Curved Sandwich Panels Research Articles

Flexural behavior of singly curved GFRP sandwich panel with polyurethane foam core

Curvilinear architecture and structures are becoming a worldwide trend for its streamlined appearance and synchronicity with the surroundings. Nonetheless, the conventional construction materials might not be able to achieve the desired curvilinear geometries in an effective and economic manner. In this regard, glass fiber-reinforced polymer (GFRP) curved sandwich panel with polyurethane foam core is able to meet the requirement of the construction efficiency and economy as well as satisfy the need for a lower energy consumption. However, few studies are available on the mechanical behavior of such panels. In this regard, this work was to conduct an experimental and numerical investigation on the singly curved GFRP sandwich panels to evaluate the flexural performance. In particular, the effect of the foam density, inclined angle, core thickness and stacking sequence of face sheet on the load-carrying capacity and failure mode was addressed. Four failure modes were identified. The singly curved GFRP sandwich panel showed an improved stiffness when compared to the flat panel, but showed more complicated failure mechanism. The stiffness of the curved panel with inclined angle 30° was 250 % higher than that of the flat panel in the test results. It was shown that the strength and stiffness increased as the density and thickness of the foam core increased. In addition, a finite element analysis was conducted via MSC.Marc and validated by the experimental results. A parametric study was performed to address the design parameters. It was found that the specimens with inclined angles of 30° and 45° showed the greatest stiffness.

Curved Polymeric Sandwich Composites Subjected to Air Shock: An Experimental Investigation

BackgroundThe vulnerability of polymeric composite sandwich structures in marine applications to air explosions highlights a significant gap in our understanding of the dynamic behavior of the curved sandwich structures, which is essential for design improvements.ObjectiveThis study aims to explore the dynamic response and failure mechanisms of curved sandwich composite panels subjected to air-blast loading, providing insights into their structural integrity under such conditions.MethodsExperiments were performed using laboratory-simulated air shocks generated by a shock tube, employing high-speed photography and digital image correlation to measure deflections on the back surface of the panels. The panels, made with PVC closed-cell foam cores of two densities (H45 and H130), were tested across three curved geometries (radii of 112 mm, 305 mm, and infinity) under various boundary conditions.ResultsFindings indicate an increase in deformation with a decreased radius of curvature under simple support conditions, a trend that reverses under arrested displacement conditions. Moreover, a reduced radius significantly enhances panel strength and resistance to interfacial damage, with the primary failure mode transitioning from core shear cracking to interfacial debonding as core density increases.ConclusionsThe study reveals that the radius of curvature, boundary conditions, and core density significantly affect curved sandwich panels’ dynamic response and performance. Panels with smaller radii and higher core densities exhibit increased strength, though boundary conditions introduce variable effects on deformation behavior.

Exploring bending behavior of curved sandwich panels with three-dimensional printed, functionally graded cores

Sandwich structures have garnered significant attention due to their high strength-to-weight ratio in various industries, particularly aerospace. Meeting application demands requires optimizing mechanical properties such as bending stiffness, peak load, specific absorbed energy, and weight. This study presents a unique approach involving the design and manufacturing techniques of curved sandwich panels with functionally graded cores, aiming to achieve a comprehensive spectrum of bending properties. Curved structures have applications across diverse fields, including landing gear. The semi-circular core of the sandwich panel comprised three distinct regions defined by angles: Ф, Υ, and 90-Ф- Υ. These angles specified both the location and proportion of different honeycomb cells, including high, medium, and low-density cells. Any variations in these angles and their cell types resulted in a new density gradient. The manufactured sandwich structures consisted of polylactic acid cores printed by a fused deposition modeling printer, sandwiched between aluminum skins. Experimental tests and finite element analysis for three models showed strong agreement, with a maximum error of 14.45%. After the simulation was validated, it expanded to cover other configurations. Subsequently, mathematical models based on the aforementioned angles were calibrated using results extracted from the simulation step. This process led to achieving various structures characterized by a wide range of stiffness (ranging from 0.29 to 0.79 kN/mm), peak load (ranging from 1.73 to 4.77 kN), and specific absorbed energy values (ranging from 41.78 to 96.09 J/kg). The proposed methodology exhibits promise in engineering the design of these structures and their multi-objective optimization.

Close-in blast responses of bowstring fold-line-core sandwich panels

Buildings, critical facilities, and military transport must maintain structural integrity when subjected to explosions. This research introduces a novel protective structure employing a bowstring design and curved sandwich panels featuring a fold-line-core designed to improve the explosion resistance of thin-walled panels. The dynamic responses and crushing modes of these bowstring fold-line-core sandwich panels were examined. The findings demonstrate that the bowstring fold-line-core sandwich panel effectively harnesses the self-supporting capacity of the bowstring structure alongside the energy absorption capabilities of the fold-line-core, resulting in exceptional anti-explosion performance. When subjected to a detonation of 200 g of TNT at a stand-off distance of 0.6 m, the designed panels exhibit minimal deformation. Moreover, the calculated proportional stand-off distance under corresponding operating conditions amounts to 1.026 kg/m1/3.

Local impact resistance of curved sandwich panel with Miura-ori foldcore

Curved sandwich structures have demonstrated great potential for engineering applications. However, little study on the impact resistance of the curved Miura-ori sandwich structure is found. In this study, the curved sandwich panel with a curved Miura-ori foldcore (CPCM) is proposed and its impact resistance is numerically investigated. The force displacement history, energy absorption, specific energy absorption, residual velocity of the projectile and the displacement of the rear face sheet are used to evaluate the performances of the CPCM. Various loading scenarios including different impact velocities and positions, different projectile sizes and geometries are considered. Moreover, the curved sandwich panel with a curved honeycomb core (CPCH) that have similar specifications and the same relative density as the CPCM is simulated as well for comparison. It is found that the CPCM shows excellent impact resistance with a ballistic limit around 61 % higher than that of the CPCH. Its energy absorption capacities and impact resistance are improved under blunt projectile impact. However, when the impact velocity is above the ballistic limit, the energy absorption EA of the CPCM remains at a constant level, irrespective of the impact velocity.

Experimental investigation on impact behavior of curved sandwich composites with chiral auxetic core

The purpose of this study is to evaluate and compare the capability of impact energy absorption of the sandwich panels with various chiral auxetic cores. To this end, flat and curved panels were subjected to impact testing at varying energy levels. Glass fiber-reinforced epoxy composites and PLA material were used as the skins and core of the examined sandwich panels, respectively. The face sheets were produced by the hand-layup method and the auxetic cores with tetrachiral, anti-tetrachiral, and hexachiral configurations were printed using a 3D printer. The wall thickness, node diameter, and ligament length of the cells, as well as the core thickness, were kept constant for all the studied core structures. Flat and curved sandwich panels were obtained by combining the skins and cores produced in flat, 100 mm, 125 mm, and 160 mm radii of curvature with the epoxy used in skin production. Drop weight tests were carried out at impact energies of 10, 25, and 80 J. The contribution of the auxetic core configuration and panel curvature to the impact behavior of the sandwich panel was evaluated by examining the relationships between contact forces and deflection and by the analysis of the energy absorption and failure mode. The comparative evaluations showed that the auxetic core structure and the curvature of the panel have a significant effect on the impact properties of the sandwich panels. It was also observed that the use of tetrachiral cores could be the ideal design option for flat panels loaded at the perforation energy level. For curved panels, it was determined that the use of a hexachiral core configuration was advantageous in terms of more energy absorption capability, while the use of an anti-tetrachiral core structure was more effective in terms of specific energy absorption.

Curved grid‐scored foam core sandwich composites under low‐velocity impact loads: Effects of curvature, stacking sequence, and core finishing

AbstractThe objective of this paper is to experimentally investigate how material and geometric parameters, including face sheet layup, curvature, and core finishing, affect the contact force‐displacement behavior, absorbed energy, and damage modes of curved sandwich composites with grid‐scored foam under low‐velocity impact loads. An instrumented drop‐weight testing machine with a hemispherical impactor was used to perform low‐velocity impact tests at different energy levels. Angled‐ply stacking had the maximum contact force and impact resistance for low curvature radii. In the event of penetration, the impact energy absorption of all curved sandwich panels increased as the curvature increased. The core finishing influenced the contact forces of the curved and flat sandwich panels but not the penetration energy. The curvature and face sheet layups affected the delamination size and pattern. Angle‐ply and cross‐ply face sheets with the smallest and maximum radius of curvature, respectively, decreased penetration depth. The resin‐filled channels reduced foam cell impact damage and face‐core debonding. LVI penetration resistance was found to be highest for angle‐ply stacking and knife‐cut foam at small curvature radii. The proposed research will also provide naval designers with valuable insight into the impact response of sandwich structures used in curved parts of the hull and deck.Highlights The effect of curvature on the LVI responses varied due to face sheet layups. Core finishing affected contact forces, but not the absorbed energy. Curvature and face sheet layups affected the damage modes. Resin‐filled channels limited damage area and acted as stoppers for debonding.

Investigating the crumpling effect in honeycomb sandwich panels under bending loads using FEA technique

Abstract In this study a representative sandwich panel is investigated statically in two different configurations under similar bending loads. In one configuration serrations are introduced in the honeycomb core while the other one has un-modified core. Three-point bend test (TPBT) has been performed on both configurations through Finite Element Analysis (FEA) technique using ANSYS Workbench considering American Society for Testing and Materials (ASTM) standards. In both configurations the same aluminium honeycomb core is modelled having an adhesive layer in between adjacent foils to simulate actual scenario instead of relying on the block properties. Honeycomb core offers highest strength in its thickness (T) direction or the z-direction by virtue of its shape. Any distortion in the shape of the honeycomb adversely affects its strength. During bending the honeycomb core witnesses multidirectional forces consequently leading to distortion or crumpling. The serrations in the structure allow bending of the honeycomb core with minimal loss of strength by limiting the deformation to a specific region consequently preserving the shape as well as the strength of the honeycomb core. The results of both samples are compared with respect to deflection, strain and reaction force. It proves that serrated core is more favourable to be used in bent or curved sandwich panels.

An analytical closed-form solution for free vibration and stability analysis of curved sandwich panels made of porous metal-foam core and nanocomposite reinforced face-sheets

This paper aims to obtain an analytical solution for free vibration and stability analysis of shallow curved sandwich panels made of a porous metal-foam core and nanocomposites reinforced sheets resting on a Winkler-Pasternak elastic foundation. In this regard, two nanocomposites, carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) are considered for reinforcing the face-sheets. The governing equations are developed by considering the transversal shear strains based on the first-order shear deformation theory (FSDT). The obtained system of differential equations representing the dynamic equilibrium and compatibility of the proposed curved sandwich panels are solved analytically, using the principal of Galerkin method. In order to examine the results of developed formulation, some benchmark examples are adopted from the existing literature and the obtained results corresponding to the considered examples are compared with those are presented in the references. Using the achieved numerical results in the framework of a comprehensive parametric study, the effects of various material and geometrical factors and also various boundary conditions on the natural frequencies and buckling loads of the proposed sandwich panels are assessed. By performing the extensive parametric study it was observed that several results corresponding to the free vibration and stability of the proposed sandwich panels can be achieved by the present method without spending much time for computations. On the contrary, in order to achieve the similar results using the numerical methods, a time-consuming process is required which can justify the novelty of the present work.

Bending performance of curved sandwich panels comprising GFRP face sheets and web cores: Experimental investigation and theoretical model

Composite sandwich-walled shells composed of glass fiber reinforced polymer (GFRP) face sheets and web cores manufactured using a new multistage filament winding (MFW) technique is a type of novel structure. The paper uses a three-point bending test and analytical model to study its mechanical response under lateral external load. The analytical model can accurately predict the deformation and ultimate bearing capacity, and it is shown that the web parameters have a crucial influence on the deformation and failure modes. The results provide a theoretical basis for the parameter design and optimization of this type of curved sandwich panel.

Improving sound insulation near ring and coincidence frequencies of cylindrical sandwich shells

This paper proposes an impedance-based design methodology for cylindrical sandwich shells, with the aim to improve the sound transmission loss properties near the ring and coincidence frequency regions. The approach enables to systematically address the poor acoustic performance, characteristic of these problematic frequency regions, while retaining the mechanical properties of these structures. This is done by seeking to suppress the mass-controlled region in the frequency spectrum, with properly tuned characteristic frequencies of the structure, completed by a degree of damping treatment. The impedance-based approach allowing this tuning is derived from the canonical wave equation with a view to sound transmission through cylindrical shells. In addition to offering fast, early design possibilities, the method provides physical insights into the vibroacoustic performance of the shell, for instance introduced to estimate the sound transmission loss of shallow curved sandwich panels in the low-frequency range. Oblique- and diffuse-field conditions are investigated, validating the analytical developments against finite element calculations.

Local impact resistance of curved sandwich panels with coaxial and concentric honeycombs

The local impact resistance of honeycomb sandwich panels with curved and flat geometries differs due to the global stress state. In this study, curved sandwich panels with coaxial and concentric honeycombs are designed and their resistance is investigated against local impact. The numerical model is calibrated with the air cannon test results and then used to compare the performance of structures that are sandwiched by different honeycombs. The comparable study shows that the impact resistance of flat sandwich structures outperforms that of curved ones at a low impact velocity, and a small radius of curvature should be avoided when considering an enhancement of the impact resistance by curvature design. In addition, under the high-velocity impact, sandwich panels with concentric honeycombs show an improved impact resistance as compared to those with coaxial honeycombs. However, the influence of honeycomb configurations on the impact resistance is reduced as the radius of curvature increases. Using the equivalent analysis, the equivalent face sheet thickness and equivalent impact velocity of curved sandwich structures with different radii of curvature, which are compared to the flat structures that are subjected to typical impact loads, are achieved.

High-velocity impact resistance of doubly curved sandwich panels with re-entrant honeycomb and foam core

This work describes the high-velocity impact behavior of doubly curved sandwich panels. The sandwich panels are manufactured using carbon/fiber epoxy composite face sheets, polyurethane foam core and 3D-printed PLA plastic cellular auxetic (re-entrant) honeycombs. High-velocity impact tests are carried out by using a single-stage air gas gun test machine. A spherical steel projectile with the radius of 5 mm is impacted to the center of the specimens with the speed of 100 m/s. The experimental data are used to validate explicit finite element models of the doubly curved structures. An analytical model is also developed for the ballistic limit of the flat and doubly curved sandwich panels, and the analytical results are compared to those obtained from the numerical ones. Parametric numerical analyses of the high-speed impact of the curved sandwich panels are then carried out considering various radii of curvature of the panels. The results show that the energy absorption is increased as the curvature is decreased for the panels with both foam and re-entrant core. In addition, the core configuration provides a key role in the impact resistance of the sandwich panels. Re-entrant models show an increase in specific energy absorption (SEA) compared to the foam core types.

Experimental and numerical analysis of a novel curved sandwich panel with pultruded GFRP strip core

Curved sandwich structure made of glass fiber-reinforced polymer (GFRP) composite is emerging in the construction of non-linear architectures and wind turbine blades. In this work, a novel curved sandwich panel with pultruded GFRP strip core was proposed and studied. Compared with the common core materials such as foam and wood, pultruded GFRP strips can provide a higher stiffness and strength, particularly when used in large-scale sandwich structures. The proposed sandwich panel was manufactured through vacuum-assisted resin transfer molding process. A series of three-point bending tests was conducted to study the flexural behavior. The effect of surface thickness on the load-carrying capacity and failure mode was addressed. Then, a finite element analysis was conducted via ABAQUS and validated by the experimental results. The parametric study was performed to address the key design parameters. Both experimental and numerical results indicated that with the increased surface thickness, the failure mode could transition from the damage of glue seam to the transverse cracking inside the pultruded GFRP strip. Moreover, the load-carrying capacity can be improved with the thickened face sheet. In the end, this work successfully demonstrated the use of multilayer shell elements in the finite element modelling of the cracking behavior of glue seams.

Nonlinear response of doubly curved sandwich panels with CNT-reinforced composite core and elastically restrained edges subjected to external pressure in thermal environments

An analytical investigation on the nonlinear response of doubly curved panels constructed from homogeneous face sheets and carbon nanotube reinforced composite (CNTRC) core and subjected to external pressure in thermal environments is presented in this paper. Carbon nanotubes (CNTs) are reinforced into the core layer through uniform or functionally graded distributions. The properties of constituents are assumed to be temperature dependent and effective properties of CNTRC are determined using an extended rule of mixture. Governing equations are established within the framework of first order shear deformation theory taking into account geometrical imperfection, von Kármán–Donnell nonlinearity, panel-foundation interaction and elasticity of tangential edge restraints. These equations are solved using approximate analytical solutions and Galerkin method for simply supported panels. The results reveal that load carrying capacity of sandwich panels is stronger when boundary edges are more rigorously restrained and face sheets are thicker. Furthermore, elevated temperature has deteriorative and beneficial influences on the load bearing capability of sandwich panels with movable and restrained edges, respectively.

Curved Sandwich Panels

AbstractDue to their excellent combination of space enclosing, heat insulating and supporting function, steel sandwich panels – mostly flat – are used for roofs and walls of standard industrial buildings. Because freely formed structures generally are playing an increasing role in contemporary architecture, curved sandwich panels would offer a high potential to architectural design. Simultaneously, the advantageous load‐bearing capacity could further increase the benefits of their usage. The necessary design strategy, the manufacturing technology for the curved cover plates and their overall mechanical behavior – all of these 3 main keys have been investigated in an interdisciplinary research project with architects, structural‐ and mechanical engineers. It has been one of the main goals in this project to find an applicable, efficient strategy for singularly produced panels (lot size 1: serial production with quantity = 1) in favour of a maximum flexibility for individual geometries.

Numerical Study on the Plastic Forming of Doubly Curved Surfaces of Aluminum Foam Sandwich Panel Using 3D Voronoi Model

This paper presents a numerical investigation on the plastic forming of doubly curved surfaces of aluminum foam sandwich panel (AFSP). A mesoscopic 3D Voronoi model that can describe the structure of closed-cell aluminum foam relatively realistically was established, and a series of numerical simulations using the model of the sandwich panel with a Voronoi foam core were conducted on the plastic forming of two typical doubly curved surfaces including spherical and saddle-shaped surfaces of AFSPs to analyze the deformation behaviors and the forming defects in detail. Multi-point forming experiments of spherical and saddle-shaped AFSPs with different target radii were implemented and the doubly curved panels with good forming quality were obtained. The simulated results of the surface illumination maps, the face sheet profiles, and the maximum strain differences in selected areas of the face sheet and the experimental results indicated that the Voronoi AFSP model can reflect the actual defects occurred in the plastic forming of doubly curved sandwich panels, and the high forming accuracy of the sandwich panel model was also demonstrated in terms of the shape error and the thickness variation.

Bending analysis of five-layer curved functionally graded sandwich panel in magnetic field: closed-form solution

In this paper, an exact closed-form solution for a curved sandwich panel with two piezoelectric layers as actuator and sensor that are inserted in the top and bottom facings is presented. The core is made from functionally graded (FG) material that has heterogeneous power-law distribution through the radial coordinate. It is assumed that the core is subjected to a magnetic field whereas the core is covered by two insulated composite layers. To determine the exact solution, first characteristic equations are derived for different material types in a polar coordinate system, namely, magneto-elastic, elastic, and electro-elastic for the FG, orthotropic, and piezoelectric materials, respectively. The displacement-based method is used instead of the stress-based method to derive a set of closed-form real-valued solutions for both real and complex roots. Based on the elasticity theory, exact solutions for the governing equations are determined layer-by-layer that are considerably more accurate than typical simplified theories. The accuracy of the presented method is compared and validated with the available literature and the finite element simulation. The effects of geometrical and material parameters such as FG index, angular span along with external conditions such as magnetic field, mechanical pressure, and electrical difference are investigated in detail through numerical examples.

Multiphysical numerical (FE–BE) solution of sound radiation responses of laminated sandwich shell panel including curvature effect

In this paper, a numerical scheme is prepared using the higher-order shear deformation type of kinematic model with the help of a coupled finite and boundary elements (FE–BE) to evaluate the vibroacoustic responses of laminated composite sandwich curved shell panels. The panel is under the influence of a harmonic point load. Further, an FE–BE combined technique is utilized to prepare a generic computer code (MATLAB environment) for the numerical prediction via the proposed mathematical formulation. The structural frequency and the subsequent sound relevant data are obtained by solving the final form of the multiphysics model. In this regard, the structural system equation is derived through Hamilton’s principle and the Helmholtz wave equation for the computation of acoustic responses. The performance of the proposed scheme is established initially through the convergence and the corresponding validation studies. The comparison cases are made with the available published benchmark frequency (free vibration) as well as the acoustic data. Appropriate numbers of numerical examples are solved to draw the meaningful inferences of various factors to show the significant influences on the acoustic radiation responses of the curved sandwich panel type of structural components. The curvature ratio is showing the accentuated influences on the sound radiation responses for the low-frequency ranges whereas the increase in the thickness ratio, i.e. the ratio of core to face leads to an accentuated radiated sound power.

Shell Structures Made of Curved Sandwich Panels: Assessment of the Load‐Bearing Capacity

ABSTRACTLightweight constructions made of sandwich panels became well established for roof and wall claddings of industrial structures. Due to their good heat insulation, their excellent weight to load ratio and high load‐bearing capacity as well as the economical manufacturing and erection process, sandwich structures are build frequently. Besides the mentioned advantages the linear manufacturing process of sandwich panels usually limits the possible building cubature to rectangular shapes. In an interdisciplinary project, architectural, civil engineering and mechanical engineering institutes of Technische Universität Darmstadt are working on a design concept building shell structures with linear manufactured curved sandwich panels.A preliminary study indicates that arched sandwich beams have a high potential regarding the load‐bearing capacity. The comparison between arched and single span sandwich beams shows that, even for asymmetric loads, resulting stresses in the two‐hinged arches are significantly lower than in the related simply supported single span beams.To verify the results of the numeric study full‐scale tests on curved sandwich panels will be performed. Furthermore, an assessment of the load‐bearing behavior of the panels joints loaded with axial forces is planned. Based on the results further numeric studies will be conducted to investigate the behavior of whole shell structures following the developed design principle by taking into account realistic load cases for exemplary building applications, giving special attention to asymmetrical loads.Moreover, further research regarding the requirements for supporting structures as well as for the connection between the shell structure and the supporting structure is necessary to take into account the high axial forces, which are not common in sandwich structures.