Composite Metal Foams Research Articles

Manufacturing and Comparison of Sr Modified or Unmodified AlSi12 Eutectic Alloy Matrix Unimodal and Bimodal Composite Metal Foams

Metallic foams are designed to be generally used by the transportation industry as energy‐absorbing reinforcements in bumper panels or as permanent cores for weight reduction. In composite metal foams (CMFs), the second phase is usually formed by hollow spheres or closed‐wall porous materials responsible for the gas (void) intake. Herein, three types of samples are compared: CMFs with unimodal small, unimodal large, and bimodally mixed small and large ceramic hollow spheres. Unmodified AlSi12 or Sr modified AlSi12 alloy is infiltrated between the spheres with low‐pressure infiltration to form the cellular structure. The effect of Sr modification on the matrix material properties and the matrix–filler interface layer is investigated. The samples are evaluated and compared based on microstructural analysis and standardized compressive tests; the fracture mechanism of the structure is analyzed using computed tomography measurements at different deformation states. The aim of this research is to develop high‐performance unimodal and bimodal CMFs, which have better specific mechanical properties than conventional metal foams, and to investigate the effect of Sr modification on the material properties. With these foams, additional weight reduction and higher energy absorption can be achieved, primarily used as automotive components.

Nonuniform metal foam design and pore-scale analysis of a tilted composite phase change material system for photovoltaics thermal management

Photovoltaics, as a direct technology to convert sunlight into electricity, possess significant potential to deal with ever-increasing environmental problems and the desire to reduce the use of fossil fuels. Thermal stability of photovoltaics is of major concern when considering large-scale commercialization under conditions in which device degradation by high temperature operation is possible. Phase change materials (PCMs) are highly promising for thermal management of such devices due to their high latent heat and inherent heat transfer properties. However, a great challenge in applying PCMs to photovoltaics is in achieving high energy density while maintaining high power density, especially with different orientations of the photovoltaics. In this work, the dynamic heat transfer characteristics of a composite PCM with embedded metal foam are systematically studied by a pore-scale lattice Boltzmann model. It is found that the melting rate of composite PCMs dramatically decreases at late-stage melting, leaving a region of solid PCM (“dead zone”) for a long time. To address this issue, we propose a special, nonuniform structure for the composite PCM that has a different porosity in the dead zone than elsewhere. The melting rate, energy density, and power density of the composite PCM can be significantly enhanced by tailoring the porosity of the composite metal foam. For instance, at a Fourier number of 0.30, the energy density of a case with a dead zone porosity of 0.80 is 6.8% higher than that with a dead zone porosity of 0.95. This work provides an effective strategy toward applying PCMs for thermal management of photovoltaics and paves a way toward optimizing energy storage capabilities of PCMs under various working conditions.

Manufacturing and Investigation of In Situ and Ex Situ Produced Aluminum Matrix Foam‐Filled Tubes

Composite metal foams (CMFs) are hybrid structures, which are usually produced from separate parts, and not in one step as functional, structural elements. Functional CMFs are characterized by high strength, high stiffness, and extreme energy absorbing properties compared with conventional metallic foams, which allow them to be used as load‐bearing and energy absorbing elements. Test specimens are made in AlMgSi0.5 tubes with the wall thickness of 5 mm. AlSi12 casting alloy is used as matrix material. To ensure the foam structure porosity, lightweight expanded clay aggregate particles (LECAPs) are used with unimodal and bimodal size distribution. The results show that low‐cost unimodal and bimodal foam‐filled tubes (FFTs) can be produced in situ by inert gas pressure infiltration. Besides their low density, these CMFs achieve high strength, high toughness, and special, functional properties compared with simple metallic foams. After heat treatment, in situ produced bimodal FFTs have the highest energy absorption capacity of an average of 67.2 J cm−3, which is 9% higher than the average value of the ex situ FFTs. Therefore, it is advantageous to produce in situ FFTs, because with proper manufacturing, it requires less machining, making the production easier, while achieving better compressive properties.

Functional aluminium matrix syntactic foams filled with lightweight expanded clay aggregate particles

Is it possible to create low-cost functional composite metal foams? In the framework of this study, composite metal foams filled tubes were produced with lightweight expanded clay aggregate particles. Specimens were manufactured by low pressure infiltration in aluminium tubes with the wall thickness of 5 mm. The properties of the transition layer between the matrix material and the material of the tube were analysed with energy dispersive X-ray spectrometry. The importance of the research was to develop lightweight, high-capacity functional composite metal foams which have higher specific mechanical properties than ’conventional‘ metal foams, thereby achieving additional weight reduction and lower material requirements, primarily as moving machine parts or automotive components, while keeping overall costs low.

Performance of Composite Metal Foam Armors against Various Threat Sizes

The ballistic capabilities of composite metal foam (CMF) armors were experimentally tested against a 14.5 × 114 mm B32 armor-piercing incendiary (API) and compared to various sizes of armor-piercing (AP) ballistic threats, ranging from a 7.62 to 12.7 mm. Three different arrangements of layered hard armors were designed and manufactured using ceramic faceplates (in one layer, two layers or multiple tiles), a combination of ceramic and steel face sheets, with a single-layered CMF core, and a thin aluminum backing. The performance of various CMF armor designs against the 14.5 mm rounds are compared to each other and to the performance of the rolled homogeneous armor standard to identify the most efficient design for further investigations. The percentage of kinetic energy absorbed by the CMF layer in various armor arrangements and in tests against various threat sizes was calculated and compared. It appears that the larger the threat size, the more efficient the CMF layer will be due to a greater number of hollow metal spheres that are engaged in absorbing the impact energy. The results from this study will help to model and predict the performance of CMF armors against various threat sizes and impact energies.

Effect of particle size and volume ratio of ceramic hollow spheres on the mechanical properties of bimodal composite metal foams

High performance bimodal composite metal foams (BCMFs) have been produced by low-pressure infiltration of EN-AW Al99.5 and EN-AC AlSi12 alloys into two sets of different nominal diameter (2.4 mm and 7.0 mm) Al2O3 ceramic hollow spheres (CHSs) in a total of five different volume ratios arranged in random closed packing distribution. The structure of the BCMFs has been studied by X-ray computer tomography and scanning electron microscopy. The mechanical properties were mapped by standardised quasi-static compressive tests. The structural investigations of the BCMFs showed proper infiltration and a higher filling ratio compared to unimodal composite metal foams. Given a specific matrix material, different volume ratios of the spheres do not have a substantial effect on the mechanical properties of the BCMFs. The mechanical properties were found to be predominantly filling rate (the volume fraction of the CHSs divided by the total volume of the sample) dependent.

Simulated pool fire testing and modeling of a composite metal foam

SummaryA series of simulated pool fire testing and modeling were conducted on steel‐steel composite metal foam (S‐S CMF) panels according to the procedure described in appendix B of 49 CFR Part 179, Specification for Tank Cars. This paper describes a series of 3‐D heat transfer calculations using the finite‐element software COMSOL Multiphysics. The purpose of the COMSOL calculations is to determine up to what extent the FDS neglects lateral heat conduction due to heat losses at the perimeter of the exposed area. To gauge the effect of the latter, the COMSOL model assumes that the heat flux at the exposed surface of the specimen is uniform. The 3‐D heat transfer calculations show that lateral heat conduction indeed needs to be included in the model to improve the accuracy of the predicted temperature distribution but that the non‐uniformity of the heat flux in the test also should be accounted for. Based on the experimental and both 1D and 3D simulation modeling results, the steel‐steel composite metal foams tested as novel insulation system met the acceptance criteria for the simulated pool fire test in 49 CFR 179 appendix B by a large margin.

Study on the Microstructure and Compression of Composite Metal Foam Core Sandwich Panels

Stainless steel composite metal foam core sandwich panels (SS-CMF-CSP) were manufactured in large-scale panels and tested under quasi-static compression. Stainless steel face sheets were attached to the SS-CMF core using two methods: diffusion and adhesive bonding. Scanning electron microscope imaging revealed grain growth in both the matrix and sphere wall for the diffusion-bonded sandwich panels. The face sheets were found to not greatly affect the deformation of the SS-CMF core under compression. However, the diffusion-bonded SS-CMF-CSP yielded a stronger product primarily due to microstructural changes that occur during the diffusion bonding heat cycle within the SS-CMF core. The diffusion-bonded SS-CMF-CSP had a plateaus stress and densification stress 17 and 10 pct higher than its baseline SS-CMF, respectively. The large-scale manufacturing was improved, and additional samples were tested with a yield and plateau strength 75 to 80 pct higher than the initial SS-CMF samples. The improved diffusion-bonded SS-CMF-CSP showed similar strengthening, with a plateau stress 16 pct higher than its base SS-CMF. Finite element analysis was completed using IMPETUS Afea that advances the current modeling of SS-CMF and was found to be in good agreement with the experimental findings.

Transient phase change heat transfer in a metal foam-phase change material heatsink subject to a pulse heat flux

Abstract In the present study, the effect of using a layer of metal foam in a composite metal foam – phase change heatsink is addressed. The bottom of the heatsink is subjected to a pulse heat flux, while the top of the heatsink is exposed to an external cooling convective flow. The melting/solidification of the Phase Change Materials (PCMs) is modeled using the enthalpy porosity approach. The partial differential equations governing the natural convective flow and the heat transfer in the clear flow region and porous layers of the heatsink are introduced and transformed into a non-dimensional form using non-dimensional variables. The Finite Element Method (FEM) with an automatic time-step and grid adaptation is employed to solve the governing equations. The model and the numerical code are validated by comparison to several results obtained in recent works available in the literature. The effect of the surrounding heat transfer by convection and the fusion temperature of the PCM on the heatsink performance and on the phase change behavior is investigated. The results show that melting heat transfer occurs during the activation of the pulse heat flux while the solidification commences with a small delay after the pulse heat flux turns off. The heatsink presents a major benefit when the external cooling power is weak. Moreover, a heatsink with a lower fusion temperature shows a better cooling efficiency. The presence of a metal foam layer notably improves the cooling efficiency of the heatsink. However, the location of the porous layer shows a minimal effect on the heatsink efficiency.

Tensile properties of composite metal foam and composite metal foam core sandwich panels

Steel-steel composite metal foam (SS-CMF) and composite metal foam core sandwich panels (SS-CMF-CSP) were manufactured and tested under quasi-static tension. The SS-CMF-CSP were manufactured by attaching stainless steel face sheets to a SS-CMF core using solid-state diffusion bonding. SEM imaging was used to inspect the microstructure of SS-CMF and compare it to that of SS-CMF-CSP. The results indicate a cohesive bond line at the interface of the core and the face sheets. The bare SS-CMF samples had an ultimate tensile strength between 75–85 MPa and a failure strain between 7.5–8%. The normalized tensile strength of the SS-CMF was approximately 24 MPa/(g/cm3), 410% higher than other comparable metal foams, with a specific energy absorption of 0.95 J/g under tension. The uniform porosities and strong bonding between the sphere wall and matrix seem to be the strengthening factor of SS-CMF under tension when compared to other metal foams. The ultimate tensile strength of the SS-CMF-CSP was 115% stronger than the bare SS-CMF at 165 MPa with an average failure strain of 23%. The normalized strength of the SS-CMF-CSP was 52% higher than the bare SS-CMF. The modulus of elasticity was approximated using the rule of mixtures for the SS-CMF and the SS-CMF-CSP and the experimental results were found to lie within the calculated upper and lower bounds.

Steel-steel composite metal foam in simulated pool fire testing

A comprehensive experimental and numerical simulated pool fire test is conducted on stainless steel composite metal foam (S–S CMF) panels and is reported in this study. The uncertainty assessments for the measured and calculated unexposed surface temperatures in the calibration and simulated pool fire tests on the S–S CMF specimens are also conducted and reported. This test procedure is designed to measure the thermal performance of new or untried thermal protection systems, such as S–S CMF, and to test for its survivability when exposed to a 100-min pool fire condition. The assembly was tested in triplicate in three consecutive simulated pool-fire exposures as specified in 49 CFR Part 179, Appendix B and achieved successful results. Based on the experimental and modeling results as well as the uncertainty studies, the 15.9 mm thick steel-steel composite metal foams tested as a novel insulation system met the acceptance criteria for the simulated pool fire test specified in 49 CFR 179 Appendix B by a large margin and is expected to pass with near certainty if the test were to be reproduced in a different laboratory. The main reason for successful performance of S–S CMF is attributed to the large air content in the material. The numerical studies reported in this study indicated that the low surface emissivity of the material is also contributing to the superior performance of the material to some extent. To complete the full test requirements of CFR Part 179 App. B, the material will need to be tested against the torch-fire exposure in duplicate. This research indicates that one of the potential applications of lightweight S–S CMF can be in tank cars carrying hazardous materials and replacing conventional structural steel with demonstrated benefits of excellent thermal insulation, fire resistance, low weight along with its established energy absorption capabilities.

Numerical Studies on the Heat Effect of Explosion Suppression by a Heat Pipe

A composite structure with a heat pipe and foamed iron-nickel composite fire suppression is proposed on the basis of the phase-change heat transfer of the heat pipe, which simultaneously attenuates the metal foam explosion energy. A numerical simulation is conducted to evaluate the feasibility of the designed construction for suppressing explosions under various thicknesses and pore diameters of the metal foam. The results demonstrate that when the foam iron-nickel metal is installed in the pipeline, the temperature reduction rate in the pipeline can reach 8.9%. The new heat pipe foam composite structure can reduce the flame temperature to 1600 K within 0.095 s. It is concluded that the heat pipe composite metal foam structure pipeline has a strong effect on suppressing combustion and explosion overpressure. Due to the combined effect of the heat pipe vacuum chamber suction energy and the foamed iron-nickel, the flame temperature decay rate increases. The maximum attenuation rate of the foamed iron-nickel for the gas explosion shock wave reaches 41.76%, and the maximum flame temperature attenuation rate reaches 64.7%. The composite heat pipe structure can quickly disperse and transfer heat, thereby effectively destroying the heat storage environment as soon as possible to prevent a secondary explosion from occurring.

Polymer infused composite metal foam as a potential aircraft leading edge material

The leading edge of aircraft wings must be free from three-dimensional disturbances caused by insect adhesion, ice accretion, and particle wear in order to improve flight performance, safety, and fuel efficiency of the aircraft. An innovative solution was explored in this work by infusing stainless steel composite metal foam (S-S CMF) with a hydrophobic epoxy resin system. S-S CMF was made with 100% stainless steel using a powder metallurgy technique. The infused epoxy filled the macro- and microporosities, unique to S-S CMF’s structure, creating a product with a density similar to that of aluminum. The contact angle, wear rate, erosion resistance, and insect adhesion of the novel infused composite metal foam were measured and compared to aluminum, epoxy and stainless steel. The infusion process was determined to fill up to 88% of the pores within the S-S CMF and was found to reduce wettability and insect residue accretion. The contact angle of the infused S-S CMF was 43% higher than its parent material, stainless steel, and 130% higher than aluminum. Insect residue maximum height and areal coverage were reduced by 60 and 30%, respectively, compared to aluminum. Grit blast experiments to simulate erosion resulted in a greater roughness increase for aluminum than for the parent epoxy resin or the resin-infused S-S CMF. These results suggest that the durability and performance of infused S-S CMF was superior compared to aluminum, which is the current leading edge material of choice. Based on the promising results under relevant wear and erosion conditions, it is concluded that the infused S-S CMF can offer a potential tailored replacement to aluminum leading edge material.

Ballistic performance of composite metal foam against large caliber threats

The goal of this study is to investigate the effectiveness of Composite Metal Foam (CMF) armors against 0.50 caliber ballistic threats. A hard armor was manufactured using a sandwich panel construction consisting of a ceramic faceplate, a CMF core, and a thin aluminum back plate. The hard armor system was tested against 0.50 caliber (12.7 × 99 mm) ball and armor piercing (AP) rounds. The CMF armors were tested with a variety of areal densities at impact velocities between 500 and 885 m/s. The armors stopped the threats at speeds up to 819 m/s without penetration. The CMF layer was found to absorb 73–76% and 69–79% of the kinetic energy of the ball and AP round respectively. When compared to rolled homogeneous steel armor (RHA), the CMF hard armors, in their current unoptimized condition, have a mass efficiency ratio of approximately 2.1. The CMF armor offers a much needed weight savings without sacrificing protection. Finite element analysis was completed using ANSYS/AUTODYN Explicit Dynamics solver to study the material interactions and impact. The results are shown to be in good agreement with the experimental findings.

Effect of Internal Structure in the Compression Behavior of Casted Al/LECA Composite Foams

In this paper, low-cost, aluminum-based composite metal foams are produced by the gravity die casting technique using lightweight expanded clay (LECA) as space holders. The influence of the voids generated by LECA particles on the syntactic composite samples density and mechanical behavior is characterized by quasi-static uniaxial compression. It is shown that smaller particles generate higher relative densities and a reduction in the value of densification strain. The use of larger particle diameter promotes an increase in yield strength and a more stable plateau region of the stress–strain curve, leading to higher values of crushing energy absorption. The influence of the internal structure on these experimental results is correlated with elasto-plastic numerical simulations, and it is suggested that a small mismatch in LECA particle diameter is advantageous for enhancing mechanical properties.

Compressive properties of granular foams of adhesively bonded steel hollow sphere blocks

Steel hollow spheres adhesively bonded together as a granular composite metal foam, is a special type of porous metal that aims to combine low weight, with ductility and energy absorption. Hollow spheres comprising steel foam shells were coated with a thermally activated epoxy in order to form different specimen geometries upon moulding and curing. The collapse propagation and energy absorption of steel hollow sphere blocks, comprising spheres of different sizes, was investigated experimentally, quantifying quasi-elastic and nonlinear properties of the steel hollow sphere assemblies in compression and comparing them with analytical and semi-empirical rules based on porous metal density and sphere packing. The results identify the initiation and nature of damage and highlight the merits of the material in absorbing high compressive deformations without significant loss of integrity.

Numerical investigation on forced convection of tubes partially filled with composite metal foams under local thermal non-equilibrium condition

In the present study, fully developed forced convection in tubes partially filled with composite metal foams (CMFs) is numerically investigated. In the CMF region, the Brinkman extended Darcy flow model and the local thermal non-equilibrium model are used to predict fluid and thermal transport. At the foam-foam interface in CMF, fluid temperature and solid energy are assumed to be continuous. At the foam-fluid interface, no-slip coupling conditions are used to couple flow and heat transfer of the foam and free regions. Governing equations are solved numerically with SIMPLE algorithm. Momentum and energy equations are discretized using the SGSD finite volume scheme for convective terms. Velocity distribution, temperature profile, the friction factor and Nusselt number in partially-filled CMF tubes are obtained. The results indicate that, porosity gradient has little effect on the friction factor at a low pore density, but the effect increases with increasing pore density. For the fixed pore density gradient, Nusselt number decreases with increasing porosity, and Nusselt number firstly increases sharply and then increases lineally with increasing Reynolds number. For the fixed material gradient, Nusselt number increases lineally with increasing Reynolds number.

Geometrical and mechanical properties of polyamide PA 12 bonds in composite advanced pore morphology (APM) foam structures

Adhesive bonds have very strong influence on mechanical properties of composite particulate metal foams. This study experimentally investigates for the first time the geometrical and mechanical properties of PA 12 adhesive bonds between spherical advanced pore morphology (APM) elements made of AlSi10 foam. A new experimentation setup for mechanical testing of bonds in APM structures is based on APM element puncturing. The results show that mechanical behaviour of adhesive bonds differs much from the basic mechanical behaviour of adhesive. Two different bond failure modes are identified, depending on the bond geometry. The geometrical and mechanical results are statistically interpreted for simpler representation, applicability, and modelling of bonds in APM composites in the future.

A study on blast and fragment resistance of composite metal foams through experimental and modeling approaches

Composite metal foam (CMF) is known for its high strength to density ratio and extraordinary energy absorption capabilities. In this study, stainless steel CMF panels are manufactured and tested against high explosive incendiary (HEI) rounds to study their resistance against explosive blast pressure and the resulting fragments. It is shown that the CMF panels were able to stop the imparted fragments of various sizes, with speeds up to 1500 m/s, and absorb the blast energy without cracking or bowing. The experimental findings were verified using IMPETUS Afea Solver and compared to the performance of a conventional aluminum armor. It is observed that despite their similar mass, the depth of penetration of the fragments into the aluminum plate is higher than that of the CMF panel. Significant front petaling and bulging is observed in aluminum plate following impact of the blast and frags. No petaling and minimal bulging is observed in all CMF panels. In addition, CMF panels are far less stressed when compared to the aluminum plate at any interval following the blast. The experimental and analytical results prove that novel CMF material can be the solution for the pressing need for effective light-weight vehicular armors.

On the Mechanical Properties of Aluminum Matrix Syntactic Foams

Metal matrix syntactic foams (MMSFs, often referred as composite metal foams (CMFs)) are lightweight materials with high specific strength. MMSFs are on the borderline between metal matrix composites and metal foams. On one hand MMSFs are composites, because they are filled by hollow particles and the particles may add strength to the material. On the other hand, they are foams, because the hollow particles ensure porosity to the material. Among metallic foams, MMSFs exhibit outstanding specific mechanical properties due to the hollow inclusions that are typically made from ceramics or high strength alloys, therefore they can be applied as structural materials. The goal of this paper is to summarize the available data on the mechanical properties of MMSFs with aluminum matrix in order to give a strong support to the design engineers. Since the foams are most frequently loaded in compression, the main part of this paper is organized around the available standard related to the compressive properties of porous materials and metallic foams. The quasi‐static results are complemented by properties measured at higher strain rates. Besides this, some insight into the basic fatigue properties as well as into the toughness of MMSFs is also provided.