilinear rigid inclusions, which are connected in a hinged manner. It is assumed that both inclusions are delaminated from an elastic matrix, thus forming an interfacial crack between the inclusions and the surrounding elastic media. Displacement boundary conditions of an inequality type are set on the crack faces that ensure a mutual nonpenetration of opposite crack faces. The problems of the family depend on a parameter specifying the coordinate of a connection point of the inclusions. For the considered family of problems, we formulate a new inverse problem of finding unknown coordinates of a hinge joint point. The continuity of solutions of the problems on this parameter is proved. The solvability of this inverse problem has been established. Using a passage to the limit, a qualitative connection between the problems for plates with flat and bulk hinged inclusions is shown. [ABSTRACT FROM AUTHOR]

The bearing capacity of a three-layer annular plate, loosely supported along the inner contour and clamped along the outer contour, is investigated. The face sides of the plate are coated with thin layers, and the middle layer is reinforced with fibers. The marix materials, fibers, and coatings are ideally plastic without strengthening, and their properties are different in tension and compression. It is shown that the plate is subdivided into five annular zones, in each of which different plastic states are realized. Static moment and kinematic deflection velocity fields are determined, equations for unknown radii separating different plastic zones, as well as equations for determining the support reaction and the ultimate load are derived. [ABSTRACT FROM AUTHOR]

In the current study, we proposed a method of differential temperature rolling with electromagnetic induction heating to prepare Ti/Al composite plates in a protective atmosphere to realize the homogeneous deformation of Ti/Al bonding rolling and improve the interfacial bonding strength of the composite plates. The temperature field required for homogeneous deformation rolling of titanium and aluminum was constructed using finite element simulation by adjusting the parameters of electromagnetic induction heating, which made a temperature difference of about 632 °C between titanium and aluminum, and the temperature of each plate was relatively uniform. The induction heating experiment was designed based on the finite element simulation, and the experiment verified the accuracy of the simulation results. The effects of rolling temperature and reduction rate of homogeneous deformation and bonding strength of Ti/Al composite plates were evaluated by rolling experiments. With the increase of rolling temperature and reduction rate of titanium, when the heating temperature of the Ti plate is 750–850 °C, and the reduction rate is 30%–48%, the reduction rate of Ti plate and Al plate gradually tend to be the same. When the titanium plate and aluminum plate temperature is 850 °C and 188 °C, respectively, with a rolling reduction rate of 48%, the deformation rate of Ti plate and Al plate is 46.8% and 48.6%, respectively. Moreover, the bonding strength of the composite plate reaches 77MPa. [ABSTRACT FROM AUTHOR]

A new model for predicting elastic flexural wave band gaps in periodic composite plate structures containing interconnected, star-shaped, transversely isotropic, magneto-electro-elastic (MEE) inclusions is developed using a microstructure-dependent Mindlin plate model. The Floquet–Bloch theorem and the plane wave expansion method for periodic media are employed to solve the non-classical wave equations and to determine the band gaps incorporating the microstructure effect. The current non-classical model recovers its classical elasticity-based counterpart as a special case if the microstructure effect is suppressed. A parametric study is performed to demonstrate the newly developed model. The numerical results of the study show that the microstructure effect on band gaps is large when the plate is very thin. In addition, the unit cell edge length, inclusion geometry and MEE coupling have significant effects on band gap sizes, and large band gaps can be generated by tailoring the controlling parameters. [ABSTRACT FROM AUTHOR]

This communication provides initial information and understanding of the manner in which a newly developed theoretical mechanism (Soldatos in Int J Solids Struct 202:217–225, 2020) is applied in specific boundary value problems met in polar linear elasticity of fibrous composites and thus enables the determination of the spherical part of the couple-stress tensor. In this context, it tests the applicability of the implied mechanism/method in the case that a rectangular plate reinforced by a single family of unidirectional fibres is subjected to pure bending. The problem solution is obtained for either non-polar or polar material behaviour, where fibres are considered perfectly flexible or resistant in bending, respectively, and provides clear evidence of the correctness of the principal argument that underpins the proposed method. Namely, that the general rotation field of the plate deformation differs from the fibre rotation field. That newly discovered method enables an extra energy term that emerges in the strain energy function of the fibrous composite plate to relate with the spherical part of the couple-stress tensor outside conventional equilibrium conventions. It thus leads to the determination of the spherical part of the couple-stress and its distribution throughout the plate body in a complete and comprehensive manner. [ABSTRACT FROM AUTHOR]

The initial-boundary value problem of thermoelastoplastic deformation of flexible reinforced plates is formulated. The possible weak resistance of such structures to the transverse shear is taken into account within the framework of Ambartsumyan theory. The geometric nonlinearity is taken into account in the Karman approximation. The temperature across the thickness of the plates is approximated by a square parabola. The solution of the 2D problem formulated is constructed by using an explicit numerical scheme. The dynamic thermoelastoplastic behavior of plane-cross and spatially reinforced fiberglass (GFRP) and metal composite plates bending under an action of air blast waves is studied. It is shown that replacing a plane scheme of reinforcement by a spatial one in GFRP structures allows a more efficient removal of the heat generated in them by the dissipation of mechanical energy. It is demonstrated that relatively thin composite plates heat up somewhat more than thick ones at the same maximum strain intensity in the binder. The heating level of reinforced structures is insignificant: the temperature increment is 1-4°C in GFRP plates and 7-10°C in metal composite plates. Therefore, the dynamic calculations of composite plates subjected to the actions of such loads as air blast waves can be carried out without taking into account the thermal action in the absence of additional heat sources of nonmechanical origin. [ABSTRACT FROM AUTHOR]

A new theoretical solution is presented to determine the stress distribution in a ten-layer simply-supported circular composite plate subjected to the low-velocity impact. The aim of the current study is the investigation of the dynamic analysis of the composite plate when a cylindrical impactor hits the top layer of the plate with an initial velocity of 1 m/s. The plate is made of two adhesive layers adhere two aluminum layers to a six-layer carbon-epoxy laminated plate. The classical non-adhesive elastic contact theory and Hunter's relationship are used to simulate the contact behavior in terms of time and contact radius. By using Hamilton's principle and Layerwise theory, thirty-two equations of motion are derived. Moreover, Johnson–Cook's criteria, the plastic simulation model, the normal stress–strain failure criterion theory were used for failure analysis of the aluminum, adhesive, and carbon-epoxy layers, respectively. The numerical method was used to solve the thirty-two differential equations of motion based on the finite difference method. Moreover, the relationship between stress and strain is re-written in the numerical code so that the failure criterion theories are satisfied. Moreover, according to the defined failure criterion for each layer, the damage is checked at the end of every time step. In addition, the damping behavior of the composite plate after applying the contact pressure caused by the impact was also investigated. The results showed that the impact resulted in residual stress in the plate. [ABSTRACT FROM AUTHOR]

In this work we investigate the buckling response of sandwich plates with a polymeric core and two face sheets reinforced by carbon nanotubes (CNTs). The problem is tackled analytically by means of a higher-order sandwich plate theory, where the face sheets are modeled according to a classical plate theory and modified strain gradient theory with temperature-dependent and moisture-dependent material properties. A Mori–Tanaka method is applied to determine the mechanical properties associated with the face sheets, while considering the agglomeration effect of CNTs. The governing equations of the problem are derived from the Hamilton's principle, whose solutions are recovered by means of a Navier–Stokes method. A thorough sensitivity study of the structural response to different parameters includes the agglomeration and volume fraction of CNTs, the material length scale parameter, the side and aspect ratios, together with the temperature variation and humidity conditions. The sandwich plates are assumed to be immersed within an orthotropic Pasternak foundation, whose normal and shear moduli can affect the overall buckling response of the structure. Numerical experiments show that sandwich plates with nanocomposite face sheets, resting on orthotropic elastic foundations, feature an increased stiffness, where the proposed formulation yields accurate results, due to the possibility of considering the variation in temperature, humidity and agglomeration of the reinforcing CNTs within the solution. [ABSTRACT FROM AUTHOR]

This article is concerned with the propagation of guided type-Lamb waves in a magneto-electro-elastic composite plate. As a numerical method, the ordinary differential equation with the Thomson Haskell parameterization of Stroh formalism is employed to determine the wave characteristics in the composite plate by imposing the traction-free boundary condition on the top and bottom surfaces. Multiple crossing appears in the dispersion curves between the symmetric and the antisymmetric Lamb modes, which makes the dispersion curves more complicated and interesting to study. We are trying in this research to find, are these modes really coupled and why? For that, a set of numerical results are presented like the dispersion curves, the non-dimensional frequency, bulk waves slowness curve as well as the mechanical displacement U1 and U3 versus the non-dimensional thickness. These results could be interesting for the analysis and design of new acoustic devices based on magneto-electro-elastic material as well as a good candidate for nondestructive testing technology. [ABSTRACT FROM AUTHOR]

Estimation of the effective homogenized properties is an essential step in the application of carbon nanotube (CNT)-reinforced composites. The difference between the experimental results and continuum-based homogenization schemes has motivated this work to present a modified Mori–Tanaka homogenization approach for CNT-reinforced nanocomposites. The agglomeration of CNT fibres in the matrix phase and slight weakening of the CNT–matrix interface are considered, which are incorporated in the effective homogenized properties of the nanocomposites using a two-parameter agglomeration model and interface spring-layer model, respectively. The nanotube fibres in the well-dispersed form are considered as cylindrical inclusions in the isotropic polymeric matrix. The bundled structure of CNTs is first modelled as cylindrical inclusions in the matrix and later as cumulative spherical inclusions in the hybrid matrix. Further, the effective material properties of nanocomposites are used to study the free vibration response of cylindrical panels reinforced with CNT fibres. Efficient higher-order shear and normal deformation theory is adopted, and fundamental natural frequencies are evaluated for a different set of agglomeration and interface weakening parameters using an analytical approach. The results show a significant reduction in the material stiffness as well as the natural frequency with increasing degree of agglomeration. At the same time, a slightly weakened interface is found less severe for stiffness reduction. An analysis of straight aligned CNTs highlighted their larger vulnerability to agglomeration than randomly distributed CNTs in the matrix. [ABSTRACT FROM AUTHOR]

We derive here a fundamental solution for the harmonic vibration of thick asymmetrically laminated composite plates. The kinematics of the plate is based on Reddy's third-order shear deformation theory (J Appl Mech 51:745–752, 1984). The fundamental solution is derived via the Fourier transform, and its final form is given in terms of definite integrals, which are evaluated numerically. All spatial singularities can be obtained explicitly, which makes the fundamental solution suitable for a boundary element method implementation. [ABSTRACT FROM AUTHOR]

The subject of the contribution is an investigation of elastic composite plates with a microperiodic structure along the plate's midsurface. The computational models of the plates are largely based on the homogenization procedures leading to equations with constant coefficients. However, the homogenization theories neglect the microstructure length-scale effect on the plate's dynamic behaviour. The objective of this research is to formulate and investigate a refined theory of the composite plates under consideration, which would describe the microdynamic plate behaviour caused by the microstructure. The possible applications of the proposed theory are shown by an example. [ABSTRACT FROM AUTHOR]

Delamination is the principal mode of failure of laminated composites. It is caused by the rupture of the fiber–matrix interface and results in the separation of the layers. This failure is induced by interlaminate tension and shear that is developed due to a variety of factors such as fatigue. Composites are known for excellent structural performance, which can be significantly affected by delamination. Such damages are not always visible on the surface and can lead to sudden catastrophic failures. To ensure a structural performance and integrity, accurate methods to monitor damages are required. This work presents a methodology for damage detection and identification on laminated composite plates using artificial neural networks fed with modal data obtained by finite element analysis. The proposed neural network to quantify damage severity achieved up to 95% success rate. A comparative study was done to evaluate the effect of boundary conditions on damage location. With the comparative study results, another neural network was proposed to locate damage position, achieving excellent results by successfully locating or by significantly reducing the search area. Both proposed ANNs use only frequency variation values as inputs, an easily obtainable quantity that requires few equipment to be acquired. The obtained results from these numerical examples indicate that the proposed approach can detect true damage locations and estimate damage magnitudes with satisfactory accuracy for this particular geometry, even under high measurement noise. [ABSTRACT FROM AUTHOR]

In this article, the free vibration response of sandwich plates with porous electro-magneto-elastic functionally graded (MEE-FG) materials as face sheets and functionally graded carbon nanotube-reinforced composites (FG-CNTRC) as core is investigated. To this end, four-variable shear deformation refined plate theory is exploited. The properties of functionally graded material plate are assumed to vary along the thickness direction of face sheets according to modified power-law expression. Furthermore, properties of FG-CNTRC layer are proposed via a mixture rule. Hamilton's principle with a four-variable tangential–exponential refined theory is used to obtain the governing equations and boundary conditions of plate. An analytical solution approach is utilized to get the natural frequencies of embedded porous FG plate with FG-CNTRC core subjected to magneto-electrical field. A parametric study is led to fulfill the effects of porosity parameter, external magnetic potential, external electric voltage, types of FG-CNTRC, and different boundary conditions on dimensionless frequencies of porous MEE-FG sandwich plate. It is noteworthy that the numerical consequences can serve as benchmarks for future investigations for this type of structures with porous mediums. [ABSTRACT FROM AUTHOR]

This study proposes a new plate formulation based on a generalized layerwise theory in the isogeometric analysis (IGA) framework to investigate the bending and free vibration behavior of a laminated composite plate. All degrees of freedom in the isogeometric formulation are only associated with the displacements (i.e., rotation-free). In IGA, NURBS functions are used both to construct the geometry and to approximate the field variables. Merits of utilizing IGA include: the exact geometrical description, high accuracy and efficiancy, higher-order smoothness. The displacement-based layerwise theory assumes an individual displacement field expansion inside each layer, and the transverse displacement component is regarded to be C 0 -continuous at the layer interfaces, thus yielding a more precise description of the stress states. The C 0 continuity enforcement across the thickness in the present formulation is easily implemented by virtue of the knot insertion technique of IGA. The capability of the present isogeometric layerwise formulation in analyzing the static and dynamic responses is evidenced by conducting some numerical tests available in the open literature and comparing the computed outcomes with the reference data. [ABSTRACT FROM AUTHOR]

This study presents the dynamic response of an eight-noded composite plate under earthquake excitation. Koyna earthquake excitation frequency is considered for the present study. Central displacement and stresses at various positions are studied extensively. Variation in response under different boundary conditions and varying geometric conditions are presented. The ply angle in a lamina and the number of layers in a plate are also varied to observe their effect on displacement and stress. In almost all the cases, 45° lamination shows maximum displacement response, whereas 0°/90° lamination scheme always shows maximum normal stress values. On the other hand, inplane shear gives maximum response whenever a − 45° layer is present. The effect of plan dimension on displacement is also presented here. The displacement response is maximum when the plate becomes square for both cross- and angle-ply laminations. The displacement response with change in total thickness of the plate is presented in this article. The response increases drastically as the plate becomes thinner for angle and cross-ply laminations. The plate becomes unstable as the side to thickness ratio increases beyond 50. The variation of stresses for cross- and angle-ply laminated plates across their layers is reported here with different boundary conditions. A very important observation made through this comparison as a 45° clamped laminated plate should be designed under transverse shear stress, whereas the simply supported plate should be designed under inplane shear stress. [ABSTRACT FROM AUTHOR]

The thermal buckling and post-buckling of geometrically perfect and imperfect hybrid laminated composite plates reinforced with shape memory alloys (SMA) subjected to a uniform thermal loading are investigated by a semi-analytical finite strip method. In this method, because of applying trigonometric functions, the energy integrations can be computed analytically. The first-order shear deformation theory in conjunction with von Karman nonlinear strain–displacement formulation is implemented. The solution procedure is based on minimization of the total potential energy and solving the eigenvalue problem or a set of nonlinear equations by using an iterative Newton–Raphson method for linear buckling and post-buckling analysis, respectively. By using 1-D simplified Brinson's model, the effect of SMA fibers on thermal buckling and post-buckling of composite plates with various boundary conditions is studied. [ABSTRACT FROM AUTHOR]

In this study, natural frequencies and vibrational mode shapes of variable stiffness composite skewed plates are optimized applying a genetic algorithm. The variable stiffness behavior is obtained by altering the fiber angles continuously according to two selected curvilinear fıber path functions in the composite laminates. Fundamental frequency and related mode shapes of the plates are optimized for two different fiber path functions using the structural model obtained based on the virtual work principle. A three-layer composite skewed plate with four types of boundary conditions and different plate geometries is considered as case study in this research. Diverse sweptback angles as well as different aspect ratios are considered as various plate geometries. The present study aims to calculate the best fiber path with maximized fundamental frequency or in-plane strengths for a composite skewed plate. The generalized differential quadrature method of solution is employed to solve the governing equations of motion. Moreover, the linear kinematic strain assumptions are used, and the first-order shear deformation theory is employed to generalize the formulation for the case of moderately thick plates including transverse shear effects. Numerical results demonstrate the effect of the fiber angles, boundary conditions, and diverse geometries on the natural frequencies of the composite plate. The optimal fiber angles of each layer are presented for the above cases in free vibration analysis. It is verified that the application of optimized curvilinear fibers instead of the traditional straight fibers introduces a higher degree of flexibility, which can be used to adjust frequencies and mode shapes. [ABSTRACT FROM AUTHOR]

An efficient method is developed to investigate the vibration and stability of moving plates immersed in fluid by applying the Kirchhoff plate theory and finite element method. The fluid is considered as an ideal fluid and is described with Bernoulli's equation and the linear potential flow theory. Hamilton's principle is used to acquire the dynamic equations of the immersed moving plate. The mass matrix, stiffness matrix, and gyroscopic inertia matrix are determined by the exact analytical integration. The numerical results show that the fundamental natural frequency of the submersed moving plates gradually decreases to zero with an increase in the axial speed, and consequently, the coupling phenomenon occurs between the first- and second-order modes. It is also found that the natural frequency of the submersed moving plates reduces with an increase in the fluid density or the immersion level. Moreover, the natural frequency will drop obviously if the plate is located near the rigid wall. In addition, the developed method has been verified in comparison with available results for special cases. [ABSTRACT FROM AUTHOR]

An analytical answer to the buckling problem of a composite plate consisted of multi-scale hybrid nanocomposites is presented here for the first time. In other words, the constituent material of the structure is made of an epoxy matrix which is reinforced by both macro- and nanosize reinforcements, namely, carbon fiber (CF) and carbon nanotube (CNT). The effective material properties such as Young's modulus or density are derived utilizing a micromechanical scheme incorporated with the Halpin–Tsai model. To present a more realistic problem, the plate is placed on a two-parameter elastic substrate. Then, on the basis of an energy-based Hamiltonian approach, the equations of motion are derived using the classical theory of plates. Finally, the governing equations are solved analytically to obtain the critical buckling load of the system. Afterward, the normalized form of the results is presented to emphasize the impact of each parameter on the dimensionless buckling load of composite plates. It is worth mentioning that the effects of various boundary conditions are covered, too. To show the efficiency of presented modeling, the results of this article are compared to those of former attempts. [ABSTRACT FROM AUTHOR]

The grain uniformity of a 316L/EH40 composite plate during multipass forming was studied by numerical simulation and hot rolling tests. In view of the total fixed deformation with a different number of passes, grain size variations on the surface, in the center, and at the interface of the base layer, and those on the surface and at the interface of the clad layer after rolling were simulated and analyzed. The rolling schedule was established to meet the adequate uniformity level of the base and clad layers. The most effective process was verified by the vacuum hot rolling test of a four-layer symmetrical billet. The metallographic images were taken in different locations of the composite plate, and the grain sizes in the images were measured by the cut-point method. Experimental results were compared with simulation data, demonstrating their reliability; the error between them was maintained within 5.5%. [ABSTRACT FROM AUTHOR]

This work aims to explore optimal design and control of thermal buckling for composite laminates with piezoelectric fiber reinforced composite (PFRC) actuators. Four-variable trigonometric shear deformation theory without introduction of a shear correction factor is used in the structural modeling. The high accuracy of the present approach is examined by analyzing the critical buckling temperature and natural frequency compared with references results. A temperature feedback control approach is proposed in designing the controller. Taking fiber angle as the optimization design variable, layerwise optimization approach (LOA) is applied to maximize critical buckling temperature of piezolaminated plate and a set of stacking sequences are obtained. The resulting analysis demonstrates that the proposed control approach can clearly increase the critical buckling temperature of piezo-laminated plates. The optimization process developed is useful in devising stacking sequences for the piezo-laminated structures in thermal environments. [ABSTRACT FROM AUTHOR]

Grid structures are among the most lightweight elements for stiffening the plates and shells or as self-sufficient structures. There are different known grid patterns, which are composed of variable numbers of parallel ribs. Selecting an optimum pattern and geometries for a grid to achieve the minimum weight and maximum load-bearing capacity is a challenging procedure for designers. In the current study, a variable ribs model (VRM) is proposed to find the optimum architecture of a grid plate. Therefore, using a genetic algorithm process, a multi-objective optimization is implemented to maximize the axial or shear buckling loads at a minimum possible weight of a grid structure. Eleven geometrical parameters including thickness, width, and the number of ribs as well as the orientation of the grid plate are considered the design variables. The multi-objective optimization is carried out employing the ε-constraint method. The buckling loads are obtained based on the first-order shear deformation plate theory using the Ritz method. [ABSTRACT FROM AUTHOR]

In the present study, a recently developed non-polynomial zigzag theory by the authors is assessed for the buckling analysis of the laminated composite and sandwich plates. This theory assumes a nonlinear distribution for the transverse shear stresses. The model satisfies the transverse shear stress free boundary conditions at top and bottom surfaces of the laminate obviating the need for a shear correction factor. An efficient C0 continuous isoparametric serendipity element is employed for the discretization of plate structure for the assessment of buckling responses. The Gauss quadrature rule with reduced integration scheme for thin laminate and full integration rule for thick laminate are implemented in the analysis. Some representative results are obtained on buckling analysis covering different features of laminated composite and sandwich structures such as modular ratios, aspect ratios, loading conditions, boundary conditions and span to thickness ratios. The evaluated results are compared with results available in the literature to ensure the efficacy of the present theory. The excellent agreement of the evaluated results with the three-dimensional elasticity results concludes that the presented models are not only accurate but also efficient. [ABSTRACT FROM AUTHOR]

In this work, we have investigated the nonlinear instability behavior of a thin laminated composite circular plate subjected to a tensile periodic load. A nonlinear system with quadratic and cubic nonlinear terms, referred to the effect of large deflection, is obtained. The method of multiple time scales is used to obtain periodic solutions for the second- and third-order systems, which directly leads to the solvability conditions of the two orders including the nonlinearity terms. Different cases of resonance with the instability criteria are taken into account. For the numerical application, the effect of the tensile periodic load was studied on a plate of graphite fabric-carbon material. [ABSTRACT FROM AUTHOR]

A method for constructing nonstationary vibration equations for electro-viscoelastic composite plates with their active damping is described. The problem is solved in an integral Fourier transform frequency space. To construct a multilayer plate model, a discrete structural approach was used, i.e., the plate is divided through the thickness into computational layers, within which the displacements and electric potentials are approximated by means of quadratic Lagrange polynomials. At the edges of the plate, the Navier conditions are met. The semi-analytical nonstationary vibration equations are derived by means of the variational convolutional Lagrange equation. To represent them in a frequency space, a direct integral Fourier transform is used, which makes it possible to use experimentally determined frequency-dependent complex characteristics directly in calculations of nonstationary vibrations of plates without additional transformations of integral physical relations. Solutions of the problem of active damping of nonstationary vibrations for the frequency images of displacements and electric potentials have been found, their convergence is analyzed. The procedure has been evaluated by analyzing the active damping of nonstationary vibrations of a three-layer edge-hinged square plate under the action of a blast wave impulse. The middle layer is made of a composite material, and the outer electro-viscoelastic layers act as a sensor and an actuator. The active damping of vibrations is provided by connecting these layers of the plate into a negative feedback circuit with the proportional-differential control law. The viscoelastic and electro-viscoelastic characteristics of the materials are taken into account by means of complex elastic, dielectric and piezoelectric moduli. The results of analyzing the active damping of nonstationary vibrations of a plate are presented. The values of the proportional and differential components of the controller as characteristics of this damping were chosen taking into account the permissible electric field strength of the actuator. The research results for the case of passive damping of vibrations are also given for comparison. The dependences of the decrement of plate vibrations on the differential component of the controller and of the maximum plate deflection on the reinforcement angle of the middle layer material have been established. The optimum reinforcement angle according to the minimum plate deflection criterion has been determined, which provides an increase in the efficiency of active damping of nonstationary vibrations of the plate owing to an increase in the differential component of the controller. [ABSTRACT FROM AUTHOR]

This study aims to examine the effect of the diameter, number, and location of the circular cutout on the free vibration response and buckling loads of the laminated composites. Eigen-buckling and free vibrations analyses are performed for the laminated composite plates by using the finite element software ANSYS. Numerical results obtained by the finite element method are compared to the experimental ones. In the numerical analyses, the effect of the delamination around the cutout on the buckling load and the natural frequency is also examined. The critical buckling load and first natural frequency values obtained by both numerical and experimental studies are used to create a prediction model using the artificial neural networks. The Levenberg–Marquardt backpropagation algorithm is used as the training method. It is observed that both the number and location of the cutout affect the critical buckling load and first natural frequency values. Numerical and experimental results are presented together with the ANN prediction results. [ABSTRACT FROM AUTHOR]

Up to now, the notched strength of a composite laminate containing an inclined elliptical hole at its center has not yet been predicted by researchers due to the absence of an appropriate failure criterion and an analytical solution. In this study, this problem is tackled by using a finite-element-based procedure, developed previously by the authors, together with a modified point stress criterion. The predicted notched strengths of composite plates containing a central inclined elliptical hole agreed well with experimental results. [ABSTRACT FROM AUTHOR]

We obtain here a new fundamental solution for the harmonic vibration of asymmetric, laminated, anisotropic plates. The fundamental solution is derived via the Fourier transform and its final form is given in terms of definite integrals, which are evaluated numerically. Moreover, we present some of the higher order derivatives of the solution and their explicit spatial singularities, which are necessary for a boundary element method implementation. [ABSTRACT FROM AUTHOR]

A conceptually simple route has been designed for the preparation of flexible plate by utilization of biodegradable cellophane film through addition of NaHCO3 powder into structure of Polypyrrole-Multiwalled carbon nanotube-Cellophane (PMC) composite and then by chemical treatment in acidic solution. A homogeneous conductive-porous structure was formed as a result of release of NaHCO3 from the composite bulk in acidic solution as well as CO2 (g) evolution. The porous PMC plate exhibited a specific capacitance of 244 mF cm−2 at a current density of 0.5 mA cm−2 and favorite rate capability. The assembled symmetric supercapacitor device showed a high areal capacitance of 309 mF cm−2 at 2.5 mA cm−2, excellent flexibility and a long cycle lifetime (89% capacitance retention after 5000 cycles). The strategy presented in this work opens a new door for environmentally friendly preparation of flexible-biodegradable supercapacitor devices with high mechanical strength. [ABSTRACT FROM AUTHOR]

A simple and effective approach based on refined plate theory (RPT) is proposed to study the static and free vibration characteristics of functionally graded CNT-reinforced composite (FG-CNTRC) plates. Compared to traditional higher order shear deformation theories (HSDTs), the proposed method shows more efficient for FG-CNTRC plates analysis. To solve the C1-continuity requirement of the RPT, we used isogeometric analysis (IGA) to approximate the displacement field, which shows more advantages than the FEA, since it can construct higher-order elements without additional variables. This is an advantage for plate structural analysis because more variables make the calculation cumbersome. Finally, four types of FG-CNTRC plates were investigated and the results show the accuracy and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

A higher-order shear deformation theory is utilized to discuss the vibration of a laminated composite plate containing four magnetostrictive layers based on Pasternak's foundations in the current article. Hamilton's principle is used to derive the governing dynamic equations related to the vibration of present smart structure under velocity feedback control with constant gain distributed. Navier's approach is utilized to give a solution of simply supported laminated composite plates. Effects of all material properties, modes, thickness ratio, aspect ratio, lamination schemes, magnitude of the feedback parameter, the elastic foundations parameters and the thickness, location and number of magnetostrictive layers, on the vibration damping characteristics of the system are investigated and extensively discussed. Findings of the damping coefficients, damped natural frequencies, damping ratio, vibration time and maximum deflection for some different laminates are computed. The influences of studied parameters on the vibration suppression of plates are illustrated graphically. The results indicate increasing of smart layers structures tends to more control of structure and elastic foundations can contribute the stability of the plate significantly. [ABSTRACT FROM AUTHOR]

This article presents the free vibration frequencies of composite plates reinforced with single-walled carbon nanotubes by using a refined simplified two-variable nth-higher-order theory. Four kinds of distribution of uniaxially aligned reinforcement material are presented. The most famous one is the uniform; in addition, three types of functionally graded distributions of carbon nanotubes in the through-thickness direction of the plates are investigated. The effective physical properties of composite media are given according to a refined rule of mixtures approach that contains the efficiency parameters. Exact closed-form formulation based on a refined simplified two-variable nth-higher-order plate theory that can be adapted to the vibration of such plates is investigated. Accuracy of presented approach is validated by comparing its results with those given by other investigators [ABSTRACT FROM AUTHOR]