Aluminum Honeycomb Core Research Articles

Sub-critical damage study of aluminium honeycomb and CFRP sandwich panels subjected to impact

Subcritical damage in sandwich panels refers to damage that occurs in the skins or core of the panel due to loading below the ultimate strength of the materials, and it can reduce the strength and durability of sandwich panels, leading to premature and unpredicted failure. In this work, a computational tool was developed for designing sandwich structures and optimizing their subcritical impact response. The model was validated experimentally on sandwich panels comprising an aluminium honeycomb core with carbon fiber reinforced epoxy skins. The study investigates subcritical damage in aluminium honeycomb and CFRP sandwich panels through mechanical experiments and finite element simulations. A novel computational tool was developed to optimize the impact response of these structures. Experimental validation was performed using standardized tests, and numerical simulations were conducted using Abaqus. Key findings indicate that the developed tool accurately predicts damage and stiffness reduction, offering significant potential for optimizing sandwich panel designs.

Experimental and numerical studies on quasi‐static behavior of sandwich composites with nano clay modified Kevlar facesheets and aluminum honeycomb core

AbstractThis study investigates the influence of nano clay reinforcement on the mechanical behavior of Kevlar/epoxy composite laminates and sandwich structures subjected to quasi‐static punch shear loading. Three types of composite face sheets were fabricated using hand lay‐up technique: Kevlar/epoxy neat, 0.5, and 1 wt. % of nano clay. The mechanical properties of these composites were characterized through compression, shear, and tensile tests. Sandwich structures were then constructed using the fabricated face sheets and an aluminum honeycomb core. Quasi‐static punch shear tests were performed on the composite laminates and sandwich specimens using hemispherical impactors. Numerical simulations of the punch shear tests were conducted in LS‐Dyna, employing appropriate material models and contact definitions for the constituent materials. Furthermore, to further investigate the failure mechanisms, scanning electron microscopy (SEM) analysis was conducted on the fractured Kevlar/epoxy composite plate specimens. The comparison between the experimental outcomes and numerical data demonstrated a strong correspondence, indicating consistency between the two methodologies. In conclusion, the incorporation of 0.5 wt. % nano clay into the Kevlar/epoxy composite resulted in a 5.09% increase in shear strength and an 11.29% increase in maximum reaction force. The study provides insights into the effect of nano clay reinforcement on the punch shear resistance and energy absorption capabilities of Kevlar/epoxy composites and sandwich structures.Highlights Proper alignment of the nano clay within the epoxy was achieved. The most efficient rate of nano clay was observed to be 0.5% by weight. The mechanical properties of nano clay‐containing composites were improved. Quasi‐static punch shear tests were performed numerically and experimentally. Numerical results were in close agreement with experimental results.

Adhesion Systems in New Supports for Mural Paintings: Reversibility Tests

ABSTRACT This article presents a study that investigates the utilization of diverse adhesives and intervention layers for affixing new supports to archaeological mural paintings that cannot be preserved in their original state. Depending on artwork characteristics (materiality, dimensions, state of conservation, location), various materials can be employed for attaching new supports, encompassing adhesives and intervention layers. Evaluating and assessing these materials is vital to ensure the stability, reversibility, and notably, the retreatability of the artwork. To this end, we have evaluated three commonly used adhesives and three intervention layers applied to new mural painting supports. We prepared test samples of mural paintings affixed to a new support structure, utilizing an aluminum honeycomb core sandwich panel (Aerolam). Through bibliographic analysis, we identified frequently used adhesives and intervention layers, and conducted an initial assessment of their behavior. Subsequently, following an aging process, we conducted color evaluations and reversibility tests to comprehensively study these materials and facilitate an objective comparison of their properties.

Experimental parametric analysis on multiple response behaviour of AA 6061 honeycomb core sandwich structure under flexural test

Sandwich structures are light weight structures with high strength to weight ratio mostly applicable in aerospace, automotive and, shipbuilding industries. In this study, the aluminium honeycomb core sandwich structure is investigated under flexural test to find the effects of honeycomb core parameters such as cell size, cell wall thickness and core height. Flexural tests such as three point and four point bend test were performed as per ASTM Standard D7250 to evaluate the flexural properties like stiffness and core shear modulus. Taguchi’s design of experiment (DOE) has been used to find the effect of structural parameters of the honeycomb core. Since this structure requires the enhancement in properties and reduction in weight, so multi response analysis has been performed by using grey relational analysis. Results shows that the cell size is the most influencing factor followed by core height. Cell wall thickness shows positive effect on flexural properties, but add more weight to the structure. Finally, these findings were confirmed by finding the percentage contribution of structural parameters by Analysis of Variance.

Pull-Through Behavior of Novel Additively Manufactured Sandwich Composite Inserts.

Joining structural components with mechanical fasteners is common in many engineering applications across all industries. This study investigates combining additive manufactured inserts with sandwich composites consisting of aluminum honeycomb cores with carbon fiber reinforced facesheets. The combination of these components offers an integrated, lightweight solution when mechanically fastening sandwich composite components using bolted joints. The experimental and numerical investigation explores the influence insert geometry has on the structural response of a sandwich composite under pull-through load scenarios. Various failure modes are observed during experimental analysis with facesheet debonding being the initial failure mode. In addition, finite element models investigate the stress fields in the honeycomb core and overall panel deflections, validating the mechanics observed experimentally. When comparing additively manufactured inserts to standard inserts, additively manufactured inserts have increases in stiffness, maximum force, and total energy absorption of 7.1%, 53.0%, and 62.3%, respectively. These results illustrate the potential of an integrated approach to mechanical joint technology by combining additively manufactured inserts with sandwich composite components using aluminum honeycomb cores.

Study on the processing characteristics of aluminum honeycomb core by longitudinal torsional composite ultrasonic vibration-assisted cutting

Aluminum honeycomb has been widely used in various industrial sectors due to its exceptional physical properties. Ultrasonic vibration machining shows significant potential in reducing machining defects. Therefore, this study employs ultrasonic vibration assisted cutting (UVC) to process aluminum honeycomb core and compares cutting force, surface morphology, and cutting defects with the conventional cutting (CC). This investigation assesses the impact of processing parameters such as feed rate and cutting depth on both UVC and CC. The results indicate that, in comparison to CC, UVC can notably reduce cutting force, minimize tearing burrs and cell deformation defects, and achieve superior surface morphology. Furthermore, the study reveals that cutting force increases with higher tool feed rates and cutting depths. Cell deformation also escalates with increased tool feed rates and cutting depths, and tearing burrs become more pronounced with deeper cuts. Excessively shallow cutting depths can lead to a sudden increase in node defects. Simultaneously, tearing burrs and cell deformation exhibit different characteristics under CC and UVC.

Investigating damage mechanisms of honeycomb cores machined with PCD circular saw blades

Aluminum honeycomb core (AHC) is extensively applied in aerospace and transportation industries for its exceptional strength-to-weight ratio. However, the unique structure of AHCs limits their manufacture. In this research, the damage mechanism of AHCs is firstly studied with polycrystalline diamond (PCD) circular saw blades to provide high-quality AHCs for wide-format honeycomb composites. The study meticulously examines the various forms of sawing damage incurred by AHCs at different material removal rates (MRR) and categorizes them accordingly. The results show that burrs of AHCs change from tiny blocks to larger strips with the MRR. At high MRR, the predominant failure modes include collapse, deformation, and hot cracking, while at low MRR, AHCs mainly suffer from cracking, micro-collapse, and oxidation by SEM and EDS analysis. A dynamic analytical model of the sawing angle is proposed based on the sawing trajectory to elucidate vibration scratching and burr formation. The effect of the sawing angle is quantified by the deformation displacement and damage area by the optical measurement. The microscopic reciprocating vibration scratching of AHCs is interpreted by the blade’s vibration state. The causes of sawing damage at different MRRs are investigated, indicating that at high MRR, the increased impact of the sawtooth leads to severe vibration scratches, collapses, and strip burrs, whereas, at low MRR, the high-frequency scratching of the sawtooth tends to result in tearing and micro-collapses. A comprehensive description of burr formation is presented by a 3D finite element model. Additionally, the cutting heat is the main cause of the oxidation of sawing surfaces by EDS. This systematic investigation analyzes and explores the sawing damage mechanisms of AHCs, offering in-depth insights for optimizing the sawing process to eliminate surface quality problems and improve the sawing efficiency and accuracy of wide-format AHCs.

Backing plate material selection for optimizing joint performance in friction stir welded aluminium honeycomb

Aluminium honeycomb core is a thin-walled cellular structure extensively used in crash resistance applications in automotive industry. To overcome current challenges in adhesive-bonded honeycomb, new fabrication route using micro friction stir lap welding has been proposed. With a specific energy absorption capacity as high as 28.2 kJ/kg in flatwise impact testing, fabricated honeycomb demonstrated its potential for industrial applications. The structure exhibited no weld cracks or cell wall delamination, unlike adhesive-bonded honeycombs. However, in friction stir welding of thin sheets (0.5 mm), achieving an optimized heat input is challenging due to limited scope for variation in process parameter and tool design. Therefore, control of heat outflow by proper selection of backing plate material is the alternative approach for achieving desirable joint performance. Experiments with backing plates having a range of thermal diffusivities demonstrated that joint produced with mild steel backplate exhibited maximum shear-tensile strength. Conversely, joint with aluminium backplate exhibited poor plastic flow of material. Effective sheet thickness and lap width were predominantly affected by heat accumulation in weld, resulting in different failure modes.

Initial performance assessment of 3D printed thin walled structures for spacecraft applications

Sandwich panels are the fundamental structural element in a wide range of applications, including in satellite primary structures. While sandwich constructions are very efficient, their complex multi-material assembly leaves room for further optimisation of the core volume and improvement in the integration phase. One key technology that can enable the transition to multifunctional sandwich panel cores tailored to certain applications is the additive manufacturing (AM) of satellite primary structure sandwich panel cores. This paper investigates the feasibility of replacing the baseline Aluminium honeycomb core with a core printed out of AlSi10Mg through Powder Bed Fusion. Sandwich panels with carbon fiber-reinforced plastic (CFRP) facesheets and printed honeycomb cores as well as fully printed corrugated panels are produced and tested under three point bending (3PB) and compression as part of the EU funded ReDSHIFT project. The Instron 5560 (3PB) and 4204 (compression) are used to perform the experiments that follow the ASTM C393-11 and C365 standards. When compared against the baseline CFRP-AL panels, the 3D printed honeycomb cores carry up to twice as much load per unit mass in bending and four times as much in compression, while also being stiffer. The fully printed corrugates samples are weaker than the honeycombs, but in conjunction with the honeycomb geometry may present a promising avenue for developing multifunctional cores. While limitations with current metal printing technology prevent AM cores from matching the mass of baseline designs, the superior specific performance and geometrical freedom make printed cores a promising design alternative.

Investigation of the feasibility of using aluminum honeycomb cores in the design of the fin of the aircraft

The issues related to the use of a honeycomb cores in the design, the weight ratio of the empennage units are considered on the example of the fin of an aircraft. The article provides a comparative qualitative assessment of the weight efficiency, manufacturability of the design and design features of the fin with the use of honeycomb panels, compared with the classical frame construction of fin units. In addition, the article discusses the problems associated with the operation and repair of honeycomb core constructions. In the article the calculations of mass determination of honeycomb panel and transverse set for cases the thickness of the profile C=13%, C=8%, C=4% were carried out. Using he method of sequential calculations of each structural part of the honeycomb panel or the frame construction, the resulting masses of units were obtained. Based on the results, we can conclude that the use of three-layer panels in the construction of the fin with a given area and construction height is not justified, since the difference in weight is negligible, and honeycomb panels have several disadvantages.

Study of impact performance of composite sandwich structure fabricated partially with natural fiber facesheet

AbstractComposite structures with a pure glass composite facesheet and an aluminum honeycomb core are widely used in aircraft interiors. Because impact‐related problems are related to structural integrity and safety performance, the behavior of these structures under impact loading is critical. Due to their promising performance, lower cost, and low environmental impact, hybrid composites have recently become one of the most widely researched composite materials in the research field. This paper aims to investigate the impact behavior of nonhybrid glass and the glass partially replaced with a flax and kenaf hybrid composite facesheet caused by a low‐velocity impact. The specimens were impacted with different impacted energies, such as 10, 20, and 30 J. All nonimpacted and impacted samples were tested and compared for postimpact flexural (three‐point bending) behavior to analyze the residual strength of sandwich structures after impact. The results revealed that the hybrid composite face sheet outperformed the glass composite sandwich structure. The hybrid composite face sheet allowed the impactor to penetrate deeper, resulting in better energy absorption than the glass composite. Compared to nonimpacted specimens, the glass and hybrid face sheet combinations demonstrated comparable residual bending performance.Highlights Experimental analysis shows the impact resistance (low‐velocity impact test) and residual load‐carrying capacity (three‐point bending test) of glass and hybrid composite face sheets. Hybrid face sheets show excellent energy‐absorbing capability compared to glass one. The residual flexural strength of the glass and hybrid composites was comparable to that of nonimpacted samples. The peel strength achieved in this study using the pre‐cure fabrication process was significantly higher than the peel strength achieved using prepreg face sheets. Reinforcing the composite face sheet of the sandwich structure by partially replacing the glass with flax and kenaf fiber exhibited comparable performance.

Optimal design of composite sandwich panel with auxetic reentrant honeycomb using asymptotic equivalent model and PSO algorithm

The composite honeycomb sandwich with auxetic reentrant honeycomb (CSP-ARH) is a typical negative Poisson’s ratio structure, which has better mechanical properties than composite structure with positive Poisson’s ratio. In this study, a 2D asymptotic equivalent model (AEM) based on the variational asymptotic method (VAM) is proposed and used to analyze the vibration and buckling problems of CSP-ARH incorporating CFRP facesheets and an aluminum honeycomb core. After validation with 3D finite element results, a particle swarm optimization (PSO) algorithm is applied to optimize the mesoscopic size of composite facesheets and honeycomb core. The primary objectives of the optimization process involve maximizing the buckling load and natural frequency, minimizing the mass while satisfying specific mechanical properties requirements. Moreover, a few additional optimization iterations are performed to find the optimal shape coefficients of the curved fibers in the CFRP facesheets for variable stiffness composite sandwich panels. The shape of the curved fiber is defined using a cubic polynomial function f(x,y) and is described by a 20 × 20 grid of discrete elements. The results indicate that CSP-ARH with optimal curved fibers shapes exhibit superior performance compared to those with straight fibers, with buckling load and natural frequency increased by 8.18% and 7.09%, respectively.

Experimental and numerical study of effecting core configurations on the static and dynamic behavior of honeycomb plate with aluminum material

The sandwich panel incorporated a honeycomb core, a widely utilized composite structure recognized as a fundamental classification of composite materials. Comprised a core resembling a honeycomb, possessing thickness and softness, and is flank by rigid face sheets that sandwich various shapes and materials. This paper presents an examination of the static and dynamic analysis of lightweight plates made of aluminum honeycomb sandwich composites. Honeycomb sandwich plate samples are 300 mm long, and 300 mm wide, the heights of the core have been varied at four values ranging from 10 to 25 mm. The honeycomb core is manufactured from Aluminum material by using a novel technique namely resistance spot welding (RSW) instead of using adhesive material, which is often used when an industrial flaw is detected. Numerical optimization based on response surface methodology (RSM) and design of experiment software (DOE) was used to verify the current work. A theoretical examination of the crashworthiness behavior (maximum bending load, maximum deflection) and vibration attributes (natural frequency, damping ratio, transient temporal response) of honeycomb sandwich panels with different design parameters was also carried out. In addition, the finite element method-based ANSYS software was used to confirm the theoretical conclusions. The findings of the present work showed that the relationship between the natural frequency, core height, and cell size is direct. In contrast, the relationship between the natural frequency and the thickness of the cell wall is inverse. Conversely, the damping ratio is inversely proportional to the core height and cell size but directly proportional to the thickness of the cell wall. The study indicates that altering the core height within 10–25 mm leads to a significant increase of 82 % in the natural frequency and a notable decrease of 49 % in the damping ratio. These findings are based on a specific cell size value of 0.01 m and a cell wall thickness of 0.001 m. Also, the results indicate that for a given set of cell wall thickness and size values, an increase in core height from (0.01–0.025) m, leads to a reduction of the percentage of maximum response approximately 76 %. Conversely, the increasing thickness of the wall of cell wall, ranging 0.3–0.7 mm with a constant core height equal to 0.015 m, resulted in a de crease of maximum transient response by 7.8 %.

Mechanistic modeling considering bottom edge cutting effect and material anisotropy during end milling of aluminum honeycomb core

In the end milling of aluminum honeycomb core, the bottom edge of the cutter and the feed direction of the cutter will have a significant impact on the surface machining quality. If the above two factors are neglected in mechanistic modeling, the surface machining quality will be difficult to improve. In this paper, a mechanistic model considering the bottom edge cutting effect and the anisotropic characteristics of the material is firstly proposed to accurately predict cutting forces. Based on the contact relationship between the bottom edge and the honeycomb wall, a cutting force model of the bottom edge is developed, which includes the geometric characteristics of the bottom edge and the thin-walled edge cutting angle. For anisotropic characteristics of the material, a dynamic variation model of the entry and exit angles in any cutting direction is established on the basis of the structural model of the honeycomb core and cutting edge trajectory. The proposed mechanistic model was validated through a series of milling experiments. The results indicate that this model can be used to predict the cutting force of various parts of the cutter (including bottom and flank edges) and any feed direction.

Space radiation environment adaptability of the domestic 5056 high-performance aluminum honeycomb

In order to investigate the influence of space radiation environment on the performance of domestic 5056 high-performance aluminum honeycomb core, the effects of different irradiation effects and different radiation doses on the nodal strength and mechanical properties of domestic 5056 high-performance aluminum honeycomb core were studied through space radiation environmental tests and mechanical property tests such as high-energy electron irradiation, γ-ray irradiation, ultraviolet irradiation, hot and cold shock test, vacuum volatilization test. The results show that under multiple environmental conditions such as high-energy electron irradiation γ-ray irradiation, ultraviolet irradiation, and hot and cold shock environment, the domestic high-performance aluminum honeycomb core shows excellent adaptability to the irradiation environment and can be used for a long time in the extravehicular environment. However, when the radiation dose is greater than 2 × 109rad, the strength of honeycomb core nodes decreased significantly. The vacuum volatilization test results sindicate that the material meets the gas requirements of aerospace raw materials and has extremely low vacuum pollution characteristics.

A novel method of fabricating aluminium honeycomb core by friction stir welding

Aluminium honeycomb structure has been recognized as an exceptional lightweight energy absorber in transportation, construction and aerospace industries. An innovative fabrication method based on friction stir welding is proposed to enhance the crashworthiness property of aluminium honeycomb and address the challenges with conventional fabrication methods. Moreover, a lab-scale fixture is designed to demonstrate the feasibility of the suggested method for industrial use. Various fabricated honeycombs with different core heights and cell counts are subjected to quasi-static flatwise compression tests to investigate their crushing characteristics. The crashworthiness parameters like yield stress, average plateau stress, specific energy absorption are analysed and compared with theoretically predicted crushing strength. The failure mode of the structure is also discussed, showing the influence of non-optimal welding parameters. Experimental results indicate that average crush force and specific energy absorption do not differ significantly with cell count and core height. The specimens under flatwise compression fold with plastic hinges symmetrically positioned without any rupture of the weld. Specific compression property of the fabricated honeycomb has been compared with other aluminium honeycombs fabricated using other methods, which favours the friction stir welded honeycomb over the other conventional counterparts.

Response of aluminium honeycomb sandwich panels under combined shock and impact loading: Experimental and numerical investigations

The performance of sandwich structures against individual shock loading and fragment impact loading has been extensively examined, but little is known about their performance in the presence of simultaneous shock and impact loading. Based on a recently developed composite projectile to simulate combined shock and single fragment impact loading, the performance of aluminum honeycomb core sandwich panels (HCSPs) against combined loading is methodically examined. The achieved results reveal that the combined loading exhibits a synergistic effect compared to the single loading, i.e., increased damage of the sandwich panel and enhanced perforation resistance of the sandwich panel. After that, a three-dimensional finite element simulation is performed to explore the underlying mechanism of the synergistic effect. Numerical analysis indicates that the increased damage is a result of perforation-induced reduction of load-carrying capacity of sandwich panel, while the enhanced perforation resistance is the result of deflecting-induced perforation time delay of the perforation process. Finally, the parametric investigation of sandwich geometries such as asymmetric face sheets, core density, and core height is comprehensively conducted. The gained results reveal that both performance and synergistic effect due to combined loading are sensitive to these parameters.

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.

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

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

Assessing the effects of critical parameters in standoff bonding

In this contribution we present the effect of several parameters that are critical for bonding standoffs onto the surface of spacecrafts’ panels with polymeric adhesives. Standoffs are an integral part of the thermal management of space satellites since they ensure that the MLI blankets are mounted and maintained in the correct position during the whole mission duration, including launch. In the recent years, there have been several de-bonding problems during qualification phases, leading to long and costly delays, oftentimes caused from poor design and preparation[1]. For these reasons, we have performed a study of the bond strength of Torlon® 5030 rods bonded over sandwich panels made of an aluminium honeycomb core and CFRP skins. The bond strength was determined by mechanical tests, conducted in tensile and shear modes, both prior and after thermal cycling. Thermal analysis was also performed on the main components under study. The study consists on the following steps: first, different surface treatments of the CFRP skins have been investigated: (i) bonding standoffs with the surface as manufactured, (ii) cleaned with a solvent and (iii) mechanically sanded before cleaning. The best performing treatment was selected and used systematically in the rest of the study. Afterward, different types of adhesives (epoxy, graphene nano-enabled epoxy, polyurethane) and bond-line thicknesses were studied. The findings of this study can help to steer the industry towards better practices regarding the standoff bonding. This will improve the integrity of future space missions.