Mechanical Properties Of Aluminum Foams Research Articles

The structural and mechanical properties of open-cell aluminum foams: Dependency on porosity, pore size, and ceramic particle addition

Aluminum foams are desired for lightweight, high-performance, and cost-effective materials, particularly in automotive, aerospace, and advanced power plants. Expansion of their applications depends on developing a detailed understanding of the structural and mechanical properties of aluminum foams. In this research, open-cell aluminum foams with 25.51–81.88 % porosity were manufactured through powder metallurgy using a space holder technique, with varying carbamide (urea) ratios (17–80 %) and particle sizes (1–1.4 mm, 1.7–2 mm, 2–2.4 mm). Three different ceramic particles, B4C, Al2O3, and SiC were used as reinforcement to improve the compression properties and energy absorption capacity of the foam materials. The study determined open and closed porosity ratios, spherical diameter, sphericity values, micropore sizes, mechanical properties, and energy absorption capacity of the foam samples both with and without ceramic additives. The results show that porosity ratio, pore size, and ceramic particle addition significantly affect aluminum foams' structural and mechanical properties, allowing for tailored properties for specific applications. It was observed that as porosity increased, compressive stress decreased, and the length of the plateau region and the shape change where densification began increased. However, there was no significant change in compressive stress and specific energy values with changing pore size. The optimal B4C addition was found to be 4 %, which significantly improved compressive strength to 3.75 MPa and specific energy to 4.24 MJ m−3.

Reinforcement effect of fly ash with different morphologies on aluminum foam prepared via powder metallurgy

Powder metallurgy has outstanding advantages in the preparation of aluminum foam fillers and special-shaped aluminum foams, which can realize near-net-shape forming. To improve the mechanical properties of aluminum foams prepared by powder metallurgy, low-cost solid waste fly ash (FA) was selected as the reinforcement phase, and the strengthening effect of the FA particles with different morphologies on the mechanical properties of the aluminum foam was analyzed. The results show that the strengthening effect of 1.0 wt% mullite whiskers prepared from the original FA on aluminum foam is superior to that of spherical raw FA or irregular granular FA. In particular, a reinforced aluminum foam with a yield strength of 20.76 MPa was obtained after precursor foaming at 610 °C for 10 min because the wettability between the whiskers and matrix is improved when the whiskers were coated with Sn in advance and the foamable precursor was obtained via hot-pressing.

Deformation failure mechanism and constitutive model of gradient aluminum foam under impact loading

The dynamic mechanical response and energy absorption characteristics of gradient aluminum foam under impact loading with strain rates of 150 s−1, 340 s−1, and 550 s−1 have been studied based on the Split Hopkinson Pressure Bar (SHPB) test in this paper. X-CT and numerical simulations were carried out to analyze the deformation of the micro-porous structure of gradient aluminum foam during impact compression. A constitutive model for gradient aluminum foam under impact load was further established. The results show that the mechanical properties of aluminum foam are positively correlated with the strain rate. The better energy absorption effect of gradient aluminum foams than the homogeneous aluminum foam under impact loading was confirmed. Negative gradient aluminum foam exhibited a 46.9 % higher specific energy absorption rate than homogeneous aluminum foam. The failure mode of homogeneous and positive gradient aluminum foam was observed to be 'from the proximal to the distal', whereas negative gradient aluminum foam exhibited a 'from the distal to the proximal' failure mode. The Sherwood-Frost model, considering the shape, density, and strain rate function correction, could accurately predict the impact stress–strain curve of gradient aluminum foam, which can be served as a reference for the optimal design of gradient aluminum foams.

Acoustic Emission Characterization Analysis of Quasi-Static and Fatigue Compression Properties of Aluminum Foam

In order to explore the evolution of physical and mechanical properties and acoustic emission (AE) characteristics of aluminum foam under fatigue and quasi-static compression from a microscopic point of view, the AE monitoring technology was used to analyze the deformation, hardening, and energy absorption characteristics of open-cell aluminum foam under quasi-static compression at different rates (2, 10 and 50 mm/min) and fatigue loading tests with different peak stress ratios k (k = maximum stress/yield stress) by means of MTS fatigue testing machine and CCD camera. The results indicated that under different compression rates, the AE ring down count had the same trend as the engineering stress–strain response of the specimens, the AE ring down count rate at the plastic deformation stage showed the same performance as the work hardening rate, and the AE energy absorption efficiency corresponded well to the experimental results. The specimen entered the densification stage with the stability of AE count and the decrease in energy absorption efficiency. During the fatigue tests of different k values, the change trend of strain was consistent with the response of acoustic emission characteristic parameters, and the fatigue compression damage caused by the deformation process of the specimen can be monitored by the change in AE characteristics. The AE characteristics can dynamically monitor the compression process and provide a new research method and idea for the study of mechanical properties of aluminum foam.

Quantitative relationships between cellular structure parameters and the elastic modulus of aluminum foam

The accurate prediction of the elastic modulus of aluminum foam is important for the application in high-tech fields, e.g. in aerospace industry. However, the scaling law based on the Gibson-Ashby model did not achieve the precise prediction of elastic modulus, in absence of complex porous structural features. In this study, we extended the scaling law by introducing the topological and morphological parameters into the multivariate equation. The 3D numerical images of aluminum foam specimens were obtained by X-ray tomography method, and the nine structural parameters were calculated and analyzed. The results show that as the porosity increases from 77% to 91%, the highest frequency of sphericity and solid material thickness of the cellular structure remains practically constant, although the distribution of cell size becomes more dispersed. The edges connections and the Inter-Branches Angle (IBA) of aluminum foam remain unchanged for all the specimens. Seven structural parameters were introduced into the extended scaling law to predict the elastic modulus with a higher residual value R2 of 0.932, in contrast to the R2 of 0.702 for the conventional scaling law. Through a stepwise linear regression method, the extended scale method was simplified by removing redundant parameters, and still achieved the elastic modulus predictions with a residual value R2 of 0.929. The remaining structural parameters in the extended scaling law, i.e. relative density, solid material thickness, and sphericity, were supposed to independently influence the elastic modulus, according to the covariance analysis. The three independent parameters offer the possibility to accurately predict and regulate the mechanical properties of aluminum foam.

Mechanical properties of aluminum foam filled re-entrant honeycomb with uniform and gradient designs

Auxetic materials have been widely studied in recent years due to their excellent mechanical properties and special deformation modes. However, the application of auxetic materials in practical engineering is limited by the low stiffness. Therefore, in order to broaden the range of applications, it is significant to improve the stiffness of auxetic materials. In this study, the re-entrant aluminum honeycomb is combined with an aluminum foam. The mechanical properties and deformation modes of the aluminum foam filled re-entrant aluminum honeycomb are studied experimentally and numerically. In addition, the effects of the geometrical parameters of such a honeycomb are investigated. The results indicate that the stiffness and the energy absorption capacity can be effectively improved by filling the re-entrant honeycomb with aluminum foam. Due to the high compressibility of aluminum foam, the structure can still retain the auxetic effect at a large strain. In addition, the concept of the functional gradient is introduced into the field of composite re-entrant honeycomb, and the influence of angle gradient and thickness gradient on the structure is analyzed. The results show that the composite structure with the designed functional gradient outperforms the uniform composite structure in terms of initial peak stress and the stress value at the platform stage. Due to its superior performance, the proposed auxetic composite structures hold promising applications in the fields of vehicle engineering, protective engineering and aerospace engineering.

Classification of Mechanical Properties of Aluminum Foam by Machine Learning

Classification of Mechanical Properties of Aluminum Foam by Machine Learning

Characterization of as-cast microstructure of aluminum foams by melt foaming method

The effect of the microstructure of cell-wall matrix on mechanical properties of aluminum foams becomes dominant supposing that the pore structure is well controlled. However, the as-cast microstructure of aluminum foams, including the morphology of primary α-Al grains, the constitution and distribution of secondary phases induced by thickening and foaming agents, are not well characterized at present. In this paper, we revealed the morphology of primary α-Al grains by anodization treatment, and phase constitution and distribution by SEM equipped with an EDS in cell-wall matrix of aluminum foams by melt foaming route. Results show that the as-cast microstructure is composed of dendritic α-Al grains, inter-grain CaAl4 phase, a small amount of Al20CaTi2 and bifilm. α-Al grains are of equiaxed type and their morphology is irregular due to the restriction effect of cell-walls. α-Al grains in cell-walls are much smaller than those in the pore-free layer. The cooling curve of aluminum foams indicates that primary α-Al formed first, followed by CaAl4 during solidification. CaAl4 will not be present in the melt and thus not be responsible for thickening.

An experimental investigation into the quasi-static compression behavior of open-cell aluminum foams focusing on controlling the space holder particle size

In this paper, the metal foams of AA332 and AA1067 alloys were produced using an economical technique called the pressurized infiltration process. The main advantage of this technique is controlling the space holder particle size during the production process which has a considerable effect on the mechanical properties of the foam and higher energy absorption capacity compared to those in the open literature accepted. The mechanical properties of aluminum foams with open-cell morphology under quasi-static compression loading were investigated. The commercial NaCl particles with different particle sizes of 3 mm, 4 mm, and 5 mm were employed as the space holder. To confirm the interconnected open-cell morphology of the foam, X-ray CT-scan images were taken. Moreover, the quasi-static compression behavior of produced foams was studied in terms of the relative density, plateau stress, energy absorption capacity, specific energy absorption, and energy absorption efficiency. The results indicated that increasing the NaCl particle size leads to decreasing all the mentioned parameters except the energy absorption efficiency. Also, compared to open-cell foams produced by AA1067 alloy, using AA332 alloy as the base material leads to improving the mechanical properties of the foam. By using AA332 base material, the average plateau stress of 27.59 MPa, energy absorption capacity of 16.77 MJ/m3, specific energy absorption of 13.43 J/g, and energy absorption efficiency of 73% were achieved at the plateau end strain. • Increasing the space holder size leads to decreasing plateau stress, energy absorption capacity, specific energy absorption parameters. • Increasing the space holder particle size leads to increasing the energy absorption efficiency. • AA332 alloy open-cell foams as the base material leads to improving the mechanical properties of the foam.

Improvement in energy absorption properties of aluminum foams by designing pore-density distribution

In the present work, effect of structural design on the mechanical properties of aluminum foams was studied. Aluminum foams with a relative density in the range of 0.28–0.48 with uniform and graded pore frequency were fabricated through powder metallurgy route by using carbamides as space holder, where double action die pressing process was used for producing green compacts. Carbamide space holders were removed by leaching in water plus heating processes, whereafter the samples were sintered at 640 °C for 2 h in air. Mechanical properties and energy absorption capability of the fabricated foam samples were evaluated by the means of compression test. The results showed that correct modification in pore distribution can significantly improve mechanical properties of the fabricated foam by compensating the undesirable density gradient created in the foam structure due to the die wall friction. So that for the foams with a relative density of 0.28, introducing desired gradation in pore frequency caused nearly 100% increase in plateau stress and more than 75% improvement in energy absorption ability of the fabricated foam.

Analysis of buckling failure modes of composite sandwich panels filled with aluminum foam

Objectives The goal of this article is to grasp the influence of panel spacing, plate thickness and other dimension parameters on the web buckling failure modes of I-type sandwich panels with aluminum foam. The change rules of its bearing characteristics during out-of-plane compression are revealed. Methods The nonlinear finite element method was used to simulate the out-of-plane compression process of composite sandwich panels. The mechanical properties of aluminum foam were obtained from experiments. Aluminum foam was realized using an isotropic crushable foam model in the FEM simulation. The accuracy of the numerical simulation methods used in this article was verified by comparing the quasi-static test results with the simulation results. Results The results show that with the decrease in the slenderness ratio, the failure modes of webs gradually transformed from material yield to plastic buckling, and five deformation modes such as plastic compression and low-order buckling appeared successively. Under high-order buckling, the stress curve will have a minimum value whenever a whole period deformation wave is generated. Under different slenderness ratios, the compressive strength of the composite sandwich panel appeared near the strain of 0.12, and was always maintained at about 9.36 MPa. Conclusions The slenderness ratio is an important factor affecting the web buckling failure modes of composite sandwich panels. The compression mechanical properties of composite sandwich panels with different slenderness ratios have obvious differences which require attention in structural optimization design.

Mechanical properties and damping properties of carbon nanotube-reinforced foam aluminum with small aperture

Abstract

Mechanical properties of aluminum foam reinforced with recycled ceramic aggregates

This research work investigates the mechanical properties of two distinct novel composites of aluminum foam made from the addition of recycled ballistic aggregates to the foams of aluminum alloy powder in regular and random patterns through powder metallurgy process. The mechanical attributes of these composites were examined in compression loading using digital image correlation (DIC) and compared to baseline properties of steel and aluminum foams obtained in the laboratory and literature respectively. The results obtained for aluminum foam ceramic composite made through the dispersion of ceramic aggregates in regular orientation showed an increase in its plateau stress, yield strength, strength/density ratio and relative density, but a decrease in its modulus of elasticity was observed. This observation was similar to the composite with a random arrangement of ceramic aggregates, except for a decrease noticed in its yield strength and elastic modulus. Keywords: Aluminum Alloy Powder, Digital Image Correlation, Mechanical Properties, Novel Composites, Powder Metallurgy, Recycled Ballistic Aggregates

Al2O3 aerogel coating modified TiH2 to enhance the mechanical properties of aluminum foam

Al2O3 aerogel coating modified TiH2 (Al2O3 aerogel-TiH2) was successfully fabricated by emulsion-gelation technique and used as foaming agent to enhance the mechanical properties of Al foam. Mesoporous Al2O3 aerogel, with specific surface area of 460.3 m2 g−1 and average pore size of 3.15 nm, is an effective thermal insulation barrier for TiH2 foaming agent. The results show that the maximum decomposition temperature of Al2O3 aerogel-TiH2 is increased to 581 °C, which is 16 °C higher than that of pristine TiH2 (565 °C). Furthermore, Al foam prepared by Al2O3 aerogel-TiH2 has smaller cell size and more concentrated cell size distribution compared with that using TiH2 as foaming agent. These improved structure characteristics enhanced the Al foam mechanical properties. The compressive strength and energy absorption capacity (compressive strain was 50%) of Al foam fabricated with Al2O3 aerogel-TiH2 are 5.59 MPa and 5.51 MJ m−3, comparing that are 1.63 MPa and 1.26 MJ m−3 of Al foam obtained with TiH2.

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.

Compressive performance and deformation mechanism of the dynamic gas injection aluminum foams

The dynamic gas injection method with high-speed horizontal oscillation could reduce the cell size and improve the cell quality of aluminum foams, so it is of interest to study the compressive performance and deformation mechanism of the foams produced with this process. In-situ compression in X-ray tomography was used for this research. Results have shown that the plateau stresses of bulk aluminum foams prepared by the dynamic gas injection method are in the range of 0.3–11 MPa. When the cell size is reduced to around 1 mm, the plateau stress could reach 22 MPa. In addition, the brittle deformation characteristics of the aluminum foams in the quasi-static compression process are obvious. The dynamic gas injection method could greatly improve the mechanical properties of aluminum foams, and aluminum foams prepared by this method have a better compressive performance compared to that prepared by static method even with the same relative density. The uniformities of the cell size and sphericity also affect the mechanical properties. The result of in-situ compression shows that there are two main failure modes for cell walls of aluminum foams: the fracture after buckles of the cell walls and the direct fracture of the cell walls. The aluminum foams prepared by the dynamic gas injection method could have a wide application prospect due to its superior compressive performance.

Research on Dynamic Accumulation Effect and Constitutive Model of Aluminum Foams Under Dynamic Impact

Aluminum foams were prepared by melt foaming process. The mechanical properties of aluminum foams under repeated impacts were studied. The porosity and pore size of the prepared aluminum foam were measured. The effects of damage accumulation on the failure morphology of aluminum foam, the transmission rate, stress–strain curve, energy absorption capacity, and the ideal energy absorption efficiency were analyzed. The influence of the number of impacts on the dynamic mechanical properties of the material under the condition of equivalent damage accumulation was studied. Based on the Sherwood–Frost equation, the damage cumulative constitutive model of the aluminum foams under repeated impacts was established. The influence of the difference between the damage cumulative energy corresponding to the reference curve of the shape function and the damage cumulative energy in multiple impacts tests on the prediction accuracy of the constitutive model was analyzed. The results show that with the increase in the number of impacts, the degree of damage to aluminum foam increases, transmission rate increases, the elastic limit stress and the corresponding strain are enhanced, and the damage accumulation effect on aluminum foam under repeated impacts is helpful to improve the ideal energy absorption efficiency. It is verified that the constitutive model can reflect the mechanical properties of aluminum foam under repeated impacts.

Compressive strain rate dependence and constitutive modeling of closed-cell aluminum foams with various relative densities

The dynamic compressive behavior of closed-cell aluminum foams with different relative densities at a wide range of strain rates up to 4000 s−1 was investigated using a 37-mm Split Hopkinson Pressure Bar (SHPB) apparatus. The 30-mm-diameter specimens with two thicknesses (i.e., 6 and 10 mm) and three nominal relative densities (i.e., 0.11, 0.16, and 0.21) were fabricated. The influences of strain rate, relative density, specimen thickness on the mechanical properties of aluminum foams (e.g., stress–strain relationship, collapse stress, plateau stress, densification strain, and energy absorption) were examined. The results indicate that the collapse stress, plateau stress, and densification strain of the aluminum foams with three relative densities exhibit obvious strain rate sensitivity. The collapse stress and plateau stress have a stronger density sensitivity and relatively weaker strain rate sensitivity. The specimen thickness has a very slight influence on the specimen strength at a lower strain rate (600 s−1), but this leads to a greater influence at a higher strain rate (2000 s−1). The energy absorption capacity of the closed-cell aluminum foams increases with increased relative density and strain rate in both quasi-static and dynamic compression. Finally, a multiparameter nonlinear elasto-plastic constitutive model was proposed to describe the typical three-stage features of stress–strain response in aluminum foams. There was acceptable agreement between theoretical predictions and experimental results.

The Effect of Aluminum Dihydrogen Phosphate on the Enhanced Mechanical Properties of Aluminum Foams

The Effect of Aluminum Dihydrogen Phosphate on the Enhanced Mechanical Properties of Aluminum Foams

Prediction of the Stress–Strain Behavior of Open-Cell Aluminum Foam under Compressive Loading and the Effects of Various RVE Boundary Conditions

The prediction of the mechanical behavior of metallic foams with realistic microstructure and the effects of various boundary conditions on the mechanical behavior is an important and challenging issue in modeling representative volume elements (RVEs). A numerical investigation is conducted to determine the effects of various boundary conditions and cell wall cross sections on the compressive mechanical properties of aluminum foam, including the stiffness, plateau stress and onset strain of densification. The open-cell AA6101-T6 aluminum foam Duocel is used in the analyses in this study. Geometrical characteristics including the cell size, foam relative density, and cross-sectional shape and thickness of the cell walls are extracted from images of the foam. Then, the obtained foam microstructure is analyzed as a 2D model. The ligaments are modeled as shear deformable beams with elastic-plastic material behavior. To prevent interpenetration of the nodes and walls inside the cells with large deformations, self-contact-type frictionless interaction is stipulated between the internal surfaces. Sensitivity analyses are performed using several boundary conditions and cells wall cross-sectional shapes. The predicted results from the finite element analyses are compared with the experimental results. Finally, the most appropriate boundary conditions, leading to more consistent results with the experimental data, are introduced.