Properties Of Closed-cell Aluminum Foams Research Articles

Influence of Cell Wall Material and Cell Numbers on Mechanical Properties of Closed-Cell Aluminum Foams

Influence of Cell Wall Material and Cell Numbers on Mechanical Properties of Closed-Cell Aluminum Foams

The strain rate and density dependence of the mechanical properties of closed-cell aluminum foam

Closed-cell aluminum foam (CCAF) is mainly employed as a load-bearing and energy-absorbing structural material due to its superior mechanical properties. However, besides the effect of microstructural and material parameters, the influence of strain rate (SR) and relative density (RD) on metallic foams (MF) on their mechanical behaviors is not fully understood. In this study, micro-computed tomography (micro-CT) imaging and finite element (FE) analysis were used to investigate the static and dynamic yield strength, energy absorption, and the effect of SR and RD on CCAFs. Micro-CT imaging was used to visualize the foam microstructure and measure its overall cell wall thickness and other structural parameters, which were then incorporated into the FE model. The results of the FE simulations were compared to experimental data to validate the constitutive relation. The findings of this study provide new insights into the mechanical behaviors of CCAFs and can be used to optimize its design and structural applications.

The Compressive Properties and Deformation Mechanism of Closed-Cell Aluminum Foam with High Porosity after High-Temperature Treatment

As a new type of structurally functional material, aluminum foam is widely used in civil engineering due to its excellent noise and energy reduction, thermal insulation, and fire protection properties. However, systematic research into the mechanical properties, application technology, and specification standards of aluminum foam materials in civil engineering application scenarios is lacking. In this work, a special experimental study on the mechanical properties and deformation mechanism of closed-cell aluminum foam materials in compression after fire was carried out. The mechanism of deformation and failure of closed-cell aluminum foam was revealed, and the variation in the mechanical properties of closed-cell aluminum foam with porosity, and heating temperature were investigated. On the basis of the experimental results, the correlation function between material parameters and material porosity in the Liu–Subhash constitutive model was established through multiparameter regression analysis. Then, an intrinsic structure model of aluminum foam that can consider porosity was proposed. The research results show that (1) the compression deformation process of closed-cell aluminum foam specimens exhibits significant stage characteristics: a quasi-elastic stage of quasi-elastic deformation of the matrix and cell structure → a plateau stage of cell structure destabilization and damage → a densification stage of cell collapse and stacking. (2) As the porosity decreases, the aluminum foam material becomes more resistant to compressive deformation and shows better compressive mechanical properties overall. With an increase in the heat treatment temperature, the elastic gradient, compressive proof strength, and plateau stress of the aluminum foam material show a small decrease in the overall trend. (3) The predicted values of the intrinsic structure model of closed-cell aluminum foam are in good agreement with the experimental results, indicating that the model can efficiently characterize the stress–strain process of the material and is referable.

Effect of Zinc Content on the Mechanical Properties of Closed-Cell Aluminum Foams

Effect of Zinc Content on the Mechanical Properties of Closed-Cell Aluminum Foams

Quasi-Static Compression Deformation and Energy Absorption Characteristics of Basalt Fiber-Containing Closed-Cell Aluminum Foam

In this work, closed-cell aluminum foams with 4 wt.% contents of short-cut basalt fibers (BFs) were successful prepared by using the modified melt-foaming method. The pore size of BF-containing aluminum foam and commercially pure aluminum foam was counted. The distribution of BF and its effect on the compressive properties of closed-cell aluminum foams were investigated. The results showed that the pore size of BF-containing aluminum foams was more uniform and smaller. BF mainly existed in three different forms: Some were totally embedded in the cell walls, some protruded from the cell walls, and others penetrated through the cells. Meanwhile, under the present condition, BF-containing aluminum foams possessed higher compressive strength and energy absorption characteristics than commercially pure aluminum foams, and the reasons were discussed.

Dynamic mechanical properties of closed-cell aluminum foams with uniform and graded densities

Abstract

Inverse identification of cell-wall material properties of closed-cell aluminum foams based upon Vickers nano-indentation tests

This study aims to develop an inverse approach to identifying the cell-wall material properties of closed-cell aluminum (Al) foams, which is based upon indentation tests, numerical simulation and optimization technique. Vickers nano-indentation tests are conducted on the cell-wall of foams, and the residual surface deformation is measured by a high definition confocal microscopy. To enhance identification efficiency, a combined 2D with 3D micromechanics modeling strategy is proposed here, in which the load-depth curve and residual imprint (pile-up) of the indentation tests are considered. In this study, the cell-wall material properties such as the yield strength and strain-hardening exponent are identified using this proposed inverse approach, while the Young's modulus is obtained directly for the unloading part of the indentation load-depth curves. The identification results indicate that the proposed inverse procedure can provide a well-posed solution to the cell-wall material properties by introducing the pile-up information. Microscopic computed tomography (μCT) technique is also utilized to reconstruct accurate 3D image-based representative volume element (RVE) model of foam structure, through which the numerical simulation is conducted for uniaxial compression. The identified cell-wall material parameters are validated by comparing the numerical simulation with the experimental data in terms of the deformation/failure modes and quantitative results. It is noted that the cell-wall of aluminum foams that are commonly made of melt foaming processes exhibits a quite different stress-strain relation when compared with the raw material of cell-wall. This study is expected to provide an effective approach for identifying the material properties that may be not easily determined through conventional testing methods.

Predicting the elastic properties of closed-cell aluminum foams: a mesoscopic geometric modeling approach

The biggest challenge in predicting the elastic properties of closed-cell aluminum foams is capturing the actual geometrical and topological characteristics precisely and efficiently such that the model can be used to predict the mechanical properties of the real foam accurately. This paper presents a mesoscopic modeling approach for constructing a geometric model that captures these characteristics and can be used to predict its elastic properties. The modeling approach introduces a new method for finding the number of seeds based on the cell diameter distribution and an algorithm for computing and assigning the irregular cell wall thickness based on reverse bubble growth. Results from the foam models developed in this work were found to have better accuracy in capturing the geometrical and topological characteristics of the real foam. All foam models generated by the proposed modeling approach have the same cell size distribution and irregular cell wall distribution as the real foam. The models have cells with around 14 faces with 5 edges on each face which is similar to real metal foams and naturally occurring foams. Numerical results from the foam models showed a better accuracy in predicting the relative Young’s modulus of the real foam than the generic Laguerre–Voronoi, Kelvin, and Grenestedt models.

Sample size effect on the mechanical behavior of aluminum foam

The aim of this work is to explore the effect of sample size in three different directions (length, height, and thickness of a sample block), with respect to its cell size, on the mechanical properties of closed-cell aluminum foams. 3D Voronoi models were used to represent a real foam block, and finite element (FE) analysis was performed to simulate the mechanical properties of samples under three different loading conditions (uniaxial compression, shear, and bending). The numerical results match the experimental results. The stiffness and strength of samples with different sizes were normalized by those properties of samples with the maximum size. The normalized stiffness and strength were expressed as functions of thickness of weak cell layers (less constraint cells) and that of the strong boundary layers (strong constraint cells). Furthermore, a parametric study was performed to investigate the effects of the thicknesses of weak cell layers and strong boundary layers on the mechanical properties of aluminum foam. It is concluded that both the stiffness and strength increase with sample size under compression and bending, while they decrease with the increase of sample height under shear. The minimum size of samples characterizing bulk materials under different loading conditions was determined.

The effect of cell-size dispersity on the mechanical properties of closed-cell aluminum foam

The mechanical properties of open-celled and closed-celled metallic foam are strongly influenced by the cellular microstructure and material properties of the base material from which the foam is made. The present study investigated the microstructure and mechanical properties of ALPORAS closed-cell Al foam. In particular, the effect of cell-size dispersity on the Young's modulus of foam was investigated through crushing experiments and numerical simulations. Crushing experiments were first conducted on two mutually perpendicular directions. Numerical models of varying cell-size dispersity and complexity were subsequently developed, including the monodispersed model that is based on the Kelvin structure, the bidispersed model, and the polydispersed model that is based on the random Laguerre tessellation algorithm. The numerical models were discretized using shell elements, and the simulations were conducted using the ABAQUS finite element method software. Relative Young's moduli with various relative densities were predicted, and the numerical convergence on the model size was studied accordingly. Numerical results obtained from all three numerical models developed were found to overestimate the experimental results by a factor of approximately 3. The difference between the numerical and experimental results can be attributed to the difference in detailed microstructural characteristics. Furthermore, the difference among numerical results obtained from the three models was insignificant.

Acoustic properties of closed-cell aluminum foams with different macrostructures

As structural materials, closed-cell aluminum foams possess obvious advantages in product dimension, strength and process economics compared with open cell aluminum foams. However, as a kind of structure-function integration materials, the application of closed-cell aluminum foams has been restricted greatly in acoustic fields due to the difficulty of sound wave penetration. It was reported that closed-cell foams with macrostructures have important effect on the propagation of sound waves. To date, the relationship between macrostructures and acoustic properties of commercially pure closed-cell aluminum foams is ambiguous. In this work, different perforation and air gap types were designed for changing the macrostructures of the foam. Meanwhile, the effect of macrostructures on the sound absorption coefficient and sound reduction index were investigated. The results showed that the foams with half-hole exhibited excellent sound absorption and sound insulation behaviors in high frequency range (>2500Hz). In addition, specimens with air gaps showed good sound absorption properties in low frequency compared with the foams without air gaps. Based on the experiment results, propagation structural models of sound waves in commercially pure closed-cell aluminum foams with different macrostructures were built and the influence of macrostructures on acoustic properties was discussed.

Thermal properties of closed-cell aluminum foams prepared by melt foaming technology

Closed-cell aluminum foam has incomparable advantages over other traditional materials for thermal insulation and heat preservation because of small thermal conductivity coefficient. Spherical bubble three-dimensional model of aluminum foam is built to deduce the relationship among pore wall thickness, porosity and average pore size. Non-uniform closed-cell foam aluminum model with different structural parameters and random pore distribution is established based on the relationship via C programming language. And the temperature distribution is analyzed with ANSYS software. Results indicate that thermal conductivity increases with the reducing of porosity. For the aluminum foam with the same porosity, different pore distributions result in different thermal conductivities. The temperature distribution in aluminum foam is non-uniform, which is closely related with the pore size and distribution. The pores which extend or distribute along the direction perpendicular to heat flow strengthen obstructive capability for heat flow. When pores connect along the direction perpendicular to heat flow, a “wall of high thermal resistance” appears to decline the thermal conductivity rapidly, which shows that only porosity cannot completely determine effective thermal conductivity of closed-cell aluminum foam.

Yield properties of closed-cell aluminum foam under triaxial loadings by a 3D Voronoi model

Considering the lack of abundant experimental data on metal foams under tensile triaxial loadings, characterization of the yield surface of metallic foam is controversial. In this paper, we explore a numerical method to study the yield properties of closed-cell aluminum (Al) foam under triaxial loadings using a three-dimensional (3D) Voronoi model. The finite element model was verified by a uniaxial compressive experiment with optimized modeling and computing parameters. Three normal stresses (including tension and compression) were proportionally applied on the cubic Voronoi foam to conduct numerical simulation experiments, in which each stress proportion of the von Mises stress over the mean stress includes at least three different combinations of triaxial loadings. Results indicated that the yield surface, covering the entire spectrum of stress paths from hydrostatic compression to hydrostatic tension in the plane of the von Mises stress and the mean stress, could be approximately depicted by a parabola or ellipse, but it is not symmetric about the zero mean stress. Owing to the asymmetry of the yield surface in the compressive and tensile states, the yield surfaces should be normalized by compressive and tensile uniaxial yield stresses, respectively, which leads to the conclusion that normalized yield surfaces are almost independent of both relative density and thickness distribution of the cell wall. Moreover, the scatter in the same proportion of the von Mises stress over the mean stress, but different triaxial stress combinations, shows that it might not be sufficient to depict the yield surface only by the von Mises stress and the mean stress.

Comparison of the Energy Absorption of Closed-Cell Aluminum Foam Produced by Various Foaming Agents

This work investigates the effect of two different foaming materials on the energy absorption of closed-cell aluminum structures. For this purpose, two different cellular aluminum samples were prepared by incorporating TiH2 and CaCO3 as foaming agents into molten A356 aluminum alloy at 700°C. The SEM observation of the foam samples revealed that the cell structure of the foam produced with CaCO3 is comprised of a smaller and more uniform structure than the sample produced with TiH2. Uniaxial compressive tests were performed on the foam samples to evaluate the mechanical properties of closed-cell aluminum foams. The results indicated that in a 50% strain, the energy absorption of aluminum foam with calcium carbonate is about 100% more than a closed-cell structure, which has been foamed with titanium hydride.

Investigation of the Effect of Internal Pores Distribution on the Elastic Properties of Closed-Cell Aluminum Foam: A Comparison with Cancellous Bone

Closed-cell aluminum foams belong to the class of cellular solid materials, which have wide application in automotive and aerospace industries. Improving the mechanical properties and modifying the manufacturing process of such materials is always on demand. It has been shown that the mechanical properties of cellular materials are highly depending on geometrical arrangement, mechanical properties of solid constituents and the relative density of these materials. In this study, using a manufacturing process of foaming by expansion of a blowing agent, we prepared two types of closed-cell aluminum foams with isotropic distribution of cells along length and foams with gradient of pores along its length. We hypothesized that such variation of pores can induce microstructural directionality along the length of foam samples and improve their mechanical properties. For this aim, we studied the microstructural properties by micro-CT imaging and found their relation to macroscopic mechanical properties of foam samples by conducting monotonic compression tests. We compared these results with the one of the bovine femur trabecular bone as they show a dominant microstructural anisotropy due to alignment with the maximum strength direction in body. We also conducted numerical analyses and validated them for the elastic part based on our experimental work.Our results showed that gradient variation in porosity in closed-cell aluminum foams have a minor effect on their macroscopic mechanical properties. Although using such materials in sandwich panel structures, the strength of the material slightly increased. In addition, parameters of a power law model for the description of mechanical properties of foam sample and their relative density and properties of the solid compartment were characterized. The presented results are considered as a preliminary study for improvement of mechanical properties of closed-cell aluminum foams.

The Influence of Titanium Hydride Pretreatment on the Compressive Properties of Aluminum Foam

Macrostructure has an important effect on the compressive properties of closed-cell aluminum foams. Meanwhile, the decomposition behavior of a foaming agent has a significant influence on the macrostructure of closed-cell aluminum foams. In order to get optimal compressive properties on aluminum foams, it is important to obtain the optimal decomposition behavior of a foaming agent. In this paper, different heat treatment temperatures and fixed heat treatment were employed to investigate the decomposition behavior of titanium hydride. For a more intuitive understanding of their decomposition characteristics of the pretreated titanium hydrides, closed-cell commercially pure Al foams were prepared by melt foaming method using different types of pretreated titanium hydrides as foaming agent. In addition, the macrostructures and quasi-static compressive properties were used to evaluate the pretreatment effect. The results showed that pretreatments have a significant influence on the macrostructure and compressive properties of aluminum foams. The decomposition characteristics of titanium hydride pretreated at 753 K for 30 min are most suitable for the preparation of closed-cell aluminum foams under present conditions, as the foams possess good combination of pore size distribution, yield strength and energy absorption capacity. DOI: http://dx.doi.org/10.5755/j01.ms.20.4.6082

Thermal properties of closed-cell aluminum foam with circular pores

The thermal property of closed-cell aluminum foam is studied numerically and the effects of the distribution of the circular pore on the thermal property are studied theoretically. When the convection and radiation are ignored, the effects of porosity, cell size, and distribution forms of pore on the apparent thermal conductivity are investigated. Moreover, the effects of air in the pore on the thermal property are analyzed as well. Simulation results show that apparent thermal conductivity linearly increases with the increase of porosity, while the cell size and the distribution have negligible effects on the thermal property. By comparison, thermal conductivity of air has slight effect on thermal property of foamed aluminum in the context of small size pore.

Progress on Research of Mechanical Properties of Closed-cell Aluminum Foams and Its Applications in Automobile Crashworthiness

Progress on Research of Mechanical Properties of Closed-cell Aluminum Foams and Its Applications in Automobile Crashworthiness

Micro–macro investigation of deformation and failure in closed-cell aluminum foams

Macroscopic mechanical properties of metal foams originate from the deformation of forming cells which happens on a micro scale. In this sense, the geometry of cells as well as the thickness and property of cell walls play a role in determining overall mechanical properties. Using simulation methods combined with some experimental tests, the inter-relationship between the micro scale deformation and the macro scale properties is investigated in this paper. In the first part of the work, the effect of relative density on the mechanical properties of closed-cell aluminum foam is investigated by numerical methods, and the results are compared with analytical predictions and experimental data. In the second part, the effect of cell topology, including cell shape and cell size, on the material behavior is investigated for aluminum foams, regardless of relative density. It is shown that cell shape causes some changes in macroscopic material behavior, which can be explained by its effect on the pattern of deformation and local failure in the material. Different mechanisms of deformation at the cell level are considered in connection with closed-cell aluminum foams. And finally, in the third part, different patterns of failure are investigated on different scales. The deformation and failure at the cell level cause localization on the macro scale. The cell shape and the inhomogeneity of the foam structure are investigated as the primary factors affecting the deformation and failure modes, and the results give some deeper understanding about the effect of cell shape on mechanical behavior. Also, some experimental tests are carried out to validate the numerical results.

Compressive properties of closed-cell aluminum foams with different contents of ceramic microspheres

In this paper, closed-cell aluminum foams with different kinds and contents of ceramic microspheres are obtained using melt-foaming method. The distribution and the effects of the ceramic microspheres on the mechanical properties of aluminum foams are investigated. The results show that both kinds of ceramic microspheres distribute in the foams uniformly with part in the cell wall matrix, some in adhere to the cell wall surface and part embed in the cell wall with portion surface exposed to the pores. Ceramic microspheres have an important effect on the yield strength, mean plateau stress, densification strain and energy absorption capacities of aluminum foams. Meanwhile, the content of ceramic microsphere in aluminum foams should be controlled in order to obtain good combination of compressive strength and energy absorption capacity. The reasons are discussed.