Aluminum Foam Sandwich Research Articles

Application of column buckling theory to steel aluminium foam sandwich panels

In steel structures, a lot of attention is paid to lightweight structures, i.e. reduction of dead load without compromising structural safety, integrity and performance. Thanks to modern steel aluminium foam sandwich panel manufacturing technology a new possibility became available for lightweight structural design. Assessment and understanding of the behaviour of this sandwich panel under in-plane compression or flexure is crucial before its application in steel structures. Column buckling theory is considered and applied to the steel aluminium foam sandwich panel to evaluate its behaviour under in-plane compressive load. In this work, various assumptions are made to generalise Euler’s buckling formula. The generalisation requires modification of the buckling stiffness expression to account for sandwich panel composite properties. The modified analytical expression is verified with finite element simulation employing various material models specific to steel face-plates and aluminium foam as well as various geometric imperfections. Based on this study, it can be concluded that Euler’s buckling formula can be successfully modified and used in the prediction of the load-carrying capacity of a sandwich panel.

Evaluating UHMWPE-stuffed aluminium foam sandwich panels for protecting spacecraft against micrometeoroid and orbital debris impact

Robotic spacecraft shielding for protection against micrometeoroid impact is typically provided by existing structural panels, thermal insulation blankets, or reinforced component containers. Here the performance of an open cell aluminium foam core sandwich panel with intermediate ultra-high molecular weight polyethylene (UHMWPE) stuffing under hypervelocity impact of spherical aluminium projectiles was evaluated. Providing comparable structural and thermal performance as honeycomb sandwich panels, foam core sandwich panels have demonstrated improved impact shielding behaviour in existing studies. The inclusion of UHMWPE stuffing is found, through experimental testing and a comprehensive numerical study, to increase the shielding capability of foam core sandwich panels (40–80% increase in critical projectile diameter) for a modest weight penalty (25%). Compared to conventional aluminium honeycomb sandwich panels with equivalent weight, the improvement in shielding performance is >100%.

Microstructural and mechanical characterisation of reinforced aluminium foam sandwich panels made by one-step squeeze casting method

ABSTRACT In just one step, a squeeze casting process was applied to produce aluminium foam sandwich panels. NaCl particles with mean sizes of 4.75 and 6.35 mm were used as space holders in different proportions. In-situ face sheet manufacturing was conducted through previously placed steel meshes in the mould. The effect of NaCl particle sizes and the proportion of each size on porosity, microstructure, and mechanical properties were investigated. Results showed a decline from 59.8% to 43.8% in the porosity amount of samples with increasing the proportion of larger NaCl particles. Accordingly, an increase in compression yield stress (from 3.2 to 6.1 kgf/mm2) and the absorbed energy were observed. Also, at the elevated densities of the sandwich panel core, the plateau stress was enhanced. The presence of Cu, Ni, Fe, and Si elements leads to the formation of brittle intermetallic compounds in the microstructure of cell walls.

Three-point bending performances of integral-forming aluminum foam sandwich

In the course of service, integral-forming aluminum foam sandwich (IFAFS) needed to bear three-point bending loads in different directions, however, its deformation mechanism and failure modes were still unclear. In this work, three-point bending performances of IFAFS under flatwise and edgewise bending conditions were investigated by experiment, in-situ micro X-ray tomography and digital volume correlation (DVC) calculation. The results showed that three-point bending performance was more stable under edgewise bending condition, and with the decrease of span length IFAFS presented three different failure modes of oblique core shear, asymmetric and symmetrical surface fracture. In addition, porosity mutation was a significant reason for crack initiation, and optimizing pore homogeneity was important to improve the performance and predictability of failure location. Different strengthening effect of sandwich structure anisotropy and different internal deformation evolutions caused by internal strain vortex were two main reasons which lead to performance difference of IFAFS with different solid panel directions. Connection of pre-existing micropores with dimple-like micropores generated during deformation process leads to the failure of IFAFS. The key factors to further optimize three-point bending performance and predictability of IFAFS was to homogenize the pore distribution of IFAFS.

Microstructural characteristics and mechanical properties of 7075 aluminum alloy foam sandwich panels fabricated via integrated forming and foaming

A new integrated forming and foaming method based on friction stir welding (FSW) was proposed for foam sandwich panels. The microstructure characteristics of the precursors and foams with different welding parameters were analyzed using optical microscopy and scanning electron microscope (SEM/EDS). The temperature field and flow field of foam precursor joint in FSW were simulated by Fluent CFD software. The microstructural characteristics of foam precursor after hot forming were analyzed using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The effect of foam precursor deformation on foam evolution was also investigated. The results show that the formability of foam precursor is the same as that of rolled plate. Aluminum foam sandwich panel with homogenous pore structure is prepared at 680 °C for 225 s. After hot forming, the equiaxed recrystallized grain is obtained, and the dislocation and the second phase provide reinforcement. In addition, Rgoss{110}〈110〉 texture component strength increases. When the tensile strain is 0.15, smaller and more uniform pores are produced. Numerical simulations show that the peak temperature gradually decreases with the increase of the distance of the stirring head center. In addition, the temperature on the advancing side (AS) is higher than that on the retreating side (RS). When the tool travel speed is 50 mm/min and rotational speed is 2000 r/min, the maximum material flow velocity at the joint section is 184.2 mm/s and the highest concentration of powder tracing particles is 0.0123 kg/m3. It is proved that the integrated forming and foaming method can solve the problem in manufacturing of complex curved AFS components.

Interface structure and bonding strength of metallurgical bonded aluminum foam sandwich (AFS) fabricated by hot-pressing

This paper proposes the aluminum foam sandwich (AFS) manufacturing process by simplifying the preparation processes and reducing costs by use of hot-pressing, where aluminum plates were used as facesheets, aluminum foam as core, and pure zinc plates as joining layers. The effect of hot-pressing distance on interface formation was first illustrated by the thermodynamic equations and bonding strength was investigated. The results showed that increasing the hot-pressing distance was beneficial to the interfacial element diffusion, but harmful to foam structure. Two failure modes of interface separation and foam core fracture were first traced by digital image correlation (DIC). Cracks and holes appeared in the zinc interlayer was the main reason for the low bonding strength. The AFS obtained by 2 mm hot-pressing distance at 450 °C possessed the highest bonding strength, greater than 2.14 MPa, and the porosity of foam core was held at 74%.

Investigation of the Indentation Resistance of Aluminum Foam Sandwich Panels with Metallurgical Bonding Interfaces under Low-Velocity Impact

The impact resistance of aluminum foam sandwich panels (AFS) with metallurgical bonding interfaces prepared by the powder cladding rolling method was investigated. Low-velocity impact tests were conducted by using a drop-weight impact facility to explore the dynamic mechanical behavior, deformation and damage mechanisms, and energy absorption of AFS with metallurgical bonding interfaces. The effects of variation of impact energy, panel thickness, and specimen density on the energy absorption performance of AFS were quantitatively evaluated by energy absorption indicators. The results indicate that the load-displacement curve illustrates prominent three-stage characteristics when the impact energy is 120 J containing the front panel yielding stage, the foam core's compressive and shear failure stage, and the back panel fracture stage. The impact strength of the sandwich structure increases with increasing panel thickness and specimen density. The AFS with metallurgical bonding interfaces presents favorable energy absorption efficiency under low velocity.

Fatigue of an Aluminum Foam Sandwich Formed by Powder Metallurgy.

In this paper, an aluminum foam sandwich (AFS) was prepared by the rolling composite-powder metallurgy method, and its fatigue properties were studied. It was compared with an AFS made by the adhesive method to study its fatigue properties more directly. In this experiment, the fatigue performance was investigated by studying the microscopic interface, fatigue life, deflection curve, and failure mode. The results show that the fatigue life of an AFS with the rolling composite-powder metallurgy method is much longer than that with the adhesive method. The failure mode of an AFS made by the rolling composite-powder metallurgy method is shear failure, and that of an AFS made by the adhesive method is shear failure and interface debonding. An AFS with the rolling composite-powder metallurgy method has better fatigue properties. This paper also explored the fatigue damage model using the fatigue modulus method, and the polynomial fitting method has a higher fitting degree.

Numerical Simulation Analysis on Surface Quality of Aluminum Foam Sandwich Panel in Plastic Forming

The surface quality of an aluminum foam sandwich panel (AFSP) is very important for its appearance and application. This paper mainly studies the surface quality of AFSP after plastic forming. Combined with three-dimensional (3D) scanning technology, the normal deviation between the experimental AFSP and the target surface was obtained, and the surface quality parameters Sq, Sz and dmax were calculated to evaluate surface quality. The AFSP models with cubic-spherical (CS) and tetrakaidecahedral (TKD) as foam structures were established respectively. A series of numerical simulations of multi-point forming (MPF) were then carried out. Equivalent strain and deformation characteristics of spherical and saddle-shaped AFSP were discussed. The main surface defects produced by AFSP in plastic forming, such as surface wrinkle, the local straight face effect and surface dimpling were analyzed. Finally, MPF experiments were carried out, and it was found that the numerical simulation results were significantly corresponded to the experimental AFSP in terms of the degree and distribution of normal deviation and surface quality evaluation parameters. The TKD model was more consistent with the experimental results than the CS model. Moreover, the results show that the surface quality can be improved by thicker face sheets and smaller core cell sizes.

The Mechanical Behavior and Enhancement Mechanism of Short Carbon Fiber Reinforced AFS Interface

The aluminum foam sandwich (AFS), which perfectly combines the excellent merits of an aluminum foam core and face sheet materials, has extensive and reliable applications in many fields, such as aerospace, military equipment, transportation, and so on. Adhesive bonding is one of the most widely used methods to produce AFS due to its general applicability, simple process, and low cost, however, the bonding interface is known as the weak link and may cause a serious accident. To overcome the shortcomings of a bonded AFS interface, short carbon fiber as a reinforcement phase was introduced to epoxy resin to reinforce the interface adhesion strength of AFS. Single lap shear tests and three-point bending tests were conducted to study the mechanical behavior of the reinforced interface and AFS, respectively. The failure mechanism was studied through a macro- and microanalysis. The result showed that after the reinforcement of carbon fiber, the tangential shear strength of the interface increased by 73.65%. The effective displacement of AFS prepared by the reinforced epoxy resin is 125.95% more than the AFS prepared by the unreinforced epoxy resin. The flexure behavior of the reinforced AFS can be compared with AFS made through a metallurgical method. Three categories of reinforcement mechanisms were discovered: (a) the pull off and pull mechanism: when the modified carbon fiber performed as the bridge, the bonding strength improved because of the pull off and pull out of fibers; (b) adhesion effect: the carbon fiber gathered in the hole edge resulted in epoxy resins being gathered in there too, which increased the effective bonding area of the interface; (c) mechanical self-locking effect: the carbon fiber enhanced the adhesive filling performance of aluminum foam holes, which improved the mechanical self-locking effect of the bonding interface.

Experimental and numerical study on ballistic resistance of aluminum foam sandwich panel considering porosity and dimensional effect

Sandwich panels have been widely used in various industries due to their high strength and energy absorption capacity. In this study, the ballistic behavior of a sandwich panel comprised of two aluminum face-sheets and an aluminum foam as the sandwich core is studied. The panels are constructed and subjected to the blunt-nosed projectile. The experimental test consists of a sandwich panel with three different ranges of foam densities and two thicknesses for the panels beside hardened steel projectiles. Then, numerical simulations of the projectile perforation in the panels are conducted that are in good agreement with the experiments. The failure mechanism of the sandwich panels is investigated and the role of foam core is discussed. Failure mechanism and the amount of plug depends on foam density and projectile velocity, such that different failure mechanisms such as plugging, petaling, and dishing occurred for the face-sheets. After that, the ballistic limit velocity (VBL) of sandwich panels was calculated via experiments and finite element simulations. The experiments and simulations showed that increasing the density and thickness of the foam core generally leads to an increase in VBL. Finally, we study the panels with the constant mass and (or) constant height with different foam densities and the effect of foam density is investigated in these cases.

Lower Limb Response to Anti-personnel Landmine Blast Explosions: Injury Assessment and Mitigation Strategies

Injuries in lower extremities due to anti-personnel (AP) landmine blasts have been a major cause of amputation in soldiers. Therefore, it is crucial to understand the mechanism of these injuries for designing advanced personnel protective equipment and superior medical interventions. Various attempts have been made to correlate lower limb cadaveric mine blast test data using surrogate models, but till date, no study has been reported to validate it using numerical methods. In this work, a finite element computational framework was developed for landmine blasts using a biofidelic human body lower limb model for validating in situ tibia forces and injury patterns with PMHS (post mortem human subjects) test data. Based on the reliability of the validated numerical analysis model, efforts were made to elucidate landmine blast physics, blast wave intensity for various mine threats, pathophysiology of lower extremity trauma, and effectiveness of various blast mitigation strategies. Numerical simulations were performed to assess the level of protection offered by a standard army combat boot to the lower limb for an M-14 mine blast. Furthermore, for attenuating the load transmission to the lower limb, aluminum foam sandwich panel has been proposed as a potential shoe insert material due to its high-energy absorption capabilities. Compared to the bare foot scenario, aluminum foam shoe insert in double-core configuration was effective in minimizing severity of M-14 mine blast injuries by reducing the peak tibia force by 34% with a significant delay in time of arrival of the peak. Additionally, the proposed mine protective shoe concept offers 25.2% more reduction in peak tibia force compared to the standard military combat boot for a charge triggered by victim’s heel.

Dynamic Response of Sandwich Tubes with Continuously Density-Graded Aluminum Foam Cores under Internal Explosion Load.

In this paper, the dynamic response of continually density-graded aluminum foam sandwich tubes under internal explosion load was studied. A 3D mesoscopic finite-element model of continually density-graded aluminum foam sandwich tubes was established by the 3D-Voronoi technology. The finite-element results were compared with the existing experimental results, and the rationality of the model was verified. The influences of the core density distribution, the core density gradient, and the core thickness on the blast resistance of the sandwich tubes were analyzed. The results showed that the blast resistance of the sandwich tube with the negative-gradient core is better than that of the sandwich tube with the uniform core. While the blast resistance of the sandwich tube with the positive-gradient core or the middle-hard-gradient core is worse than that of the sandwich tube with the uniform core. For the sandwich tube with the negative-gradient core, the core density gradient increased, and the blast resistance decreased. Increasing the thickness of the core can effectively decrease the deformation of the outer tube of the sandwich tube, but the specific energy absorption of both the whole sandwich tube and its core also decreases.

Three-Point Bending Behavior of Aluminum Foam Sandwich with Different Interface Bonding Methods.

The interface bonding method has a great influence on the mechanical properties of aluminum foam sandwich (AFS). This study aims to investigate the effect of different interface bonding methods on the mechanical properties of AFS. In this paper, the metallurgical-bonding interface-formation mechanism of AFS prepared by powder metallurgy was investigated. The shear properties of metallurgical-bonded AFS were determined by the panel peeling test. The flexural properties and energy absorption of metallurgical-bonded and glued AFS were analyzed through the three-point bending test. The results show that the magnesium, silicon, and copper elements of the core layer diffuse to panels and form a metallurgical composite layer. The metallurgical-bonding strength between the panel and core layer is higher than that of the foam core layer. The peak load of metallurgically-bonded AFS is 24% more than that of glued AFS, and energy absorption is 12.2 times higher than that of glued AFS.

Strength and Deformation Characteristics of Carbon Fibre Reinforced Composite Wrapped Aluminium Foam Beams

Sandwich structures fabricated from an aluminium skinned foam enclosed within a carbon fibre reinforced composite structure have the potential application for high-performance on- and off-road automotive vehicles. The deformations and failure of these types of structures are presented, and results indicate that the application of aluminium face sheets with aluminium foam (AF) aids to prevent the delamination of the outer layers of carbon fibre reinforced polymers (CFRP). The load carrying capacity has been increased by utilising a manufacturing method to maintain the adhesion between the core and the skins until the failure stage is reached. The core shear and de-bonded issue associated with this type of sandwich structure can be addressed by this manufacture method. The peak average flexure load capacity of an aluminium foam sandwich structure (AFSS) with a completely wrapped around CFRP skin was 2800 N with a mass of 191 g. This compares favourably with previously used AFSS without the skins, which had a peak average load of 600 N and a mass of 125 g. An initial finite element model for comparison purposes has been developed to represent the structure’s behaviour and predict the associated failure loads. It is proposed that CFRP wrapped around AFSS enhances the structural performance without significant weight gain.

Local deformation on damping performance of integral-forming aluminum foam sandwich

Damping performances of porous metals are generally measured by dynamic mechanical analysis (DMA) method which has strictly dimensional requirements on specimens especially on their thickness. In this work, based on sinusoidal excitation and Fourier transform, a new set of test equipment suitable for evaluating damping performances of large-scale porous metals was constructed. On this basis, the influence of local compression deformation on the damping performances of the newly developed integrated-forming aluminum foam sandwich (IFAFS) was investigated by means of single-point excitation method. Damping performances of different regions were obtained through partition measurement and the reasons were discussed which are beneficial to evaluate damping performances of IFAFS after local deformation.

Numerical studies on ballistic limit and cellular dispersion of aluminium foam sandwich panel under hypervelocity impact

This study presents the ballistic limit and cellular dispersion analysis for open cell aluminum foam sandwich panel. Systematic simulation of cell-based open-cell aluminum foam sandwich models is completed and a numerical method for determining ballistic limit is developed. The validity of the simulation technique can be verified by comparing the simulated ballistic limits with the experimental results and this approach can be used to get the ballistic limit of foam materials with arbitrary cellular parameters. It is found that the ballistic limit of foam core sandwich exhibits dispersion characteristics. A comparative analysis of protection performance of aluminum foams with different cellular parameter was carried out, and aluminum foam with smaller cell size has better protection performance under the same relative density condition; in addition, the topology of the foam also had a significant influence on the shielding performance.

Quasi-Static Three-Point Bending Behavior of Aluminum Foam Sandwich with CFRP Face-Sheets

Aluminum foam sandwich panels are excellent structure–function integrated materials. With high specific strength, cushioning energy absorption and sound absorption of aluminum foam material, they overcome the disadvantage of the low strength of single aluminum foam materials. In this paper, the response of aluminum sandwich panels comprising aluminum foam cores and carbon fiber reinforced plastic (CFRP) face-sheets was investigated under quasi-static three-point bending, and the effect of core thickness as well as core density on flexural loads and deformation modes was studied. The experimental results show that increasing the thickness and the density of the core materials can increase the flexural load and bending stiffness in the bending process. The aluminum foam sandwich panels mainly include the following deformation modes in the three-point bending process: indentation, core shear, face-sheet fracture and debonding.

Dynamic and quasi-static compressive performance of integral-forming aluminum foam sandwich

Dynamic and quasi-static compressive performance of integral-forming aluminum foam sandwich

Performance of sandwich cladding with modular truncated square pyramid foldcore under projectile impact

In this study, a novel sandwich cladding with modular truncated square pyramid (TSP) folded structures was proposed and its impact mitigation performance was experimentally investigated by using an air cannon testing system. A multi-stage mould pressing technique was applied to achieve efficient mass production of the foldcore. The prepared cladding specimens were impacted by projectiles using an air cannon testing facility. A custom-made measuring system which consists of five individual load cells was placed behind the proposed sandwich cladding to record the transmitted force for evaluation of the impact mitigation performance. Various impact scenarios including different projectile head geometries, different impacting speeds and locations were considered. An aluminium foam sandwich cladding with the same mass was tested as well for comparison. The impact mitigation performances of the cladding were investigated by evaluating and comparing the transmitted impact force histories recorded at different locations. It was demonstrated that the TSP cladding can be a significantly cheaper and effective alternative of aluminum foam cladding for mitigating impact load. Its mitigation is very effective with a uniformly distributed and smaller transmitted force when impacted by flat-head projectile on the TSP cell, but is less effective under point impact where the impact location is in between the TSP cells.