Multilayer Panels Research Articles

Numerical investigation on ballistic resistance of aluminium multi-layered panels impacted by improvised projectiles

This paper presents a numerical study of perforation of the aluminium multi-layered targets impacted by steel projectiles in the shape of a ball, nut and nail. For the construction of the protective panels arc-, rectangular-, V- and U-shaped sheets of metal were considered. During the tests the panel thickness was constant at 160 mm. The panels were composed of 1.5-mm-thick aluminium sheets, and the initial speed of debris was 500~mathrm{m{/}s}. A comprehensive numerical study indicated the shape of the layer that had superior ballistic resistance and the best strength-to-weight ratio. Computational analyses were also used to investigate the influence of thermal softening and strain rate hardening in the Johnson–Cook constitutive model on the ballistic performance of layered targets. The number of layers required to stop the penetrating objects was compared for the rigid and deformable projectiles. Based on the comparative studies, some guidelines for engineering tasks involving exploration of number of possible technical solutions were proposed.

Exterior walls covering system to improve thermal performance and increase service life of walls in rehabilitation interventions

The main objective of the current study was to develop a product for wall coverings that would allow an easy application, in particular for building rehabilitation, and the walls’ protection improving buildings’ energy efficiency.A multilayer panel was developed, with two different decorative finishes. The panel is applied by bonding with a mortar fixative to the walls. The performance assessment test allowed to verify that these covering panels are easy to apply and improve buildings’ energy efficiency.Some fragilities were pointed out. Although, it was possible to conclude that this solution is viable in terms of production and application.

Acoustic properties of multilayer sound absorbers with a 3D printed micro-perforated panel

This paper investigates the acoustic absorption capability of a multilayer micro-perforated panel absorber (MPPA) whose front layer is produced by additive manufacturing. The MPPA layers are printed using a polymer material, where the different hole spacing is used to create different perforation ratios. The sound absorption coefficients are experimentally measured by using an impedance tube test, to investigate the effects of the perforation ratio and the depth of an airgap behind the MPPA. Also, a porous sound absorbing material layer is attached behind the MPPA layer in order to produce a multilayer acoustic absorber. The measurement results are compared to a theoretical approach. The comparisons show that the measured sound absorption coefficients agree fairly well with the theoretical model. The use of a porous sound absorbing material behind the MPPA broadens the frequency bandwith of the multilayer acoustic absorber. The frequency of the maximum sound absorption coefficient can be varied, by altering the perforation ratio of the MPPA and/or the depth of the airgap behind the panel.

A Study on Structural Improvement of Image Slider Using Multi-layer Control Panel with Flexible Structure

이미지슬라이더는 웹 UI 요소의 하나로서, 웹 사이트에서 슬라이딩 방식으로 이미지에 포함되어 있는 정보를 전달하는 중요한 역할을 한다. 최근에는 메인페이지 상단에 놓여 웹 사이트의 전체적이고 함축적인 정보를 표현하기도 한다. 이러한 중요한 역할에도 대부분의 웹 사이트에서 서비스되고 있는 이미지슬라이더는 단순하고 획일적인 구조를 하고 있다. 이에, 본 논문에서는 가변구조를 갖는 다층 컨트롤패널을 이용한 새로운 구조의 이미지슬라이더 구현 방법을 제안한다. 제안한 방법은 멀티슬라이딩 기법을 사용하여 시각적인 효과를 향상할 뿐만 아니라 메인이미지슬라이더에 이미지 분류기능을 갖춘 서브이미지슬라이더를 탑재함으로써 기존의 이미지슬라이더에 비해 검색기능을 향상할 수 있다.

Preliminary Study on Multilayer Bulletproof Concrete Panel: Impact Energy Absorption and Failure Pattern of Fibre Reinforced Concrete, Para-Rubber and Styrofoam Sheets

Abstract This manuscript presents the preliminary test results from the multilayer bulletproof concrete panel project. The purposed multilayer panel consisted of steel fibre reinforced concrete, Para-rubber and Styrofoam sheet. In this study, the failure patterns and energy absorption of each material with different thickness subjected to direct fire arm with 9 and 11 mm. bullets were investigated. The obtained information will later be used in designing the multilayer bulletproof concrete panel based on combination of energy absorption. The results showed that the energy absorption of each material increased with the increasing thickness. In case of FRC, the energy absorption also depended on fibre type and volume fractions. Comparing at the same thickness, FRC was the most effective energy absorption followed by Para-rubber and Styrofoam sheet.

Numerical evaluation of natural vibration frequencies of thermo-modernized apartment buildings subjected to mining tremors

Prefabricated, with load-bearing walls, apartment buildings represent a significant group of objects, especially occurring in the countries of Central and Eastern Europe. They were built in 50’s, 60’s and 70’s of 20th century. Nowadays, the new European Union environmental regulations forced such buildings’ modernization, mainly regarding energy efficiency. Usually, in order to improve their energy properties and, as the result, to reduce the energy losses, the external walls thermal insulation is performed. This is one of the fastest and cheapest method increasing the thermal resistance of walls of buildings constructed using relatively old technology. Extra thermo-modernization layers of the prefabricated walls (consisting of materials such as styrofoam, reinforced mortar, glass fibre textile mesh) bring additional mass to the building and could change its stiffness. The dynamic properties of the structure could be changed as the result. Changes in the natural frequencies of vibrations are the most important among them–calculations of these values are necessary especially in the case of buildings located in paraseismic or seismic areas. In the paper the influence of the additional multilayer thermal insulation of the external walls on the natural vibration frequencies of high (12 storey) actual apartment buildings subjected to mining tremors is investigated. Numerical calculations were carried out using finite element method software. Various approaches to the modelling of prefabricated load bearing walls before and after thermo-modernization were analyzed and discussed. A simple one layer model of walls with equivalent stiffness as well as multi-layer one were taken into consideration. Finally, the simple model reducing multi-layer panel to one layer panel with equivalent (substitute) Young modulus and equivalent (substitute) Poisson’s ratio was recommended for the practical calculations of the dynamic properties of buildings. Numerically evaluated natural vibration frequencies of the buildings before and after thermo-modernization were verified by the experimental data obtained for actual structures.

Effect of applied magnetic field on sound transmission loss of MR-based sandwich panels

This study aims to investigate the sound transmission loss (STL) capability of sandwich panels treated with Magnetorheological (MR) fluids at low frequencies. An experimental setup has been designed to investigate the effect of the intensity of applied magnetic field on the natural frequencies and STL of a clamped circular panel. It is shown that the fundamental natural frequency of the MR sandwich panel increases in proportion to the applied magnetic field. In addition, the STL of the panel at the resonance frequency increases as the magnetic field is amplified. Furthermore, the classical plate theory and Ritz method have been utilized to develop the governing equations of motion of the finite multilayered circular panels comprising two elastic face sheets and MR fluid core layer. The radiated sound power from the panel is derived using Rayleigh integral as a function of the transverse velocity of the panel which is subsequently used to evaluate the STL. The theoretical study is validated comparing the simulation results with the experimental measurements. Experimental and analytical parametric study have also been conducted to study the effect of the core layers’ thickness on the natural frequency and the STL of sandwich panel.

Investigation on energy absorption efficiency of each layer in ballistic armour panel for applications in hybrid design

This study aims to reveal different energy absorption efficiency of each layer when armour panel is under ballistic impact. Through Finite Element (FE) modelling and ballistic tests, it is found that when fabrics are layered up in a panel, energy absorption efficiency is only 30%–60% of an individual fabric layer with free boundary condition. In addition, fabric layers in front, middle, and back exhibit different ballistic characteristics. Therefore, a new hybrid design principle has been proposed. A multilayer panel can be divided into three groups. Two hybrid panels that are combined different Twaron fabrics and Dyneema UD laminates are designed. Ballistic tests results show that for a given areal density of the panel, BFS behind the hybrid panel decreases 31.54% than that of the woven fabric panel. When the areal density of armour panel is reduced, the hybrid panel is more likely to stop the projectile. These findings provide a guide for hybrid design of ballistic armour panel.

Shell elements with through-the-thickness variable kinematics for the analysis of laminated composite and sandwich structures

Abstract Several efforts have been made in the last years to improve the efficiency and the effectiveness of structural models for the analysis of laminated shell structures. Among the others, many recent and past works in the literature have been aimed at formulating theories of structures that maximize the accuracy of analysis meanwhile reducing the computational costs. In this paper, this objective is pursued by implementing advanced shell theories with through-the-thickness variable kinematic capabilities. By employing the Carrera Unified Formulation (CUF), the proposed shell model is obtained by expressing the displacement field as an arbitrary and, eventually, hierarchical expansion of the primary unknowns along the thickness. Thus, Equivalent-Single-Layer (ESL), Layer-Wise (LW) models as well as variable kinematic models which combine ESL and LW approaches within the shell thickness can be obtained in a straightforward and unified manner. After the unified shell model is formulated, the governing equations and the related finite element arrays are obtained by employing the principle of virtual work. A nine node finite element is implemented to approximate the solution field, and the Mixed Interpolation of Tensorial Components (MITC) method is used to contrast the membrane and shear locking phenomena. Some numerical examples are discussed, including three- and ten-layered cross-ply shells under bi-sinusoidal load and simply-supported boundary conditions, a multilayered spherical panel subjected to bi-sinusoidal load and a sandwich cylinder undergoing bi-sinusoidal pressure. Moreover, various thickness and radius-to-thickness ratios are considered. Whenever possible, the results are compared with those from the literature and from exact elasticity solutions. The analysis of the results clearly shows the enhanced capabilities of the present variable-kinematic shell element, which allows the analyst to opportunely reduce the computational costs and enhance the accuracy of the model only in those regions of the thickness domain where an accurate evaluation of the stress/strain field is needed.

Numerical Study on the Projectile Impact Resistance of Multi-Layer Sandwich Panels with Cellular Cores

THE PROJECTILE IMPACT RESISTANCE OF SANDWICH PANELS WITH CELLULAR CORES WITH DIFFERENT LAYER NUMBERS HAS BEEN NUMERICALLY INVESTI-GATED BY PERPENDICULAR IMPACT OF RIGID BLUNT PROJECTILE IN ABAQUS/EXPLICIT. THESE PANELS WITH CORRUGATION, SQUARE HONEY-COMB AND PYRAMIDAL TRUSS CORES ARE IMPACTED AT VELOCITIES BE-TWEEN 100M/S AND 900M/S WHILE THE RELATIVE DENSITY RANGES FROM 0.005 TO 0.20. THE EFFECTS OF CORE CONFIGURATION, RELATIVE DENSITY AND LAYER NUMBER ON PROJECTILE IMPACT RESISTANCE OF SANDWICH PANELS WITH CELLULAR CORES ARE STUDIED. AT LOW IMPACT VELOCITY, SANDWICH PANELS WITH CELLULAR CORES OUTPERFORM THE CORRESPONDING SOLID ONES BUT NON-MONTONICITY BETWEEN RELATIVE DENSITY AND PRO-JECTILE RESISTANCE OF SANDWICH PANELS IS FOUND AND ANALYZED. THE INITIAL PEAK LOAD VALUE IS REDUCED UP TO 71.8% BY MULTIPLYING LAYER AND MOREOVER INTERACTION TIME BETWEEN PROJECTILE AND CORRUGATION AND PYRAMIDAL TRUSS SANDWICH PANEL CAN BE EXTENDED BY INCREAS-ING LAYER NUMBERS. AT HIGH IMPACT VELOCITY, THOUGH CORRUGATION AND HONEYCOMB SANDWICH PANELS ARE INFERIOR TO THE EQUAL-WEIGHTED SOLID PANELS, PYRAMIDAL TRUSS ONES WITH HIGH RELATIVE DENSITY OUT-PERFORM THE CORRESPONDING SOLID PANELS. MULTIPLYING LAYER IS NOT ALWAYS A DESIRABLE WAY TO IMPROVE HIGH-VELOCITY PROJECTILE RE-SISTANCE.

Influence of the type of fastening of multi-layered closing panels on the estimate of the sound transmission loss

Industrialized closing systems appear as rational solutions in steel-structured construction. These closing systems, consisting of multi-layered panels, have been applied in projects where it is intended to obtain a high sound transmission loss without raising the cost and without using a lot of mass. However, acoustic isolation depends on several factors, including the type of connection between the panels, requiring a preliminary study of the acoustic performance of the closing system to prevent future interventions. This paper uses a simplified graphical method to evaluate the influence of the type of connection (line-line, line-punctual or punctual-punctual) of industrialized closing panels on the estimation of the sound transmission loss that occurs across the wall constituted by these panels. The panels are combined, forming multi-layered closings interleaved by a layer of air, either without or with a sound-absorbing material between them. The results show that it is necessary to check the effectiveness of each type of fastening of the closing systems because, for example, for the frequency range between 500 and 2,000 Hz, the sound transmission loss of a closing system consisting of cementitious plate with glass wool and line-punctual and punctual-punctual connections exceeds in 6.25% the sound transmission loss of the same system with line-line fastening. For a system composed of expanded polystyrene with glass wool, the sound transmission loss provided by line-line fastening exceeds in 7.0% the sound transmission loss of the same closing system with line-punctual and punctual-punctual fastenings.

Investigation of energy absorption mechanisms in a soft armor panel under ballistic impact

This study aims to identify different contributions of each layer to ballistic resistance and energy absorption distribution in a soft armor panel under ballistic impact. Different ballistic responses of each fabric layer and energy absorption mechanisms of a multilayer panel were investigated through finite element (FE) analysis using Abaqus. FE models were created to simulate transverse impact of a projectile onto multilayer panels before clay. FE results show that fabric layers in front, middle and back of the panel exhibit different extents of transverse deformation and stress distribution characteristics. Energy absorption in each layer is increased from the front layer to the peak value at the last perforated layer and then gradually decreased in following back layers of the panel. This pattern remains the same regardless of increasing total number of layers in the panel. When increasing the impact velocity, the position of the peak value of energy absorption with the last perforated layer is shifted towards back of the panel. These fundamental understandings contribute to the hybrid design of soft armor panel.

FDTD Simulation of Lightning Current in a CFRP Panel: Comparison of the Use of Conductivity Matrix Approach With That of Triangular Prism Cells

The transient distribution of lightning current, which flows in a multilayer carbon-fiber-reinforced plastic (CFRP) material of aircraft, has been studied using the finite-difference time-domain (FDTD) method. Each layer of the multilayer CFRP panel has a fiber direction of 45°, 90°, –45° or 0°, and, therefore, has an anisotropic conductivity: the conductivity is high in the fiber axial direction and low in other directions. It is impossible to represent such an anisotropic layered panel using the FDTD method with common rectangular prism or cubic cells. In this letter, two approaches are employed: one is the application of conductivity matrix having off-diagonal elements and the other is the application of triangular-prism cells. The transient distribution of the magnetic field over the surface of the CFRP panel, computed with the former approach, is compared with that computed with the latter approach. Also, the results are compared with the corresponding measured ones.

In Russian

In this paper heterogeneous subjects are investigated, namely laminated nanoparticles and flat-layered media. Common feature of objects under consideration is presence of surfaces divided into slabs with different physical characteristics. The aim of the work is to demonstrate large possibilities and certain preferences of transfer matrices method for solution different problems of applied physics and generalization of the results taken out by author early. The method is especially convenient for analysis of such systems under action of different external physical fields. The method makes possible to transfer boundary conditions from slab to slab, to avoid the necessity of consideration of high order algebraical systems and matrices inversion problem is reduced to theirs simple multiplication. We presented a general scheme of building transfer matrices based on conversion of partial differential equations to ordinary differential equations with using expansion by a system of orthogonal functions. In addition to known results, the transfer matrices for inhomogeneous differential equations are constructed, i.e. those for physical systems with internal energy sources. Transfer matrix method has been used to solve some applied problems, especially problems of electromagnetic scattering on ellipsoidal nanoparticles (electrostatic approximation), spherical particles (electrostatic and wave approximations), expressions for calculations of electrical energy in slabs are found. Solution of Eigen value problems for multilayer panels is constructed, design formulas for determination of oscillation Eigen frequencies of multilayer panel with using three-dimensional elasticity theory are also obtained. Design formulas and some typical artwork are presented.

Fire Behavior of Sandwich Panels for Roofing Applications

Cement-based multilayered panels represent a promising and cost-effective solution for the roofing of modern prefabricated buildings. Due to the spread of such technologies, it is deemed necessary to evaluate the structural performances also with reference to the fire scenario. In the framework of a research project financed by national and regional authorities, Politecnico di Milano coordinated a wide experimental campaign aimed at assessing the mechanical behavior of innovative composite elements (2.5 m wide, 5 m long). The paper presents the results pertaining to the full-scale test of a prototype at high temperatures - mainly focusing on Temperature-Time and Displacement-Time diagrams - and provides a fire resistance classification compatible with the observed failure mode.

Frequency-dependent mechanical modelling of poro-elastic materials for sound transmission loss simulations

Multilayer panels made of sheet steel, a poro-elastic layer and an impervious mass are widely used in noise control for increasing sound insulation. A complete description of the vibro-acoustical behavior of the poro-elastic material used in these panels requires knowledge of mechanical parameters (i.e. complex modulus and Poisson's ratio) in order to model the wave propagation through the elastic structure constituting its skeleton. Although many of the materials used for noise and vibration control have viscoelastic behavior, prediction models currently make use of the linear elasticity theory. As a consequence, acoustical quantities, such as sound transmission loss, are predicted by using static or quasi-static values of mechanical properties. In this research, an experimental time domain approach in combination with an analytical model for linear viscoelasticity is utilized for determining the frequency-dependent complex modulus and increasing the accuracy of sound transmission loss simulations in practical applications.

Approaching a methodology for the development of a multilayer sound absorbing device recycling coal bottom ash

The aim of the present work has been to develop a methodology which accurately predicts the acoustic behavior of a material without having to manufacture large panels and testing them in reverberation room. Moreover, it can be predicted the sound absorbing performance at normal and random incidence of the sound wave on a material for different thicknesses and multilayer configurations, dramatically reducing the number of experimental tests. This methodology might decrease the cost of the investigation, which is particularly important when dealing with recycled materials that must compete with commercial products used in the same application.The designed methodology consists of determining the acoustic intrinsic properties (open porosity, tortuosity and static airflow resistivity) of bottom ash-based concretes with different particle sizes by an indirect method. This method uses the acoustic absorption coefficient measurements obtained in the impedance tube and the mathematical equations that describe the acoustic behavior of porous materials, implemented in the software CARAM. With the intrinsic properties, the thickness of the panel and the vibroacoustic behavior simulation software SIMAM, simulations of the sound absorption coefficient are performed and compared to the experimental results at normal incidence in the impedance tube and at diffuse incidence of a multilayer panel tested in reverberation room.From the results obtained it can be concluded that the methodology proposed in this work gives accurate results of the acoustic absorption of products at industrial scale, with the advantages of requiring small specimens of the materials to carry out the characterization tests, and decreasing the total cost of the investigation.

Bamboo-Derived Fuel from Dendrocalamus latiflorus, Phyllostachys makinoi, and Phyllostachys pubescens Waste

Bamboo is used as a raw material for producing chopsticks, artifacts, utensils, plywood, fiberboard, and decorated multi-layered panels. The manufacturing process generates a large amount of bamboo residual waste. In this study, bamboo-derived fuels were prepared from the residual waste of Dendrocalamus latiflorus, Phyllostachys makinoi, and Phyllostachys pubescens. The combustion behaviors of bamboo-derived fuels were also investigated. The characteristics of derived fuels made from bamboo waste with engine oil waste showed that the ash content was less than 5% and that the calorific value reached 5,000 kcal/kg, which was higher than derived fuels standards. Additionally, the derived fuel of bamboo waste had a high combustion efficiency and low nitrogen, sulfur, and chlorine emission levels, which were lower than the derived fuels standards. Thus, bamboo-derived fuel prepared from Dendrocalamus latiflorus, Phyllostachys makinoi, and Phyllostachys pubescens waste mixed with engine oil waste is a suitable fuel alternative.

Modeling and experimental analysis of polypropylene honeycomb multi-layer sandwich composites under four-point bending

The behavior of a simple and innovative multi-layer sandwich panels having a polypropylene honeycomb core has been investigated carefully, theoretically and experimentally. A four-point bending test was performed to detect the mechanical characteristics of the multi-layer core. The experimental results emphasize a better rigidity of the multi-layer structure compared to the weakness displayed by the single-layer configuration. In fact, a small increase in the final weight of the component leads to a significant increase of the mechanical properties. In the second part of this study, analytical and numerical homogenization approaches were developed to compute the effective properties of the single polypropylene honeycomb core. The numerical model complies with the experimental protocol, and the simulation conducted is aiming to reproduce a typical four-point bending test on a polypropylene honeycomb multi-layer sandwich panel. Both numerical and experimental results are presented in details and a good correlation between them is highlighted.

Blast Resistance of Hybrid Elastomeric Composite Panels

In this study, a finite element model was developed to understand the deformation and failure mechanisms of a multi-layered composite panel under blast. Fibre (E-glass fiber) and matrix (vinylester resin) damage and degradation of individual unidirectional composite laminas were modelled using the Hashin failure model. The delamination between laminas was modelled by a traction-separation cohesive law. A Polyurea layer was placed at the rear of the panel to study its effects on the damage evolution in the composite laminas, and was modelled using a Mooney-Rivlin constitutive law. The model-predicted deformation histories, fiber/matrix damage patterns, and inter-lamina delamination were compared between monolithic and composite panels. The model revealed that the Polyurea plays an important role in improving the panel’s performance.