Multilayer Sandwich Structure Research Articles

Analysis of laminated composites and sandwich structures by variable-kinematic MITC9 plate elements

In this paper, classical as well as various refined plate finite elements for the analysis of laminates and sandwich structures are discussed. The attention is particularly focussed on a new variable-kinematic plate element. According to the proposed modelling approach, the plate kinematics can vary through the thickness within the same finite element. Therefore, refined approximations and layer-wise descriptions of the primary mechanical variables can be adopted in selected portions of the structures that require a more accurate analysis. The variable-kinematic model is implemented in the framework of the Carrera unified formulation, which is a hierarchical approach allowing for the straightforward implementation of the theories of structures. In particular, Legendre-like polynomial expansions are adopted to approximate the through-the-thickness unknowns and develop equivalent single layer, layer-wise, as well as variable-kinematic theories. In this paper, the principle of virtual displacements is used to derive the governing equations of the generic plate theory and a mixed interpolation of tensorial components technique is employed to avoid locking phenomena. Various problems are addressed in order to validate and assess the proposed formulation, including multi-layer plates and sandwich structures subjected to different loadings and boundary conditions. The results are compared with those from the elasticity theory given in the literature and from layer-wise solutions. The discussion clearly underlines the enhanced capabilities of the proposed variable-kinematic mixed interpolation of tensorial component plate elements, which allows, if used properly, to obtain formally correct solutions in critical areas of the structure with a considerable reduction of the computational costs with respect to more complex, full layer-wise models. This aspect results particularly advantageous in problems where localized phenomena within complex structures play a major role.

Synthesis of a hybrid zinc hydroxystannate/reduction graphene oxide as a flame retardant and smoke suppressant of epoxy resin

The zinc hydroxystannate/reduction graphene oxide (ZHS/RGO) hybrid was successfully prepared through the hydrothermal route, and its structure, composition and thermal properties were confirmed by XRD, FTIR, XPS, SEM, TEM, Raman spectra, and TG. ZHS/RGO hybrid is multilayer sandwich structure by morphological characterization. ZHS/RGO was applied to reduce fire hazards of epoxy (EP) as a flame retardant and smoke suppressant. The incorporation of 3.0 mass% ZHS/RGO provided fire-retardant properties to epoxy resin, testified by the results of cone calorimetry. The results indicated that ZHS/RGO can suppress the formation of smoke and toxic carbon monoxide as well as enhance the flame retardancy of the EP composites. The heat release rate, total heat release, smoke production rate, and total smoke production of EP-ZHS/RGO were greatly decreased compared with the pure EP. During the combustion process, ZHS/RGO may exhibit gaseous phase effect and condensed phase effect.

Plastic analysis of multilayer sandwich beams with metal foam cores

The plastic behavior of fully clamped multilayer sandwich beams with metal foam cores is investigated. A plastic yield criterion for multilayer sandwich structures with metal foam cores is proposed. Analytical solutions are derived for the multilayer sandwich beams transversely loaded by a flat punch considering the interaction of bending and stretching induced by large deflections. Numerical calculations are carried out, and good agreement is achieved between the analytical solutions and numerical results. The effects of the multilayer, punch size and core strength are discussed. Using the analytical formulae, optimal design charts are constructed to maximize the load-carrying capacity of the multilayer sandwich beams for a given mass. It is demonstrated that the present analytical model can reasonably predict the post-yield behavior of the multilayer sandwich beams with metal foam cores.

Exact and approximate shell geometry in the free vibration analysis of one-layered and multilayered structures

The present paper proposes the study of the approximation of the curvature terms in the three-dimensional (3D) equilibrium shell equations used for the free vibration analysis of one-layered and multilayered composite and sandwich structures. 3D equilibrium equations written for spherical shells degenerate into 3D equilibrium equations for cylindrical shells and plates considering one of the two radii of curvature or both as infinite, respectively. The approximation of curvature terms has been introduced in 3D equilibrium equations in order to study its effects in terms of frequency values. This study has been conducted by means of a comparison between 3D equilibrium equation results and 3D approximate curvature equilibrium equation results. These effects depend on the thickness and curvature of the considered structure, on the embedded material and lamination sequence, on the frequency order and vibration mode. The 3D equations have been considered in exact form for simply supported structures. The system of partial differential equations has been solved by means of the exponential matrix method. A layer-wise approach is considered for multilayered structures. The approximation of the curvature has been introduced in the 3D equilibrium shell equations and not in the interlaminar continuity conditions and in the top and bottom boundary and loading conditions. This choice has been made for numerical reasons. The investigation of curvature approximation effects in the equilibrium equations allows an exhaustive analysis to understand the importance of curvature terms in the free vibration problems.

Approaching Roll-to-Roll Fluidic Self-Assembly: Relevant Parameters, Machine Design, and Applications

This paper presents the implementation of an automated roll-to-roll fluidic self-assembly system based on the surface tension driven self-assembly with applications in the field of macroelectronics. The reported system incorporates automated agitation, web motion, component dispensing, and recycling. The process enables the assembly and electrical connection of semiconductor dies/chips in a continuous and parallel fashion over wide area substrates. At present, the method achieves an assembly rate of 15000 chips per hour and an assembly yield exceeding 99%, testing assembly of standard square-shaped dies, 300-1000 μm size. Scaling the system to any desired throughput is possible due to the parallel manner of selfassembly. The identification and the modeling of the relationship between process parameters and forces have been studied and experimentally verified by testing the effect of the web angle, agitation on assembly, and detachment rates. As an application, we demonstrate the realization of a solid-state lighting module. This particular application requires the assembly of a conductive multilayer sandwich structure, which is achieved by combining the introduced assembly process with a novel lamination step.

Structural design of iron–aluminum multilayer composite for geomagnetic field shielding

Two types of multilayer structure with high magnetic shield effectiveness are presented experimentally and theoretically. Aluminized coatings were deposited on the two sides of pure iron substrate by using hot dip aluminizing. After diffusion heat treatment, iron–aluminum multilayer composite was obtained with Fe–Al alloy/Fe/Fe–Al alloy structure, which could be seen as three permeable magnetic layers in macro scale. A spacer was inserted between a couple of iron–aluminum multilayer composite plates to form sandwich structure with permeable magnetic layer/non-magnetizer/permeable magnetic layer structure. The results indicate that good bonding exists between the pure iron substrate and the Fe–Al reaction layer with a clean and flat interface after heat treatment. Geomagnetic shielding factor (SF) of iron–aluminum multilayer composite arrives at 25.5, which is about 7.7 times of pure iron substrate. The value of SF for sandwich structure can reach 210, about 8.2 times as high as for the multilayer composite magnetizer. Mathematical equation of SF for multilayer composite and sandwich structure are derived according to magnetic reluctance and magnetic circuit method. The three permeable magnetic layers in multilayer composite shunt the magnetic field in parallel and the sandwich structure can shunt magnetic field twice to achieve excellent shielding effectiveness. The theoretical computational results of SF agree well with the experimental values.

Large-Area, Low-Cost Infrared Metamaterial Fabrication Via Pulsed Laser Deposition with Metallic Mesh as a Shadow Mask

Metamaterials are artificial periodic structures with negative permittivity and permeability. Several interesting properties can be obtained in metamaterials, such as negative index behavior, which can be used for building perfect lenses, cloaking, antennas, etc. As the metamaterial’s properties are determined by its structure, the key challenge is to reduce the fabrication cost of the periodic structure on the micrometer or nanometer scale for realistic applications. In this paper, we experimentally demonstrate a new one-step method for the fabrication of a large-area infrared metamaterial at extremely low cost. A metallic mesh is used as a shadow mask during the pulsed laser deposition (PLD) process to fabricate a FeNi/SiC/FeNi multilayer sandwich structure on Si substrate (cm2 level). The sample shows a strong absorption peak in the infrared frequency range, and the absorption intensity changes with the sample’s geometry.

Reactive Ion-Assisted Deposition of Cerium Oxide Hole-Blocking Contact for Leakage-Current Suppression in an Amorphous Selenium Multilayer Structure

Cerium oxide has proven as a proper hole-blocking contact in multilayer amorphous selenium X-ray detectors to reduce leakage current by limiting hole injection. To further improve its blocking properties, one of the key factors is to prepare a thin layer of cerium oxide with full oxidation. In this paper, a cerium oxide thin film was deposited by reactive oxygen ion assisted e-beam evaporation that utilized an independent oxygen ion source to create ionized oxygen, allowing for a refined oxidation control without requiring high process temperatures. Compared with films obtained without ion-beam assistance, oxygen ion assisted deposition enhanced the refractive index of oxide film from ~1.8 to 2.2 at a wavelength of 550 nm and improved the electrical resistivity from ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> Qcm. X-ray photoelectron spectroscopy and X-ray diffraction measurements further gave insights into the stoichiometry and the crystal structures. To investigate blocking effectiveness, multilayer selenium sandwich structures with and without the cerium oxide blocking contact were fabricated and the leakage current was evaluated.

In Situ Fabrication of Low-Friction Sandwich Sheets Through Functionalized Graphene Crosslinked by Ionic Liquids

Graphene is considered a wonder material for fundamental research and industrial application, whereas its poor dispersibility and incompatibility in lubricants have impeded the application for solving lubrication problems. Here, in situ fabrication of effectively functionalized graphene sheets was developed through a moderate electrochemical method for exfoliating graphite into graphene sheets in ionic liquids solution. The as-fabricated graphene sheets with the charged groups of ionic liquids (ILs) could be self-assembled together to form the multilayer sandwich structure through the electrostatic interaction. Self-assembly multilayer graphene (MLG) exhibits so high-density coverage of functional groups that some amorphous regions are formed on the graphene basal plane, which significantly improves its dispersibility and stability in ILs lubricant. Moreover, the functionalized MLG as a novel lubricant additive greatly enhances the friction-reducing and antiwear abilities for the contact of steel/steel (friction coefficient and wear volume lubricated by ILs with MLG at applied load of 200 N and 150 °C were reduced by up to 55.9 and 84.2 %, and under high vacuum were reduced by up to 36 and 94.3 % with pure ILs as a comparison, respectively), which is attributed to the synergies of ILs and MLG because ILs with functionalized MLG can form the physical adsorptive film and tribo-chemical reaction film on the rubbing surface during friction process.

High specific capacity retention of graphene/silicon nanosized sandwich structure fabricated by continuous electron beam evaporation as anode for lithium-ion batteries

A graphene/silicon (Si) multilayer sandwich structures are fabricated using electron beam (EB) deposition without air exposure. The graphene and Si thin films are formed on Cu current correctors through a continuous process in high-vacuum EB chamber. Synthesized graphene should be suggested to the stacked multiple layer from Raman analysis. The fabricated multilayer films are used as anodes. In the beginning, the half-cell, which used a seven-layer of each thickness 50-nm graphene and Si film, exhibits good specific capacity retention over 1000mAhg−1 after 30 charge/discharge cycles. The capacity value changed with the number of graphene and Si layers. In this study, the number of layers that exhibited optimal properties is seven. Morphological investigation showed a fine layer-by-layer structure. The relationship between different thicknesses of graphene and Si is investigated at 7L. A 100-nm thickness exhibited optimal properties. Finally, the optimal 7L and 100-nm thick graphene/Si exhibited high discharge capacitance >1600mAhg−1 at a current density of 100mAg−1 after 30 cycles. Initial coulombic and reversible efficiencies exceed 84%. The capacity retention (30th/1st discharge value) at 100nm and 7L exceeds 90%. Finally, the soft package battery is assembled by combining the fabricated graphene and Si electrode as anode, LiCoO2 as cathode, separator and liquid electrolyte. It can be used for commercial light-emitting diode (LED) lighting even under bending status.

Microwave Absorbing Properties of Lightweight Nanocomposite/Honeycomb Sandwich Structures

Thin glass-fiber/epoxy-composite sheets filled with multiwalled carbon nanotubes (MWCNTs) are manufactured to make lightweight honeycomb sandwich microwave absorbers. A multilayered sandwich structure of thin nanocomposite sheets and honeycomb spacers have been also proposed and developed to work in a wide frequency range. The nanocomposite sheets are prepared from 0.5, 1.0, 1.5, 2.0, and 2.5 wt. % of MWCNTs. A commercially available simulation software computer simulation technology (CST) microwave studio was used for the designing and development of radar absorbing structure (RAS) composed of MWCNTs/glass-fiber/epoxy-composite sheets and honeycomb cores. The measurements of return loss (RL) from sandwich structures with 5 mm and 20 mm honeycomb cores in the Ku band (11–17 GHz) show that maximum RL is achieved at 11 GHz and 16 GHz, respectively. The stacking of three nanocomposite sheets and three 5 mm-thick honeycomb spacers produced a wide band microwave absorber with −10 dB RL over 9 GHz bandwidth.

Vibration Modeling of Multilayer Composite Structures with Viscoelastic Layers

This work deals with the vibration of orthotropic multilayer sandwich structures with viscoelastic core. A finite element model is derived from a classical zigzag model with shear deformation in the viscoelastic layer. The aim of the present work is to establish numerical models and develop numerical tools to design multilayer composites structures with high damping properties. To fulfill this purpose, a finite element model has been developed for vibration analysis of a sandwich plate (elastic orthotropic)/(viscoelastic orthotropic)/(elastic orthotropic). A numerical study from the variation of the damping properties of the structures was performed according to the faces materials fibers orientation.

Modeling of axial and shear stresses in multilayer sandwich beams with stiff core layers

In order to optimize the load-bearing behavior of sandwich structures and adapt it to specific requirements, their core may be composed of layers of different materials with tailored properties. These layers may consist not only of soft foam or honeycomb materials but also comprise stiff materials, e.g. timber, or even very stiff laminates in the case of fiber-reinforced polymer (FRP) materials. In this paper, new analytical models for predicting axial and shear stresses in multilayer sandwich structures composed of stiff core layers and intermediate laminates are presented. The models are based on new formulations for calculating the bending and shear stiffness of multilayer sandwiches. They have been validated by finite element modeling (FEM) and the results from four-point bending experiments on GFRP-balsa sandwich beams with complex core assembly. In contrast to existing models, e.g. the high-order sandwich panel theory (HSAPT), the new models are able to accurately predict axial and shear stresses in stiff cores and intermediate FRP laminate layers.

A Solution Processed Flexible Nanocomposite Electrode with Efficient Light Extraction for Organic Light Emitting Diodes

Highly efficient organic light emitting diodes (OLEDs) based on multiple layers of vapor evaporated small molecules, indium tin oxide transparent electrode, and glass substrate have been extensively investigated and are being commercialized. The light extraction from the exciton radiative decay is limited to less than 30% due to plasmonic quenching on the metallic cathode and the waveguide in the multi-layer sandwich structure. Here we report a flexible nanocomposite electrode comprising single-walled carbon nanotubes and silver nanowires stacked and embedded in the surface of a polymer substrate. Nanoparticles of barium strontium titanate are dispersed within the substrate to enhance light extraction efficiency. Green polymer OLED (PLEDs) fabricated on the nanocomposite electrode exhibit a maximum current efficiency of 118 cd/A at 10,000 cd/m2 with the calculated external quantum efficiency being 38.9%. The efficiencies of white PLEDs are 46.7 cd/A and 30.5%, respectively. The devices can be bent to 3 mm radius repeatedly without significant loss of electroluminescent performance. The nanocomposite electrode could pave the way to high-efficiency flexible OLEDs with simplified device structure and low fabrication cost.

Effect of Core Thickness and Intermediate Layers on Mechanical Properties of Polypropylene Honeycomb Multi-Layer Sandwich Structures

Abstract Sandwich structures are widely used in lightweight construction especially in aerospace industries because of their high specific strength and stiffness. This paper investigates the effect of core thickness and intermediate layers on the mechanical properties of a polypropylene honeycomb core/composite facing multilayer sandwich structure under three points bending. We developed a theoretical model which makes it possible to calculate the shear properties in multi-cores. The results obtained by this model are agreed with our experimental results, and the results obtained with bending test showed that the mechanical properties of the composite multilayer structures increase with core thickness and intermediate layers.

A Diblock-Diblock Copolymer Mixture under Parallel Wall Confinement

A cell dynamics simulation is performed for a diblock-diblock copolymers mixture confined between parallel walls. Much richer morphologies are observed in the mixture than in pure diblock copolymers. Multiple novel morphological transitions occur by changing the wall-block interaction and the distance between walls (confinement degree), and both perpendicular and parallel multilayered sandwich structures are obtained in the mixture.

Phase behaviors in a binary mixture of diblock copolymers confined between two parallel walls

The phase behaviors in a binary mixture of diblock copolymers confined between two parallel walls are investigated by using a cell dynamics simulation of the time-dependent Ginzburg—Landau theory. The morphological dependence of the wall-block interaction and the distance between walls (confinement degree) has been systematically studied, and the effect of repulsive interactions between different monomers is also discussed. It is interesting that multiple novel morphological transitions are observed by changing these factors, and various multilayered sandwich structures are formed in the mixture. Furthermore, the parametric dependence and physical reasons for the microdomain growth and orientational order transitions are discussed. From the simulation, we find that much richer morphologies can form in a binary mixture of diblock copolymers than those in a pure diblock copolymer. Our results provide an insight into the phase behaviors under parallel wall confinement and may provide guidance for experimentalists. This model system can also give a simple way to realize orientational order transition in soft materials through confinement.

Thermo-mechanical characteristics and stability boundaries of antenna structures in supersonic flows

In a supersonic airflow, a smart skin antenna model is analyzed to investigate the thermo-mechanical characteristics and stability boundaries of the structure. The skin is modeled as a multi-layer sandwich structure with a dielectric polymer. Especially, the polymer layer is embedded on the middle surface of the face sheets similar to the honeycomb core to perform the role of antenna or radar. In order to formulate the structural model including the geometric non-linearity, first-order shear deformation theory of plate and von Karman strain–displacement relations are adopted in this work. Also, aerodynamic pressure is obtained by the first-order piston theory for the aerodynamic. To get the numerical results, finite element method is used and Newton–Raphson iterative method is applied to solve the nonlinear equations of motion. For the validation of this work, present results are compared with previous data. And then, thermo-mechanical characteristics of the skin structures are fully discussed, especially. Additionally, effects of sizes and various shapes of dielectric layer relative to the enclosure layer are analyzed.

Finite element model for damping optimization of viscoelastic sandwich structures

In this work a simple and efficient finite element model is used for the damping optimization of multilayer sandwich plates, with a viscoelastic core sandwiched between elastic layers, including piezoelectric layers. The elastic layers are modeled using the classical plate theory and the core is modeled using Reddy’s third-order shear deformation theory. The finite element formulation is obtained by assembly of N “elements” through the thickness, using specific assumptions on the displacement continuity at the interfaces between layers. The free vibration response of damped multilayer sandwich structures is characterized by solving an eigenvalue problem to obtain the fundamental natural frequency and corresponding modal loss factor. The optimization is conducted in order to maximize the fundamental modal loss factor, using gradient based algorithms, and afterwards, considering steady state harmonic motion the analysis is conducted in time domain to obtain the structure response. The model is applied in the solution of some illustrative examples and the results are presented and discussed.

On the comparison of the polarisation behaviour of exchange-biased AF/F NiMn/Fe37Co48Hf15 bi-layer and multi-layer films with increased ferromagnetic cut-off frequencies

Antiferromagnetic/ferromagnetic (AF/F) NiMn/Fe37Co48Hf15 films were investigated with respect to their exchange bias, in-plane unidirectional anisotropy, polarisation and high frequency behaviour. After deposition, carried out by r.f. magnetron sputtering, the films were post-annealed for 4h at 300°C in a static magnetic field, in order to induce exchange-bias, which results in a unidirectional anisotropy. Dependent on the presence of a bi-layer or multi-layer sandwich structure the films show a different exchange-bias field–ferromagnetic inter-layer thickness behaviour with exchange-bias fields μ0⁎Heb between 2 and 10mT. The in-plane uniaxial (single film) or unidirectional anisotropy fields μ0*HUF were between 4 and 18mT. This results in a significant increase of the cut-off frequency in the GHz range in comparison to a single Fe37Co48Hf15 film, which is shown by frequency-dependent permeability plots. High damping in the imaginary part of the permeability, i.e., high resonance line broadening could be observed for films with high coercivity μ0*Hc of around 7mT in the easy axis of magnetisation.