Multilayer Sandwich Research Articles

A Broadband H-plane Printed Horn Antenna with Sandwich Substrate Structure for Millimeter-wave Applications

Antenna is a very important element and plays a key role in communication systems for radiating energy. Based on high data rate speed requirements and large volume multimedia applications, 3G, 4G and now 5G technologies have been introduced and implemented. This paper presents a low profile antenna with novel structure and large continuous bandwidth for 5G broadband and millimeter-wave wireless applications. It is an H-plane printed horn antenna with multi-layered sandwich substrate. There are two Rogers (RO3003(tm)) substrates that make a sandwich structure with eight stainless steel columns. The proposed antenna is expected to give an impedance bandwidth 20-45 GHz with S11 <-10dB and 8.64dBi gain at 28 GHz design frequency. ANSYS 18.2 HFSS simulator is used for designing and optimization of the profile antenna. A comparison between simulated and measured results confirms the validity of the proposed design.

Thermal decomposition of multilayer honeycomb core laminate sandwich composite panels in cone calorimeter apparatus – Effect of the top decomposed layer

Multilayer composite materials are frequently used in aircraft interiors. Even though they have high properties (such as physical, chemical and mechanical properties), their application is limited due to lack of knowledge of their decomposition process and on the interaction between different layers in fire. In the present work, two types of composites with 3 and 4 layers are studied. The fire characterization of multilayer composite is studied in 3 different phases using ISO-5660 cone calorimeter at two heat fluxes (35 and 50 kW.m−2). Phase-I mainly concentrates on the decomposition of single layer materials (paint, laminate and honeycomb) while in phase-II and phase-III, different assemblies are formed using a single layer material and studied in the same experimental configuration. In all the three phases, back surface temperatures of the materials or assemblies are measured and analyzed with different gas productions which allow to understand the dynamics of the decomposition process. The finding from the cone calorimeter study suggests that the ignition primarily depends on the top layer behavior of the composite. The permeability analysis on the top layer of the composite confirms that decomposed layer of paint offers more resistance to the volatile gases escaping from the composite. At the end of the study, thermal conductivity is determined and the ignition temperature of both the composite is determined.

Buckling of sandwich struts with a particular application in composite multi-layer glazing

Sandwich-like structures can significantly reduce the self-weight and size of load-bearing elements. However determining the flexural response of multi-layered sandwich structures is not a trivial task, particularly their buckling response. This study consists of novel theoretical work for extending Allen’s and Southwell’s buckling theories in order to develop a comprehensive model for the buckling response of multi-layered composite sandwich struts. The new model is applied here to predict the buckling of composite glazing, made of glass face-sheets separated by and adhesively-bonded to inner core profiles, thereby reducing the weight and thickness of conventional glazing panels. Existing physical test data on composite glazing is currently limited to flexural responses under out-of-plane loading and no published data exists for in-plane loading. Therefore three composite glazing struts were fabricated and tested in axial compression in this study, and the test data is used to validate the new model. As expected, failure of the composite glazing struts originated at regions of high shear stress close to end supports. It was found that the critical buckling loads predicted by the new analytical model are within 4% of those obtained from Southwell plots of the experimental data. Similarly, the new model provides a very good fit to the load–deflection and the load-stress responses from the experiments. This is a significant improvement on traditional Euler-based layered or monolithic models that, for this particular application, produce an underestimation of 90% and an overestimation of 40% of the critical buckling loads, respectively, and would therefore result in uneconomic or unsafe designs, respectively.

A 2020 view of tension-based cortical morphogenesis

Mechanical tension along the length of axons, dendrites, and glial processes has been proposed as a major contributor to morphogenesis throughout the nervous system [D. C. Van Essen, Nature 385, 313-318 (1997)]. Tension-based morphogenesis (TBM) is a conceptually simple and general hypothesis based on physical forces that help shape all living things. Moreover, if each axon and dendrite strive to shorten while preserving connectivity, aggregate wiring length would remain low. TBM can explain key aspects of how the cerebral and cerebellar cortices remain thin, expand in surface area, and acquire their distinctive folds. This article reviews progress since 1997 relevant to TBM and other candidate morphogenetic mechanisms. At a cellular level, studies of diverse cell types in vitro and in vivo demonstrate that tension plays a major role in many developmental events. At a tissue level, I propose a differential expansion sandwich plus (DES+) revision to the original TBM model for cerebral cortical expansion and folding. It invokes tangential tension and "sulcal zipping" forces along the outer cortical margin as well as tension in the white matter core, together competing against radially biased tension in the cortical gray matter. Evidence for and against the DES+ model is discussed, and experiments are proposed to address key tenets of the DES+ model. For cerebellar cortex, a cerebellar multilayer sandwich (CMS) model is proposed that can account for many distinctive features, including its unique, accordion-like folding in the adult, and experiments are proposed to address its specific tenets.

Investigation of novel multi-layer sandwich panels under quasi-static indentation loading using experimental and numerical analyses

In this study, the effect of multi-layering in sandwich panel composite structures with different configurations of corrugated cores under the effect of quasi-static indentation loading is investigated experimentally and numerically. Composite plates and corrugated cores with equal weight fraction were manually made using ML506 epoxy resin with 15% hardener and the overall volume fraction of 45% for woven glass fibers. Experiments were performed using a cylindrical indenter with a diameter of 20 mm and a semi-spherical nose shape, and the behavior of the composite structure was evaluated in the case of energy absorption, contact force, and fracture mechanisms for different corrugated cores (rectangular, trapezoidal and triangular). Progressive damage analyses of the composite samples were investigated using well-known 3D failure criteria developed in ABAQUS software, and an acceptable agreement between the experimental and numerical results was observed. Experimental results show that multi-layering of composite sandwich panels not only increases the structural strength in quasi-static indentation process but also increases the energy absorption of specimens by increasing the peak load, instantaneous force, and dislocation displacement up to the complete penetration. By comparing different geometries of the corrugated cores in terms of maximum force, energy absorption, and specific energy, it was shown that the functionality of specimens with rectangular cores is the best. Among the most important damage mechanisms of the examined sandwich panel specimens (visual analysis) in the quasi-static indentation process, matrix cracking, fiber breakage, delamination, cell walls buckling and crushing, face sheets and core debonding, and specimens complete penetration are noticeable.

A smoothed iFEM approach for efficient shape-sensing applications: Numerical and experimental validation on composite structures

A smoothed inverse finite element method (iFEM(s)) is developed by coupling the inverse finite element method (iFEM) and the smoothing element analysis (SEA) for real-time reconstruction of displacement field utilizing a network of discrete strain-sensor measurements. This reconstruction is commonly referred to as “shape sensing”. The shape-sensing capabilities of iFEM(s) in multilayered composite and sandwich structures are validated using both numerical and experimental strain data. The iFEM(s) approach first recovers continuous (smoothed, full field) strains from discrete strain measurements and subsequently employs these strains in the least-squares variational principle to obtain the deformed structural shape. To model through-the-thickness displacement distributions accurately, the kinematic relations of the refined zigzag theory (RZT) are incorporated into the mathematical formulation of iFEM(s). The least-squares functional accommodates the membrane, bending, zigzag, and full transverse-shear section strains. Moreover, simplified forms of this functional are derived for both woven composite and sandwich structures. Subsequently, a four-node quadrilateral inverse-plate element, iRZT4, is implemented for discretization of the geometry and approximation of kinematic variables. The high accuracy of present computational framework is successfully demonstrated by performing shape- and stress-sensing analyses using numerical strain data. Then, the predictive capabilities of iFEM(s) are also explored on a twill-woven wing-shaped sandwich laminate using experimental strain measurements from surface mounted strain gauges and embedded fiber Bragg grating (FBG) sensors. Finally, the improved shape-sensing predictions of iFEM(s) for both numerical and experimental cases are compared to the conventional iFEM application.

Shape sensing of multilayered composite and sandwich beams based on Refined Zigzag Theory and inverse finite element method

An accurate and effective reconstruction method, which is commonly known as “shape sensing”, is presented for real-time reconstructing the deformation field of multilayered composite and sandwich laminated beam using the measured surface strains is presented. The proposed strategy uses the inverse finite element (iFEM) as a general framework and the Refine Zigzag Theory (RZT) as improved theory. Compared to the traditional iFEM, an additional kinematic variable is introduced to improve reconstruction accuracy of the axial displacement through the depth of the beam. Initially, the displacement fields, strain fields and equilibrium relations are presented. Then, the deformed displacement fields are described by the isogeometric analysis method, where the order of kinematic variables can be determined based on the equilibrium relations and the criteria for element interpolations. Next, transformation relationships are established between measured surface strains and section strains. And the number of strain sensor is further reduced through the boundary conditions. Finally, a least-square function is employed to establish the strain–displacement model. A cantilevered beam is used as a case to compare the reconstructed displacements with the theoretical displacement solutions. The numerical results demonstrate the superior accuracy capability and potential applicability of presented approach for performing accurate shape prediction of the RZT beam.

Graphene/Magnetite (Fe3O4) Hybrid Fillers for Thermoplastic Composites: X-Band Electromagnetic Interference Shielding Characteristics

Hybrid composites of poly(methyl methacrylate) (PMMA) and polyvinyl chloride (PVC) with multilayered graphene/iron oxide (MLG/Fe3O4) were prepared by solution casting. Tensile and viscoelastic characteristics of the hybrid nanocomposites were studied in comparison with the corresponding pure polymer and polymer/MLG composite. Increase in Fe3O4 content in the hybrid composites reduces their electrical conductivity and thermal stability. The hybrid composite films were hot stacked to get a 2-mm-thick multilayered sandwich structure and tested for their X-band microwave absorption characteristics. The decrease in electrical conductivity resulted in lower overall shielding effectiveness of the hybrid composites. Hybrid composites with 2.5 wt.% Fe3O4 exhibited satisfactory electromagnetic interference (EMI) shielding effectiveness at par with the polymer/MLG composites. The hybrid nanocomposites had a significantly higher influence of absorption in the overall shielding effectiveness when compared to the respective polymer/MLG composites. Both PMMA-based and PVC-based graphene/Fe3O4 hybrid nanocomposites with proper filler contents are found suitable␣for EMI shielding solutions with higher absorption requirements.

Dynamics properties of multi-layered composite sandwich doubly-curved shells

The present work deals with the dynamics properties of two kinds of multi-layered composite sandwich doubly-curved shells with two-layered viscoelastic cores based on first order shear deformation theory (FSDT). The Hamilton’s principle is adopted to deduce the equations of motion that govern the free vibrations of the sandwich doubly-curved shells. The vibration frequencies and associated loss factors of shells are obtained by solving these equations as an eigenvalue problem based on the Navier method. Then, the validity of present solutions is confirmed comparing with those available in the published literatures. Next, the change rules of frequencies and loss factors with structural parameters are evaluated and presented graphically. New results for dynamics properties of multi-layered composite sandwich doubly-curved shells with two-layered soft cores are proposed for the first time.

Multilayered electrospinning strategy for increasing the bioaccessibility of lycopene in gelatin-based sub-micron fiber structures

The main drawback of gelatin nano- and sub-micron fibers for delivery of lipophilic compounds such as lycopene is its quick dissolving in the oral phase. Herein, electrospinning is used to design a multilayer sandwich structure to enhance the bioaccessibility of lycopene in the target site, small intestine. For this purpose, the gelatin layers loaded with 0.05 and 0.075% (w/w) lycopene were sandwiched between the two layers of the hydrophobic electrospun proteins of zein. The rheological, physicochemical and bioaccessibility properties of the designed solutions and spun samples were comprehensively studied. The most favorable conditions for electrospinning of each layer were selected and judged by the morphological, fiber diameter distributions, production efficiency and particularly higher protection of lycopene. The encapsulation efficiencies of lycopene for the sandwich samples were measured between 83.97 and 90.51% which is in a highly acceptable level. The FTIR and DSC analyses confirmed the presence of lycopene, suggested its chemical or physicochemical interactions with protein. The improvement in the thermal resistance of encapsulated lycopene was also confirmed by DSC experiment. The release behavior of lycopene was evaluated by Kopcha, Peppas-Sahlin and Korsmeyer-Peppas models in the simulated digestive environments whereby a Fickian diffusion assisted with matrix erosion was observed. The fast and higher release of lycopene in the small intestine phase was also seen, so that the highest bioaccessibility reached to the 16.44% for the multilayered sample loaded with 0.075% (w/w) lycopene. These findings show a promising approach for designing safe delivery systems based on electrospun fibers with higher bioaccessibility for lipophilic compounds.

Influences of angular deceleration on the thermoelastoplastic behaviors of nonuniform thickness multilayer FGM discs

In this article, the stresses of a rotating nonuniform thickness disc subjected to a nonlinear temperature field are obtained numerically using the finite difference method. The disc is composed of a number of laminated layers forming a multilayer (sandwich) FGM structure, and each layer has its constant volume fraction. The thermoelastoplastic analyses are conducted based on the von Mises theory. Investigating some key parameters enlightened that the proposed volume fraction distribution can be used to process FGM structures efficiently while bearing in mind the circumferential stress-jumps. The angular speed is assumed to be exponentially decaying with time inducing shear stress that promotes occurrence of plasticity. About 18% of the disc was in the plastic zone during the elastic solution that jumped to 39% by considering the elastoplasticity. Therefore, it has to be considered for accurate investigations. Furthermore, the disc thickness profile and volume fractions have decisive roles on its behaviors.

A novel magnetorheological elastomer-based adaptive tuned vibration absorber: design, analysis and experimental characterization

The present study aims at the development of a novel semi-active adaptive tuned vibration absorber (SATVA) capable of tuning its natural frequency adaptively in low frequency range. The absorber consists of a multilayer sandwich beam featuring magnetorheological elastomer (MRE) and integrated U-shaped electromagnets which are attached at the top and bottom layers of the sandwich beam. Electromagnets are designed to provide the required magnetic field to alter the stiffness of the MRE layers while also acting as the active mass of the absorber. Based on the characterization of the shear and loss modulus of the fabricated MRE samples, the finite element (FE) model of the proposed SATVA has been developed to analyze the absorber to meet the design requirements and also to evaluate its dynamic performance. The proposed SATVA is then fabricated and experimental set-ups are designed to validate the electromagnet and FE models. The frequency response function of the proposed SATVA is then investigated under different levels of the applied current to the electromagnets. It has been shown that good agreement exists between simulation and FE results. A frequency-shift of approximately 9% was achieved while maintaining a reasonable factor of safety for material constraints. Finally, using the validated FE mode, a parametric study has been conducted to investigate the effect of different design parameters.

Free Vibration Analysis of Functionally Graded Beams with Cracks

This study introduces the free vibration analysis of multilayered symmetric sandwich Timoshenko beams, made of functionally graded materials with two edge cracked, using the finite element method and linear elastic fracture mechanic theory. The FG beam consists of 50 layers, located symmetrically to the neutral plane, whose material properties distribution change along the beam thickness, according to power and exponential laws. The constituent of each layer of the beam is different, but each layer is isotropic and homogeneous. Natural frequency values of a cantilever beam are calculated using a developed MATLAB code. There is good agreement between the present results and the published results from the literature. A detailed study is carried out to observe the effect of crack location, crack depth ratio, power law index and material distribution on the first four natural frequencies.

Multilayer Ti–Ta–Ni–TiC–TiB Composite by Combustion-Aided Joining

Multilayer Ti–Ta–Ni–TiC–TiB composite (cermet) was obtained by combustion-aided joining in multilayer sandwiches formed by Ti–C and Ti–B reactive layers and metal foils (Ti, Ta, Ni) and characterized by thermographic analysis and rapid video filming. Thin plates of resultant composite (32 × 14 × 1.5 mm) were formed within 0.2 s after ignition (burning velocity 195 mm/s). Ta foils were found strongly joined with Ti ones due to development of high combustion temperatures in the reactive layers yielding TiC and TiB ceramics. The presence of ceramics afforded for reducing material density, on retention of its heat/corrosion resistance. Our results open up new horizons for SHS-assisted fabrication of new refractory materials with required structure/properties.

Compression and hysteresis responses of multilayer gradient composite lattice sandwich panels

In order to improve the combat effectiveness, stealth and safety of the marine structures, we design and fabricate the multilayer gradient composite lattice sandwich panels (MGCLSPs) to achieve excellent mechanical properties, vibration isolation characteristics and lightweight features of structures in the present study. The ideas of bionic gradients and material mixtures are incorporated in the design to improve the damping and vibration isolation behaviors of the MGCLSPs. The compression and hysteresis responses of the empty and polyurethane foam-filled MGCLSPs are investigated experimentally and numerically. It is found that the MGCLSPs have better energy absorption characteristics than the non-gradient panels, and the MGCLSP specimen D1 which is positive gradient absorbs the most energy. The experimental results also show that the addition of polyurethane foam can enhance the strength and energy absorption characteristics of MGCLSPs.

Tunable Wettability of Biodegradable Multilayer Sandwich-Structured Electrospun Nanofibrous Membranes.

This research aims to develop multilayer sandwich-structured electrospun nanofiber (ENF) membranes using biodegradable polymers. Hydrophilic regenerated cellulose (RC) and hydrophobic poly (lactic acid) (PLA)-based novel multilayer sandwich-structures were created by electrospinning on various copper collectors, including copper foil and 30-mesh copper gauzes, to modify the surface roughness for tunable wettability. Different collectors yielded various sizes and morphologies of the fabricated ENFs with different levels of surface roughness. Bead-free thicker fibers were collected on foil collectors. The surface roughness of the fine fibers collected on mesh collectors contributed to an increase in hydrophobicity. An RC-based triple-layered structure showed a contact angle of 48.2°, which is comparable to the contact angle of the single-layer cellulosic fabrics (47.0°). The polar shift of RC membranes on the wetting envelope is indicative of the possibility of tuning the wetting behavior by creating multilayer structures. Wettability can be tuned by creating multilayer sandwich structures consisting of RC and PLA. This study provides an important insight into the manipulation of the wetting behavior of polymeric ENFs in multilayer structures for applications including chemical protective clothing.

Self-assembly and ion transport behaviour of liquid-crystalline graphene oxide multilayer sandwich nanopapers

ABSTRACT The controllability of ion channel size is critical for ion transport and sieving. Graphene oxide (GO) has a planar two-dimensional structure and a rich functional group as a binding site, and the liquid crystal material generally undergoes an orientation change under the action of an external force field. Therefore, this property can be incorporated into GO, and the distance between the layers of GO can be controlled by designing the liquid crystal cell which meets the requirements and adjusting the external force field, thereby controlling the transport of ions. In this paper, multilayer sandwich nanopapers were fabricated by liquid crystals and GO via hydrogen bonding, and the controlled ion transport behaviour was investigated. In the presence of external electric or magnetic field, ion channels in the interlayer distance of sandwich GO nanopapers can be adjusted due to the changes of mesogen orientation; therefore, ion conductivity can be adjusted when a lithium-ion solution pass through the nanopapers. Such nano-paper materials show promise in many fields such as ion transport, separation systems, ion battery and capacitor devices.

Biomimetic Nacre-Like Silk-Crosslinked Membranes for Osmotic Energy Harvesting

As an approach to harvesting sustainable energy from ambient conditions, the osmotic energy between river water and seawater contributes to solving global issues such as the energy shortage and environmental pollution. Current attempts based on a reverse electrodialysis technique are limited mainly due to the economically unviable power density and inadequate mass transportation of membrane materials. Here, we demonstrate a benign strategy for designing a multilayer graphene oxide-silk nanofiber-graphene oxide biomimetic nacre-like sandwich as an osmotic power generator. Enhanced interfacial bonding endows the composite membranes with long-term stability in saline, and meanwhile, the two-dimensional nanofluidic channel configuration also reduces the ion transport resistance and provides large storage spaces for ions. Thus, the output power density of the proposed membrane-based generator achieves a value of up to 5.07 W m-2 by mixing seawater and river water. Furthermore, we experimentally and theoretically demonstrate that the thermal-field drives the increased output power density due to the advances in ionic movement range and activity of electrode reaction, showing the promise of strengthened thermo-osmotic energy conversion.

Free vibration analysis of a single edge cracked symmetric functionally graded stepped beams

Free vibration analysis of a single edge cracked multi-layered symmetric sandwich stepped Timoshenko beams, made of functionally graded materials, is studied using finite element method and linear elastic fracture mechanic theory. The cantilever functionally graded beam consists of 50 layers, assumed that the second stage of the beam (step part) is created by machining. Thus, providing the material continuity between the two beam stages. It is assumed that material properties vary continuously, along the thickness direction according to the exponential and power laws. A developed MATLAB code is used to find the natural frequencies of three types of the stepped beam, concluding a good agreement with the known data from the literature, supported also by ANSYS software in data verification. In the study, the effects of the crack location, crack depth, power law gradient index, different material distributions, different stepped length, different cross-sectional geometries on natural frequencies and mode shapes are analysed in detail.

On low-velocity impact response of foam-core sandwich panels

This study aimed to investigate low-velocity impact responses and crashworthiness of different aluminum foam-core sandwich structures. Several drop-weight dynamic impact tests were first conducted on both sandwich structures and their individual components to explore the mechanism of energy absorption and interactive effect between the foam core and facesheets. Different shapes and sizes of impactors were used in the experiments. The full-field deflection distribution was acquired by a 3D optical scanner to assess the failure patterns. A full-scale finite element model was then created to simulate the low-velocity impacting response of the foam-core sandwich panels. After the finite element model was validated against the experimental results, it was used to further explore the crash behavior of multi-layered sandwiches. It was found that multi-layer sandwich structure had much better performance in the crush force efficiency than those with single-layer foam core. Based upon the energy principle, an energy-based analytical model was also derived to estimate the initial peak load. It was demonstrated that the analytical predictions were in good agreement with the experimental and numerical results. The presented experimental, numerical and analytical studies are anticipated to provide systematic understanding and new knowledge for design of multilayer sandwich configurations aiming at more desirable impact resistance and better lightweight characteristics.