Metallic Sandwich Panels Research Articles

Blast resistance of metallic tube-core sandwich panels

A tube-core sandwich panel was designed to serve as anti-blast panel of blast resistant walls. Steel tubes are non-expensive and strong for anti-blast walls, and can be easily connected with face sheets through welding. Static three-point bending experiments, close-in explosion experiments and contact explosion experiments were performed to explore its anti-blast ability. The tough interface and shear-resistant tube-core endow the panel with high bending rigidity. In close-in explosion, the front face mitigates the shock wave corrugations through corrugated plastic deformation and the panel is rigid enough to resist the shock wave. In contact explosion, the panel attenuates the shock wave through tube-crushing and skin-tearing. Appropriate thicknesses of the front face and the tube wall promote energy absorption. The experiments indicate that spaced tube-core panel is the better choice for close-in explosions while connected tube-core panel has advantages under contact explosions.

Failure maps and optimal design of metallic sandwich panels with truss cores subjected to thermal loading

Sandwich panels with truss cores have been widely investigated due to their superior mechanical performances. When being used in the thermal protection system of a high-speed aircraft, sandwich panels are usually subjected to intense thermal loading and may fail due to various mechanisms. This paper presents a theoretical and numerical analysis on the failure mechanisms and optimal design of metallic sandwich panels with truss cores subjected to uniform thermal loading. Five failure modes are considered: global buckling, face sheet buckling, face sheet yielding, core member buckling and core member yielding. Failure maps of sandwich panels with several truss core topologies are developed based on these failure modes. Taking the five failure modes as constraint conditions, sandwich panels with truss cores are optimally designed for the minimum weight at given thermal loadings. It is found from the optimal analysis that sandwich panels with Kagome and X-type truss cores are more efficient than those with tetrahedral and pyramidal truss cores. Sandwich panels with fully-clamped boundary conditions have superior thermal loading resistance than those with simply-supported boundary conditions.

Optimum core design to improve noise attenuation performance and stiffness of sandwich panels used for high-speed railway vehicles

In this study, we optimally design the core of a metal sandwich panel used in high-speed railway vehicles to minimize the amount of metal solid in the core and subsequently reduce its weight. The optimum core must satisfy constraints regarding sound transmission class (STC) and compliance. Because the solid-void layout in the core strongly affects the acoustic and static characteristics of sandwich panels, the core layout should be carefully designed when reducing the amount of metal solid. To this end, three topology-optimization problems and one size-optimization problem are formulated and sequentially solved. A single unit cell is periodically repeated in the core. Thus, structural and acoustic topology-optimization problems are first formulated and solved for the unit cell. Based on the optimal topologies obtained for the unit cell, a moderate initial solid-void layout in the unit cell is determined for the size-optimization problem to optimally design core. The effectiveness of the current design approach for the core of the sandwich panel is validated by comparing the STC and compliance values of the optimal core design and a reference design.

Blast resistance of metallic sandwich panels subjected to proximity underwater explosion

A series of close-in underwater blast tests were performed on sandwich panels consisting of two aluminum alloy face-sheets and a honeycomb core to investigate blast resistance of metallic sandwich panels. The blast resistance of sandwich panels was assessed in terms of structural deformation resistance represented by back face-sheet deflection and intensity of the secondary pressure wave, which is determined by the maximum velocity of the back face-sheet. It was found that the secondary pressure wave shows an inverse trend with face-sheet thickness while a positive relationship with core density, which is determined by foil thickness in this study. A failure mode map was adopted to indentify the effect of design parameters on the structural failure mechanism at this blast magnitude. Finally, a comparison of underwater blast resistance between sandwich panels and monolithic plates of equivalent mass was performed. The comparative study provided further experimental evidence for the benefit of sandwich construction in terms of deformation resistance and secondary pressure wave intensity even at high blast magnitude. It was also suggested that the benefit of deformation resistance was amplified with increase in equivalent thickness.

Dynamic response of circular metallic sandwich panels under projectile impact

The dynamic response of circular sandwich panels with aluminium honeycomb and corrugated cores under projectile impact was investigated experimentally and numerically. Impulse loaded on the panel was controlled by projectile launching velocity and the deformation process of sandwich panels was recorded by a high-speed camera in the experiments. Typical deformation/failure modes of face-sheets and cores were obtained and analysed. The back face-sheet deflections and strain histories of face-sheets were measured and discussed. A parametric study was conducted by LS-DYNA 3D to analyse the effect of geometrical configuration on energy absorption mechanism and back face-sheet permanent deflection of circular sandwich panels. The results indicated that the impact resistance of the structure was sensitive to geometrical configuration. Increasing face-sheet thickness and core relative density significantly improved sandwich structure impact resistance. Increasing foil thickness improved the panel impact resistance more efficiently than decreasing wall side length. The results have important reference value to guide engineering application of the sandwich structure subjected to impact loading.

Finite element analysis of sandwich panels with stepwise graded aluminum honeycomb cores under blast loading

This paper presents details and brief results of an experimental investigation on the response of metallic sandwich panels with stepwise graded aluminum honeycomb cores under blast loading. Based on the experiments, corresponding finite element simulations have been undertaken using the LS-DYNA software. It is observed that the core compression stage was coupled with the fluid–structure interaction stage, and the compression of the core layer decreased from the central to the peripheral zone. The blast resistance capability of sandwich panels was moderately sensitive to the core relative density and graded distribution. For the graded panels with relative density descending core arrangement, the core plastic energy dissipation and the transmitted force attenuation were larger than that of the ungraded ones under the same loading condition. The graded sandwich panels, especially for relative density descending core arrangement, would display a better blast resistance than the ungraded ones at a specific loading region.

Optimization of Grit-Blasting Process Parameters for Production of Dense Coatings on Open Pores Metallic Foam Substrates Using Statistical Methods

Open pore metallic foam core sandwich panels prepared by thermal spraying of a coating on the foam structures can be used as high-efficiency heat transfer devices due to their high surface area to volume ratio. The structural, mechanical, and physical properties of thermally sprayed skins play a significant role in the performance of the related devices. These properties are mainly controlled by the porosity content, oxide content, adhesion strength, and stiffness of the deposited coating. In this study, the effects of grit-blasting process parameters on the characteristics of the temporary surface created on the metallic foam substrate and on the twin-wire arc-sprayed alloy 625 coating subsequently deposited on the foam were investigated through response surface methodology. Characterization of the prepared surface and sprayed coating was conducted by scanning electron microscopy, roughness measurements, and adhesion testing. Using statistical design of experiments, response surface method, a model was developed to predict the effect of grit-blasting parameters on the surface roughness of the prepared foam and also the porosity content of the sprayed coating. The coating porosity and adhesion strength were found to be determined by the substrate surface roughness, which could be controlled by grit-blasting parameters. Optimization of the grit-blasting parameters was conducted using the fitted model to minimize the porosity content of the coating while maintaining a high adhesion strength.

Sound Transmission Loss of Adhesively Bonded Sandwich Panels with Pyramidal Truss Core: Theory and Experiment

In this paper, an analytical model is developed to investigate sound transmission loss characteristic of adhesively bonded metal sandwich panels with pyramidal lattice truss cores based on 3D elasticity theory. Meanwhile, practical specimen is fabricated to conduct corresponding sound insulation experiment test via a standing wave tube method. The effective elastic constant of truss cores is derived using one homogenization theory on account of equivalent strain energy. It is found that satisfactory agreement is achieved between theoretical solutions and experiment results, and damping effect of adhesive bonding interface between facesheets and core has a great impact on transmission loss. Further parameter investigations demonstrate the significant effect of the elevation and azimuth angles of the pyramidal cores, which can be conveniently changed to tailor the acoustic performance of the sandwich panels in the whole frequency range.

Dynamic Crushing of All-Metallic Corrugated Panels Filled With Close-Celled Aluminum Foams

Under quasi-static uniaxial compression, inserting aluminum foams into the interstices of a metallic sandwich panel with corrugated core increased significantly both its peak crushing strength and energy absorption per unit mass. This beneficial effect diminished however if the foam relative density was relatively low or the compression velocity became sufficiently high. To provide insight into the varying role of aluminum foam filler with increasing compression velocity, the crushing response and collapse modes of all metallic corrugate-cored sandwich panels filled with close-celled aluminum foams were studied using the method of finite elements (FEs). The constraint that sandwich panels with and without foam filling had the same total weight was enforced. The effects of plastic hardening and strain rate sensitivity of the strut material as well as foam/strut interfacial debonding were quantified. Three collapse modes (quasi-static, transition, and shock modes) were identified, corresponding to different ranges of compression velocity. Strengthening due to foam insertion and inertial stabilization both acted to provide support for the struts against buckling. At relatively low compression velocities, the struts were mainly strengthened by the surrounding foam; at high compression velocities, inertia stabilization played a more dominant role than foam filling.

Dynamic response of metallic trapezoidal corrugated-core sandwich panels subjected to air blast loading – An experimental study

The dynamic response of metallic trapezoidal corrugated core sandwich panels under air blast loading is studied by experimental investigation. The sandwich panels composed of two thin face skins and trapezoidal corrugated core, were designed and fabricated through folding and laser welding technology. The influences of the stand-off distance, face sheet thickness, core web thickness, core height and corrugation angle on the deformation/failure mechanisms and the permanent deflections of the trapezoidal corrugated core sandwich panels were investigated. Results revealed that the deflection and damage level of panel increased with the decrease of stand-off distance. The effect of front face sheet thickness on the deflection is more evident than that of the back face sheet. Increasing the core web thickness and corrugation angle improved the blast performance of panel with a lower deformation, while increasing the core height led to a larger localized deformation at the front face and a lower deflection of back face. Finally, a dimensional analysis based on the experimental results was conducted. Good agreement between the experimental data and the prediction results was obtained by introducing the stand-off parameter and the proposed core supporting parameter.

Mechanical Properties of a Metal Sandwich Panel Manufactured Using Longitudinally Laminated Forming Tools

Sandwich panel structures are increasingly used in applications where the most important demands are the weight saving and long service life. Utilizing sandwich panels, extremely light-weight, stiff and robust structures can be manufactured. In this study, sandwich panels were produced by specially designed cost-effective forming tools. Various kind of test materials were used for corrugated cores and skin plates: conventional low-carbon steel grade EN 10130 and ferritic stainless steel grade 1.4509 with plate thicknesses of 0.6 and 0.75 mm. A common S355 structural steel was used as a reference for bending strength comparison.For measuring the stiffness, MTS tensile and fatigue testing machine was selected to determine the bending resistance of the sandwich panels. The bending force, needed for yielding and fracture, related to the bending length and intensity was compared with the results from bending of the reference plates. Results showed that the bending force of the panels is significantly higher than that of a plate having similar intensity. The best results were obtained with the stainless steel (SS) panel that had 27% higher bending force at the yield point than 5 mm thick S355 plate having 3 times larger intensity. The carbon steel panel was approximately 40% weaker than the SS-panel and both panel types lost strength when loading direction was changed from transverse to 45 degree and further to 90 degree load (longitudinal).

Analytical Investigation on Optimum Member Angle of Lattice Truss Structures

Metallic sandwich panels based on lattice truss structure have been developed for a wide range of potential applications with their lightweight and multi-functionality. The study focused on the analytical approach to investigate compression and shear characteristics of pyramidal and tetrahedral truss unit cells. With various unit cell models which have the same weight per unit area but different member angle, analytical solutions for effective stiffness and strength have been predicted and compared with each other. The results showed that there are the most optimal core configuration to maximize effective mechanical properties.

Dynamic response and optimal design of curved metallic sandwich panels under blast loading.

It is important to understand the effect of curvature on the blast response of curved structures so as to seek the optimal configurations of such structures with improved blast resistance. In this study, the dynamic response and protective performance of a type of curved metallic sandwich panel subjected to air blast loading were examined using LS-DYNA. The numerical methods were validated using experimental data in the literature. The curved panel consisted of an aluminum alloy outer face and a rolled homogeneous armour (RHA) steel inner face in addition to a closed-cell aluminum foam core. The results showed that the configuration of a “soft” outer face and a “hard” inner face worked well for the curved sandwich panel against air blast loading in terms of maximum deflection (MaxD) and energy absorption. The panel curvature was found to have a monotonic effect on the specific energy absorption (SEA) and a nonmonotonic effect on the MaxD of the panel. Based on artificial neural network (ANN) metamodels, multiobjective optimization designs of the panel were carried out. The optimization results revealed the trade-off relationships between the blast-resistant and the lightweight objectives and showed the great use of Pareto front in such design circumstances.

High Velocity Impact Response of Composite Lattice Core Sandwich Structures

In this research, carbon fiber reinforced polymer (CFRP) composite sandwich structures with pyramidal lattice core subjected to high velocity impact ranging from 180 to 2,000 m/s have been investigated by experimental and numerical methods. Experiments using a two-stage light gas gun are conducted to investigate the impact process and to validate the finite element (FE) model. The energy absorption efficiency (EAE) in carbon fiber composite sandwich panels is compared with that of 304 stainless-steel and aluminum alloy lattice core sandwich structures. In a specific impact energy range, energy absorption efficiency in carbon fiber composite sandwich panels is higher than that of 304 stainless-steel sandwich panels and aluminum alloy sandwich panels owing to the big density of metal materials. Therefore, in addition to the multi-functional applications, carbon fiber composite sandwich panels have a potential advantage to substitute the metal sandwich panels as high velocity impact resistance structures under a specific impact energy range.

Blast resistance and multi-objective optimization of aluminum foam-cored sandwich panels

In this work, a group of metallic aluminum foam-cored sandwich panels (AFSPs) were used as vehicle armor against blast loading. The dynamic responses of the AFSPs with various combinations of face-sheet materials were analyzed using LS-DYNA. It was found that the AFSP with an aluminum (AA2024 T3) front face and a Rolled Homogeneous Armor (RHA) steel back face (labeled T3-AF-RHA) outperformed the other panel configurations in terms of maximum back face deflection (MaxD) and areal specific energy absorption (ASEA). It was also found that boundary conditions and the standoff distance (SoD) between an explosive and a target surface both have a remarkable influence on the blast response of the AFSPs. Using artificial neural network (ANN) approximation models, multi-objective design optimization (MDO) of the T3-AF-RHA panel was performed both with and without variations in blast load intensity. The optimization results show that the two objectives of MaxD minimization and ASEA maximization conflict with each other and that the optimal designs must be identified in a Pareto sense. Moreover, the Pareto curves obtained are different for varied blast impulse levels. Consequently, it is concluded that loading variation should be considered when designing such sandwich armors to achieve more robust blast-resistant performance.

Metallic sandwich panels subjected to multiple intense shocks

The mechanical response and fracture of metal sandwich panels subjected to multiple impulsive pressure loads (shocks) were investigated for panels with honeycomb and folded plate core constructions. The structural performance of panels with specific core configurations under multiple impulsive pressure loads is quantified by the maximum transverse deflection of the face sheets and the core crushing strain at mid-span of the panels. A limited set of simulations was carried out to find the optimum core density of a square honeycomb core sandwich panels under two shocks. The panels with a relative core density of 4%–5% are shown to have minimum face sheet deflection for the loading conditions considered here. This was consistent with the findings related to the sandwich panel response subjected to a single intense shock. Comparison of these results showed that optimized sandwich panels outperform solid plates under shock loading. An empirical method for prediction of the deflection and fracture of sandwich panels under two consecutive shocks – based on finding an effective peak over-pressure – was provided. Moreover, a limited number of simulations related to response and fracture of sandwich panels under multiple shocks with different material properties were performed to highlight the role of metal strength and ductility. In this set of simulations, square honeycomb sandwich panels made of four steels representing a relatively wide range of strength, strain hardening and ductility values were studied. For panels clamped at their edge, the observed failure mechanisms are core failure, top face failure and tearing at or close to the clamped edge. Failure diagrams for sandwich panels were constructed which reveal the fracture and failure mechanisms under various shock intensities for panels subjected to up to three consecutive shocks. The results complement previous studies on the behavior and fracture of these panels under high intensity dynamic loading and further highlights the potential of these panels for development of threat-resistant structural systems.

An equivalent material formulation for sinusoidal corrugated cores of structural sandwich panels

Metal sandwich panels with corrugated cores are an appealing industrial solution as structural components thanks to their high stiffness-to-mass ratio. Nevertheless, using detailed finite element models for numerical computation of their properties leads to large models and long solution time, especially for acoustic simulations. Therefore, reduction of the complex shaped core to an equivalent homogenous material is commonly used.In this paper, an innovative aluminum sandwich panel with sinusoidal corrugated core is investigated. The properties of the equivalent material are determined both analytically and numerically for the chosen Reissner–Mindlin orthotropic representation. The two derived models are compared in a comprehensive parametric study to validate the computationally much cheaper analytical formulation. Moreover, a validation of the equivalent models is done based on the bending stiffness per unit width of the sandwich panel. Finally, the acoustic behavior of the structure is investigated comparing the reduced layered model with the fully detailed 3D model.

Numerical simulation of Lamb wave propagation in metallic foam sandwich structures: a parametric study

The propagation of guided Lamb waves in metallic foam sandwich panels is described in this paper and analyzed numerically with a three-dimensional finite element simulation. The influence of geometrical properties of the foam sandwich plates (such as the irregularity of the foam structure, the relative density or the cover plate thickness) on the wave propagation is investigated in a parametric study. Open-cell and closed-cell structures are found to exhibit similar wave propagation behavior. In addition to the finite element model with fully resolved microstructure, a simplified, computationally cheaper model is also considered – there the porous core of the sandwich panel is approximated by a homogenized effective medium. The limitations of this homogenization approach are briefly pointed out.

Deformation and fracture of impulsively loaded sandwich panels

Light metal sandwich panel structures with cellular cores have attracted interest for multifunctional applications which exploit their high bend strength and impact energy absorption. This concept has been explored here using a model 6061-T6 aluminum alloy system fabricated by friction stir weld joining extruded sandwich panels with a triangular corrugated core. Micro-hardness and miniature tensile coupon testing revealed that friction stir welding reduced the strength and ductility in the welds and a narrow heat affected zone on either side of the weld by approximately 30%. Square, edge clamped sandwich panels and solid plates of equal mass per unit area were subjected to localized impulsive loading by the impact of explosively accelerated, water saturated, sand shells. The hydrodynamic load and impulse applied by the sand were gradually increased by reducing the stand-off distance between the test charge and panel surfaces. The sandwich panels suffered global bending and stretching, and localized core crushing. As the pressure applied by the sand increased, face sheet fracture by a combination of tensile stretching and shear-off occurred first at the two clamped edges of the panels that were parallel with the corrugation and weld direction. The plane of these fractures always lay within the heat affected zone of the longitudinal welds. For the most intensively loaded panels additional cracks occurred at the other clamped boundaries and in the center of the panel. To investigate the dynamic deformation and fracture processes, a particle-based method has been used to simulate the impulsive loading of the panels. This has been combined with a finite element analysis utilizing a modified Johnson–Cook constitutive relation and a Cockcroft–Latham fracture criterion that accounted for local variation in material properties. The fully coupled simulation approach enabled the relationships between the soil-explosive test charge design, panel geometry, spatially varying material properties and the panel's deformation and dynamic failure responses to be explored. This comprehensive study reveals the existence of a strong instability in the loading that results from changes in sand particle reflection during dynamic evolution of the panel's surface topology. Significant fluid–structure interaction effects are also discovered at the sample sides and corners due to changes of the sand reflection angle by the edge clamping system.

Indentation of metallic foam core sandwich panels with soft aluminium face sheets

A closed-form analytical model is presented for the deformation and fracture behaviour of sandwich panels with ductile foam cores and low yield-strength face sheets when subjected to quasi-static indentation with hemispherical indenters of various diameters and compared with an extensive experimental investigation. The aim is to predict the indentation strength and the influence of the indenter size on it. The face sheet is assumed an isotropic thin sheet undergoing large tensile deformation and bonded to a rigid-plastic foundation. The indentation strength of the sandwich panel is presented as a superposition of the force contributions of the skin, the foam core and the interfacial shear at the skin-foam interface at the point of skin fracture. To validate the model, sandwich panels with 0.32mm thick sheets of AA 1100-O aluminium alloy and aluminium closed-cell foam core are quasi-statically indented with spherical indenters of 10, 15 and 20mm diameters. It is established that failure of the sandwich panels is governed by radial skin fracture, and that the indenter size and the foam resistance greatly influence the indentation response as larger indenters are associated with higher failure loads. A simple parameter for system failure is ascertained, the subtended angle at the indenter-skin contact, which is dependent on the product of the indenter radius and the foam compressive strength. The developed model closely predicts the experimental load-displacement history and the failure loads and may be applied to any thin soft sheets bonded to a rigid-plastic foundation, and thus, to other sandwich constructions of similar constituents.