Design Of Sandwich Structures Research Articles

Experimental and numerical analysis of additively manufactured foamed sandwich beams

This work examines the feasibility of using foamable polymer filaments to create lightweight composite beams using additive manufacturing. To accomplish this, monolithic and sandwich beams, with non-foamed face sheets and a foam core were fabricated using MEX 3D printers. The non-foamed and foamed PLA components were created by extruding foamable PLA with nozzle temperatures of 200 °C and 220 °C, respectively. Tensile testing samples were printed and tested and used to provide data for numerical models. A range of different sandwich structures were printed and tested in 3-point bending and their performance was compared to monolithic non-foamed and foam beams and to analytical and numerical models.The stiffness, yield load, and maximum load of sandwich beams with non-foamed face sheets and foamed cores are much greater than those of pure foamed beams. With sandwich foam beams, weight reductions of around 30 % are both observed and predicted compared to non-foamed beams with equivalent stiffness. Analytical and numerical models using experimental data show value in aiding the design of sandwich structures of this type.

Low-Velocity Impact Resistance of 3D Re-Entrant Honeycomb Sandwich Structures with CFRP Face Sheets

Lightweight sandwich structures have been receiving significant attention. By studying and imitating the structure of biomaterials, its application in the design of sandwich structures has also been found to be feasible. With inspiration from the arrangement of fish scales, a 3D re-entrant honeycomb was designed. In addition, a honeycomb stacking method is proposed. The resultant novel re-entrant honeycomb was utilized as the core of the sandwich structure in order to increase the impact resistance of the sandwich structure under impact loads. The honeycomb core is created using 3D printing. By using low-velocity impact experiments, the mechanical properties of the sandwich structure with Carbon-Fiber-Reinforced Polymer (CFRP) face sheets under different impact energies were studied. To further investigate the effect of the structural parameters on the structural, mechanical properties, a simulation model was developed. Simulation methods examined the effect of structural variables on peak contact force, contact time, and energy absorption. Compared to traditional re-entrant honeycomb, the impact resistance of the improved structure is more significant. Under the same impact energy, the upper face sheet of the re-entrant honeycomb sandwich structure sustains less damage and deformation. The improved structure reduces the upper face sheet damage depth by an average of 12% compared to the traditional structure. In addition, increasing the thickness of the face sheet will enhance the impact resistance of the sandwich panel, but an excessively thick face sheet may decrease the structure's energy absorption properties. Increasing the concave angle can effectively increase the energy absorption properties of the sandwich structure while preserving its original impact resistance. The research results show the advantages of the re-entrant honeycomb sandwich structure, which has certain significance for the study of the sandwich structure.

Realizing an Ultrahigh Depolarization Temperature near the Curie Point and Large d33 with Superior Temperature Stability in Lead-Free Ceramics via a Sandwich Structure Design

An imminent challenge of lead-free Bi0.5Na0.5TiO3-based (BNT) piezoceramics is that the giant piezoelectric constant (d33) caused by the morphotropic phase boundary is incompatible with a high depolarization temperature (Td) and ultralow temperature coefficient (Ttc) of the real-time d33, which severely hinders their industrial application in the field of elevated temperatures. Herein, a sandwich-structured 0.94Bi0.5Na0.5TiO3-0.06BaTiO3/0.89Bi0.5Na0.5TiO3-0.11BaTiO3/0.94Bi0.5Na0.5TiO3-0.06BaTiO3 (SWS-6/11/6BT-y, where y refers to the weight fraction of the BNT-11BT solid solution) ceramic composite is engineered for mitigating the conflict between d33, Td and Ttc. Following this strategy, ultrahigh Td near the Curie point (225 °C, close to that of the BNT-11BT layer) and relatively large d33 (130 pC/N, close to that of the BNT-6BT layer) are simultaneously realized in a SWS-6/11/6BT-40%-Q ceramic composite. More importantly, the ultralow Ttc (0.07%) of real-time d33 is also achieved in this work. The structural heterogeneity yields the high piezoresponse, and the built-in field resulting from layer-type ceramic composites provides the driving force to promote the diffused ferroelectric-relaxor phase transition and the resultant ferroelectric order with high Td. The above synergistic contributions realize the remission of the d33-Td-Ttc conflict in a sandwich-structural SWS-6/11/6BT-40% ceramic composite. Thus, our work provided a path for designing the BNT-based piezoceramics with potential for industrial applications.

Simulation study on the anti-penetration performance and energy absorption characteristics of honeycomb aluminum sandwich structure

This work studied the anti-penetration performance and energy absorption characteristics of the honeycomb aluminum core structure. Tests of penetrating depth were conducted. The response and deformation resistance of the aluminum sandwich structure with a regular hexagonal honeycomb were studied through numerical simulation. The effect of the face/back plate thickness ratio and the shape of the core layer unit on the performance of the aluminum sandwich structure with a regular hexagonal honeycomb were compared and analyzed with a theoretical model of equivalent target calculation. Based on the results, the aluminum sandwich structure with a regular hexagonal honeycomb has the strongest anti-penetration capability when the thickness ratio of the face/back plate is set to 2.5:1. In terms of the energy consumption, the Arrow and concave hexagonal honeycomb aluminum sandwich structures are 14.7% and 25.9%, respectively, than the aluminum sandwich structure with a regular hexagonal honeycomb. The typical hierarchical honeycomb aluminum sandwich structure has better energy absorption characteristics than the aluminum sandwich structure with a regular hexagonal honeycomb. Therefore, the anti-penetration performance of the honeycomb aluminum sandwich structure can be improved by adjusting the thickness ratio of the face/back plate and changing the shape of the core layer. The research results are of great significance in guiding the design of the honeycomb aluminum sandwich structure.

Anti-impact and vibration-damping design of cork-based sandwich structures for low-speed aerial vehicles

Anti-impact and vibration-damping design of cork-based sandwich structures for low-speed aerial vehicles

Effect of Impact Angle on the Impact Mechanical Properties of Bionic Foamed Silicone Rubber Sandwich Structure.

In this paper, a red-eared slider turtle is used as the prototype for the bionic design of the foamed silicone rubber sandwich structure. The effect of impact angle on the performance of the foamed silicone rubber sandwich structure against low-velocity impact is studied by the finite element method. The numerical model uses the intrinsic structure model of foamed silicone rubber with porosity and the three-dimensional Hashin fiberboard damage model. The validity of the model was verified after experimental comparison. Based on the finite element simulation of different impact angles and velocities, the relationship between impact velocity and residual velocity, as well as the penetration threshold at various impact angles are obtained, and the change law of impact resistance of foamed silicone rubber sandwich structure with impact angle and velocity, as well as the damage pattern of sandwich structure at different impact angles and velocities are given. The results can provide a basis for the impact resistance design of the bionic foamed silicone rubber sandwich structure. The results show that, at a certain impact speed, the smaller the impact angle, the longer the path of the falling hammer along the plane of the sandwich structure, the lighter the damage to the sandwich structure and the greater the absorbed energy, so that avoiding the impact from the frontal side of the sandwich structure can effectively reduce the damage of the sandwich structure. When the impact angle is greater than 75°, the difference in impact resistance performance is only 2.9% compared with 90°, and the impact angle has less influence on the impact resistance performance at this time.

An efficient method for design of lattice core sandwich structures with superior buckling strength under compression

ABSTRACT Buckling failure is a major concern in lightweight lattice core sandwich structures (LCSSs). This study proposes an efficient method for designing LCSSs with superior buckling strength under uniaxial compression. In this approach, the buckling-resistant non-uniform shapes of single struts with different slenderness and inclination are first identified, and then they are directly used to replace uniform struts in LCSSs. This method can save considerable design time compared to conventional methods, which require conducting optimizations on entire LCSSs. Numerical results demonstrate that four designed representative non-uniform LCSSs can gain over 15% improvement in buckling strength compared to their counterpart uniform LCSSs. This improvement is even comparable to the solutions from optimizations on entire LCSSs. Two LCSSs with non-uniform struts are 3D printed, and the test results validate at least 10% improvement in compressive strength. Based on the proposed method, various LCSSs with superior buckling strength could be designed for different loadings.

Toughness-improving design of lattice sandwich structures

The lattice sandwich structure has become a focus of research in aerospace and other fields because of its light weight and high impact resistance. However, research on the impact resistance of lattice sandwich structures is still focused on simulations and experiments and presently lacks theoretical models. In this paper, we proposed a toughening design method based on the failure modes of lattice sandwich structures. The toughening model was established, the dimensional effect was analysed, and the mechanism of synergistic toughening was studied. The results show that the mass of the sandwich structure we designed is reduced by 67.7% compared with the solid part, which has the same outline sizes, and its impact toughness is increased by 119.0%.

Research Progress of Sandwich-structured Flexible Energy Storage Dielectric Materials

Polymer dielectric materials show wide applications in smart power grids, new energy vehicles, aerospace, and national defense technologies due to the ultra-high power density, large breakdown strength, flexibility, easy processing, and self-healing characteristics. With the rapid development of integration, miniaturization and lightweight production of electronic devices, it is required to develop such storage and transportation dielectric system with larger energy storage density, higher charge and discharge efficiency, good thermostability and environmental friendly. However, the contradiction between dielectric constant and breakdown strength of dielectric materials are the key factors and bottleneck to obtain high performance dielectric materials. It is accepted that controlling charge distribution and inhibiting charge carrier injection are important to improve the energy storage characteristics of polymer dielectrics. In recent years, designing sandwich or stacking structured materials exhibits outstanding advantages in inhibiting charge injection and promoting polarization, thereby the permittivity and breakdown strength of polymer dielectrics can be simultaneously enhanced. Accordingly, this paper reviews the research progress of sandwich-structured polymer dielectric films in improving the energy storage performances from the perspectives of materials composition, structural design, and preparation methods. The influence of dielectric polarization, charge distribution, charge injection, interfacial barrier and electrical dendrite growth on the energy storage performance and the synergistic enhancement mechanisms in such sandwich-structured dielectric materials are systematically summarized, implying good development and vast application prospects. In brief, introducing easy polarization, wide-gap and deep-trap nanofillers has greater designability and regulation in the dielectric and breakdown properties. In addition, using the hard layer as the outer layer can reduce charge injection more effectively, achieving high breakdown resistance performance easily. Sandwich structure design also possesses advantages over other methods in maintaining good flexibility and dielectric stability of dielectric materials, thus becoming a hot-topic research area in recent years. In the future, it is necessary to combine low conductivity and high thermal conductivity of dielectric polymers to achieve high temperature energy storage and efficiency. Research on recyclable, self-repairing sandwich insulating films is good for the service life and safety of electronic components and will further expand the application of dielectric polymers. Finally, effective evaluation of sandwich-structured dielectric and energy storage performances through simulation and theoretical modeling is very helpful to reveal the breakdown and thermal failure mechanisms, and theoretically guide the design of polymer dielectric materials.

Optimizing stiffness and lightweight design of composite monocoque sandwich structure for electric heavy quadricycle

Optimizing stiffness and lightweight design of composite monocoque sandwich structure for electric heavy quadricycle

Explicit Dynamics Simulation and Design of Sandwich Composite Structures Reinforced by Multilayer Lattice

Explicit Dynamics Simulation and Design of Sandwich Composite Structures Reinforced by Multilayer Lattice

A novel design of blast proof sandwich structure with hybrid skin

In the present modern age, explosive terrorist attacks are increasing day by day. Explosive attacks can take place anytime and anywhere. This is a hazard to both people and property. Hence, blast-proof structures are in demand for the current era to protect humans and properties. An effort has been made to design a novel blast-proof sandwich to fulfil this requirement. A sandwich structure made of steel was designed using a square honeycomb core (Model-1). The blast resistance analysis of the designed honeycomb sandwich structures was performed on ABAQUS/Explicit. The modelled sandwiches were subjected to conventional weapons effects program (CONWEP) air-blast loads ranging from 1 kg to 3 kg trinitrotoluene (TNT) for a fixed stand-off distance (SoD) of 150 mm. After the mesh convergence study and validation of the Model-1 with experimental results available in the literature, the 5 mm steel front skin was replaced by 1.5 mm steel/2 mm carbon fibre reinforced polymer (CFRP)/1.5 mm steel hybrid skin for Model-2 to reduce the weight of the structure with improved blast performance. In Model-3, both the 5 mm steel front skin and the 5 mm steel back skin were replaced by 1.5 mm steel/2 mm CFRP/1.5 mm steel hybrid skins for a further reduction in the weight of the structure. The blast resistance of sandwich configurations was evaluated in terms of the protective back skin deflection during blast loads. The use of hybrid skins in a sandwich structure drastically improves blast resistance in terms of smaller skin deflection. The square honeycomb core used sandwich with the hybrid front skin (Model-2) has the best blast proof characteristics and is recommended for armoured vehicles and skid plates of automobiles to protect the lives of humans.

Design and optimization of micro-perforated ultralight sandwich structure with N-type hybrid core for broadband sound absorption

We propose a novel ultralight multifunctional micro-perforated sandwich structure with N-type hybrid core, which exhibits excellent sound absorption as well as good load-bearing capacity and heat transfer performance. Sound absorption coefficient of the sandwich structure is calculated by establishing an analytical model. To validate the analytical model predictions, both experimental measurements and numerical simulations are carried out, with good agreement achieved. Physical mechanisms leading to the excellent acoustic performance of the structure are revealed, and effects of geometric parameters are quantified. For maximized sound absorption at minimal structural weight, an optimization strategy is developed with the Simulated Annealing algorithm. Compared with non-optimal sandwich structures, the optimal structure enables reduced weight and better absorption within broader frequency range. The proposed ultralight sandwich structure with integrated multifunctional attributes has significance in engineering applications demanding excellent mechanical, thermal, acoustic performances as well as low mass and volume.

Application of finite element analysis to honeycomb sandwich structures: a review

Honeycomb sandwich is really one of the fundamentals to make a composite strong, stiff, very light, safe and have wonderful performance. Honeycomb materials are majorly used where high strength to weight ratio, stiffness to weight ratio is needed. Honeycomb sandwich consist of two face sheet or skin and a light core which can take many shapes, the common is hexagonal shape. The core handles shear load, while the skins resist compression and tension. This paper aims to guide the design of honeycomb sandwich structures done with finite element analysis software. The characteristic of honeycomb at microstructure and unit cell will be discussed Moreover, much demand on light weight honeycomb structures that can withstand heavy loads under different working condition are on high demand. Experimental approach can be time consuming and costly, this created room for massive research using FEA on loading response with various cores and thickness, in order to investigate the mechanical properties. This study will focus on the FEA of honeycomb sandwich done by many researches currently on commercial software’s ANSYS and ABAQUS, this will be a guideline for researches to see what has been done and what is obtainable using FEA software.

Dynamic crushing performance of bio-inspired sandwich structures with beetle forewing cores

A novel design of Sandwich Structure inspired by Beetle Forewing (SSBF) is proposed in this study by mimicking the internal structure of beetle forewing. The viscoelastic material and the arch shape of hollow cavity structures found inside the forewing structure of the beetle are imitated by utilising the shear thickening fluid (STF) and semi-arch cores, respectively. The coupling interaction between fluid and structural components is analysed using a fluid-structure interaction (FSI) technique in LS-DYNA. It is found that the proposed SSBF by partially filling the core with STF generates a higher mean crushing force and stabilises the crushing force-displacement profile without a noticeably high initial peak crushing force as compared with the empty, polyurethane (PU) foam-filled, or Newtonian viscous fluid-filled counterparts. Furthermore, this stable crushing force of SSBF enhances with the increase of crushing speed, showing ideal behaviour for energy absorption and crushing resistance for the adaptation to the design of structures to resist impact loads.

On the nonlinear post-critical responses of VAT sandwich beams with variable stiffness composite skins under axial compression

In this article, the nonlinear post-critical problem of Variable Angle Tow (VAT) sandwich beams with variable stiffness composite skins under axial compression is studied for the first time. The present sandwich beam model is constructed from a modified version of extended high-order sandwich panel theory (EHSAPT), in which the first-order shear deformation theory with von Kármán’s strain–displacement relation is utilized for the skin layer, whereas the high-order theory with linear strain–displacement is applied to characterize the deformation of the core layer. Based on the principal of virtual work, a system of differential equations with variable coefficients is firstly formulated for the postbuckling problem of VAT sandwich beams with variable stiffness composite skins under plane-strain state. Meanwhile, a more efficient Rayleigh–Ritz approach combined with variational formulas is employed to derive the nonlinear algebraic equations in weak forms, and thereafter a sophisticated path-tracing technique is applied to determine the postbuckling equilibrium path. Both super-critical and sub-critical postbuckling states of VAT sandwich beams can be readily captured under the present analytical model framework. The accuracy and effectiveness of the developed Rayleigh–Ritz procedure are validated by comparing against the results available in literature. Effects of variation in skin stiffness on both the critical instability and post-critical behaviours of VAT sandwich beams are discussed in numerical examples. It is found that the change in skin stiffness plays a determinative role in the formation of nonperiodic wrinkling patterns of VAT sandwich beams. In addition, the change in skin stiffness may cause global and local instability loads to be close to each other, and accordingly, the possibility of encountering interactive buckling is increased. The results presented herein may be beneficial for the design of VAT sandwich structures under compression.

Multi bandgaps design of sandwich metamaterial plate with embedded membrane-type resonators

A metamaterial plate with multi bandgaps is proposed for vibration suppression by integrating membrane-mass structures that can be used as locally resonant metastructure into a honeycomb sandwich structure. The finite element method is employed to calculate the band structure and the transmission spectra. The formation mechanisms of the locally resonant bandgaps are investigated via the analysis of the mode shapes of the membrane-mass resonator and face plate in a unit cell. The effects of the location of the attached mass on the bandgap property and an improved multi bandgaps structure is designed and discussed. Results show that the proposed multifunctional metamaterial exhibits an excellent vibration suppression performance, as well as a significant designability. Moreover, a specimen of the proposed metamaterial is fabricated and experimental measurements are performed, and a good agreement between the numerical predictions and the experimental results is obtained. The results of this study will be useful for the design of sandwich structures with multiple vibration bandgaps.

Local buckling on large sandwich panels used in light aviation: Experimental setup and failure scenarios

The design of light aircraft sandwich structures is driven by a local buckling phenomenon named “wrinkling” which can be the primary cause of failure of such structures. Structural tests using the VERTEX methodology were performed to access the wrinkling behaviour of 558x536mm2 technological sandwich specimens representative of the design used in light aviation. The operating principle of the VERTEX machine is the use of four hydraulic actuators to load a rectangular box structure, the upper part of the central box being closed by the sandwich under test. Thus, sandwich specimens were tested under compressive and shear loading. A wrinkling scenario was identified thanks to Stereo Digital Image Correlation and a high-speed camera. Wrinkling localisation is driven by mechanical and geometrical aspects. Experiments on wrinkling in sandwich panels remain rare in the literature at this level of the test pyramid for certification of aeronautical structures. This upper scale presents some advantages as it allows multiaxial loading and boundary conditions consistent with a lightweight aeronautical structure. Technological elements can also be added to study their influence on the structure. The result will lead to interesting future investigations on the dialogue between experiments and models in a forthcoming paper.

Failure mechanisms of fluted-core sandwich composite panels under uniaxial compression

Fluted-core sandwich composite structures are major load-bearing components used in launch vehicles. Herein, analytical models were proposed to investigate the failure mechanisms of fluted-core sandwich composite panels, including global buckling, local buckling, and material failure. Failure mode maps of fluted-core sandwich panels were constructed to analyze the intrinsic impact mechanism of geometric parameters on failure behavior. Integrated fluted-core sandwich composite panels were then fabricated by adopting the integrated forming process and co-cured method. Uniaxial compression tests and finite element simulation were also conducted to verify the analytical predictions with good consistency. The effects of the geometric variable on both load-bearing capacity and failure modes of the structures were explored. The results indicated the occurrence of global buckling at small distances between the top and bottom face sheets, resulting in undesired load-carrying capacities. The decrease in width of short span or increase in thickness of face sheets prevented such local-buckling behavior, resulting in material failure. The triangular-shaped core with zero short spans was identified as a better option for material failure as dominant failure mode for designing load-bearing sandwich panels. These findings look promising for lightweight and load-carrying applications, providing a reliable reference for the initial design of such sandwich structures.

A comprehensive investigation on bending stiffness of composite grid-stiffened and functional foams sandwich beam

This paper investigates the bending stiffness of composite grid-reinforced sandwich beams with functional foam cores by a combination of analysis, simulation, and experiment. First, the sandwich layer composed of stiffeners and foam cores is homogenized, and the equivalent mechanical parameters of the sandwich layer are proposed. Then, based on the first-order shear deformation theory, the three-point bending deflection of the beam is derived and verified by tests and simulations. Finally, the factors affecting the bending stiffness are investigated, such as the elastic modulus of the foam cores, the thickness of the stiffeners, the longitudinal and transverse spacing of the stiffeners, and the fiber lay-up angle of the stiffeners. The results of this paper are of great significance to the stiffness design and parameter optimization of composite grid-stiffened sandwich structures with foams for underwater vibration and noise reduction.