Foam Core Research Articles

Analysis of electrothermal damage in a radome exposed to electromagnetic radiation

Abstract After nearly 9 months of electromagnetic irradiation with a power density of 10 W/cm2, the unit blocks of an A-sandwich radome in the electromagnetic beam scanning area experienced electrothermal damage. Both the inner skin and core layer foam of the A-sandwich unit blocks in that area present different levels of damage. The inner skin is wrinkled and cracked, and the core layer foam is locally charred, carbonized, and ablated. The temperature images recorded through the infrared thermal beam method show that the temperature distribution of the unit blocks in the beam irradiation area is abnormal and strongly related to the discontinuous structure distribution of the core foam and resin. The non-uniformity of core material is the main cause of the electrothermal damage to unit blocks. By process improvements, the shaping of the polyurethane foam core layer is changed from cutting, resin bonding, and splicing to one-step foaming without resin binder, and the continuity of the core layer material is ensured. The usage results of unit blocks made by the new process show that the temperature field distribution is uniform, with a maximum temperature of only 31.3°C, which is 71.62% lower than the maximum temperature of 110.3°C in the damaged block.

Damage of Nickel-coated glass/epoxy foam-core composites induced by artificial lightning strikes

In the field of composite materials, many reports have shown that catastrophic structural damage is caused by lightning strikes. In this study, new design concepts were proposed for the lightning-strike protection of nickel-coated glass/epoxy foam-core composites. Instead of using a neat metal mesh, glass fibers were modified with nickel particles via a plating technique to improve their thermal and electrical conductivities. In addition, a thin Invar plate was inserted at the middle of the structure and a foam core was introduced to reduce damage to the structure. Three models with different materials and stacking sequences were used in this study. Severe damage was experimentally observed following artificial lightning at a peak current of approximately 150 kA when considering a waveform A. Furthermore, numerical prediction was performed to identify the damage mechanisms of the structures. Besides the heat flux source, a mechanical source known as the shock wave overpressure was investigated separately as a new factor for dielectric materials. These two sources of lightning were determined as minor reasons for the structural damage. The failure modes were analyzed for further discussion about the failure mechanism in this study.

CO2-foam flood with wettability alteration for oil-wet carbonate reservoirs

Carbon dioxide (CO2) flooding in carbonate reservoirs often suffers from poor sweep efficiency, attributed to unfavorable mobility ratio, gravity segregation, and reservoir heterogeneity. CO2-foam injection is a promising strategy to control CO2 mobility. The stability of CO2-foam is affected by reservoir wettability. This study aims to systematically investigate the effectiveness of CO2-foam flood coupled with wettability alteration in an initially oil-wet carbonate rock at a pressure below the minimum miscibility pressure. Three types of surfactants, including a nonionic surfactant Soloterra 843, a cationic surfactant CETAC-30, and a zwitterionic surfactant LMDO, were evaluated as potential foaming agents. Contact angle tests were conducted to assess the wettability alteration capability of these surfactants. Bulk foam stability tests and foam rheology tests were conducted under reservoir conditions. Finally, foam core flood experiments were performed using oil-wet carbonate core samples. Results from contact angle experiments indicated that only CETAC-30 was effective at altering rock wettability from oil-wet to water-wet by removing the negatively charged organic acid components from the rock surface. Foam stability and rheological tests revealed that LMDO exhibited highly stable CO2-foam in the absence of crude oil. However, the presence of crude oil adversely affected CO2-foam stability for all the surfactants. Core flooding experiments demonstrated that injecting wettability alteration surfactant, CETAC-30, in form of foam could not only alter the wettability of rocks, but also enhance the foam strength. Continuous gas injection (without foam) increased oil recovery by 14.4 % due to the near-miscibility of CO2 and oil. Both CETAC-30 and LMDO surfactants increased the oil recovery by about 35 % after waterflood, but the wettability altering surfactant showed the highest mobility reduction factor (MRF). These findings provide valuable insights into the complex interplay between near-miscibility, wettability alteration and foam strength in carbonate reservoirs, offering a basis for optimizing CO2-foam flooding strategies for enhanced oil recovery and carbon sequestration.

Experimental and numerical investigation of shear strain and failure in sandwich panels with foam-core and jute/glass composite faces under 3-point bending

There is a growing demand for natural fibers related to cost and environmental issues. This work focuses on the influence of the stacking sequence and hybridization on the shear strain of sandwich panels with glass/jute composite faces and polyethylene terephthalate foam core. Behavior comparison followed analytical, experimental, and numerical approaches. Failure analyses of the panels were performed numerically using the finite element method, with progressive damage and Hashin failure criterion. Digital image correlation was used to examine total surface deformation. Results showed that the hybrids presented better overall mechanical properties.

Axial Impact Performances of Composite Aluminum Foam Tubes

An improved melt foaming method is employed to fabricate composite aluminum foam tubes (CAFTs) with varying diameter ratios, achieving metallurgical bonding between the aluminum foam and aluminum tubes. Based on the structural characteristics of aluminum foam‐filled tubes and traditional numerical formula for calculating the energy absorption properties of metal foams, a new calculation formula is proposed to accurately evaluate energy absorption performance of CAFTs under axial load, enabling more precise numerical calculation of total energy absorption. Furthermore, drop weight impact tests and finite element simulations are conducted to investigate the axial impact performance and deformation mechanism of CAFTs. The influence of diameter ratio on crashworthiness and energy absorption performance is also analyzed. As the diameter ratios decrease, both the impact resistance and total energy absorption of CAFTs increase, while the degree of tube damage gradually decreases. Moreover, finite element simulation results demonstrate that metallurgical combination between aluminum foam and aluminum tubes effectively transfers stress to thin‐walled tubes with better load‐bearing performance, preventing concentrated collapse of aluminum foam core. Additionally, the presence of aluminum foam provides robust restraint against deformation or rupture in thin‐walled tubes.

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.

Experimental and analytical investigations on single and repetitive impact failure responses of composite sandwich panels with orthogonal woven GFRP facesheets and PVC foam cores

Due to the unique design requirements for high load-bearing capacity of ship structures, composite materials used in the marine industry are gradually being developed with the characteristics of multi-layer sandwich structures with large thickness and cross-section, which are different from thin-walled composite materials widely applied in the aeronautical industry. However, sandwich composite materials used in marine structures have high susceptibility to impact event during in-service applications. The impact induced damage may seriously affect their mechanical performance and structural safety. Therefore, a comprehensive investigation in this paper on the failure mechanisms of composite sandwich panels with orthogonal woven GFRP facesheets and a PVC foam core layer is carried out with a series of single and repetitive low-velocity impact tests. The variations of impact force, dent depth, structural stiffness, failure modes, energy absorption and so on of composite sandwich panels against impact energy levels and impact numbers were explored. The results demonstrate that the delamination damage threshold at the first impact, the sudden drop of peak force and the slow descent process of impact force are the three typical characteristics of impact responses that corresponded to delamination initiation and fibre breakage of the upper panel, and compression damage of the core layer, respectively. The accumulated impact-induced damage has a significant negative effect on load-bearing and energy-absorption capabilities of composite sandwich panels. Moreover, an approximate theoretical analytical method is presented to solve the impact resistance of composite sandwich panels. The analytical results are compared well with experimental results. This research provides a detailed understanding of the damage mechanisms of composite sandwich panels under impact loadings and a guidance for impact resistant design of ship protective structures.

A Comparative Blast Mitigation Performance Evaluation of Metallic Sandwich Panels with Honeycomb, Corrugated, Auxetic, and Foam Cores

Due to the high energy absorption capability and excellent bending strength of the sandwich panels, they are mostly preferred as protective structures against explosive blast attacks. The evaluation of their blast-mitigation characteristics through experiments is highly dangerous, costly, time-consuming, and polluting for the environment. Therefore, in this presented work, a series of numerical analyses were performed to evaluate the blast mitigation of the outstanding sandwich panels with honeycomb, corrugated, auxetic, and foam cores. The masses of sandwich panels were kept constant, and their areal densities were maintained constant throughout the study to effectively compare their performance under identical air blast loading conditions. To apply the air blast loads to the designed sandwiches, 1–3[Formula: see text]kg of spherical-shaped trinitrotoluene charges were used for a 100[Formula: see text]mm stand-off distance. The sandwiches are made of high-strength AL-6XN steel and crushable aluminum foam. The rate-dependent Johnson–Cook constitutive model of plasticity and the crushable foam model with volumetric hardening were used for the evaluation of sandwich panels’ plastic deformations. The findings of the work depicted that the honeycomb core is more efficient than the other core structures of the same masses because the sandwich panels with honeycomb core provide smaller back skin deflections, globalized core crushing, and higher core energy absorption than the other sandwich panels for extreme conditions of air blast loading.

Cutting failure behavior of foam core sandwich plates

During the ship, collisions with reefs or grounding may cause damage to the hull of ships made of sandwich plates. The cutting failure mechanism of sandwich panels is still not fully understood. In this paper, the failure behavior of metal foam sandwich plates under cutting load by a wedge-shaped indenter is studied through analytical, experimental, and numerical methods. An analytical model is proposed to describe the cutting failure behavior of foam core sandwich plates. Based on experimental results, three distinct failure modes of foam sandwich plates with varying thicknesses are observed. Numerical simulations are performed, and analytical and numerical results capture experimental results reasonably. The effects of core thickness, face-sheet thickness, and tip angle and cutting angle of wedge indenter on the failure mode, load-carrying capacity and energy absorption performance of the sandwich plates are explored. The present analytical model can effectively predict the cutting failure behavior of sandwich plates.

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.

Static and dynamic analysis of polyethylene terephthalate foam core and different natural fiber-reinforced laminated composite-based sandwich plates through experimental and numerical simulation

This study explores the flexural behavior and free vibration analysis of sandwich plates including natural fiber-reinforced polymer composite faces and Polyethylene Terephthalate (PET) foam cores under a range of edge situations. ABAQUS is used to do numerical simulations with three-dimensional solid elements (C3D8R). To ascertain the natural frequencies of the plates, experimental procedures such as impact hammer testing and Fast Fourier Transform (FFT) analysis are carried out. The inference of different geometrical parameters on the natural frequencies is investigated through numerical simulation in ABAQUS. The study gives brief outlines regarding the sandwich plates for different engineering applications.

Mechanical Properties of Eco-Friendly, Lightweight Flax and Hybrid Basalt/Flax Foam Core Sandwich Panels.

Greener materials, particularly in sandwich panels, are in increasing demand in the transportation and building sectors to reduce environmental impacts. This shift is driven by strict environmental legislation and the need to reduce material costs and fuel consumption, necessitating the utilisation of more sustainable components in the transportation and construction sectors, with improved load-bearing capabilities and diminished ecological footprints. Therefore, this study aims to analyse and evaluate the structural performance of polyethylene terephthalate (PET) core and flax or basalt/flax FRP sandwich panels as an alternative to conventional synthetic materials. The novel eco-friendly sandwich panels were manufactured using the co-curing technique. Four-point bending, edgewise compression and core shear tests were performed and insights into how the skin properties affect the strength, stiffness and failure mode of specimens were provided. The stress-strain behaviour, facing modulus and strength, flexural rigidity, core shear strength and failure modes were evaluated. The flexural facing modulus of the flax and flax/basalt sandwich skins were found to be 5.1 GPa and 9.8 GPa, respectively. The flexural rigidity of the eco-friendly sandwich panel was compared with published results and demonstrated a promising structural performance. The environmental benefits and challenges were outlined and critically evaluated focusing on transportation and construction applications.

Molding simulation of airfoil foam sandwich structure and interference optimization of foam-core

During the Co-Cure Molding (CCM) of airfoil foam sandwich structure, it is challenging to avoid collapse of foam core at the trailing edge. Herein, an Equal Proportional Thickening (EPT) method is proposed to optimize the interference of polymethacrylimide (PMI) foam core during the CCM process. Firstly, based on some basic parameters of composite skin and foam core obtained by experiments or multi-scale simulations, a thermal-curing-mechanical coupling analysis for the CCM of foam sandwich structure is performed and the results show that the maximum stress within foam core occurs at the completion of mold-closing, which tends to decrease during the subsequent CCM process. Then, the foam core is thickened by traditional equidistant-thickening method, and the simulation reveals that the foam core at the trailing edge tends to collapse because of stress concentration. Conversely, if the foam core is thickened by the proposed EPT method, the mold-closing caused collapse at the trailing edge can be effectively avoided, and a thickening ratio range of 0.6%–2.0% is obtained, which is further proved by practical verifications. Therefore, the interference design scheme proposed can ensure the molding quality and effectively reduce the scrap of molded products.

Crack growth in sandwich-structured foam core graphite epoxy laminate composite using a phase-field modelling approach

The laminated sandwich composites have wide structure-making applications in the automotive and aviation fields due to their lightweight and superior flexural rigidity properties. Making grooves or holes to assemble more than one structure induces crack discontinuities near the stress concentration region in these sandwich structures. The present work examines the effect of crack discontinuities on the mechanical performance and failure process of the sandwich structures under different loading conditions. Phase field method (PFM) has been presented and implemented using in-house developed MATLAB code. The effect of holes, multiple cracks, number of cores, and loading conditions are analyzed for the mechanical and fracture behavior of the structure. Load-carrying capacity, threshold displacement value for crack initiation, crack propagation trajectory, and energy absorption capacity are compared for various crack discontinuities under different loading conditions. Approximately 35% increase in load carrying capacity is observed in equivalent multiple core sandwich structures.

Multifunctional sandwich composites with optimized phase change material content for simultaneous structural and thermal performance

This work aims at developing novel multifunctional sandwich composites with optimized thermal energy storage and structural load-bearing performance by incorporating microencapsulated phase change materials (PCMs) into polyurethane (PU) foam cores. The optimized foam containing 20 wt% PCM, balancing good latent heat storage (up to 29 J/g) with low thermal conductivity (up to 0.035 W/(m·K) at 50 °C), was used to produce sandwich panels with high-performance epoxy/carbon fiber laminate skins. Microstructural characterization confirmed excellent interfacial adhesion between the core and skins. The multifunctional panels exhibited comparable flexural strengths (150 kPa) and facing stresses (25 MPa) to neat PU sandwich controls. By integrating thermal regulation from PCM phase change with structural reinforcement from the sandwich architecture in a single multifunctional material system, this work contributes to the development of lightweight, energy-efficient composite materials suitable when weight reduction and thermal management are paramount, such as in aeronautics and cold chain logistics.

Shear Behavior of Reactive Powder Concrete Ferrocement Beams with Light Weight Core Material

In this paper, the shear behavior of ferro-cement hollow beams is investigated experimentally and analytically. Ten reinforced concrete beams with cross-sectional dimensions of 100 × 200 × 1300 mm and a clear span of 1000 mm were cast and tested until failure under a two-point loading system. Ferrocement beams in this research contained either an autoclaved aerated lightweight brick core (AAC) or an extruded foam core (EFC) and were reinforced with either expanded metal mesh (EMM) or welded wire mesh (WWM). The structural behavior of the studied beams, including first crack, deflection, ultimate load, crack pattern, failure mode, and ductility index, was investigated. The experimental data were used to validate finite element models created with the ABAQUS finite element program. It can be concluded that the optimum performance of ferrocement beams can be achieved using beams with a second layer of expanded steel mesh as additional reinforcement, which led to an increase in the ultimate load and maximum deflection by 12.9% and 22.8%, respectively. Furthermore, the Numerical results agreed with the experimental results, where the ratio between the NLFE ultimate loads and the experimental ultimate loads varies between 1.02 and 1.07, with an average ratio of 1.04.

Blast Performance of Polyurea-Coated Modular Structure Composed of Fiber-Reinforced Polymer and Foam Sandwich Panels

Lightweight modular structures have become a requirement in today’s world, especially for areas that are prone to occurrence of extreme events, such as earthquakes and blasts, and are situated in difficult terrains with challenging accessibility. Sandwiched composites can be one of the most suitable building units for construction of these structures due to their engineered mechanical and physical properties. Therefore, in this numerical study, performance assessment of a sandwich modular structure in the shape of a truncated cylinder is conducted under blast load. The sandwich modular structure is composed of flat and curved carbon fiber-reinforced polymer (CFRP) and extruded polystyrene (XPS) foam sandwich panels. A three-dimensional (3D) finite element (FE) model of the sandwich modular structure is developed considering the orthotropic behavior of CFRP facesheets and the crushing foam behavior is accounted for the XPS foam core in the FE modeling. The damage assessment in the CFRP facesheet is performed using Hashin’s damage criterion. Furthermore, the effect of polyurea with varying thicknesses on the blast-resistance of the structure is investigated. The polyurea is modeled as hyperelastic material using the Mooney-Rivlin model. The influence of polyurea positioning is studied when (a) applied externally to flat and curved walls of the structure directly exposed to the blast and (b) applied internally to flat and curved walls of the structure opposite to the exposure of the blast (rear face). It is observed that the flat walls of the structure are more vulnerable to the blast load than the curved walls of the structure. Moreover, a quadratic and linear reduction in the deflection of flat and curved walls with increasing thickness of polyurea coating is obtained, respectively. In addition, with increasing thickness of the additional polyurea coating, a logarithmic reduction in the kinetic energy of the sandwich modular structure is reported.

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.

A Bio‐Inspired Dendritic MoOx Electrocatalyst for Efficient Electrochemical Nitrate Reduction to Ammonia

AbstractDrawing inspiration from the nitrate reductase enzymes, which catalyze nitrate to nitrite in nature, here a bio‐inspired, reduced molybdenum oxide (MoOx) shell is introduced that is grown on top of a dendritic nickel foam core (NiNF). The resulting MoOx/NiNF material is prepared via a facile, two‐step electrodeposition strategy using commercially available, low‐cost precursors. This catalytic material displays a remarkable faradaic efficiency (FE) of 99% at −0.5 V versus RHE and a high ammonia (NH3) yield rate of up to 4.29 mmol h−1 cm−2 at −1.0 V versus RHE in neutral media. Most importantly, MoOx/NiNF exhibits exceptional stability for the nitrate reduction reaction (NO3RR), maintaining operation for over 3100 h at a high current density of −650 mA cm−2, with a yield rate of 2.6 mmol h−1 cm−2 and a stable average NH3 FE of ≈83%. Through combined XPS and in situ Raman spectroscopy it is shown that the pronounced affinity of MoOx/NiNF for nitrate is associated with a substantial presence of oxygen vacancies within the material.

Anti-penetration properties of negative Poisson’s ratio honeycomb sandwich structure filled with foam

The ballistic responses of negative Poisson’s ratio honeycomb sandwich structures filled with aluminum foam are investigated using numerical simulation method. The residual velocity of the projectile, the energy absorption, and the failure forms of the sandwich structures are systematically analyzed. The influence of the impact position and incidence angle of the projectile, wall thickness, and concave angle of honeycomb, as well as the thickness of the front and back sheets of the structure on the penetration resistance is discussed. The results show that the foam-filled honeycomb sandwich structure has a better penetration resistance than the foam core sandwich structure with the same areal density, and the penetration resistance of the foam-filled honeycomb sandwich structure can be improved by designing its geometric parameters.