Multilayered Composite Structures Research Articles

RF Signal Multiplexer Embedded Into Multifunctional Composite Structure

This article describes the design and fabrication of an active four-port microwave switching network embedded into a multilayer aerospace composite structure. The multifunctional design is based on three broadband Integrated Device Technology (IDT) F2972 single-pole-double-throw (SP2T) RF switches and also includes a control and power supply circuit. The composite structure has been developed using a preimpregnated structural glass (S-Glass) material (Hexcel HexPly 914E). The conductive tracks of the switch and its ground plane have been fabricated using a nonwoven carbon–nickel–copper (CNC) veil material and a semiflexible conducting silver ink. This article contains an analysis of the electrical properties of both materials at microwave frequencies. The equivalent electrical conductivities of materials were determined using a curve fitting method that was then used to verify the computational modeling of the switching network. The RF switching network was developed based on a hybrid manufacturing approach. The RF transmission lines and a component of the control circuitry were transferred onto uncured pre-preg material using a laser to ablate select regions of the CNC veil material. Postcuring, flexible silver ink was additively printed onto the surface to create the remaining control circuits. The RF performance of the design has been evaluated, and it indicates that the overall performance was consistent with the measured S-parameters of the same circuit fabricated on Rogers 5880 substrate.

RESEARCH AND IMPROVEMENT OF NONCONTACTING TECHNIQUE OF THE ULTRASONIC THROUGH TRANSMISSION METHOD OF NON-DESTRUCTIVE TESTING

Operation capabilities of ultrasonic through transmission method of non-destructive testing of products from polymeric composite materials and multilayer glued structures are considered. It is shown that for detection of defects in products from easily damaged materials, from the hydroscopic materials which are not allowing wetting by liquids, in designs with rough surface, and also for detection of the under surface defects which are not revealed by contact methods, effective use of ultrasonic through transmission noncontacting method. The calculation procedure and designing of ultrasonic through transmission noncontacting probes on the frequency of 200 kHz, allowing to reveal defects in products from polymeric composite materials and in multilayer glued structures with higher sensitivity, than noncontact ultrasonic probes applied now on frequencies 20, 40 and 80 kHz is offered. The constructive scheme of the vibrator with two piezoelectric plates from ceramics TsTS-19, included inphase, with the metal lap playing role of wave guide, and matching layer from foam plastic is provided. It is specified that two piezoelectric plates works in “short circuit” mode therefore sound pressure piezoelectric plates increases by acoustic line twice, and oscillation strength four times.

Enhanced solar evaporation efficiency based on the inserted preheating zone of silver nanowires

In this paper, a new type of floating solar evaporator with a three-layer composite structure has been successfully fabricated, with the carbon nanotube (CNT) as the photothermal layer, the silver nanowires as the preheating layer and the glass fibers as the insulation layer. The solar evaporator exhibited excellent solar absorption and photothermal conversion properties, and the surface temperature of the dried evaporator could reach 106 °C under one solar irradiation intensity. Importantly, the pure water evaporation rate and the solar evaporation efficiency of this evaporator were 1.70 kg/m2 h and 95%, respectively. Based on the multi-layer composite structure of the evaporator, the addition of the silver nanowires as the preheating layer effectively reduced the loss of the thermal energy of the photothermal layer as the heat source and the evaporation region. The purpose of this study is to improve the solar energy efficiency by reducing heat conduction losses through the design of evaporators.

Fabrication and rheological behavior of tape‐casting slurry for ultra‐thin multilayer transparent ceramics

AbstractDisk transparent ceramics with multilayer composite structure serves well as laser gain medium because of its excellent thermal and optical properties. For such a type of material, the preparation of corresponding outstanding slurry is the first yet most essential step, and it may determine the quality of both subsequent green tape and the sintered ceramics. In this work, the tape‐casting slurry with typically pseudoplastic behavior was carefully modulated in the mixture solvent of anhydrous ethanol and ethyl acetate, and its rheological property was systematically investigated using fine‐controlled rotary rheometer. The obtained result reveals 4wt.% fish oil to be the best dispersed agent. With the obtained slurry for tape‐casting followed by lamination and warm isostatic‐pressing, the multilayer ultrathin TCs was successfully fabricated via high‐temperature vacuum sintering technology. The obtained full‐dense microstructure with high optical quality may endow the studied ceramic with great potential for highly efficient solid‐state laser gain medium.

Dynamic response of a 2-2 multi-layered cement-based piezoelectric composite under arbitrary mechanical load

Theoretical analyses of the dynamic properties of a 2-2 multi-layered cement-based piezoelectric composite are presented based on the theory of piezoelasticity and D’Alembert’s principle. An arbitrary mechanical load acts on the free end of the composite in the form of pressure. The Taylor series expansion method is introduced for the arbitrary mechanical load, and the theoretical solutions of the composite are obtained mainly based on the eigenfunction expansion method, Duhamel integral, and Laplace transform. Comparisons between the theoretical results, numerical results, and four related theoretical studies are presented, and good agreements are found. Furthermore, the theoretical expression of magnification factors of the composite under the harmonic load are obtained and analyzed. In addition to providing a theoretical basis for the design and experimentation of 2-2 cement-based piezoelectric composites under the arbitrary loading, the theoretical methods presented in the article could be extended to analyze the dynamic characteristics of any multilayered composite structure.

Research on influence of special‐shaped honeycomb radar absorbing structure for wide‐band absorbing design

To realise wide-band stealth of radar absorbing material, a special-shaped honeycomb radar absorbing structure within nested cone-shaped scattering configuration is designed. Based on the HS theory and the impedance matching design, the rule about the influence of the geometry parameter and electromagnetic parameter on the absorbing performance is analysed. In addition, the reflectivity performance is analysed on the condition of oblique incidence angles. By optimising the geometry parameters of the special-shaped honeycomb structure and designing the multilayer composite structure based on impedance matching theory, the results indicate that the two absorbing peaks can be formed for the special-shaped honeycomb radar absorbing structure, and the reflectivity is improved for both the vertical and oblique incidence angles.

Compositional and structural design of thermoplastic polyurethane/carbon based single and multi-layer composite sheets for high-performance X-band microwave absorbing applications

In this study, morphological features, dielectric properties, and microwave absorbing performances of thermoplastic polyurethane composite sheets prepared with solution mixing method by using different amounts and types of carbon fillers, carbon black (CB), graphite (G), carbon nanofiber (CNF), and multiwalled carbon nanotube (MWCNT) were investigated, in detail. Microstructural properties and microwave absorbing characteristics of composites were analyzed with scanning electron microscope and vector network analyzer by transmission line method, respectively. Reflection loss (RL) analyses of composites showed that CNF and CNT were more efficient than CB and G for improving the electromagnetic wave absorbing performances of sheets at low filler contents. It was found that the broadest effective absorption area (EAA) (10.03–12.96 GHz) was obtained with the sample having 3 phr of CNF. However, single layer TPU/carbon composite sheets were not effective “RADAR stealth” materials because their RL values were higher than −10 dB at X-band. Thus, multilayer (two, three, and four-layer) composite structures were designed to obtain higher microwave absorption performance within this frequency range via genetic algorithm approach. Multilayer design and modeling works showed that a four-layer composite with a total thickness of 4.8 mm yielded excellent microwave absorbing performance and broad EAA, 6.98–13.415 GHz, at X-band.

Behavior to Dynamic Loads of Multi-layer Composite Structures

The explosive effect and high velocity penetration of the ballistic projectiles of various sizes, design and compositions, on impact with different targets (armors composed of a combination of different metals) are complex. Both practical experiments and mathematical modeling of the phenomena associated to the interaction projectile-target are required to estimate their effect or to design more efficient projectiles and armor. In this study, the basic element of the simulation model is an incendiary projectile of caliber 7.62 mm with medium piercing power, launched with a maximum speed of 750 ms-1 on the multi-material target, which contains 4 different layers assembled into a ballistic cassette made of aluminum. The purpose of this ballistic cassette is to ensure a better contact and handling of multi-layer materials. The proposed model was calculated using mathematical modeling and empirical material constants to describe the nonlinear transitory impact process. Mathematical simulation of the impact between the projectile and target during impact shows that the projectile moves sequentially through the ballistic package, causing perforation, plastic deformation and heating, the resulting fragments being then expelled into the space around the target. The model indicates that the projectile will penetrate the front aluminum plate, as well as the AlCrFeCoNi and steel plates, but will be stopped by the aluminum backing plate. The real impact tests carried out using the ballistic cassette at dynamic impact with the 7.62mm incendiary projectile confirm the model assumptions, which prove the capacity of the composite model to safely stop the projectile.

Image reconstruction and characterisation of defects in a carbon fibre/epoxy composite monitored with guided waves

In this extensive experimental study, the structural health monitoring (SHM) of a large 1 m × 1 m carbon fibre reinforced polymer laminate was performed using guided waves. Multiple hole- and crack-type defects were induced in the structure and the guided wave signals were collected using a circular network of piezoelectric disc transducers permanently bonded to the structure. Images representing each damage state of the composite plate were obtained by applying the (total focusing method, TFM with full matrix capture) on guided wave signals. Several variations in the image reconstruction algorithm were investigated by using two different baselines—pristine signals or signals collected during the last damage state-, processing only the positive amplitude by implementing a lower limit threshold and normalising the signals. The algorithms’ ability to detect and localise multiple defects, inside and outside the array, including holes as small as 2 mm in diameter, was evaluated. TFM images, involving the use of a lower threshold limit in the signal processing, resulted in more accurate detection. In addition, images obtained using both types of baseline provided complementary information leading to increased confidence in the system. All defects in the plate were detected and located even in the presence of multiple defects. Also, regions corresponding to crack- and hole-type of defects in the resulting images were identified, quantified and differentiated using geometric circularity and eccentricity shape factors. This ability of accurately identifying multiple defects and reducing location error are important contributions in the effort of establishing a reliable SHM system for multi-layered composite structures.

Tria and quad plate finite elements based on RZT(m) for the analysis of multilayered sandwich structures

Aim of the paper is to develop and to assess a class of plate finite elements for the analysis of multilayered composite and sandwich structures. The adopted model is the mixed Refined Zigzag Theory (RZT(m)), based on the kinematics of the Refined Zigzag Theory (RZT) and on the assumption of transverse shear stresses coming from integration of indefinite equilibrium equations. A triangular and quadrilateral flat finite element are developed by means of the Reissner’s Mixed Variational Theorem and an interpolation strategy to eliminate shear locking. Several numerical examples are discussed to demonstrate the accuracy of RZT(m) and related finite elements for static response, free-vibrations and critical load problems of sandwich structures.

Defect Estimation in Non-Destructive Testing of Composites by Ultrasonic Guided Waves and Image Processing

The estimation of the size and location of defects in multi-layered composite structures by ultrasonic non-destructive testing using guided waves has attracted the attention of researchers for the last few decades. Although extensive signal processing techniques are available, there are only a few studies available based on image processing of the ultrasonic B-scan image to extract the size and location of defects via the process of ultrasonic non-destructive testing. This work presents an image processing technique for ultrasonic B-scan images to improve the estimation of the location and size of disbond-type defects in glass fiber-reinforced plastic materials with 25-mm and 51-mm diameters. The sample is a segment of a wind turbine blade with a variable thickness ranging from 3 to 24 mm. The experiment is performed by using a low-frequency ultrasonic system and a pair of contact-type piezoceramic transducers kept apart by a 50-mm distance and embedded on a moving mechanical panel. The B-scan image acquired by the ultrasonic pitch-catch technique is denoised by utilizing features of two-dimensional discrete wavelet transform. Thereafter, the normalized pixel densities are compared along the scanned distance on the region of interest of the image, and a −3 dB threshold is applied to the locations and sizes the defects in the spatial domain.

Unit cell modeling on torsion damage behavior of a novel three-dimensional integrated multilayer fabric-reinforced composite tubular structure

Torsion damage behaviors of composite tubes are key factors in the design of tube structures, such as transmission shafts. During service, torsion in the transmission shaft induces delamination damage. A novel three-dimensional fully integrated multilayer tubular fabric aimed to eliminate delamination was invented by authors. This fabric is in tubular form with several layers of crimp-free in-layer yarns oriented at prescribed orientations and fully interlocked by a set of through-layer yarns, which are often made of the same type of fibers as the in-layer yarns. We investigated torsion damage behaviors of the integrated fabric-reinforced composite tubes. The torque–torsion angle curves were obtained and the torsion damages were phenomenologically analyzed. A unit cell model of the integrated fabric composite circular tube was established to numerically reveal the torsion damage mechanisms. For optimizing the torsion behaviors, the axial yarns should have high stiffness and the binder yarn should have high strength. More specifically, the axial yarn should use carbon fiber tows, and high-strength polymer fiber tows could be used for the binder yarns.

Numerical modelling of SH-wave propagation in initially-stressed multilayered composite structures

Purpose The purpose of this paper is to develop a numerical (finite-difference) model exploring phase and group velocities of SH-wave propagation in initially stressed transversely isotropic poroelastic multi-layered composite structures and initially stressed viscoelastic-dry-sandy multi-layered composite structures in two distinct cases. Design/methodology/approach With the aid of relevant constitutive relations, the non-vanishing equations of motions for the propagation SH-wave in the considered composite structures have been derived. Haskell matrix method and finite-difference scheme are adopted to deduce velocity equation for both the cases. Stability analysis for the adopted finite-difference scheme has been carried out and the expressions for phase as well as group velocity in terms of dispersion-parameter and stability-ratio have been deduced. Findings Velocity equations are derived for the propagation of SH-wave in both the composite structures. The obtained results are matched with the classical results for the case of double and triple-layered composite structure along with comparative analysis. Stability analysis have been carried out to develop expressions of phase as well as group velocity in terms of dispersion-parameter and stability-ratio. The effect of wavenumber, dispersion parameter along with initial-stress, porosity, sandiness, viscoelasticity, stability ratio, associated with the said composite structures on phase, damped and group velocities of SH-wave has been unveiled. Originality/value To the best of authors’ knowledge, numerical modelling and analysis of propagation characteristics of SH-wave in multi-layered initially stressed composite structures composed of transversely isotropic poroelastic materials and viscoelastic-dry-sandy materials remain unattempted inspite of its importance and relevance in many branches of science and engineering.

Innovation gradient mousse material processing technology research

The purpose of this research is to investigate the properties of the gradient mousse multi-layer composite structure in terms of phase change and solidification of the material, and to optimize the crystallization characteristics of the material, from the upper soft layer to the lower solid roughening layer, through the material distorting intermediate binding layer to form a unique sandwich structure. This research will be based on material processing and transformation technology, layered curing, and finally observed by optical microscopy and surface elastic tension, etc. Ratio of the upper layer of soft material is preferred solid-liquid ratio of 1:10 to fusion emulsified soft upper layer. The optimal material ratio of the lower layer of solid roughening layer is 2:1. The final preliminary optimal results are obtained through material analysis. The spirit of this research can be extended to the discussion of food processing in the field of materials science and the research on the issues related to food processing safety.

Microstructure, adhesion and tribological behaviors of Si interlayer/Si doping diamond-like carbon film developed on nitrile butadiene rubber

Si doping diamond-like carbon (Si-DLC) films were prepared on NBR (nitrile-butadiene rubber) in order to improve its friction and wear resistance. Prior to the Si-DLC film deposition, a Si layer was firstly deposited on NBR as an interlayer, and the influence of the Si interlayer thickness on the microstructure, adhesion and tribological behavior of the films on the NBR and Si wafer substrates were systematically compared. The results showed that the surface morphology of the Si-DLC top layer on NBR exhibits a fractured morphology (crack-like network), and all Si-DLC films were characterized by a dense columnar-free microstructure. The deposition rate of films on NBR is faster than that of films on Si wafer. Furthermore, the highest ID/IG ratio and G peak position (sp2 content) could be obtained by the introduction of Si interlayer with a proper thickness of ~1.04 μm, which effectively relieves the compressive stress and thus significantly enhances the adhesion strength between film and NBR, and guarantees an excellent tribological performance. The lowest friction coefficient was achieved (~0.23 compared to 0.27 for the film without Si interlayer and 0.87 for the original NBR) under the relatively high load of 3 N. Meanwhile, the brittle fracture of Si-DLC films on NBR is one of the main factors leading to its lubricating failure under a high load, which suggests that it is necessary to deposit an interlayer to enhance the adhesion and the load-bearing capacity of the film (reducing its hysteresis), and to apply the different element doping and multi-layer composite structures to improve the toughness of the film.

Vibration Analysis of Composite Multilayer Floor of High‐Speed Train

Mechanical properties of floor prototypes made for high‐speed trains from composite multilayer floor structures of different materials and thicknesses were tested. Based on the test results, the equivalent mechanical parameters of different layers of the panels, core materials, etc., were calculated, and the multilayer mixed finite element model of the floor was built and verified. The multilayer mixed floor model was introduced into the car body of a high‐speed train, and the test signals of the high‐speed train were used as inputs to calculate the vibration response of composite floor structure. Vibration spectra of the high‐speed train composite floor made of different materials and structures were compared and analyzed. The results show that the calculation of the floor vibration response of the vehicle car body within the framework of the equivalent model of the multilayer structure based on the mechanical performance test is an effective method to evaluate vibration characteristics. The vibration isolation performance of the stainless steel panel floor is better than that of the aluminum alloy panel, but its large mass is not favorable in lightweight body design. The vibration energy of birch core material floor is significantly smaller than the alder core material of the same size. The vibration isolation performance of the floor enhanced with the increase in the thickness of the outer metal panel, but when the outer metal panel thickness exceeds 0.8 mm, the influence becomes small. Therefore, the stainless steel‐birch core composite floor with a large panel thickness has the best vibration isolation performance and can be used for the floor above the bogie and the suspended excitation source. Then, an optimal analysis considering mass and vibration characteristics was carried out, and the results show that there exists an optimal solution for the high‐speed train. Regarding the overall design basis of the vehicle, the aluminum alloy panel lightweight structure can be used in combination with other general parts.

A Damage Classification Approach for Structural Health Monitoring Using Machine Learning

Inspection strategies with guided wave-based approaches give to structural health monitoring (SHM) applications several advantages, among them, the possibility of the use of real data from the structure which enables continuous monitoring and online damage identification. These kinds of inspection strategies are based on the fact that these waves can propagate over relatively long distances and are able to interact sensitively with and uniquely with different types of defects. The principal goal for SHM is oriented to the development of efficient methodologies to process these data and provide results associated with the different levels of the damage identification process. As a contribution, this work presents a damage detection and classification methodology which includes the use of data collected from a structure under different structural states by means of a piezoelectric sensor network taking advantage of the use of guided waves, hierarchical nonlinear principal component analysis (h-NLPCA), and machine learning. The methodology is evaluated and tested in two structures: (i) a carbon fibre reinforced polymer (CFRP) sandwich structure with some damages on the multilayered composite sandwich structure and (ii) a CFRP composite plate. Damages in the structures were intentionally produced to simulate different damage mechanisms, that is, delamination and cracking of the skin.

A variable ESL/LW kinematic plate formulation for free-vibration thermoelastic analysis of laminated structures

In this article, a fully-coupled thermoelastic formulation is developed to deal with the free-vibration analysis of multilayered plate composite and sandwich structure. Some advanced theories are obtained by expanding the unknown displacement variables along the thickness direction and using equivalent-single-layer (ESL) models, layer-wise (LW) models, and variable-kinematic models. The variable-kinematic models permit to reduce the computational cost of the analyses grouping some layers of the multilayered structure with ESL models and keeping the LW models in other zones of the multilayer. This model is here extended for the free-vibration analysis of fully-coupled thermomechanical problems. The used refined models are grouped in the Carrera unified formulation (CUF), and they accurately describe the displacement field and the temperature distributions along the thickness of the multilayered plate. The governing equations are derived from the principle of virtual displacement, and the finite element method (FEM) is employed to solve them. Isotropic plates, cross-ply composite plates, and sandwich structures with composite skins and simply-supported edges are analyzed. Various aspect ratios are considered. The results, obtained with different theories within CUF context, are compared with the elasticity solutions, and other higher-order analytical and FEM solutions given in the literature. From the results, it is possible to conclude that the plate element based on the CUF is very efficient in the study of thermomechanical problems of composite structures. The variable-kinematic models combining the ESL with the LW models, permit to have a reduction of the computational costs, respect with the full LW models, preserving the accuracy of the results.

High-Resolution UHF Near-Field Imaging Probe

Imaging probes which work at relatively low microwave frequencies in the ultrahigh frequency band (UHF) facilitate imaging through high loss dielectric materials and yield manageable imaging system complexity. However, acquiring images with resolutions on the order of few millimeters at frequencies within the UHF band requires super-resolution imaging methods and probes. In this paper, a compact near-field imaging probe working in the UHF band is proposed for high-resolution noninvasive imaging applications. The proposed probe is based on an electrically small loop loaded with a miniaturized spiral resonator. The probe is analyzed in this paper using numerical electromagnetic simulations and its equivalent circuit model is consequently developed. A prototype of the proposed probe operating at 426 MHz is fabricated and its spatial resolution as well as sensitivity are experimentally verified. A spatial resolution of around $\lambda $ /140 is demonstrated in simulations and verified experimentally. In order to highlight the utility of the probe for practical applications, images of many test samples including multilayer dielectric composite structures and corroded metallic substrate are acquired using the fabricated prototype. It will be shown that the images obtained using the proposed probe is comparable with those produced using an open-ended rectangular waveguide operating at 24 GHz. The salient features of the proposed probe include its high sensitivity and resolution while operating at relatively low frequency.

A three-dimensional multibody tire model for research comfort and handling analysis as a structural framework for a multi-physical integrated system

A tire is an extremely integrated and multi-physical system. From only a mechanical point of view, tires are represented by highly composite multi-layered structures, consisting of a multitude of different materials, synthesized in peculiar rubber matrices, to optimize both the performance and the life cycle. During the tire motion, due to the multi-material thermodynamic interaction within the viscoelastic tire rubber matrix, the dynamic characteristics of a tire may alter considerably. In the following paper, the multibody research comfort and handling tire model is presented. The main purpose of the research comfort and handling tire is to constitute a completely physical carcass infrastructure to correctly transmit the generalized forces and torques from the wheel spindle to the contact patch. The physical model structure is represented by a three-dimensional array of interconnected nodes by means of tension and rotational stiffness and damper elements, attached to the rim modeled as a rigid body. Research comfort and handling tire model purpose is to constitute a structural physical infrastructure for the co-implementation of additional physical modules taking into account the modification of the tire structural properties with temperature, tread viscoelastic compound characteristics, and wear degradation. At the stage, the research comfort and handling tire discrete model has been validated through both static and dynamic shaker test procedures. Static test procedure adopts contact sensitive films for the contact patch estimation at different load and internal pressure conditions, meanwhile the specifically developed sel test regards the tire dynamic characterization purpose at the current stage. The validation of the tire normal interaction in both static and dynamic conditions provided constitutes a necessary development step to the integration of the tangential brush interaction model for studying the handling dynamics and to the analysis of the model response on the uneven surfaces.