Multilayered Composite Structures Research Articles

Application of low field magnetic resonance for defect detection in multi-layered cylindrical composite structures

ABSTRACT Polymer-based Glass composite cylindrical structures consisting of multi-layered configuration for special applications were tested with low magnetic field nuclear magnetic resonance (NMR) technique. Relaxation times of chemical species at the interface of adhesive bond were investigated. Studies indicated that the single-sided NMR inspection of such composite structures is a feasible non-destructive evaluation technique to study the adhesive bond interface properties. Results of single-sided inspection over cylindrical surface using low field NMR having magnetic field strength of 0.3 T (12.88 MHz RF frequency) indicated distinct signal intensity values for different constituent materials. Interfacial defects such as de-bond and voids were detectable through the multi-layers of the structure. Overlapping defects at multiple interfaces have no bearing on the signal as well as relaxation times of constituent materials.

Dynamic behavior of multi-layer heterogeneous composite magneto-elastic structures for surface wave scattering

The paper is focused on the surface wave field in functionally graded multi-layer transversely isotropic heterogeneous magneto-elastic reinforced media. The Geometry of the problem is formulated by considering the (n−1) finite layer composite structure over a semi-infinite substance, occupying the domain: −∞<x,y<∞,hi−1≤z≤hi,i=1,2,⋯n−1,h0=0 and hn−1≤z≤∞. Mechanical properties of magneto-elastic heterogeneous reinforced media in wave scattering are an essential part of this study. A generalized Haskell’s [1] technique has been applied to obtain the wave scattering relation in multi-layer heterogeneous magneto-elastic media using suitable boundary conditions. Estimated wave scattering relation is in affirmation with the general Love-type surface wave relation in case of a single layered medium over a semi-infinite substance as well as multi-layered media over the semi-infinite substance. A finite difference technique is derived to obtain the group and phase velocities with shear deformation in the magneto-elastic heterogeneous reinforced media. To study the group and phase velocity in a square grid, stability conditions for introducing finite difference techniques have been derived. Using graphical representation, it has been examined that phase velocity, group velocity, and wave scattering in the layered media are affected by heterogeneity, reinforced, magneto-elastic coupling parameters, and stability ratio.

Development of Eco-friendly Shock-absorbing Cork Composites Enhanced by a Non-Newtonian Fluid

Cork composites present interesting properties for several applications such as damping, shock absorption, crashworthiness and thermal insulation. In this work, the enhancement of their impact resistance, by means of shear thickening fluid (STF) reinforcement was studied. The analysis was carried in multi-layered structures consisting of cork laminates with STF as the interfacial element. To make the study concise, a constant thickness was established for the structure and the variables were the number of cork laminates and thus, the thickness of each laminate and the amount of STF. The STF employed was based on fumed silica and polyethylene glycol (PEG). Rheological measurements were carried out on the developed STF, which was also subjected to scanning electron microscopy (SEM). The multi-layered composite structures were subjected to low-energy impact testing, for three energy levels: 5, 10 and 15 J. Direct comparison was established between cork structures with and without STF, determining the influence of STF in the impact performance. Results are promising, reducing the maximum impact force for some designs (max. reduction of 36%), showing the potential of STF to enhance the impact performance of cork composites.

Research on the design of multi-layer steel structure module and steel frame composite building structure

The composite of multi-layer steel structure module and steel frame, as an important design form in Chinese house construction, is widely used in the architectural design of houses. The multi-layer steel structure module and steel frame composite building structure are different from the traditional. This kind of building mechanism adopts the prefabricated type, which has the advantages of fast construction speed and few limiting factors, and plays a very important guiding role in modern building construction. Based on this, this article will analyze and compare the similarities and differences between steel structure modular buildings and traditional steel frame structures, and explore the design of multi-layer steel structure modules and steel frame composite building structures, hoping to be helpful to relevant people.

Research on the influence of humid heat environment on the mechanical properties of multilayer composite structure

For resin-based composite materials, the hot and humid environment has a very obvious impact on its performance. Moisture can penetrate into the composite material through diffusion and capillary action, which causes the resin matrix with plasticization, swelling and hydrolysis, and swelling and infiltration of liquid will lead to micro-stress inside the material. Thus, the polymer macromolecular chain will stretche or even break, and it can lead to the weakening of the interface properties of the resin and the fiber, which in turn leads to fluctuations in the mechanical properties of the composite material. In this paper, we carried out damp and heat tests on multilayer composite structures to study the effects of different temperature and humidity environments on the physical and chemical properties and mechanical properties of composite materials. The law of moisture absorption characteristics of composite materials is clarified, and the moisture absorption in the initial stage of moisture absorption is proportional to the moisture absorption time t1/2. With time increasing, the moisture absorption gradually tends to balance, and the higher are the damp and heat conditions, the greater the moisture absorption of the composite material will be. The moisture absorption is between 0.13% and 0.78% with different damp and heat environments. The chemical structure of the composite material itself has not changed significantly, and the damp-heat effect will induce the destruction of the fiber-matrix interface and the expansion of cracks along the pores, which weakens the bonding strength of the interface. As a result, the moisture makes the transverse performance and shear performance of the composite material greatly reducing, but has little effect on the longitudinal performance.

Ultrasonic detection of manufacturing defects in multilayer composite structures

The authors have considered practical aspects of the use of ultrasonic method for identification of foreign objects in the structure of laminated composite. The paper presents the results of laboratory investigations aimed at determination of shape and dimensions of artificially created defects and the analysis of specific aspects of ultrasonic detection of fragments of prepreg protective coating.

Numerical simulation study on band gap characteristics of surface phononic crystal with spherical composite column

In the study of acoustic characteristics of micro-scale surface phononic crystal, the band gap characteristics below 100 MHz need to be further optimized. In this work, a piezoelectric surface phononic crystal with a composite column composed of nickel balls and epoxy backing is proposed. The finite element method is used to calculate the band gap characteristics and displacement vector field of the model. The influence of column radius on the band structure is studied, and meanwhile, the effect of the multi-layer composite column structure on the band gap is discussed via increasing the number of elements in the composite column, while the reason for the opening of the high-order band gap is analyzed in detail by combining the vibration mode. Furthermore, the temperature adjustability of the band gap is further studied. The results show that the spherical composite column deposition structure can open a wider complete band gap of surface acoustic wave in a lower frequency range than the existing inverse conical surface phononic crystal structure with the same lattice constant (Hsu J C, Lin F S &lt;ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://doi.org/10.7567/JJAP.57.07LB01"&gt;2018 &lt;i&gt;Jpn. J. Appl. Phys.&lt;/i&gt; &lt;b&gt;57&lt;/b&gt; 07LB01&lt;/ext-link&gt;). The restricted cavity mode is easily formed between the hard boundaries with the increase of column radius, which provides a possible way for low-order vibration modes to open high-order band gaps. There exist mode inheritance and energy coupling between adjacent modes, which leads the band gap to flatten and anti-flatten. Moreover, the real-time adjustment of band gap frequency by external temperature field can be realized via introducing the temperature-sensitive material epoxy resin into the structure. The band gap frequency range can be effectively reduced by increasing the number of composite cylinder layers, while the multi-vibrator structure can generate multipole resonance coupling with traveling wave and finally open a complete band gap between high-order frequency bands. This work provides a theoretical reference for analyzing the low-frequency band gap mechanism of micron-scale surface phononic crystal.

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.

Comparative study of tubular composite structure subjected to internal pressure loading: Analytical and numerical investigation

The purpose of this paper is to study the mechanical behaviour of a multi-layered composite tubular structure with various orientations subjected to internal hydrostatic pressure. The first part of this paper is devoted to studying stress analysis using the analytical approach. The 3 D analysis of the composite pipe originally made with carbon/epoxy is studied and compared with a pipe made of E-glass/epoxy; each layer is examined with five orientations. The hoop, axial, longitudinal, transversal, and shear stresses are obtained for each layer of the composite pipe simultaneously. The hybrid composite pipe is done to take advantage of the properties of each fiber and the studied hybridisation. `To validate some cases of the presented results, a numerical model is developed in ANSYS workbench software; this particular model is characterized by very close to the theoretical results. Throughout the investigation, it is observed that the behaviour of composite carbon/epoxy is the most resistant compared to glass/epoxy, and the results obtained in the case of hybrid shows that the variability of the stacking sequences generates the variation of the behaviour on composite hybrid pipe. It can be increased the design material utilisation and working pressure level by winding angle variation or hybridized between stacking sequences. The ability of this new 3 D model to simulate the stress evolution in the full-scale composite tubular structure under internal pressure events were demonstrated.

High-precision resistance strain sensors of multilayer composite structure via direct ink writing: Optimized layer flatness and interfacial strength

The layer flatness and interfacial strength for the direct ink writing (DIW)-fabricated multilayer sensors are two significant factors in dominating the printing precision and the structural integrity of the sensors, respectively. However, it is still a challenge to control the interfacial strength and layer flatness of the multilayer sensors due to the multiplicity of materials and inherent lines-to-plane forming process of DIW technology. Here we probe a set of DIW fabrication parameters to optimize the layer flatness and design the interfacial strength of the multilayer sensors. The nonlinear thickness-dependent interfacial strength is then measured by single-lap joints experiments, which can be further predicted by an analytical model and finite element simulations. Finally, the high precision and stability of the printed strain sensors with considerably flat layers and high interfacial strength are further tested under static and cyclic tensile loadings. This study provides a feasible approach for parametrically designing and precisely manufacturing multilayer sensors based on the widely used DIW technology.

Interlaminar stress analysis of composite shell structures using a geometrically nonlinear layer-wise shell finite element

This work aims to calculate interlaminar stress distribution through the thickness of multilayered composite shell structures by employing a novel nonlinear layer-wise shell finite element formulation. Adapting the Mindlin– Reissner theory in each layer, the shear-deformable layer-wise shell element presents the interlaminar shear stress distributions by increasing the number of layers. The interlaminar normal stress distribution is then determined using the finite difference solution of the general form of equilibrium equation in the non-orthogonal curvilinear grid along the Gaussian points. Two boundary conditions at the bottom and the top surfaces are satisfied by adopting the linear Lagrange interpolation function. The developed formulation is assessed through some illustrative problems solved using a proprietary finite element computer program. The results compare very well with those available in the literature and those obtained by simulations with the commercial finite element software Ansys.

Heterogeneities in the microstructure and mechanical properties of high-Cr martensitic stainless steel produced by repetitive hot roll bonding

A multi-layered plate with robust interfacial strength composed of high-Cr martensitic stainless steel was produced via repetitive hot roll bonding (RHRB) at elevated temperature. The minimum processing temperature required for the production of multi-layered plates turned out to be in the two-phase region between the A1 and A3 temperatures of stainless steel. Decarburization took place on the surface layer of each process cycle and multi-layered plates were produced with a carbon content that fluctuated along the thickness direction that constitutes a composite plate. The multi-layered composite structure revealed an effective combination of strength and ductility. Also, strong bonding results at each interface were validated via tensile testing with in-situ observation from the sides of the specimens during deformation.

Sensitive electrochemical platform for trace determination of Pb2+ based on multilayer Bi-MOFs/reduced graphene oxide films modified electrode.

A multilayer Bi-BTC/reduced graphene oxide (Bi-BTC/rGO) (BTC, 1,3,5-benzenetricarboxylic acid) film electrode was adopted to construct a highly sensitive Pb2+ electrochemical sensor. The multilayer Bi-BTC/rGO films were prepared via alternate cast of Bi-BTC and graphene oxide (GO) on a glassy carbon electrode, followed by electro-reduction of the GO components. Bi-BTC has porous broom-like structure and its organic ligand has abundant functional groups, which are favorable for Pb2+ adsorption and preconcentration. The introduction of rGO layer improves the conductivity of the MOFs material. Moreover, the multilayer composite structure greatly increased the exposure of active sites and the surface area of reactive contact, finally realizing the highly sensitive detection of Pb2+. Pb2+ was determined by differential pulse anodic stripping voltammetry and the response current was recorded at - 0.62V. The [Bi-BTC/rGO]2 electrode provides a wide linear response ranging from 0.062 to 20.72μg/L and a low limit of detection (LOD) of 0.021μg/L (S/N = 3) for Pb2+, which is lower than the guideline value proposed by the World Health Organization. The method has been applied to determine Pb2+ in industrial wastewater with recoveries of 99.2-104% and RSDs of 3.4-4.0% (n= 3). Graphical abstract Graphical abstract Schematic representation of an electrochemical sensor for the detection of Pb2+ was designed based on long broom-like structure bismuth(II) metallic organic framework/reduced graphene oxide ([Bi-BTC /rGO]2).

Influence of environmental relative humidity on the polarization behaviour of paper and paper-dielectric structures

In paper containing multilayer composite structures and laminates, polarization is usually investigated under dry environmental conditions. The aim of this research is to determine polarization dependence of paper and paper-dielectric structures on environmental relative humidity (RH). The role of each component was identified. The obtained and recorded data are used for identification and clarification of the physical mechanism of polarization. The polarization was studied by applying a dosed charging and forced discharge method and was evaluated by a depolarization potential and its formation kinetics. The polarization level of investigated structures increases with RH and is determined mainly by the paper (cellulose) and moisture content in it. In composite structures of the paper between dielectric films and dielectric on paper the polarization dependence on RH correlates with moisture absorption isotherm. It was found that the surface electrical conductivity of paper distorts the results of the paper and structure paper on dielectric. Analysis of the formation kinetics of the depolarization potential together with the potential decay of the charged paper has determined the role of orientation polarization and space charges. The formation of space charges is faster than orientation polarization and dominates in polarization process at higher RH. The process modeling by superposition of two exponents confirms this polarization mechanism.

Metal Island Structure as a Power Booster for High‐Performance Triboelectric Nanogenerators

AbstractThe development of the Internet of Things requires the availability of compact and efficient power sources for the supply of autonomous systems. In recent times, electromechanical transduction devices like triboelectric nanogenerators (TENGs) have gained strong attention as they permit simple, robust, and cost‐effective techniques. However, TENGs generally do not achieve the electrical power density required for the targeted applications, and the challenges of optimization are therefore to increase their generated power density. In this work, a multilayer flexible composite structure is developed by employing an insulator–metal–insulator island architecture in place of a single insulator material to accumulate and store the charges created by triboelectrification. This increase in stored charges has a strong effect in inducing free charges on the electrodes resulting in a maximum output power density of 4.8 W m−2, which is ≈150‐fold increase compared to the structure without metal inclusions. The results demonstrate a maximum charge density of 1076.56 µC m−2, which is to the knowledge, the best charge density value ever reported for TENGs in ambient working conditions. Therefore, this work proposes a new direction to significantly increase the electrical power density in obtaining high‐performance triboelectric nanogenerators attractive to future applications for active sensors and portable electronics.

CREATION OF GRANULAR COMPOSITE MATERIALS WITH MULTILAYER STRUCTURE

Granular products are widely used in many industries for the production of catalysts in oil refining and organic synthesis, drugs, food products, fertilizer production, etc. The main advantages of granular products are ease of operation and storage. Depending on the morphological structure, the granules obtained as a result of the technological process are divided into one-component, single-layer, composite-coated granule, multilayer granule, frame granule, and combinations thereof. In this paper, we consider, as an example, the technological basis of granulation of aqueous solutions of ammonium sulfate with impurities of humates, calcium carbonate and other substances with the formation of multilayer composite granules in a fluidized bed granulator. The processes of dehydration and mass crystallization during granulation, namely the influence of the drying rate and impurities on the kinetics of the evaporation process of the dispersed heterogeneous solution on solid particles have been studied. In the process of mass crystallization, when the saturation concentration is reached by removing the solvent, the processes of nucleation and crystal growth occur with the formation of a crystalline framework of ammonium sulfate crystals between, which impurities of organic matter and other components are evenly distributed in the volume of the formed micro layer. It was confirmed that the obtained granules of the composite granular fertilizer have a composite multilayer structure with a uniform distribution of suspended particles in the volume of the granule. Bibl. 14, Fig. 4.

Study on transient electric field of multi-layer composite insulation structure during polarity reversal

Outgoing line device is an important structure of converter transformer. Multilayer composite insulation structure is widely used in the outgoing line device. Polarity reversal is special working state of converter transformer. In the process of polarity reversal, due to the influence of the space charge on the interface of composite insulation structure, there will be instantaneous high field strength, which threatens the normal operation of the outgoing line structure. In this paper, starting from the typical multi-layer composite insulation structure in the outgoing line device, the change rule of interface space charge and transient electric field in different polarity reversal time is analyzed under the condition of the equal temperature and temperature gradient. On this basis, the research object of the overall composite insulation structure of the outgoing line device is analyzed, and the change rule of the transient electric field in the process of polarity reversal is analyzed. The research in this paper can provide a theoretical basis for the development of the outgoing line structure of converter transformer.

Aero-structural Design of Composite Wings for Airborne Wind Energy Applications

In this work we explore the initial design space for composite kites, focusing on the configuration of the bridle line system and its effect on the aeroelastic behaviour of the wing. The computational model utilises a 2D cross sectional model in conjunction with a 1D beam model (2+1D structural model) that captures the complex composite coupling effects exhibited by slender, multi-layered composite structures, while still being computationally efficient for the use at the initial iterative design stage. This structural model is coupled with a non-linear vortex lattice method (VLM) to determine the aerodynamic loading on the wing. In conjunction with the aerodynamic model, a bridle model is utilised to determine the force transfer path between the wing and the bridles connected with the tethers leading to the ground station. The structural model is coupled to the aerodynamic and bridle models in order to obtain the equilibrium aero-structural-bridle state of the kite. This computational model is utilised to perform a design space exploration to assess the effects of varied load introduction to the structure and resulting effects on the kite.

Development of an equivalent shell finite element for modelling damped multi-layered composite structures

A new equivalent shell finite element (FE) for modelling damped multi-layered structures is presented in this study. The method used for developing the new FE for such structures is based on the idea that the strain energy of the equivalent single-layer FE must be equal to the sum of the strain energies of individual layers. The so-called energy coefficients are defined for this purpose for the extensional, bending and shear deformations of the composite structure. These coefficients are then determined and used as correction multipliers during stacking the elemental matrices of individual layers. Two approaches, based on second-order strain or stress distribution assumption through the composite thickness, are investigated for deriving the shear energy coefficients. The damping capability of the FE developed here originates from using complex Young’s modulus to define the material properties of individual layers. The resulting equivalent single-layer shell element with four nodes has six degrees-of-freedom per node. The accuracy, advantages and limitations of the composite FE developed in this work are investigated using experimental as well as theoretical results. In the light of the finding of these investigations, further enhancement in the formulation is made by also utilising a new shear correction factor for the individual layers in the equivalent shell element. Final results for free- and constrained-layered structures confirm that the equivalent shell FE developed here can be used effectively for the prediction of the modal properties of damped multi-layered structures.

Study of Factors Affecting Vibration Damping Properties of Multilayer Composite Structures

At the present time, mechanical vibration is undesirable in many cases. Therefore it is necessary to minimize unwanted vibrations in any appropriate manner. This paper is focused on a study of factors influencing vibration damping properties that were investigated using multilayer composite structures. Frequency dependencies of the displacement transmissibility over a frequency range of 2?1500 Hz were determined by the method of forced oscillations. It was found in this study that the vibration damping properties of investigated multilayer structures are significantly influenced by number of material layers, excitation frequency of mechanical vibration, applied materials in multilayer structures, inertial mass, material thickness and density. It was also observed that a superior ability to damp mechanical vibration leads to a shift of the first resonance frequency peak position to lower excitation frequencies.