Sandwich Materials Research Articles

Study on the effect of different sandwich materials on the impact resistance of laminated glass

In this paper, four types of laminated glass with various sandwich materials, polyvinyl butyral (PVB), polyurethane (PU), ethylene vinyl acetate (EVA), and SentryGlas® Plus (SGP), were selected to obtain the impact mechanical parameters and crack space development of laminated glass under different impact velocities by using light gas gun flyer plate variable velocity impact combined with CT scan-3D reconstruction technique. The findings demonstrated that different impact velocities had various demands on the elastic modulus of the sandwich material, showing the impact resistance demands of low velocity-high flexibility and high velocity-high rigidity. From the full-dimensional crack characterization under the medium-velocity impact, it could be seen that the comprehensive characteristics of the sandwich material viscosity, ductility, and rigidity led to different total volume, density, and spatial distribution complexity of cracks. This research provides important practical value and technical support for the selection and improvement of laminated glass.

Enhanced piezoelectric properties of flexible PDMS sponges modified by PTFE solid films and nanoparticles

• Elastomer-based sandwich material with enhanced piezoelectric performances. • emarkable stability in harsh environments. • Low cost and simple fabrication process. Polydimethylsiloxane (PDMS) sponges are widely used in many application areas due to their porous structure. In this paper, we present a PDMS sponge-based piezoelectric material which is composed of a PTFE-PDMS composite sponge sandwiched between a pair of Polytetrafluoroethylene (PTFE) solid films. After corona charging, pores inside the sandwich material are internally charged, and charges of positive or negative polarity are produced. The introduction of PTFE nano-particles creates PTFE-PDMS interface traps that can trap charges with stability. The design of the sandwich structure enhances the breakdown strength of the sandwich material, which avoids the early breakdown during poling. The results of the experiments demonstrate the sandwich material exhibits excellent piezoelectric performance and stability.

Investigation of bird-strike resistance of composite sandwich curved plates with lattice/foam cores

Bird strike is one of the most significant threats to the safe operation of aircraft. Lattice material with high porosity and excellent energy absorption provides more designability for aircraft structures. This paper uses the Finite Element Method and Smoothed Particle Hydrodynamics to investigate the bird impact resistance of composite sandwich curved plates. Lattice material, foam, and lattice-foam hybrid cores are used in this study to enhance the composite against bird impact. The effects of different panel configurations and core structures on the impact response are considered. The results show that the lattice core sandwich structure can enhance the impact resistance of composite materials, mainly reflected in the minor deformation of the structure, which can significantly reduce the bird impact force and reduce the residual kinetic energy of the bird. A thinner front face-sheet assigned to the lattice material sandwich plate would give it better resistance to impact and deformation than the other two sandwich types. Furthermore, a thicker front face-sheet can better resist damage to the composite panel caused by bird impacts.

Nonlinear axisymmetric buckling analysis of the FGM sandwich shallow spherical shells under thermomechanical loads

Functionally graded material (FGM) sandwich shallow spherical shells are promising composite sandwich structures for modern engineering applications. In this paper, the axisymmetric snap-through buckling of spherical shells under uniform external pressure and non-uniform temperature rise along the shell thickness was studied. Based on the classical shell theory and the Sanders nonlinear kinematics equations, we established a two-point boundary value problem (BVP) posed by the displacement-type nonlinear ordinary differential equations governing the axisymmetric buckling of the FGM sandwich shallow spherical shells and the clamped boundary conditions. Then, the solutions of the above BVP were obtained using the numerical shooting method. The influence of initial term numbers of the infinite series defining the non-uniform temperature field on the accuracy of the solution was examined. Numerical calculations showed that a considerable initial term number of the series were needed to obtain the applicable solutions for engineering. Some valuable conclusions were drawn through detailed parameter studies. As the radius of the bottom circle increases, the lower critical load of shells decreases, the jump amplitude of buckling increases, and the upper critical load remains almost unchanged. The upper and lower critical loads and the jump amplitude increase as the circle radius of the middle surface of shells decreases. When the thickness of shells increases, their upper and lower critical loads increase, whereas the jump amplitude of buckling reduces. The gradient index has a significant effect on the steady-state response of pre-buckling spherical shells but little effect on that of post-buckling spherical shells. When the temperature rises, the upper critical load and the buckling jump amplitude of shells increase, but the lower critical load decreases. When the gradient index is greater (less) than about 0.35, the upper critical load decreases significantly (increases slightly) with the increase in the relative thickness of the FGM core. The present numerical results are well consistent with the finite element results and those in the available literature.

Thermal strain energy induced wave propagation for imperfect FGM sandwich cylindrical shells

An investigation is developed to analyze the heat-induced wave propagation characteristics of imperfect functionally graded material (FGM) sandwich cylindrical shells composed of a metal core layer and two functionally graded materials (FGMs) surface layers in a thermal environment by using the first-order shear deformation (FSD) shell theory. The temperature-dependent material properties are assumed to vary continuously along the thickness direction. Two types of porosity in FGMs layers of sandwich cylindrical shells are taken into account. To describe the porosity effects, the new porosity function composed of the porosity distribution function, core-to-thickness ratio, and porosity volume fraction is proposed. A novel thermal strain energy approach is established for cylindrical shell structures in a high-temperature environment by introducing Green’s nonlinear strains. The Hamilton’s principle is applied to derive the wave motion equations that govern the wave propagation behaviors. The analytical solutions of dispersion relations are determined by solving a generalized eigenvalue problem. In addition, a parametric investigation is conducted to study the effects of axial and circumferential wave number, porosity type and volume fraction, core-to-thickness ratio, power-law exponent, temperature changes, and radius-to-thickness ratio on the wave propagation characteristics of imperfect FGM sandwich cylindrical shells in high-temperature environments.

Thermomechanical characterization and thermal simulation of a new multilayer mortar and a light-weight pozzolanic concrete for building energy efficiency

A brand-new sandwich material has been developed with a pozzolan-granular, plaster composite core and two cement mortar protective layer. The main goal of this study is to test the thermal behavior of a new sandwich material as well as the thermomechanical characteristics of pozzolanic concrete. The effects of granulomere sizes on the thermal properties of sandwich materials, as well as the volume fraction of pozzolan on the thermomechanical properties of lightweight concrete, have been studied. As a reference, mortar and concrete samples were made. The morphology and chemical composition of pozzolan granular were studied using scanning electron microscopy and X-ray fluorescence respectively. An energy building simulation of a prototype by Using TRNSYS simulator software, with variable internal and external walls composition, is performed; in order to evaluate the energy performance of sandwich material and lightweight concrete with optimum mechanical and thermal properties obtained from this work. Experimental results have shown that the incorporation of pozzolan as aggregates in the multilayer material and the concrete improves their thermal behavior. For multilayer material, it was shown that thermal conductivity varies from 0.682 W.m−1.K−1 to 0.42 W.m−1.K−1 for a sandwich sample having a granular size of pozzolan (7–20 mm) compared with reference mortar with 21.17 % mass gain. Concerning effusivity and diffusivity, of the same samples are varied from 723 to 575 J m−2.K−1.s−1/2 and from 3.51 to 2 10–7 m2.s−1 respectively. While for concrete without pozzolanic aggregate compared with a lightweight concrete sample having 100 % of volume fraction of Pozzolan, the thermal conductivity varies from 1.5 W.m−1.K−1 to 0.79 W.m−1.K−1 respectively with 31 % mass gain. Unfortunately, the mechanical performance decreases. The results of the thermal simulation have shown that sandwich material and lightweight concrete might be used in the thermal building envelope and walls. It offers significant reductions in cooling and heating energy consumption of 22 % and 14 %, respectively, as well as a significant yearly decrease in CO2 emissions of roughly 611.57 kg CO2e and 810 KgCO2e. When compared to other common wall materials, the results reveal that the new green construction materials have exceptional self-insulation properties.

Experimental and numerical study on seismic performance of a novel type of cold-formed steel shear wall with built-in sandwich panels

The purpose of this paper is to study the seismic behavior of the cold-formed thin-walled steel composite wall with built-in honeycomb sandwich and analyze its failure mechanism. A total of 13 monotonic and cyclic loading tests of wall specimens were completed in this paper, including four for observing the force and failure mode of the built-in sandwich of cold-formed steel (CFS) frame specimens, and nine specimens sheathed with double-sided oriented strand board (OSB). The mechanical performance indicators such as shear bearing capacity, stiffness, ductility, energy dissipation capacity and stiffness degradation of the honeycomb sandwich and other sandwich CFS shear walls were compared and analyzed. The experimental results demonstrate that the failure mode of the wall specimens is mainly ductile failure, including chord stud buckling or tearing, screw tilted, sank into the panel, or cut off at the connection between the honeycomb sandwich and the track. The built-in honeycomb sandwich can play a better role as a skin, which can significantly improve the shear bearing capacity and stiffness of the composite wall, but reduce the ductility. The sheathing and studs can effectively limit the out-of-plane buckling deformation of the sandwich panel and give full play to the properties of the sandwich material, thereby improving the shear bearing capacity, stiffness and energy dissipation capacity of the wall, as well as improving the ductility. The effects of wall aspect ratio and sandwich thickness on the seismic behavior for the built-in honeycomb sandwich CFS shear wall were analyzed by finite element analysis (FEA) and compared with the flat steel plate sandwich and OSB plate sandwich wall. And the nonlinear simplified analysis model of the composite wall under cyclic loading was established by SAP2000.

Porosity-dependent buckling analysis of elastically supported FGM sandwich plate via new tangent HSDT: A meshfree approach

In this paper, new tangent shape function-based higher-order transverse shear deformation theory (NTHSDT) is proposed to compute the buckling behavior of the elastically supported functionally graded material (FGM) sandwich plates under porous medium. The proposed theory is found to be variationally consistent and fulfills the zero traction boundary conditions on the bottom and top layer without a shear correction factor. The material properties are presumed to be graded in the thickness direction as characterized by a modified power law distribution in terms of volume fraction of constituents. The governing equations are derived using Hamilton’s Principle. A strong form of solution discretizes the governing equations by employing a thin plate spline radial basis function-based collocation (TSRBFC) method. The proposed theory is efficient, reliable, and is in close agreement with the results in the literature. Comparison studies show that the NTHSDT is more accurate than other plate theories and is simple in analyzing buckling behavior. A parametric study is done to examine the effects of grading index, porosity index, sandwich schemes, aspect ratio, side-to-length thickness ratio and foundation stiffness.

Practical Study to Find the Best Sound Insulation for Walls From Different Building Materials

The sound insulation of walls made of different building materials was tested in various places from Tikrit University in Iraq, with a number of up to 14 walls, distributed in the Department of Environmental Engineering, the Department of Civil Engineering and Chemical Engineering, the Deanship of the College of Arts, the College of Education, the College of Arts, the Department of Psychology, and the Deanship of the College of Computer. It was found through the results that the highest value of sound insulation was obtained for the wall of sequence 13, which amounted to 44.86 dB, but it is for a wall built of thermiston material, and this indicates that thermiston gave the greatest value for sound insulation. The study showed that there are building materials for other walls that can give excellent sound insulation, which is a material republican bricks covered with wood and walls built of sandwich material with a thickness of 10 cm and walls concrete coated with PVC, as well as sandwich walls with a thickness of 7 cm, reaching. The highest values for the rest of the sound insulation results for the top five values were (38.6, 38.43, 37.13, 34, 33.76) dB decibel. The results showed that the perforated brick is no doubt excellent sound insulation and proof of that all the walls built of perforated bricks provided insulation Excellent sound with the rest of the additional isolators used. The study also showed that for the walls of the sandwich panels, with the increase in thickness, the value of sound insulation increases. Where the value of sound insulation (38.43 dB, 34 dB and 30.36 dB) for walls with thickness (10cm, 7cm and 5cm) respectively. Finally, it is important to mention that the lowest value of the measured sound insulation for measured walls was 23.23 decibels, but for a brick wall from the outside of the squirt spreading cement and from the inside with plaster and borax in the College of Engineering - Department of Environmental Engineering building.

Transport of Moisture in Car Seat Covers

Abstract Transport of liquid water is one of the basic producer requirements to ensure the suitable physiological comfort of drivers. This paper deals with the investigation of car seat covers’ efficiency from the point of view of their moisture management. Two methods were used for the evaluation of moisture transport in the car seat cover structures. Both of them use a thermography system for water transport detection. The first method evaluates dynamic water spreading in cross-section in the frontal plane; the second one examines horizontally dynamic spreading of liquid drops on the upper face of the sample. The tested materials were designed to understand the role of the middle layer of textile sandwich car seats in their moisture management behavior. The same PES woven structure in the top layer was used for all tested samples. Knitted spacer fabric (3D spacer fabric), polyurethane foam, and nonwoven were used as padding in the middle layer in car seat covers. In summary, the distribution and transport of liquid moisture in a sandwich structure are fundamentally affected by the middle layer of composite, especially by material composition and the value of porosity. The best results were shown in 3D spacer fabric for car seat covers.

Free vibration analysis and optimization of doubly-curved stiffened sandwich shells with functionally graded skins and auxetic honeycomb core layer

A review of the literature reveals a dearth of works on functionally graded material sandwich shells having an auxetic core layer. This study contributes an analytical approach for the free vibration analysis of doubly curved stiffened sandwich shells with the face sheets of functionally graded materials and the core layer of the auxetic honeycomb material. The theoretical formulation is established based on first-order shear deformation theory associated with the smeared stiffener method. The free vibration solution of simply supported shallow shells with the rectangular platform is derived using Navier’s form. The proposed methodology is general and can be applied to examine the natural frequencies of various shell types, including flat, cylindrical, spherical, and hyperbolic paraboloidal panels. Numerical results indicate that the fundamental frequency is largely influenced by the relative proportion of the constituent materials of the face layers, the geometrical parameters of the auxetic honeycomb core layer, as well as the stiffeners. Additionally, a simple optimization technique based on Rao algorithms is introduced to obtain the maximum fundamental frequency of the shell. It is shown that the shell parameters, particularly the thickness of the auxetic core and the number of stiffeners, can be tailored to maximize the natural frequency. Moreover, the optimal solutions are fully dependent on the material proportion of the functionally graded material, the geometry of the shell, and the geometrical parameters of the auxetic honeycomb core.

Environmentally friendly bio‐inspired folded sandwich panels—Fabrication and mechanical behavior

AbstractA manufacturing method of folded and straight corrugated plate structure printed by environmentally‐friendly polylactic acid filled with environmentally‐friendly paraffin wax is proposed. Experimental investigations are conducted to characterize the out‐of‐plane compressive behaviors, including stress–strain curve, deformation processing, failure mode, strength, and energy absorption. By filling paraffin wax, the out‐of‐plane compression failure mode of sandwich materials from buckling (corresponding to empty corrugated sandwich panels) to wrinkling or crushing, which greatly improves the strength. Due to paraffin wax and its interaction with composite origami core, the energy absorption capacity is significantly enhanced. The research shows that the half‐filled folded corrugated sandwich structure not only has excellent specific energy absorption advantages, the paraffin wax has excellent heat absorption and release performance, and the unfilled part is just used as a heat flow channel to facilitate the flow of heat. This work has created a new method for rapid preparation of lightweight sandwich materials with not only high specific strength and high specific energy absorption, but also thermal channels.

On mechanical behavior of two-layer functionally graded sandwich curved beams resting on elastic foundations using an analytical solution and refined Timoshenko beam theory

For the first time, static bending, free vibration, and buckling studies of the two-layer functionally graded sandwich (TFGS) curved beams resting on Pasternak’s foundation utilizing the analytical precise solution and the refined Timoshenko beam theory (RTBT) are carried out in this study. The curved beam system is composed of two layers of single curved beams that are connected together by shear connectors. Each single curved beam layer is constructed entirely of FG sandwich material, including the bottom surface, core, and top surface. With the introduction of the new distribution shape function, it is possible to get a parabolic distribution of the transverse shear strain and shear stress throughout the whole thickness of the beam, with zero values at the beam's surfaces. The Navier solution is used to investigate the static bending, free vibration, and buckling of simply supported TFGS curved beams. The modified beam theory has been shown to be effective for analyzing the static bending, free vibration, and buckling responses of the beam system. The comparison of the deflection, normal and transverse shear stresses, natural frequency, and mechanical buckling load of curved beams computed using this proposed theory and other methodologies illustrates the new theory's correctness and effectiveness. Additionally, the influence of parameters such as the upper and lower layers' material volume exponents, the material ratio, the open angle, the thickness ratio, and the elastic foundation stiffness is explored. The study finding of this paper are really significant in terms of calculation and application in engineering practice. Contributing to the advancement of numerical computational mechanics by enhancing its development. Moreover, this is a critical and credible resource for future research on this sort of construction.

Assessment of the Tribological Properties of the Steel/Polymer/Steel Sandwich Material LITECOR

The article presents the results of tribological investigations into the steel/polymer/steel sandwich material LITECOR® developed by ThyssenKrupp Steel Europe for applications in the automotive industry. Friction tests were carried out by means of a strip drawing test with the use of a special tribotester mounted on a uniaxial tensile test machine. The influence of sheet deformation on the value of the coefficient of friction (COF) was considered. For this purpose, the samples were subjected to a pre-deformation of 4%, 8% and 12%. Friction tests were carried out with different force values and under different friction conditions, i.e., in dry friction conditions and lubrication of the sheet surface with L-AN 46 machine oil. The highest values of COF were observed for as-received sheets. In contrast, apart from the friction process under the conditions of the lowest force analysed, the lowest value of the COF was observed for pre-strained sheets with a deformation of 12%. The lubrication efficiency of the pre-strained strip specimens with ε = 4% was between 10.5% and 16.3%, with a trend of increasing lubrication efficiency with increasing force. For pre-strained sheets with deformation ε = 12%, there was a trend of decreasing effectiveness from 14.9% to 9.03% with an increase in force.

Moisture Absorption of cork-based Biosandwich Material Extracted from Quercussuber L. Plant: ANN and Fick’s Modelling

ABSTRACT The building sector is one of the most dynamic in terms of energy consumption, consuming about 40% of the world’s energy. This same sector is also responsible for about 1/3 of the world’s greenhouse gas emissions. In recent years, the adoption of composite materials, particularly those strengthened through the use of natural fibers is growing in all areas. This increase is the direct result of the important performances offered by these materials and that includes lightness, thermal, and acoustic insulation along with respect for the environment. This led to the integration of materials, such as bio composites or bio sandwiches, into various building structures constructions relating to civil engineering. However, numerous researches related to bio composites showed the need to explore them further particularly concerning the issue of moisture absorption as the presence of water affects the behavior of plant fibers both in terms of swelling and degradation. It is within this context that the present study focuses on modeling the water absorption behavior of bio sandwich materials having an agglomerated cork core associated with fibers extracted from the plant Quercussuber L. Fick’s law and Artificial Neural Network (ANN) are applied to model the experimental results pertaining to this absorption behavior. The experimental investigation starts by placing the original samples in tank filled with distilled water at an ambient temperature of 25°C. Mass samples are later and periodically taken on specimen with cork core having different thicknesses (5, 10, and 20 mm) as well as on laminated skin sandwiches made of short flax fibers until saturation that lasted around 25 days. The two Fick’s diffusion characteristic parameters represented by the mass gain at saturation (Mm ) and the diffusion coefficient (D) were determined analytically and water absorption kinetics behavior was recorded and later compared to the curves predicted by Fick’s laws. Statistical processing of the results was carried out through the application of the analysis of variance ANOVA.

A high-order continuation for bifurcation analysis of functionally graded material sandwich plates

A high-order continuation for bifurcation analysis of functionally graded material sandwich plates

A simplified equation for the collapse pressure of sandwich pipes with different core materials

Sandwich pipe with high-pressure resistance and the adequate insulation performance is a potential deepwater offshore oil and gas development solution. This paper establishes a two-dimensional finite element numerical model for sandwich pipe collapse prediction under external pressure using the finite element software ABAQUS. The developed numerical model is validated successfully using experiments in the literature. Parametric modeling is implemented with the help of the scripting language Python. A total of 3125 FEM models are established to analyze the influence of the sandwich pipe's geometric parameters, material properties, and interlayer adhesion properties on the collapse strength. The results show that the sandwich pipe's geometric parameters and core layer materials significantly influence the collapse strength. In contrast, the change of steel pipe steel grade has less influence. Moreover, the interlayer adhesion properties can significantly improve the collapse strength of the sandwich pipe. Finally, based on the numerical simulation results, a simplified equation for the collapse strength of the sandwich pipe is proposed for different core layer materials under frictionless interlayer conditions, which has an average error of 6.98% under the present assumptions.

Mechanical Characterization and Finite Element Analysis of Hierarchical Sandwich Structures with PLA 3D-Printed Core and Composite Maize Starch Biodegradable Skins

The objective of this research is the fabrication of biodegradable starch-based sandwich materials. The investigated sandwich structures consist of maize starch-based films as skins and biodegradable 3D-printed polylactic filaments (PLA) as the core. To investigate the tensile properties of the skins, conventional and nanocomposite films were prepared by a solution mixing procedure with maize starch and glycerol as the plasticizer, and they were reinforced with sodium montmorillonite clay, cellulose fibers and fiberglass fabric, with different combinations. Test results indicated a significant improvement in the mechanical and morphological properties of composite films prepared with sodium montmorillonite clay in addition with cellulose fibers and fiberglass fabric, with 20 wt% of glycerol. The morphology of the skins was also examined by scanning electron microscopy (SEM). Three orders of hierarchical honeycombs were designed for the 3D-printed core. To investigate how the skin material and the design of the core affect the mechanical properties of the starch-based sandwich, specimens were tested under a three-point bending regime. The test results have shown that the flexural strength of the biodegradable sandwich structure increased with the use of a second order hierarchy core and starch-based skins improved the strength and stiffness of the neat PLA-based honeycomb core. The bending behavior of the hierarchical honeycombs was also assessed with finite element analysis (FEA) in combination with experimental findings. Flexural properties demonstrated that the use of starch-based films and a PLA honeycomb core is a suitable solution for biodegradable sandwich structures.

Dynamics of viscoelastic material sandwich beam

ABSTRACT In this study, the non-linear dynamics of a horizontal motioned hub-beam system with passive constrained layer damping treatment are presented. The beam is constructed with three layers, viz., the host layer and the constrained layer with isotropic material, and the core layer of viscoelastic material. The system is non-linear due to coupling between the rigid motion of hub and flexible motion of the beam and also due to consideration of the beam curvature effect of bending. The equations of motion are derived using Hamilton’s principle based on expressing the kinetic energy and potential energy of the manipulator system in terms of generalised coordinates. The problem is approached by the finite element method, and the Newmark’s beta time integration scheme is adopted. Numerical simulations show that the viscoelastic material not only reduces the amplitude of elastic deflection but also quickly attenuates the vibration to zero. The results are evaluated for different values of thickness of the constrained layer, viscoelastic layer, payloads, and elastic modulus of each layers. It is observed that the vibration amplitude could be controlled through the use of the passive layer of damping.

Thermal and Mechanical Characterisation of Sandwich Core Materials for Climatic Chamber Shells Subjected to High Temperatures

Climatic chamber testing conditions are becoming more demanding. A wide range of temperatures is used to check the quality of products and materials, since they are constantly being improved. However, there is no literature on how the components of the climatic chamber panels react under high temperatures. The present work therefore sets out to perform a thermal and mechanical characterisation of four core materials often used in sandwich panels: balsa wood, mineral wool, and polyethylene terephthalate and polyurethane rigid foams. The thermal characterisation focused on thermal conductivity and the specific heat was characterised using an indirect method developed previously by the authors to simulate a real application scenario where one surface of the sandwich panels was subjected to high temperature, while the opposite surface was kept at room temperature. Steady and unsteady conditions were analysed up to 200 °C. Balsa and mineral wool exhibited a nonlinear increase in thermal conductivity with temperature, and the polymeric foams showed linear behaviour. The specific heat results also increased with temperature, and the relation was nonlinear for all the tested materials except for polyethylene terephthalate, which showed linear behaviour. Higher temperatures had the least effect on the specific heat for balsa wood and mineral wool. The polyethylene terephthalate foams were the most affected by temperature. Temperature variation was tested using the impulse excitation technique. The polymeric foams and balsa wood were studied up to 100 °C and 160 °C, respectively. The elastic modulus decreased with temperature. After 24 h of cooling, the tests were repeated and the elastic modulus had regained or even increased its initial value, for all the materials.