Multilayer Panels Research Articles

The effect of micro-architecture on the failure response of multi-layered lattice sandwich panels under three-point loading

In this study, the failure behaviour of lattice sandwich panels under three-point loading has been studied using a nonlinear finite element analysis. This paper develops on a previous paper, where the similar failure behaviour was discussed. However, the originality of this paper lies in the fact that it investigates the effect of the micro-architecture of the lattice unit-cell on the failure response of lattice sandwich panels by introducing three geometrical parameters γx, γy and γz. In addition, lattice sandwich panels have been fabricated using a selective laser metal melting machine, and quasi-static bending tests on the panels were conducted and the accuracy of the present method for predicting the failure load is discussed by comparing the experimental data with the analytical results. It has been shown that the analytical results agree reasonably well with the experimental results.

A Moisture Penetrating Humidity Pump Directly Powered by One Sun Illumination

The humidity control has a broad and substantial demand all over the industrial, commercial and residential situations. The current humidity pumping technologies require high-intensive maintenance due to the complexity of the mechanical structures. Furthermore, the indirect utilization of solar energy increasing both cost and energy loss. Here, we demonstrate a new humidity pumping concept based on multi-layer moisture permeable panels. Such panels, with a simple structure, may allow the penetration of moisture from indoor(adsorption) to outdoor(desorption) with little heat loss. One sun illumination is introduced as the energy source. A proof-of-concept prototype is designed and established, and successfully dehumidifies the indoor air with a best dehumidification rate of 33.8 g·m-2·h-1. By applying such humidity pump, the indoor latent heat load can be handled independently and consumes no electricity. To our scope, this is the first design to realize humidity pumping under one sun illumination without any auxiliary unit.

Calculation features of wall panels with monolithic cement bond of layers in the stages of installation, transportation and maintenance

Introduction. When building residential, public and administrative buildings of various spatial structural designs (monolithic, precast-monolithic, precast, etc.), it is common practice to design self-sustaining (non-structural) outer walls within a storey. Developing and using new design and fabrication solutions of multilayer industrial-made wall panels in modern construction practice makes actual the issue of improving methods of their calculation in different stages of maintenance and under various sorts and combinations of loads and effects. However, there is an infinite variety of possible loading levels in practice and, therefore, the same variety of design approaches would be required. This is obviously unacceptable for engineering calculations, hence it is necessary to provide a monolithic matrix bond of layers, both technologically and structurally, which can provide a generalized approach to the calculation of multilayer enclosing structures in accordance with current design standards. Materials and methods. The article describes structural features of a multilayer wall panel made of structural concrete with the middle layer of concrete with low thermal conductivity and monolithic bond of layers. These features have an influence on creation of a design model and a calculation procedure in the stages of transportation, installation and maintenance. Results. The article has examined the structures described above in the sense of design parameters that provide their competitive advantages in strength and maintenance as compared with conventional mass-built enclosures. Conclusions. The studies demonstrate that when combining loads of force and non-force character, stresses in the considered structure do not exceed allowable values in all the stages what proves the prospects of using the multilayer panels with monolithic bond of layers for erection of various-purpose frame-panel buildings.

Evaluation of compressive properties of SLM-fabricated multi-layer lattice structures by experimental test and μ-CT-based finite element analysis

The influence of inherent imperfections should be systematically investigated to ensure the safety and utilization of additive manufacturing-fabricated multi-scale parts and structures. Herein, two different types of multi-layer lattice sandwich panels, BCC and BCCZ, are prepared by selective laser melting (SLM) using the AlSi10Mg material. X-ray micro-computed tomography (μ-CT) is employed to capture the realistic geometrical information of lattice struts. Based on the statistical characteristics, a novel finite element model is established, which considers the specific non-uniform distribution of geometrical imperfection. Uniaxial compressive tests are performed to evaluate the influence of defects and number of layers on the overall mechanical performance and energy absorption capability. The results reveal that the diameter deviation of struts is changed with the change of strut location and built angle. In terms of compressive modulus and initial crushing strength, the prediction results of the reconstruction model are consistent with experimental results as compared to the as-designed and statistical average models. The layer-by-layer crushing behavior is the main failure mode for the multi-layer lattice panels. With the increase of layers number, the densification strain and crash load efficiency increased, whereas the specific energy absorption gradually decreased due to the impact of boundary conditions and failure modes.

Broadband design of multilayer micro-slit panel absorbers for improved transparency using Bayesian inference

Multilayer Micro-Slit panels (MSP) are assessed for their potential as broadband absorbers that simultaneously maintain visual transparency. The late Dah-You Maa introduced micro-Slit panel absorbers as a continuation of his previously developed Micro-Perforated panel (MPP) absorbers. Like MPPs, Micro-Slit panels allow high absorption coefficients to be achieved without using fibrous materials but are limited to a narrow frequency bandwidth. Broadband absorption can be achieved by combining panels into a multilayer absorber. The complexity of determining the optimum set of parameters required to fulfill a design scheme necessitates implementation of the Bayesian framework. This probabilistic method automatically determines the most concise number of layers required and gives parameters for each layer of the resulting composite. Various slit patterns and algorithms introduce a family of solutions, which satisfy the design scheme, for optimization of visual transparency. The Micro-Slit samples can be fabricated and tested to validate acoustic performance and assess visual properties.

Multilayered architectured ceramic panels with weak interfaces: energy absorption and multi-hit capabilities

Combining high strength and high toughness still remains a challenge in engineered materials. With the aim of improving the toughness of high-strength ceramics, multilayered architectured ceramic panels were developed inspired by natural materials such as nacre and conch shell. These panels were manufactured by stacking laser-engraved architectured ceramic tiles and commercial monomer Surlyn or Ethylene-vinyl acetate (EVA) resins. The mechanics of the multilayered architectured ceramics was investigated both numerically and experimentally by subjecting them to out-of-plane quasi-static and impact loads. Digital image correlation (DIC), computed radiography technique, micro-CT scanning and 3D laser scanning microscopy were used for multiscale damage assessment during and after loading. The finite element analysis was performed using ANSYS LS-DYNA to model the quasi-static and impact responses and to investigate the effects of architectural parameters on the energy absorption and multi-hit capabilities of architectured ceramic panels. It was found that the multilayered ceramic panels with optimized architectures showed up to 20% and 48% improvements in energy absorption performance in quasi-static testing and impact loading, respectively, with only a 5–10% stiffness reduction compared to plain ceramics. The deformation analysis showed localized failure in the architectured ceramics (opposed to the plain ones) and improved impact resistance of architectured ceramics originating mostly from the energy dissipation due to the plastic deformation in adhesives (up to 35%) as well as the frictional energy dissipation (up to 55%) upon sliding of the tiles, mechanisms that are absent in plain ceramics.

Investigation of elastic properties of paper honeycomb panels with rectangular cells

Multilayer panels that have paper cores with hexagonal cells continue to have a limited application in furniture production. In contrast, there are no sandwich honeycomb panels with cores containing rectangular cells employed in this industry. Such cores should distinguish themselves by strong orthotropic advantages, in particular, for designing shelves and partitions of cabinet furniture. Hence, the objective of this study was to determine the effect of core rectangular paper cells on the mechanical properties of three-layer furniture panels. The authors decided to ascertain relative density and elasticity constants of the designed cells. The results of empirical experiments of cell elasticity moduli were compared with the results of the analytical calculations. The impact of sample width on their mechanical properties was determined. It was demonstrated that cores with hexagonal cells in furniture panels could be replaced by cores with rectangular cells.

Optimal design and experimental validation of sound absorbing multilayer microperforated panel with constraint conditions

Sound absorption performance of the multilayer microperforated panel can be improved through optimal design of structural parameters. Theoretical model of sound absorbing coefficient of the multilayer microperforated panel with different layers was constructed according to Maa’s theory. Structural parameters of the multilayer microperforated panel with layer number from 1 to 8 were optimized through the cuckoo search algorithm with constraint conditions. Preliminary verifications of the achieved optimal parameters were conducted by the analog simulation according to the finite element method. The obtained optimal design of multilayer microperforated panel with no more than 4 layers was finally validated by testing experiments based on the standing wave method, and the optimal average sound absorbing coefficients in the frequency range of 100–6000 Hz were 57.21%, 66.29%, 68.33%, and 69.36%, respectively. Through theoretical modeling, parameter optimization, analog simulation, and experimental validation, an effective method for development of the desired sound absorber was proposed, which will be propitious to promote the applications of the multilayer microperforated panel products in the field of noise reduction.

Edge effects in elastic and piezoelectric laminated panels under thermal loading

An analytical solution for accurately predicting the edge effects in elastic and hybrid multilayered panels integrated with piezoelectric actuator and sensor layers under thermal gradient loading is presented. The associated thermal problem is solved independently by performing a heat transfer analysis. The extended Reissner-type mixed variational principle is employed to develop the governing equations of the three dimensional (3D) piezothermoelasticity problem. Their solution is obtained using the mixed-field multiterm extended Kantorovich method, developed recently by the author group. The mixed field solution exactly satisfies all the mechanical and electric boundary conditions pointwise, leading to an accurate solution. The formulation is general, and is applicable for composite, sandwich and hybrid panels with arbitrary lay-up and boundary conditions. The solution is validated against the exact 3D solution available for simply supported panels. The free edge stress field in sandwich and hybrid composite laminates is investigated under uniform as well as gradient thermal loading. The solution successfully captures the singularity in free edge interlaminar stresses. The significance of pyroelectric coupling on the free edge thermal stress field is investigated, and the feasibility of its control through electric field actuation is examined.

Quality control of welding in titanium panels, made using method of diffusion welding and superplastic forming

Results of studies of nondestructive control of multilayer titanium panel, made by the method of diffusion welding and superplastic forming, are considered. By ultrasonic control of the echo method with the use of a direct piezoelectric transducer, areas on which diffusion did not occur or has not occurred completely, as well as various inclusions trapped in the welded joint area during assembly, are determined. The quality of the formation of the inner surface (corrugated sheet) can be controlled by radiographic inspection, and according to the results of the control, it is possible to detect breaks, cracks, and the violation of the shape of internal partitions that appear from a technological process failure.

A multilayer microperforated panel prototype for broadband sound absorption at low frequencies

Microperforated panel (MPP) absorbers are one of the most promising alternatives to porous sound absorbing materials. However, these structures cannot achieve high and broadband absorption at low frequencies. To be effective, once defined the material properties the geometrical parameters of the absorber need to be optimized to match the prescribed absorption level. This paper presents a multiple layer MPP absorber with a high sound absorption coefficient and broadband absorption at low frequencies. An electro-acoustical equivalent circuit model was used for a parametric analysis to study the relationships between the absorption mechanism and the absorbers geometrical parameters in the proposed multilayer MPP. A prototype of this absorber was machined and tested in an impedance tube test ring and the experimental acoustical properties in terms of absorption coefficient were extracted using the transfer function method. It was demonstrated that the five-layer MPP absorber was capable of guaranteeing a high absorption (constantly over 90%) in a frequency range from 400 to 2000 Hz. The results indicate that the proposed multilayer MPP absorber provides a good alternative for sound absorption applications.

Thermal protection system integrating graded insulation materials and multilayer ceramic matrix composite cellular sandwich panels

Current integrated thermal protection systems (ITPS) are generally devised with single layer metal sandwich panel and uniform insulation material, inevitably leading to limited thermal insulation effect and high risk of buckling failure. By contrast, here, ITPS, which incorporates graded insulation materials and multilayer ceramic matrix composite cellular sandwich panels, is devised to raise both thermal insulation effect and buckling strength. The effective thermal and mechanical properties are theoretically established. Transient heat transfer characteristics are numerically calculated. The results reveal that ITPS with specific graded insulation materials can present lower temperature and better temperature distribution uniformity than those of ITPS filled with uniform insulation material, demonstrating that graded insulation layers can firmly enhance the insulation effect. Besides, the insulation effect of ITPS, in which the densities and thermal conductivities of graded layers are taken arranged from low to high, is much better than those of ITPS which have opposite sequence. Moreover, the buckling strength is demonstrated to be significantly improved through the approach of integrating multilayer sandwich panels. The thermal short effect can be also suppressed, since it is demonstrated that the multilayer sandwich panels in the ITPS can reduce the temperature on bottom facesheet and raise the temperature distribution uniformity.

Experimental Determination of Acoustic and Vibroacoustic Characteristics of Multilayer Composite Panels

Comprehensive studies have been carried out on determining the acoustic and vibroacoustic characteristics of multilayer polymer composite panels of variable thickness installed in the opening between reverberation chambers. The acoustic insulation and acoustic excitability of the panels excited by a diffuse acoustic field, as well as their modal density, radiation loss factor, and total loss factor, have been determined for excitation with a vibration exciter in a wide frequency range. It has been shown that the panel characteristics have a universal character. Simple empirical relations have been derived to describe these characteristics. The measured vibroacoustic characteristics of the panels made of a polymer composite material have been compared to those of a traditional stiffened fuselage panel.

Effects of viscoelastic and porous materials on sound transmission of multilayer systems

Multilayer structures allow obtaining good performance in acoustic insulation to eliminate unwanted noise in the medium and high frequencies in many applications such as building and transport industry. In this paper, the sound transmission of multilayer systems is stu- died using the Transfer Matrix Method (TMM). The studied multi-layered panels include elastic, viscoelastic and porous materials. Several configurations of multilayer systems are studied, and their corresponding transmission loss TL is computed. Also, the effects of po- rous material characteristics are studied to evaluate the impact of each parameter.

Free vibration study of multilayer sandwich spherical shell panels with viscoelastic core and isotropic/laminated face layers

The present work deals with the free vibration and damping characteristics study of multilayer sandwich spherical shell panels with viscoelastic material core layers and elastic face layers based on first order shear deformation theory. The displacements of the core layers are assumed to vary linearly along the thickness. Longitudinal and transverse deformations of the core layers are taken in to account with the consideration of independent transverse displacements of the elastic layers. The equation of motion is derived using Hamilton's principle in conjunction with the finite element method. Eight number of sandwich shell panels are studied mainly in two groups viz. sandwich panels with laminated base layer and isotropic base layer. Fundamental frequencies and associated system loss factors of different sandwich shell panels are deduced by solving the equation as an eigenvalue problem. The effect of thickness of the constraining layers, thickness of the core layers, viscoelastic material loss factor and aspect ratio on the natural frequencies and system loss factors of the sandwich structures are investigated.

A systematic pattern generation system for manufacturing customized seamless multi-layer female soft body armour through dome-formation (moulding) techniques using 3D warp interlock fabrics

Female participants in different perilous tasks including law enforcement offices have been considerably increased in the last few decades. However, they mostly wear men’s body armour with smaller sizes which brings a negative upshot not only in ballistic protection performance, comfort, fitness but also in a psychological point of view. Hence, manufacturing female soft body armour based on their unique morphological differences for better ballistic protection without conceding fitness and comfort are in great demand. This research work presented a novel method using a systematic 3D design approach through parametrization process to generate block patterns for manufacturing successive layer in the panels. The deformable mesh on the 3D virtual adaptive female model was developed with grading values of zero. Parametrization process based on the thickness of each layer in the 3D design database was applied to generate the different successive meshes on the virtual mannequin with appropriate coordinates. Later, the multi-layers mesh developed on the virtual 3D female body has been flattened to acquire the different layer’s pattern. Due to its excellent mouldability behaviour, 3D warp interlock fabrics made of high-performance fibre has been designed and developed to manufacture the seamless female body armour with a dome-formation process. The manufactured multi-layer panels were draped on the standard female physical mannequin for experimental validations. The result shows that the new 3D design approach and its manufacturing system was found easy and precise to generate the different multi-layer panels pattern for developing seamless female soft body armour.

Comparison Sound Absorption Methods of Multilayer Micro-perforated Panels

Micro-perforated panel (MPP) absorbers as the next-generation sound absorbers are getting more widely use in aviation, automobiles, construction and other fields. It’s a complex problem to predict the acoustic performance using surface impedance methods. The acoustic absorption performance of micro-perforated panels were compared in terms of Transfer matrix method and Equivalent electric circuit approach (EECA). The calculated results show that transfer matrix method is more convenient and effective than the equivalent circuit approach especially to multiply layer micro-perforated absorbers.

Crushing behavior of multi-layer metal lattice panel fabricated by selective laser melting

With the development of the additive manufacturing technique, periodic lattice structures have received increased attention due to their excellent stiffness-to-weight ratio. In this study, the effects of layer and cell numbers on the quasi-static compressive responses of a lattice sandwich panel are systematically investigated through theoretical modeling, experimental testing, and finite element method. A theoretical model is proposed to predict the compressive modulus and initial crushing strength of the multi-layer lattice panels with body-centered cubic with vertical strut (BCCZ) cells. A series of BCCZ panels with various layers is fabricated by selective laser melting (SLM) using AlSi10Mg. The deformation mode and failure mechanism of the structures are analyzed based on the compressive results. Finite element analysis (FEA) is conducted, and its results are compared with the experimental and theoretical results. Modulus and strength decrease remarkably with the increase in layer number ascribing to the weak boundary of cells close to the edge. Layer-by-layer progressive damage is the main failure mode in the multi-layer panel, and multiple peak stresses are observed. The theoretical prediction results are in line with the experimental and FEA results. This work can provide guidance in the design of lightweight lattice structures.

Moisture related elastic and viscoelastic behaviour of wood adhesives by means of in-situ nanoindentation

The adhered wood in multi-layered panels is subjected to different stress and strain states as a result of moisture induced swelling and shrinking. Consequently, it is expected that the adhesive layer has to compensate these stresses and responds beside elastic with viscoelastic deformation.To better understand the humidity dependent mechanical behaviour of commonly used cured wood adhesives, different adhesive systems that are currently used in furniture and flooring industry (emulsion polymer isocyanate EPI, polyvinyl acetate PVAc, urea formaldehyde UF and ultra-low emitting formaldehyde amino adhesive ULEF) were investigated by means of in-situ nanoindentation. Therefore, spruce (Picea abies) lamellas were adhesively bound under laboratory conditions. Micro-mechanical properties of adhesive layers, such as elastic modulus, creep and relaxation were investigated in quasi-static mode at constant temperature and different controlled humidity levels to monitor the mechanical response of the cured adhesive polymers in the corresponding ambient.As a general trend, all adhesives respond with decreasing elastic modulus to increased humidity. EPI revealed the most stable elastic behaviour to moisture. In contrast PVAc, UF and ULEF show significant differences with changing relative humidity levels. Lowest creep and relaxation was observed for UF and ULEF, followed by EPI. The most sensitive behaviour to moisture was observed for PVAc adhesive polymer.

Experimental study on quasi-static penetration process of cylindrical indenters with different nose shapes into the hybrid composite panels

The main aim of the present research is to investigate the quasi-static penetration process of cylindrical indenters with different nose shapes into multilayered composite panels made of Dyneema and Glass woven fibers, and aluminum face sheets. For better understanding of the perforation mechanism of the composite panels, effects of indenter geometry, stacking sequences, and boundary conditions are studied and their effects on energy absorption, specific absorbed energy, maximum deformation, peak load, and failure modes are evaluated and discussed. Samples with different layering configurations loaded under quasi-static punch and indentation with loading rate of 5 mm/min using universal testing machine and cylindrical rigid indenters with different nose shapes geometries consist of blunt, hemispherical, conical, and ogival. Regarding the boundary condition effects, two different rigid fixtures are designed and manufactured with the same external square perimeter (250 × 250 mm) and two different internal perimeters of circular and square shapes respectively, with diameter of 15 mm and edge side of 100 mm. Results show that the hybrid composite panels composed of Dyneema sheets, exhibits significantly better load carrying capacity and specific absorbed energy under both loading conditions. Indenter nose shape significantly affects elastic load, peak load, and energy absorption and maximum deformation. Furthermore, from visual observations based on digital microscopic images, fiber breakage, fiber pull out, intralaminar delamination, and debonding between the composite layers within the damage zone were inspected and recognized as the main damage mechanisms of panels. Output data obtained from all the experimental investigation were reported, discussed, and commented upon.