Properties Of Metal Foams Research Articles

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.

Characterization of the Aluminium-Based Metal Foam Properties for Automotive Applications

AbstractMetal foams are solids where the gas is filled inside uniformly in the metal matrix. Blowing agent supplies air inside the parent metal, and metal foam has emerged to be a promising material because of its low density, high absorption capacity, low thermal conductivity and high strength which finds its huge applications in automobile components. The present work deals with the application of the aluminium metal foam with different densities 200 and 400 kg/m3 in automobiles. Various tests such as toughness, hardness, bending and compression are carried out for four chosen densities, and the values are compared with the aluminium base metal. The result showed that the hardness value increased significantly by 24.48% with the rise in the density from 200 to 400 kg/m3. Maximum modulus of resilience for the low-density specimen is found to be 2.21 MJ/m3. Surface topography showed irregular pore shapes with discontinuity, resulting in a loss of cell integrity with the neighbouring cell walls. This affected the performance of the foam significantly. Thermal experiments were carried out to determine the thermal conductivity where thermal conductivity increased by 122% with the rise in the density from 200 to 400 kg/m3. Based on the results, it is concluded that aluminium foam with density 400 kg/m3 can be recommended for use in automobile applications due to its lightweight properties, which contribute to improving fuel efficiency, impact absorption capacity and the vehicle’s speed. Additionally, the air trapped within the foam cells serves as a sound barrier and insulator in cars.

Numerical simulation of heat transfer performance in an enclosure filled with a metal foam and nano-enhanced phase change material

Nowadays phase change materials are widely used in different engineering systems to perform effective cooling techniques for heat-generating elements or to accumulate the thermal energy effectively. The disadvantage of the phase change material is a low thermal conductivity, but it can be improved using porous media or metal nanoadditives of high thermal conductivity. The present research is devoted to the mathematical simulation of conjugate thermal convection in a closed chamber partially filled with metal foam saturated with nano-enhanced phase change material. The governing equations have been formulated using the Oberbeck-Boussinesq equations with the Stefan problem approach for the liquid phase and the heat conduction equation for the solid phase. The finite difference technique in combination with non-primitive variables has been used for numerical analysis. The developed in-house numerical program has been verified using the grid independence test as well as the experimental and theoretical outcomes of other authors. The effects of the metal foam properties and nanoadditives characteristics on melt behavior and thermal energy transport parameters have been studied. The main attention is paid to the influence of a filling height ratio of the metal foam on the heat transport process. It has been revealed that the impact of the metal foam on thermal dissipation is essentially higher compared to the nanoadditives influence. Therefore, in the case of full height foam, the effect of nanoparticles is weak, but in the cavity with a partial height of the porous medium, NePCM can be melted faster than pure PCM and has a negative effect on the heater temperature. It has been also found that changing the filling height ratio from 0.167 to 0.5 does not lead to a significant change in the temperature of the heater.

Investigation of the Bending Properties of Ex situ Functional Metal Foams

In each industry, compromises have to be made when choosing materials. Lower-density materials have a significant advantage in the automotive sector, especially due to rising fuel prices, since weight reduction can lower overall fuel consumption. The advantageous properties of metal foams, such as low density, high specific strength, and excellent energy absorption, should be researched and exploited in as many areas and ways as possible. This research aims to perform and evaluate the bending tests of ex situ functional metal foams: aluminum alloy matrix (AlSi7Mg) was used, which was filled with Ø2.5–3.0 mm lightweight expanded clay aggregate particles and surrounded by thin-walled aluminum tubes (AlMgSi0.5) with a wall thickness of 2 mm and an outer diameter of Ø32 mm. Empty tubes, foam-filled tubes (with and without structural epoxy adhesive) and metal matrix syntactic foams were compared based on their flexural strength and energy absorption capacity. Quasi-static three-point bend tests were carried out up to 25 mm deflection. The foam-filled tubes with epoxy adhesive showed an average of 6% increase in flexural strength compared to the foam-filled tubes without adhesive and a 145% increase compared to the metal matrix syntactic foams.

Experimental and Numerical Investigation of Flow Boiling in Additive Manufactured Foam Structures With Vapor Pathways

Abstract The unique properties of metal foams make them potential candidates for a range of applications, including microsystem thermal management. Using additive manufacturing to create foam-type structures can improve upon prior thermal solutions by eliminating thermal interface materials and allowing for customization/local control of parameters. In the present investigation, flow boiling in additive-manufactured metal foams is investigated both experimentally and numerically. Two test samples, one with uniform structure and the other with pathways for vapor removal, are compared both experimentally and numerically. A conjugate computational fluid dynamics and heat transfer (CFD-HT) model utilizing a three-dimensional volume of fluid (VOF) model with accompanying evaporation/condensation model provided in-depth visualization of the boiling flow phenomena. The experiments generated the thermohydraulic performance over a range of heat fluxes, demonstrating that the sample incorporating dedicated vapor pathways performed better in both pressure and heat transfer performance metrics compared to the uniform foam. Additionally, negative system-level effects (i.e., hydraulic oscillations) were shown to be abated using the vapor removal structures. The numerical model yielded further insight into the factors contributing to the improved performance. Results indicated the pathways functioned as vapor removal channels, allowing the generated vapor to vent from the foam structure into the lanes. Further computational investigations demonstrated changes in flow regimes, where the addition of vapor channels caused the flow to change from churn to annular. Bubble behavior unique to the vapor pathway structure was studied, showing stagnant regions that eject vapor into the channel.

Effect of Heating Temperature, Holding Time and Stabilization Temperature on the Al-Foam Properties

The interest in metallic foam is increasing since their cellular structures have a unique combination of properties such as high stiffness, low density, lightweight, high specific strength, and thermal insulation. Commonly, the performance of metallic foam can be improved by the heat treatment process. However, the previous heat treatment methods still present the brittle crack path and the research on heat treatments of the metal foam properties is very limited. In this study, individual parameters in stress relieving treatment that contribute to Al-Foam properties were investigated. The stress-relieving process of the samples was performed using a vacuum furnace. The composition of aluminium foam was determined by X-Ray Fluorescence (XRF). The hardness test was conducted using a microhardness tester. Quasi-static compression test was conducted by a universal testing machine. From the SEM-EDX elemental images, it can be observed that traces of Ca, Fe, Ti, and Si have a homogeneous distribution in the Al-matrix. In the result obtained, the mechanical properties of aluminium alloy foam decrease when the heating temperature is enhanced. The mechanical properties of closed-cell aluminium alloy increase with the reduction of the holding temperature. This was due to the recovery and recrystallization process which depended on time and temperature during the heat treatment process. The mechanical properties of aluminium foam were raised after increasing the stabilization temperature. This finding was due to the vibrational atomic motion in the recovery process.

Investigation on mechanical properties of nickel open cell metal foam after heat treatment

This investigation aims to assess the mechanical behavior and energy absorption properties of the open-cell nickel foams. The metal foams produced by electroforming of nickel on PU foams, also a heat treatment has applied to evaporate the PU foam, then a uniaxial compression test was applied to measure maximum compressive strength, energy absorption density, efficiency, and normalized stresses. The results indicate that compared with typical open-cell nickel foams and polymer precursors when the electroforming time is 12 h and a heat treatment has applied, the aforementioned properties of the metal foams had a significant improvement. Improvement of properties will change by increasing the time of electroforming. The heat treatment improved the energy absorption density of open-cell nickel foams for 3.7 times. For the best sample which is a metal foam with 12 h of electroforming with heat treatment the first maximum compressive strength, energy absorption density, and energy absorption efficiency reach 1.84 (MPa), 3.29 (mJ/mm3), and 73%, respectively.

Young’s Modulus of Metal Foams Based on Resonance Frequencies

Abstract Estimating the mechanical properties of metal foams is becoming important in developing new materials and advancing new manufacturing processes. Among various mechanical properties, effective Young’s modulus as one of the key properties may be evaluated through several measurement methods, but because of some limitations, merely a few techniques can be used in each application. Metal foam as a novel conventional material is one of the significant materials with limited methods for effective Young’s modulus measurement. Recently, several empirical relationships have been developed between effective Young’s modulus and metal foam’s porosity to estimate its elasticity based on the material’s relative density. The present study uses the finite element method to examine a cuboid-shaped sample with various porosities to develop a better model for the relationship between resonance frequencies and elasticity. In addition to the relationship between elasticity and porosity, an empirical correlation between resonance frequencies and elasticity is proposed. The results of this research allow the researchers to estimate the porosity and effective Young’s modulus of metal foams based on the resonance frequencies.

On the hydrodynamics of macroporous structures: Experimental, CFD and artificial neural network analysis

Porous metallic structures play a critical role in mass and heat transfer processes due to their high surface areas, fixed porosity, and high stiffness – so understanding their fluid flow behaviour is crucial in designing materials that perform efficiently in mass and heat transfer. In view of this, a multi-disciplinary approach is employed to study the hydrodynamics of aluminium foams produced by a liquid melt infiltration technique using experimental, computational fluid dynamics (CFD) modelling and simulation, as well as artificial neural network (ANN) machine learning backpropagation. X-ray computed tomography datasets were used to characterize pore-structure-related properties of replicated materials, followed by three-dimensional advanced imaging of workable representative volume elements. Hydraulic flow information was acquired for the porous matrices using the constant-head permeameter technique. Experiments showed the permeability and Forchheimer coefficient dependence on pore-structure-related properties for fluid-flowing within the pre-Forchheimer and fully developed Forchheimer regimes. Flow permeability of 8.479 × 10−09m2 was highest in the material with the widest mean pore openings (0.212 mm) and lowest (1.291 × 10−09m2) in the material with the narrowest mean pore openings (0.106 mm). Conversely, Forchheimer coefficients were higher for materials with lower porosities and lower for materials with higher porosities. CFD calculations accurately predicted the fluid properties of metallic foams, as well as the influence of intrinsic foam properties on permeability and the Forchheimer coefficient. The ANN model framework was also able to provide valuable information about the hydrodynamics of these materials. Convolution and non-linearity of the ANN model were improved by adding supplementary neurons to the hidden layers allowing deviations within 0.3 and 9.0 percent to be attained.

Simulative Determination of Effective Mechanical Properties for Digitally Generated Foam Geometries

Metal foams constitute a promising and emerging material class in the context of lightweight construction. There exists a variety of different foam topologies, on which resulting mechanical properties depend. To maximize the potential of foams in material use under mechanical load, the present work addresses the question how different geometrical parameters influence the material behaviour. Therefore, an algorithm for digital generation and design of open pore foam structures is presented, that allows to regulate the geometry precisely. A method for retrieving effective mechanical properties from numerical simulations of compression tests in the elastic regime is introduced. Additionally, the representativeness of foam volumes considered for simulations is investigated. This yields a fully digital workflow, which enables the investigation of geometry influence on mechanical properties. This approach is used to conduct simulation studies on generated foam structures with a systematic variation of geometrical parameters. Herein, a range of effective Young's moduli varying by up to a factor of 1.3 for different foam structures at the same porosity is found. This shows a significant impact of the foam geometry on the elastic properties of metal foams. The presented methodology yields insights, which can guide design and optimization of materials for specific applications.

Thermal performance investigation of metal foam heat exchanger for micro-gas turbine

This study presents the experimental monitoring of heat transfer performance of metal foams in transient state. Micro gas turbines require a compact recuperator with high effectiveness to achieve higher thermal efficiency. Porous media such as metal and ceramic foams are characterised by high surface-to-volume ratio. They are known to increase heat transfer and potentially can be incorporated in recuperators. Their structure is ideal for thermal management of compact and lightweight applications. The idea is to combine excellent thermal properties of metal foams with turbine gases heat fluxes exploitation, in order to elevate the temperature of a different working fluid such as water or compressed air before it enters the combustor. A novel facility was designed and developed for monitoring heat transfer mechanisms that occur in metal foams. A copper cylinder is filled with metal foam which is heated in transient state by a sudden switch from cold to hot water flow whereas a cold stream cools the device in a crossflow configuration. The study demonstrates a method based on computerisation of true-colour analysis of digital images for surface temperature visualisation using thermochromic liquid crystals (TLC). Results of temperature as well as local and mean heat transfer coefficient were obtained showing that the hot flow inside the foam was more dominant in heat transfer than the cold flow in the empty channel. The method is promising for the evaluation of transient phenomena in a tube that is filled with porous media.

Study on the effect of the size irregularity gradient of metal foams on macroscopic compressive properties

Size irregularity gradient and cell wall gradient, combined as the density gradient in previous studies, affect the macroscopic mechanical properties of the gradient metal foam. More and more complex mesostructures are designed and applied in metal foams, and the density gradient becomes insufficient to describe the difference in mesostructures. To explore the effect of mesostructures carefully, this study focuses on the effect of the size irregularity gradient on the macroscopic compressive properties of metal foams. A series of metal foam models were developed using the 3D Voronoi technique. These models have the same average relative densities, the same average diameters and different size irregularity gradients. Simulation results indicated that the macroscopic mechanical properties of cell wall gradient metal foams are significantly different from those of size irregularity gradient metal foams, though these models have the same relative density gradient. To explore the effect of size irregularity gradient, a theoretical model was developed to characterize the compression process from the first cell-collapse to full condensation. Theoretical results showed a linear relationship between the nominal stress and the current relative density. These findings can provide efficient guidance for the design and applications of gradient metal foams.

Metal foams: A review for mechanical properties under tensile and shear stress

Due to their mechanical properties, metal foams are used in various fields. The aim of the present research is to collect different studies about the important mechanical properties of metal foams, such as Young’s modulus, tensile and shear strength, relative density, etc. under tensile and shear loading. Gaps were identified in the methodological embodiments of the experiments due to the use of different standards, as well as in the calculation of mechanical properties through mathematical relations in tensile and shear, which led to deviations between the experimental results and these. Furthermore, this work records sequences and connections between experimental results of different tasks as well as solutions to the aforementioned issues.

Microstructure and Mechanical Properties of Metal Foams Fabricated via Melt Foaming and Powder Metallurgy Technique: A Review

Metal foams possess remarkable properties, such as lightweight, high compressive strength, lower specific weight, high stiffness, and high energy absorption. These properties make them highly desirable for many engineering applications, including lightweight materials, energy-absorption devices for aerospace and automotive industries, etc. For such potential applications, it is essential to understand the mechanical behaviour of these foams. Producing metal foams is a highly challenging task due to the coexistence of solid, liquid, and gaseous phases at different temperatures. Although numerous techniques are available for producing metal foams, fabricating foamed metal still suffers from imperfections and inconsistencies. Thus, a good understanding of various processing techniques and properties of the resulting foams is essential to improve the foam quality. This review discussed the types of metal foams available in the market and their properties, providing an overview of the production techniques involved and the contribution of metal foams to various applications. This review also discussed the challenges in foam fabrications and proposed several solutions to address these problems.

A review of the compressive properties of closed-cell aluminum metal foams

Materials scientists and engineers have been trying to create porous metals and metal foams for many years. Naturally occurring porous materials such as bone, coral, cork, balsa wood, etc., are responsible for initiating research in the area of producing porous metals and metal foams. Metal foam is a cellular structure made up of a solid metal-containing a large volume fraction of gas-filled pores. These pores can either be sealed (closed-cell foam), or they can be an interconnected network (open-cell foam). The closed-cell foam is referred to as metal foams, while the open-cell foam is referred to simply as porous metal. Some of the key properties of the metal foam are, ultra-light material (75–95% of the volume consists of void spaces), very high porosity, and high compression strengths combined with good energy absorption characteristics. This paper provides a comprehensive review of mechanical characterizations of closed-cell aluminum metal foams (CCAFs) or porous aluminum alloys, the trends in their mechanical behavior specifically their compressive performance. The significant factors influencing this behavior are intricately studied in light of the available literature. The aim of this work is to facilitate a channelized development over the past few decades in the field of mechanical behavior of CCAF that may be of help to the researchers, academicians, and industries for the critical understanding of the failure criteria and mechanical properties of closed-cell aluminum metal foams.

High-temperature and dynamic mechanical characterization of closed-cell aluminum foams

Metallic foams exhibit great application prospects in some extreme working conditions such as high temperatures and/or high-velocity impact environments, but predominantly, their mechanical behavior has remained to be fully understood to date. In this study the uniaxial and biaxial tests are conducted on closed-cell aluminum foams at elevated temperatures. It is indicated that both drop stress and initial failure strength exhibit approximately linear relationship with the applied temperature, while the densification strain keeps almost at a constant value. The higher foam density or lower applied temperature, the larger the initial failure surface characterized in the von Mises - mean stress plane. However, the normalized failure surfaces nearly do not depend on foam density or temperature, and can be well fitted in terms of elliptical or parabolic function. Dynamic compressive tests under constant strain-rates reveal that the compressive strength is correlated to strain-rate positively, but the densification strain negatively. A novel rate-dependent constitutive model is proposed to describe the compressive constitutive behavior of Al foams. Finally, the crushable foam model with the tabular input of yield ratio approach can produce satisfactory numerical predictions compared to dynamic experimental results. This study provides new insights into the intrinsic mechanical properties of metallic foams under some extreme conditions.

Modeling of the quantitative effect of temperature on key mechanical properties of metal foams

In this study, the effect of temperature and external force on the plastic collapse of metal foams was briefly analyzed firstly. Subsequently, the maximum energy density for the plastic collapse of the material at different temperatures was put forward. Finally, a temperature-dependent energy absorption model, a temperature-dependent plastic collapse strength model, and a temperature-dependent plateau stress model were developed. The proposed models have no fitting parameters and simple structure. The accuracy and practicality of the models are well verified by comparison with the available 12 sets of experimental data over a wide temperature range (the highest temperature reached 0.83Tm). The temperature-dependent energy absorption model and the temperature-dependent plastic collapse strength only need data at room temperature to quickly predict their energy absorption and plastic collapse strength at different temperatures. These two models can be used as an optional method for rapidly assessing the high-temperature mechanical properties of metal foams. This work has important implications for the further development of metal foams applications in high-temperature service environments such as aerospace.

Production of Closed-Cell Foams Out of Aluminum Chip Waste: Mathematical Modeling and Optimization

The main aim of this research is to mathematically describe the influence of the processing parameters of metal foam production from machining chip waste. Using this method, metal foams were produced without a remelting step, which should be both economically and environmentally effective. Firstly, expensive metal powders were replaced with waste in the form of machining chips. Secondly, machining chip waste was recycled without any significant material losses, which usually occurs during conventional recycling (using the melting process). To describe the innovative process and to relate metal foam properties to foaming temperature, the blowing agent weight percentage, and foam density (controlled by foaming height), response surface methodology, and the design of experiments were used. The quality of the produced metal foams was evaluated by determination of density, yield strength, compression strength, plateau stress, energy absorption, pore perimeter, and pore inhomogeneity for specimens obtained following the experimental plan. It was proven that pore inhomogeneity increased in the range from 1.41 to 4.81 mm with a higher temperature and the addition of a foaming agent. However, higher energy absorption and yield strength were obtained with a higher temperature but a lower percentage of TiH2. Despite the production from machining chips, pores were homogenous without significant cracks. These kinds of metal foams are comparable to commercial foams made of metal powders.

Study on enhanced heat transfer performance of open-cell metal foams based on a hexahedron model

Due to its high heat transfer performance, the open-cell metal foam has a great potential of applications in heat exchanger industries. Based on the cell structure of the perforated metal foam, a simplified hexahedral structure model was proposed herein. The fluid flow in metal foams was simulated by computational fluid dynamics software. The accuracy of the model was verified by experiments. Based on the numerical simulation, heat transfer performance and the mechanism of enhanced heat transfer were investigated and discussed. The results show that the hexahedron model proposed in this article is feasible and accurate. The heat transfer and pressure drop properties of metal foams were numerically calculated and analyzed at the inlet air velocity of 1–5 m/s. At a certain PPI (pores per inch) and porosity, with the increase of Reynolds number Re, both the heat transfer coefficient h and pressure drop ΔP/L increase gradually. The comprehensive performance of convective heat transfer of metal foams with a lower PPI is relatively better. Increasing PPI or decreasing porosity is conducive to the destruction of the fluid boundary layer, enhancing the fluid disturbance, thus forming a vortex at the back of the skeleton and strengthening the heat transfer.

Effects of microscopic morphology of ligament and porous parameter on spectral radiative properties of nickel foams

The radiative properties of metal foam are determined by the complex multi-scale characteristics. The effects of microscopic morphology of ligament and porous parameter on the apparent and volumetric radiative properties are investigated by performing a trans-scale simulation, which are respectively presented by the absorptance and transmittance, the extinction coefficient and scattering albedo here. The spectral reflective property of ligament surface ranging from 0.5 ∼ 7 μm is firstly modeled with Finite Difference Time Domain (FDTD) method considering the micro-scale roughness, and then compared with other three simplified reflection models (specular, diffuse and harmonic reflection). With the reconstructed foam structure and Monte Carlo method simulation, the spectral radiative properties of different nickel foam slabs are repetitively calculated to analyze the effects of above two factors. The results show that three reflection models for the ligament surface all have a non-negligible deviation, and the maximum greater than 20% is found. Besides, micro-scale morphology of ligament significantly affects the absorptance, transmittance and scattering albedo of the nickel foam slab. By contrast, porous structural parameters have noticeable influence on the apparent properties and extinction coefficient, while negligible effect on the scattering albedo.