Hybrid Sandwich Structures Research Articles

Mechanical characterization of a 3D printed lattice core sandwich structure

AbstractSandwich structures have garnered interest as versatile structures for applications in advanced engineering structures. To fabricate sandwich structures, plastics have replaced conventional materials; however, most of these plastics remain in the environment beyond their functional lifespan. This study describes the fabrication of sustainable hybrid sandwich structures with 3D printed poly‐lactic acid (PLA) cores and self‐reinforced polyethylene terephthalate (srPET) face sheets. The mechanical responses of the hybrid sandwich structures with three types of lattice cores, S‐90, S‐45, and S‐V, were compared with those of the parent material sandwich structures after performing bending and impact tests. The face sheet in the hybrid sandwich structure transferred the load to the core without failure. The hybrid sandwich structure containing the S‐90 core exhibited a higher fracture strength (52.4 MPa) and tangent modulus of elasticity (2860 MPa) than those of the other structures. S‐V exhibited the highest fracture strains of 3.3% and 5% for parent material and hybrid sandwich structures, respectively. This study highlights the sandwich structures with excellent mechanical properties for structural applications.Highlights Novel sandwich structures with 3D printed PLA cores are fabricated. Three‐point bending and low‐velocity impact tests are performed. Failure occurred in the core, but the Sr‐PET face sheets did not deform. Hybrid sandwich structures significantly improve mechanical performance.

Numerical study of composite structures behavior under ballistic impacts

The aim of this paper is to introduce a finite element study of the behavior of composite plates subjected to ballistic impacts. The work studies different configurations of laminated composite structures, with and without reinforcements, subjected to high-speed projectile impacts (400-1000 m/s). The investigation focuses on the response of different composite materials' stacking sequences, as well as the impact of epoxy carbon reinforced with carbon nanotubes and the behavior of hybrid sandwich structures made of Kevlar epoxy and glass epoxy. The purpose is to develop a strategy of composite material damage modelling, identify the effects of multi material hybridization, and the influence of reinforcement by carbon nanotubes, on the structures' resistance to ballistic impacts. Numerical simulation provides a detailed description of plate damage. Results show that composite plates with 2% carbon nanotubes (CNT) displays a better impact energy absorption compared to 1% CNT and plates without CNT. The study also revealed the hybridization sequences offering the greatest energy absorption.

Multi-functional hybrid sandwich composite structures: Evaluating damage mechanics and tolerance using compression after impacts

Building upon previous researches that introduced an innovative foam core hybrid-sandwich composite structure for radome applications, showcasing promising performance under low-velocity impacts (LVIs), this paper delves into the assessment of damage tolerance and mechanics through Compression After Impact (CAI) testing. The primary objective is to analyze disparities in damage tolerance, damage mechanisms, displacements, deformations, energy absorption, and residual strengths resulting from LVIs followed by CAIs on dissimilar materials on opposite faces of the hybrid structure. The extent of damage is evaluated through Computed Tomography (CT) scans. During LVIs, impacts on the S glass face sheets side demonstrated different energy dispersion and absorption mechanisms, leading to variations in indent damage depths and widths across all impact energy levels, unlike the impact damages observed from the Kevlar side. During CAI testing, this difference becomes more evident, with Kevlar specimens (KS3 & KS5) showing greater indentation depths and narrower widths, and S glass specimens (SK3 & SK5) experiencing buckling. These effects are due to the unique damage absorption and dispersion properties of Kevlar and S glass. These variations prompted an in-depth investigation of the structure using CAI to comprehend damage tolerance and mechanisms under compressive loads. This study, unparalleled in existing literature, proposes hybrid sandwich structures with superior specific impact and residual strength compared to various composite sandwich structures documented in published literature, expanding their utility beyond radomes.

Effect of core densities on quasi‐static and low‐velocity impact behaviors of AFRP‐aluminum foam hybrid sandwich beams

AbstractThe hybrid sandwich structures possessing composite faces and an aluminum foam (ALF) core exhibit lightweight and superior impact resistance. However, limited studies pay attention to the mechanical behavior of hybrid sandwich beams with various ALF densities. The present article has focused on the influence of foam densities on the quasi‐static and low‐velocity impact (LVI) behaviors of hybrid sandwich beams with aramid‐fiber‐reinforced polymer (AFRP) faces and ALF core. The failure mode, loading response, and energy absorption of sandwich beams have been obtained experimentally and the failure map with a wide range of dimensional configurations has been established theoretically. Increasing core density significantly enhances the load‐carrying capacity of the sandwich beam, and the enhanced effect becomes more obvious for a thicker core. The medium‐density ALFs provide the maximum specific energy absorption, while the high‐density ALFs offer the highest energy absorption for hybrid sandwich beams. The applicability of core densities in hybrid sandwich structures is provided.Highlights Normal strain distribution under quasi‐static loading is analyzed using DIC. AFRP face microbuckling provides higher impact resistance than core failure. The applicability of core density in hybrid sandwich structures is given.

Empirical and numerical analysis of damage tolerance in multifunctional hybrid sandwich fiber reinforced polymers composite structures for aerospace applications using compression after impact (CAI) testing

AbstractThis study presents a novel hybrid‐sandwich composite structure, customized for nose radomes applications, incorporating a foam core and distinct opposite face sheets composed of Kevlar and S‐Glass materials. Addressing in‐phase electromagnetic properties, UV protection and low velocity impact responses in our previously published work, this paper empirically and numerically investigates the damage tolerance response of the proposed structures through compression after impact (CAI) testing. The low velocity impacts (LVIs) on S‐Glass face sheets exhibited unique energy dispersion and absorption mechanisms, resulting in variations in indent damage depths and widths across all impact energy levels as compared with LVIs on Kevlar face sheets. After experimentally assessing the CAI behavior, a FE model is developed to predict CAI behavior, which closely aligned with experimental findings. This study, unprecedented in existing literature, proposes hybrid sandwich structures for nose radome aerospace applications, with superior specific impact and residual strength compared to various composite sandwich structures documented in the published literature expanding its utility beyond radomes.Highlights Innovative composites with superior low velocity impact response, tested for compression after impact performance. Designed for nose radomes found suitable for other impact prone applications. Experimental and numerical modeling showed comparable results. Major differences observed in damage mechanics, resistance, and tolerances.

Analytical and numerical analysis of composite sandwich structures with additively manufactured lattice cores

In this study, an analytical and numerical analysis of a hybrid sandwich structure with a lattice core produced by additive manufacturing with composite facesheets is carried out. This paper aims to analytically calculate the mechanical behavior of the hybrid sandwich structure under three-point bending and to verify the results by the finite element method. The analytical method used in this article for the analysis of the composite sandwich structure is the First-Order Shear Deformation Theory (FSDT). The numerical analysis of the hybrid sandwich structure was performed in ANSYS. In the analyses, homogenized models of lattice structures, which had been previously validated, were employed to reduce the number of elements and thereby save time during the solution process. As a result of the study, an extensive investigation into the deformation, shear, and normal stress values of sandwich structures with lattice cores of varying aspect ratios has been carried out. The findings suggest a potential for optimization in lightweight structures, which could lead to innovative advancements in design and manufacturing processes within the aerospace and automotive sectors.

A New FE Modelling Approach to Simulate the Inter‐Layer Adherence in Hybrid Sandwich Structures Achievable by Additive Manufacturing

A New FE Modelling Approach to Simulate the Inter‐Layer Adherence in Hybrid Sandwich Structures Achievable by Additive Manufacturing

Supercapacitive performance of solution processed free standing TiO2-rGO-TiO2 sandwich film electrodes

The development of flexibility and robustness in functional devices is an important feature for the next generation of devices for long operational periods. It infers applications for the compactness of batteries, bio- sensors, supercapacitors, wearable devices, and photovoltaics as well. Here, we report a two-step low-cost solution-based process to synthesize (a) free-standing films of graphene oxide (GO) and reduced graphene oxide (rGO) and (b) hybrid sandwich structures of titania and rGO by using simple chemical bath deposition. The microstructure and morphological study are carried out using X-ray diffraction, atomic force microscopy, and scanning electron microscopy. Its electrochemical performance for supercapacitor electrodes were evaluated using three electrode cyclic voltammetry and galvanostatic charge-discharge system at different current density. In our experiment, graphene oxide is showing pseudo capacitance like behaviour, rGO and TiO2-rGO-TiO2 sandwich structure shows supercapacitor like behaviour. The value of capacitance for rGO is found 57.61 F/g. The sandwich structure with 0.17 M titania layers showing 121.92 F/g at 1.5 A/g current density with the highest power density observed 416 W/kg. Thus, this hybrid approach is not only having the potential to significantly boost the performance of future energy storage technologies but can also be used to develop cost-effective wearable electronics.

Investigating damage resistance in aerospace radome applications: Experimental analysis of hybrid sandwich composites

This research introduces an innovative hybrid sandwich composite structure tailored for specific applications, featuring a foam core and dissimilar face sheets made of Kevlar and S-Glass materials to address in-phase electromagnetic properties, UV protection, and impact response. Building on our prior work on design optimization for electromagnetic performance and aero/inertial loading, this paper investigates the low-velocity impacts (LVIs) response of the composite structure through drop-weight testing at various energy levels. Utilizing computed tomography (CT) scanning for damage analysis, distinct failure modes were observed for different face sheet combinations, with notable variations (energy absorption characteristics) in damage depth and width between the S-Glass and Kevlar face sheets. This study, unprecedented in existing literature, proposes hybrid sandwich structures with superior specific impact strength compared to various composite sandwich structures documented in the published literature expanding its utility beyond radomes.

High-Performance Photodetector based on ZnO/CsPbBr3 Quantum-dot-level-contact Hybrid Sandwich Structure

Perovskite quantum dot photodetectors have attracted intensive research interest due to their outstanding optical and electronic properties. However, the nonradiative recombination of photo-generated electron-hole pairs on the surface of CsPbBr3...

Multi-disciplinary optimization of hybrid composite radomes for enhanced performance

The focus of this research is to develop a specialized multidisciplinary design optimization framework for composite sandwich-structured radomes. Radomes play a crucial role in safeguarding antenna systems from challenging environmental conditions. However, they can adversely impact the electromagnetic performance of the antenna. Unlike traditional approaches that separately address electromagnetic performance and mechanical responses, our framework considers both aspects concurrently, resulting in a more efficient process. The main objectives of the optimization are to enhance electromagnetic performance while also accounting for deformations, material integrity, and structural stability. To evaluate the electromagnetic performance, a 3-dimensional numerical simulation is employed to analyze parameters such as electromagnetic transmission loss, bore sight error, and side lobe characteristics. The model's accuracy is verified through experimental testing in an anechoic chamber, utilizing a hybrid sandwich structure. The results indicate minimal attenuation, with an average loss of only 1.5 % in the transmission of antenna signals, using the proposed radome thickness. Furthermore, the configuration of the material provides structural stability, ensuring a factor of safety of 2.5 while satisfying operational constraints. Hence, the proposed multidisciplinary optimization model represents an efficient and feasible approach to radome design. This advancement in the field equips engineers and researchers with a valuable tool to develop dependable and effective radome systems.

Mechanical behaviour of hybrid FFRP/aluminium honeycomb sandwich structures

The combination of lightweight properties and high energy absorption capacity makes sandwich structures suitable for applications in transportation industry, such as automotive, aerospace, and shipbuilding industry. In these fields, the gas emissions reduction, fuel saving, vehicle safety and load capacity increase are currently important requirements. This research deals with the study of the mechanical behaviour of a “green” hybrid honeycomb sandwich structure made by an aluminium honeycomb core and flax fibres reinforced skins. Specific interest has been addressed to their mechanical behaviour in terms of bending properties and low-velocity impact response. For the impact tests, two indenters having hemispherical geometry with a diameter of 10 mm (H10) and 20 mm (H20) were selected. The results were compared with other hybrid structures analysed in previous studies. The static three-point bending tests produced different collapse modes, depending on the support span distance. Non-destructive evaluation was carried out for failure mode analysis by optical microscopy and digital radiography (DR). In the aluminium-flax hybrid sandwich structures it is found an increase in the impact strength of 25 % compared to the unreinforced aluminium honeycomb sandwich structures. In terms of specific energy absorption (SEA), it is interesting to underline an increase of 50 % compared to traditional AHS structures.

Lightweight hybrid composite sandwich structures with additively manufactured cellular cores

This study focuses on advancing sandwich structures by designing and fabricating complex two- and three-dimensional cellular cores combined with Carbon Fiber Reinforced Polymer (CFRP) skins. Numerical analysis is used to investigate the effect of core design and density on the bending performance. Optimal configurations are identified and experimentally validated. Professional Fused Filament Fabrication (FFF) equipment with a heating chamber is employed for manufacturing the core samples to enhance layer cohesion and material joint stiffness. A high-performance technical polymer with a superior strength-to-weight ratio is employed to maximize structural capabilities. Hybrid sandwich structures with PEI Ultem cellular cores demonstrate stiffness and strength comparable to reference materials, outperforming foam cores while slightly trailing behind Nomex® and aluminum honeycombs. In addition, the results demonstrate more efficient cell morphologies achievable through additive manufacturing technologies, surpassing the hexagonal design. This work provides valuable insights into hybrid composite materials and the potential of additive manufacturing in creating lightweight, high-performance sandwich panels.

Sandwich Structures With Bio-Inspired Viscoelastic Optimized Suture Face Sheets for Blast Mitigation

In this paper, the performance of a novel bio-inspired face sheet in mitigating the effects of blast loading is investigated. The new design of the face sheet consists of an optimized bio-inspired suture structure sandwiched between two aluminium plates. The suture profile is obtained by performing structural optimization using Genetic Algorithm, wherein the dynamic responses obtained using a novel viscoelastic finite element formulation are used. The performance of this optimized suture-based face sheet is experimentally tested in a vertical shock tube which validates the results obtained using commercial finite element software Abaqus. The hybrid sandwich structure composed of an aluminium honeycomb core sandwiched between the developed face sheets is evaluated numerically for its blast resistance performance. The study shows that the proposed face sheet design, not only reduces the stresses in the face sheets significantly, but also reduces the core stresses compared to conventional aluminium face sheet–based sandwich structures. Several parametric studies are presented for axial and transverse shock loading on this hybrid sandwich structures that give more insight into their wave propagation characteristics.

Blast analysis of efficient honeycomb sandwich structures with CFRP/Steel FML skins

The explosive blast is a major threat in the form of a terrorist attack to damage defense, aerospace, as well as civilian structures. This hazard of an explosive attack affects the lives of people and property. As a result, the modern era is searching for blast resistance structures to save humans and properties from these serious attacks. However, the current numerical analysis represents an effort in the novel design of blast-proof sandwich structures to meet the current era's demand. A stainless-steel sandwich structure using a square honeycomb core was designed to perform conventional weapons effects program (CONWEP) air-blast analysis on ABAQUS/Explicit. After a mesh sensitivity study and validation of the steel sandwich structure with experimental data published in the literature, the effect on blast characteristics of the aluminum (Al) foam-filled honeycomb and carbon fiber reinforced polymer (CFRP) with steel skins using fiber metal laminate (FML) for the front, back, or both skins of the sandwich structure was investigated. The entire finite element (FE) modeled sandwich structures were subjected to 1 to 10 kg of TNT air-blast loads at stand-off distances (SoD) ranging from 150 mm to 200 mm, and their blast resistance performance was evaluated using skin deflection and energy absorption. The damage initiation and evolution of composite laminates in the FML skins were investigated by the Hashin, Puck, and Singh failure criteria, respectively. These criteria were implemented via the VUMAT code. The obtained results showed that using FML skin for the sandwich structure diminished both the front and back skin deflection while improving specific energy absorption. A positive impact on blast mitigation by sandwich structures was observed with an increase in SoD. The lightweight FML front skin and steel back skin used bare square honeycomb hybrid sandwich structure had the smallest back skin deflection and the highest energy absorption up to 3 kg TNT. For the same combination of skins, the hybrid sandwich with foam-filled square honeycomb core represented a positive impact on the blast proof characteristics for high-intensity blasts ranging from 5 kg to 10 kg TNT. However, the novel designed hybrid sandwiches are recommended as a protective structure for defense, ships, automotive, etc.

The impact and post-impact flexural behaviors of CFRP/aluminum-honeycomb sandwich

This study investigates the medium velocity impact response and post-impact flexural behavior of hybrid sandwich structures. A series of experiments are performed over a range of impact energies to evaluate the effect of structural parameters of sandwich beams on the impact damage and how impact damage affects the residual flexural strength. The experimental results show that the CFRP face sheets play a dominant role in the impact resistance of sandwiches. The impact-induced damage significantly reduces the residual flexural deformation of the sandwiches, as well as their bending strength and stiffness. A theoretical method is proposed to achieve deformation and failure mode prediction of post-impacted CFRP/aluminum-honeycomb sandwich beams. This work provides fundamental understandings on the relationship of pre-impact damages and residual flexural behaviors, so as to guide damage resistant design of composite sandwiches.

Comparison of hole quality after drilling and helical milling of the Al/CFRP stacks

Hybrid sandwich structures composed of aluminium alloys and CFRP (Carbon Fibre Reinforced Polymer) are now frequently used in the aerospace industry. One of the factors inhibiting their application is the difficult processing resulting from the anisotropic nature of this type of construction. These materials are often joined by screws or rivets requiring mounting holes. One of the main problems is ensuring the quality of the holes after machining. The aim of this study is to assess the hole quality (dimensional and shape accuracy) and the occurrence of delamination after machining of a Al 2024/CFRP sandwich structure. In this experiment drilling and helical milling results were compared. A traditional HSS twist drill and a PCD milling cuter with a straight cut were used. The machining was carried out with a variable cutting speed. The tests were performed for two strategy of the machining – Al/CFRP (Al 2024 T3 – Carbon Fibre Reinforced Polymer) and CFRP/Al (Carbon Fibre Reinforced Polymer – Al 2024 T3).

Investigation of the Surface Roughness and Surface Uniformity of a Hybrid Sandwich Structure after Machining.

The parameters of surface roughness Ra, Rz and Rmax as well as surface topography Sa, Sz, Sp and Sv of the two-layer sandwich structure composed of an AW-2024 T3 aluminum alloy (Al) and a carbon-fiber-reinforced polymer (CFRP) were measured to determine an impact of the machining configuration (arrangement of the materials forming a sandwich structure) and the type of tool (presence of the tool coating) on the quality of the surface obtained through circumferential milling. The measurements revealed that milling produced different values of surface roughness for the aluminum alloy and the CFRP composite with values of 2D and 3D surface roughness being higher for the composite layer. The highest value of Ra of 1.10 µm was obtained for the surface of the CFRP composite using the CFRP/Al configuration and a TiAlN-coated tool. The highest values of the Rz (6.51 µm) and Rmax (8.85 µm) surface roughness parameters were also obtained for the composite layer using the same machining configuration and type of tool.

Novel design of honeycomb hybrid sandwich structures under air-blast

In this study, dynamic explicit analysis was performed to examine the air-blast performance of various hybrid sandwich designs in terms of face plate deflections and energy dissipation capacity under the conventional weapons effects program (CONWEP) air-blast loads ranging from 3 kg to 8 kg trinitrotoluene for stand-off distance ranges from 150 mm to 200 mm. The blast resistance of honeycomb sandwich configurations was evaluated using steel honeycomb with different core topologies, crushable Al foam-filled steel honeycomb, and steel or steel with 3D Kevlar/polypropylene laminate employing fiber metal laminate (FML) front face. For an accurate prediction of the deformation mechanism of all steel parts, the Johnson-Cook (J-C) model was used. The composite failure criteria of Hashin, Puck, and Matzenmiller were implemented to accurately examine the fiber and matrix damage behavior. The novel hybrid design of the honeycomb sandwich structure’s blast resistance is improved by the employment of foam-filled honeycomb, an FML front face, and a circular honeycomb core. In comparison to other sandwich configurations, a novel designed hybrid sandwich construction composed of foam filled circular honeycomb with FML front facing and steel back facing (FCH-1KP0.5) achieved the highest blast resistance due to its lowest face deflection with the smallest plastic dissipation energy.

Crash-worthiness studies on multistage stiffened honeycomb core sandwich structures under dynamic impact loads

The high-velocity impact performance of honeycomb sandwich structures is enhanced by adopting multi-stage structures with varying cell wall thickness, and cell wall inclination, after preserving the structural mass. The performance of the enhanced structures is simulated considering bullet penetration tests. The penetration is observed to be reduced by 4.82% in case of two stage sandwich structures, as compared to the single stage sandwich structures. Furthermore, the reduction in penetration is estimated to be up to 11.34% when the cell wall thickness is increased from 0.05 mm to 0.15 mm. Moreover, honeycomb cores are stiffened using ribs in two different configurations, within the available space. The improvement in crash-worthiness is estimated by measuring the penetration of the single and two stage hybrid sandwich structures. The penetration distance of stiffened single and two stage structures is found to be reduced by 28.4% and 31.97%, respectively, as compared to the corresponding structures without stiffeners. On the other hand, inclination of the cell walls at an angle to the normal of the face plates is found to enhance the stiffness, and hence the penetration resistance. The honeycomb sandwich structure with oblique unit cells is estimated to dissipate three times more energy as compared to a regular structure. As a result, the impactor is unable to pierce through the sandwich structure. Therefore, two stage hybrid sandwich structures with oblique hexagonal unit cells are recommended for energy absorption in impact applications.