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This study explores the simulation and analysis of the infiltration process for manufacturing A356 aluminum alloy foams using vacuum pressure. The infiltration technique, known for its versatility in liquid-state metal processing, is widely employed for metal foam production due to its ease of application. The study investigates the relationship between the geometric parameters of the preform, system pressure, and filling times, revealing a correlation. The simulation using the Flow 3D software determines the pressure and vacuum time required to achieve successful aluminum foam without filling failures. Experimental validation through infiltration casting using NaCl as a removable preform aligns with the simulated results, yielding high-quality aluminum foam samples with diverse pore sizes (0.5 mm, 1.0 mm, and 2.0 mm), uniform and interconnected pore distribution, average porosity percentages of 65%, and a relative density of 0.35. The research contributes insights into optimizing the infiltration process for aluminum foam fabrication, bridging the gap in limited literature on cellular metals. [ABSTRACT FROM AUTHOR]

To enhance the sound absorption performance of open‐cell aluminum foam, the double main pores‐porous cell walls (DMP‐PCW) aluminum foams via infiltration casting of preforms mixed with two sizes of NaCl particles are prepared. The pore structure, sound absorption performance, and mechanism of DMP‐PCW aluminum foam are investigated. The pore structure consists of double‐sized main pores similar to the NaCl particles and the cell wall pores formed by the connections between NaCl particles. It is found that the static flow resistivity of DMP‐PCW aluminum foam reaches an optimum value of 28105 Pa.s m−2 when the volume proportion of small main pores increases, the size of cell wall pores decreases, and the number of cell wall pores per unit main pore surface area (NPPA) increases. At 800–6300 Hz, the average absorption coefficient is 0.89. In addition, the Wilson model predicts the sound absorption properties of DMP‐PCW aluminum foam. The predicted values agree well with the measured values. The finite‐element acoustic simulations and dynamic viscous‐thermal permeability calculations reveal that the improved sound absorption performance of DMP‐PCW aluminum foam is correlated to the enhanced sound transmission caused by increased NPPA and increased viscous‐thermal loss due to the double main pore structure. [ABSTRACT FROM AUTHOR]

The production of closed-cell metallic foams has been of interest to the scientific community and industry for decades, owing to their unique properties, which include high specific strength and stiffness, buoyancy, shock absorption, and crash worthiness. One of the approaches for their fabrication relies solely on the use of powders and is manifested in what has been referred to as the powder metallurgy (PM) route. This review discusses the underlying fundamentals of the process, and recent developments together with our current understanding. The effect of process parameters on the developed foam structure is reviewed for a range of metals, alloys, and metal matrix composites. Fundamental foaming mechanisms and characteristics are discussed. [ABSTRACT FROM AUTHOR]

Silicon (Si) has a significant influence on the cellular structure and microstructure of the aluminum (Al) foams, which in turn will notably affect their mechanical responses. Herein, the Al–Si foams are fabricated via a novel powder metallurgy foaming approaches with multiple Si contents to investigate the role of Si concentrations on the structural and mechanical properties. The results show that the certain contents of Si can not only delay the expansion process, but also increase the maximum expansion rate to improve the cellular structure. Specifically, the AlSi7 foams process the optimal comprehensive compressive properties of yield stress (4.36 MPa), plateau stress (6.02 MPa), and energy absorption capacity (3.47 MJ m−3) with the relative density of 0.15. However, excessive Si can decrease the expansion rate and deteriorate the cellular structure. Moreover, the deformation mode of the Al foams during compressive process converts from plastic mode to brittle mode by the adding of Si. Generally, the AlSi7 foams possess an excellent trade‐off between toughness and brittleness and exhibit the optimal mechanical responses. [ABSTRACT FROM AUTHOR]

Closed-cell aluminum foams are gaining widespread acceptance, especially in automotive, aviation and defence sectors, by virtue of their high strength-to-weight ratio, good energy absorption performance and affordable manufacturing costs, which makes them a shock absorber material with enormous potential. Microstructural parameters such as cell size, cell aspect ratio, cell wall thickness variation, cell wall geometry and cell shape irregularity, have a by no means negligible influence on the compressive response of closed-cell aluminum foams. The most recent studies, both experimental and numerical, on the macroscopic properties-microstructure relationship are scrutinized and their results are discussed in this work. [ABSTRACT FROM AUTHOR]

Aluminum foams are porous and recyclable lightweight materials with outstanding mechanical features, such as their energy absorption capabilities, their most noteworthy property. In view of these qualities, this class of material is a great candidate to use as sacrificial layers applied on structures under threat for blast load protection. Few works studied the coupled behavior between the sacrificial layer made of aluminum foams and the protected structure while commonly neglecting the nonlinearity of the protected structure and impact events caused by the foam. Nevertheless, the efficiency of the foam as an energy absorbent was not adequately addressed in all the existing works. The model suggested in the work is formulated using the shock front theory and validated against experimental results. It is designed to address physical aspects that have remained unaddressed in previous numerical models. Moreover, the model is employed to examine the efficiency of the foam as an energy absorbent, along with a novel methodology proposed in the current work, aiming to carry out adequate testing. Finally, the proposed model is used to evaluate the foam behavior against a wide range of pressure and impulse combinations, leading to unprecedented behavior in the reduction of peak displacements and consequently damage mitigation. The finding of the current study shows a new direction in testing the efficiency of sacrificial layers as energy absorbents. • The coupling behavior between aluminum foams and protected structures is studied. • A model that accounts for all aspects is developed based on the shock front theory. • Validation against previous test results is performed. • New methodology for examining the foam efficiency is suggested. • Parametric study on a load spectrum showed unprecedented damage mitigation behavior. [ABSTRACT FROM AUTHOR]

The current research focuses on studying the process parameters affecting the physical and mechanical behavior of open-cell Aluminium A356 alloy foams manufactured by infiltration casting. This technique includes pressurizing molten metal into the intercellular distances of a compacted preform composed of leachable particles. The parameters investigated are the preform compaction pressure, particle size, and gas infiltration pressure. The characterization starts by evaluating physical properties like relative density and strut thickness. Next, compression tests are performed for mechanical characterization. The compression curves are used to evaluate the mechanical properties like the plateau stress, densification strain, and energy absorption. Mechanism analysis is conducted in terms of statistical models and physical phenomena interpretation. Finally, a mathematical model is proposed and validated to interpret the behavior of the foams during the plateau phase. Among the findings is the significant effect of the compaction pressure on almost all the measured physical and mechanical responses, while the infiltration pressure and particle size affected the properties less significantly. The physical and mechanical properties of the produced foams are comparable to commercial open cell aluminum foams, which allows employing the current setup to produce foams for industrial applications. [ABSTRACT FROM AUTHOR]

In this paper, a power-law strain-dependent variable order is first incorporated into the fractional constitutive model and employed to describe mechanical behaviors of aluminum foams under quasi-static compression and tension. Comparative results illustrate that power-law strain-dependent variable order is capable of better describing stress–strain responses compared with the traditional linear one. The evolution of fractional order along with the porosities or relative densities can be well qualitatively interpreted by its physical meaning. Furthermore, the model is also extended to characterize the impact behaviors under large constant strain rates. It is observed that fractional model with sinusoidal variable order agrees well with the experimental data of aluminum foams with impact and non-impact surfaces. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Interpenetrating porous composite structures were prepared by in situ method. • Interfaces with partially metallurgical bonding enhance lobal mechanical properties. • The introduced reinforcement confined the expansion of cracks in composites. • Structural designing is feasible to enhance the mechanical properties of composites. Aluminum foam (AF) has extensive application prospects due to its high specific strength and specific energy absorption. However, low compressive strength and plateau stress of AF limit their total energy absorption. This study introduces a combined way of melt foaming and infiltration casting for fabricating bi-continuous interpenetrating porous composites (BIPCs), which formed partial metallurgical bonding interfaces while ensuring three-dimensional mechanical bond constraints. Four types of three-dimensional structures were designed to reinforce AF. Mechanical behavior of AF and the composites under quasi-static compression was analyzed by combining compressive tests and the finite element method (FEM). The results showed that all reinforcements can efficiently improve the energy absorption of composites by preventing the expansion of cracks in aluminum foam. The structure reinforced along the body diagonal and the path of the center lines connecting the three pairs of parallel surfaces of the cube exhibited the best mechanical properties, whose energy absorption, specific energy absorption and specific compressive strength were 9.58, 3.48 and 2.89 times greater than those of AF, respectively. The critical stress of the rods to buckling and stretching failure of the four configurations were calculated. Results showed that large critical stresses tended to appear in the 1/4 and 1/2 round rods, which revealed that the fracture failure easily occurred at the intersection edges of plane surface and curved surface of struts. [Display omitted] [ABSTRACT FROM AUTHOR]

A study on the use of chemical conversion coating as a preparative technique for foam-based structured catalysts, in the water gas shift reaction, is presented. The results showed a significant correlation between the textural properties of the structure and the preparation technique, highlighting how chemical conversion coating is a suitable technique for highly porous structures. In the first part of the paper, the performance of two structured catalysts obtained by coating commercial aluminium foams, with different porosity, was compared. The activity tests suggested that diffusion phenomena occurred in the case of the uncompressed foams. These results were confirmed by evaluating the performance of a catalyst obtained by coating a compressed 5 PPI pore size commercial aluminium foam, which showed much higher activity, at the same contact time, with respect to the catalyst obtained with the corresponding non-compressed foam. Finally, the performance of a catalyst obtained by coating an aluminium sponge, synthesized by the replication technique, was compared to that of a catalyst obtained by coating a compressed 40 PPI pore size aluminium foam. The higher activity of the sponge-based catalysts confirmed the dependence of the activity on the textural properties of the structure: X-ray computed tomography images highlighted the narrow distribution of the pore sizes and the presence of "bottleneck type" connections in the sponge structure, which are beneficial for the activity of the catalyst. [Display omitted] • Chemical conversion coating can be used in structured catalysts preparation. • The best coating technique depends on the textural properties of the structure. • The "bottleneck type" connections in replicated sponge favour the activity. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this work, SiC reinforced aluminum composite foams were successfully fabricated by laser melting deposition (LMD). The microstructure, energy absorption capacity, and compressive properties of Al/SiC composite foams were investigated systematically, and the results indicated that with increasing the content of SiC nanoparticles, the porosity and average pore size of aluminum foams decreased. Compared with the pure aluminum foams, the compressive strength and energy absorption of the Al/SiC composite foams increased by 43.8% and 16.0%, from 28.5 MPa and 55.5 × 10 ^6 J m ^−3 to 41.0 MPa and 64.4 × 10 ^6 J m ^−3 , respectively. The research indicates that SiC nanoparticles are effective additives to homogenize the pore size and enhance the mechanical performance of aluminum foams by the LMD method.

Aluminum foams are becoming potential materials for applications in several industrial fields, due to an intriguing combination of physical and mechanical properties. Their performances can be enhanced by using them as core of reinforced systems, like sandwich structures. Traditional reinforced foams usually present metal sheets or composite materials as skins, but these solutions are in contrast with some requirements of industrial applications, like lightness and high-temperature resistance. This work proposes an innovative single-step process, based on the powder compact melting technique, for the manufacture of aluminum foam panels reinforced by a steel wire mesh-grid, also acting as a mold. In doing so, problems of cost-effectiveness and flexibility typical of the conventional in-mold processes can be overcome on one hand and light-weight, high-temperature resistant aluminum foam sandwiches can be made on the other. A manufacturing campaign yielded the optimal foaming temperature for the production of the sandwich panels. In addition, mechanical tests highlighted the effectiveness of the mechanical coupling between the core and skin and a significant improvement of the bending load carrying capacity, compared with plain foam panels, of these innovative sandwiches. [ABSTRACT FROM AUTHOR]

The interesting properties of Al 6061 aluminum foams have boosted the research on the correlation between foam composition and morphology and its mechanical response under dynamic conditions. In this study, ingots of an Al 6061-T4 foam were sectioned and analyzed in order to determine their microstructural and morphological characteristics, and then quasi-static and dynamic tests (10−3 to 3 × 102 s−1) were carried out to determine the material mechanical behavior. Dynamic tests, carried out by using the split Hopkinson bar, highlighted that the studied foam is characterized by a very good energy absorption capability, due to its ductile behavior. Nevertheless, the conducted research showed that cell morphology and distribution affect its mechanical behavior in dynamic conditions in which localized cell collapse may result in a decreased energy absorption and efficiency of the foam.

Plasma electrolytic oxidation (PEO) treatment is carried out to improve the mechanical properties of the open-cell aluminum foams. Two different pore densities of open-cell aluminum foams (20 PPI and 40 PPI) were treated in an alkaline solution with a low silicate concentration at different current densities and times. The microstructure and phase composition of samples were investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. The coating thickness of the struts was increased with the increasing of treatment time. Ceramic coatings were composed of corundum, gamma alumina, and mullite phases. It was found that the compressive properties of the pore density of 20 PPI composite foams were significantly improved by using PEO treatment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highlights • A novel and efficient method to fabricate CNTs reinforced Al alloy matrix composite foams is put forward. • CNTs are homogeneously dispersed in the matrix. • The effects of CNTs on pore structure during foaming process is discussed. Abstract Uniformly dispersed carbon nanotubes (CNTs) reinforced aluminum (Al) alloy matrix composite foams were successfully fabricated by the combination of in-situ chemical vapor deposition and powder metallurgy using titanium hydride as a blowing agent. The effects of CNTs on the pore structure were systematically studied. The results showed that compared to the Al alloy foam, the introduction of CNTs could significantly improve the pore uniformity and reduce the pore size. As a result, the compressive property of composite foam had an obvious increase. The reasons for the enhanced pore structure mainly lie in that the CNTs increased nucleation sites for the decomposed hydrogen and the limited the movements of bubbles in the melt during foaming process. [ABSTRACT FROM AUTHOR]

In the present study, closed-cell aluminum foams with different percentages of erbium (Er) element were successfully prepared. The distribution and existence form of erbium (Er) element and its effect on the compressive properties of the foams were investigated. Results show that Er uniformly distributes in the cell walls in the forms of Al3Er intermetallic compound and Al-Er solid solutions. Compared with commercially pure aluminum foam, Er-containing foams possess higher micro-hardness, compressive strength and energy absorption capacity due to solid solution strengthening and second phase strengthening effects. Additionally, the amount of Er element should be controlled in the range of 0.10wt.%-0.50wt.% in order to obtain a good combination of compressive strength and energy absorption properties.

The processing of aluminum (Al) foams with maximum porosity of around 70 %, regular pore size and interconnected pores were successfully produced by means of the powder metallurgy method of Sintering Dissolution Process (SDP). The metal powder used for the present study was Al powder with 99.5 % of purity and diameters between 75 μm and 200 μm. The chosen Space Holder Particles (SHP) were spherical carbamide CH4N2O particles with diameters ranging from 1 to 2 mm. The optimum sinterization temperature was found at 620°C, at this temperature, a number of necks between Al particles surfaces were observed; indicating a good cohesion between Al particles, while keeping the porous structure of the green compact. The level of porosity was dependent of the carbamide content and the voids formed within the Al particles after the sinterization process. The sample with 60 wt.% of carbamide showed the lowest yield stress value than those for the samples with 40 and 50 wt.%. The strain values significantly increased when the carbamide content increased from 40 to 60 wt.%. Finally, the results obtained from a new sintering device for producing metallic foams at temperatures below 900°C are also discussed.

In the recent years, metal foams have become promising candidate materials in the engineering sector owing to their light weight and excellent energy absorption properties. Friction stir processing (FSP) has emerged as a cost-effective route to fabricate metal foam precursors from bulk substrates. Although the short processing time in FSP is able to provide high productivity, the cost of the foaming agent, TiH _2 in the case of aluminum foams is still high. This paper introduces flame heating to achieve localized foaming of aluminum alloy AA5754 to explore the possibility of using magnesium carbonate as a foaming agent stirred using multi-pass FSP. A specially designed slot based strategy using two plates arranged in lap configuration is devised to stir the foaming agent and understand the material movement after each subsequent pass. Microscopy techniques were carried out to evaluate the distribution of the foaming agent after each pass and the resulting microstructure of the processed plates as well as the morphology of the foamed sample. EDX results showed higher Mg and O content around the pore walls.

Various aluminum foams were fabricated with a structure comparable to the Terrapene carolina (box turtle) shell hierarchy as a synthetic means of attaining the lightweight, yet impact-resistive, nature of the biological counterpart. Each foam was constructed from a single aluminum alloy but with different morphologies and foam densities. By borrowing from the sophistication of biological design, the aluminum foams were shown to exhibit robust mechanical performance. High strain rate experimentation, via split Hopkinson pressure bar, was utilized to reveal the strain rate sensitivity of the foams as well as a metric to compare impact performance. The structure-property relations, necessary for accurate material modeling, were also characterized by way of optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and nanoindentation tests. The robust varying mechanical performance was attributed to the biologically inspired materials design.

This paper describes a new method for optimizing the cellular structure of AlMg4Si8 alloy foams manufactured via powder metallurgy. The cellular structure was improved by pretreating TiH 2 with a layer of Sn powder, which was then remixed with an AlMg4Si8 alloy used as the raw material for the preparation of the precursor. TiH 2 was completely encapsulated in the molten Sn at an early stage of foaming when the matrix alloy was still solid, so that liberated H 2 was fully captured when TiH 2 began to decompose. The interpore flow of H 2 along the cracks in the solid matrix was avoided, improving the utilization ratio of TiH 2 as a blowing agent. After determining that 4.0 wt% Sn cladding was capable of almost completely encapsulating 0.5 wt% TiH 2 , the final cellular structure was optimized and regular circular pores were obtained. [ABSTRACT FROM AUTHOR]

This paper deals with an experimental study of a turbulent forced convection in a rectangular channel partly fitted with aluminum metallic foam blocks. Experiments were carried out on samples having a constant porosity of 93.8%, different grades of 5, 20 and 40 PPI, and three different height ratios of 0.6, 0.8 and 1. The blocks were arranged in a baffle like configuration. A constant heat flux of 2 W/cm 2 was applied on the bottom wall of the test section, while air velocity was varied from 1 to 5 m·s −1 . Temperatures of the wall along the flow direction as well as those of the inlet and outlet sections have been measured. Additionally, pressure drop measurements across the aluminum foam samples were performed. The results showed that there is an optimal choice of the height and the grade of the metal foam for which the heat transfer and pressure drop (for an optimal design of heat exchangers) to reach the design goal. Moreover, this configuration was compared to solid fins aluminum baffles widely used in heat exchangers. [ABSTRACT FROM AUTHOR]

Quasi-static compression tests for a novel type of spherical cell porous aluminum prepared by the space-holder method were conducted. Formation and evolution mechanisms of deformation bands on the macro and micro scale were monitored and discussed by using a digital image correlation procedure. Effect of micro strain concentrations on the formation process and morphology of deformation bands at the macro level was analyzed in detail. In total three deformation modes of spherical cells and four failure modes of cell membranes including bending, shear, combined compression-shear, and eventually tearing were identified. [ABSTRACT FROM AUTHOR]

Efficient multi-path heat dissipation is urged to be designed for balancing the heat density generated in highly integrated electronic devices. Herein, aluminum foam/carbon composites were fabricated by chemical bath and annealing method to realize the effect of strengthening the effective thermal conductivity while retaining the convective heat transfer characteristics of the porous structure. The results show that the continuous and high crystalline carbon coating can be obtained in the optimized composites prepared with 350 g dopamine addition at 600 °C annealing temperature. When compared with amorphous carbon, the phonons in crystalline carbon can carry more energy during the heat transport in terms of high phonons density of states, and their scattering behavior can be alleviated. A smaller temperature gradient is further established in the system. Hence, a desirable thermal conductivity, 21.44 W m−1 K−1, is obtained in the optimized composites, which is almost 3 times that of pristine aluminum foam (7.67 W m−1 K−1). Additionally, the remarkable cooling efficiency of 24.71% in comparison to other studies, suggests that aluminum foam/carbon composites hold great potential as thermal management materials in addressing the issue of intense heat generation. [Display omitted] • Aluminum framework composites are prepared by chemical bath and annealing method. • Alleviated phonon scattering and larger MFP are observed in crystalline carbon. • High PDOS facilitates a rapid heat transport and a low temperature gradient. • Porosity inheritance and multipath design ensure the efficient heat dissipation. [ABSTRACT FROM AUTHOR]

Open-cell aluminum foams were manufactured by a sponge replication technique having a total porosity of ~90%. The influence of the thermal processing conditions such as atmosphere and temperature on the cellular structure, phase composition porosity, thermal conductivity, and compressive strength of the foams was studied. It was found that the thermal processing of aluminum foams in Ar at temperatures up to 800 °C led to aluminum foams with a reduced strut porosity, a lower amount of aluminum oxide, a higher thermal conductivity, and a higher compression strength, compared to foams thermally processed in air. These results were explained by the lower amount of aluminum oxide after thermal processing of the foams.

The favorable energy absorption characteristics of foam structures originate from their layer-by-layer deformation behavior. In this paper, the effects of cell morphology on the compressive performance of thin-walled aluminum foams were studied by a finite element method using a three-dimensional, thin-shell Kelvin tetrakaidecahedron model. Models with varying cell structure parameters were established so that the effects of relative density, cell size, cell wall thickness, and cell anisotropy on the plateau stress and energy absorption capacity of the foams could be investigated. Both the numerical deformation behavior and stress-strain curves of aluminum foams are found to have good agreement with the experimental results under quasi-static compressive loading. Moreover, the deformation behaviors of those foams with a certain anisotropy ratio are compared for different loading directions. The cell shape is a key factor affecting the plateau stress as well as the relative density. [ABSTRACT FROM AUTHOR]

This paper aims to demonstrate the thermodynamics of a thermal storage system based on the latent heat of a composite Phase Change Material (PCM). The paper investigates the flow and heat transfer of solid-liquid phase transitions at the pore level using the Lattice Boltzmann method. The phase transitions process is described using the enthalpy method. A porous medium at the pore scale is constructed here by binarization processing of photograph. The single phase change process is compared with phase transitions in porous media. The simulation results indicate that during the whole heat transfer process, the conduction effect dominates in porous medium composite phase materials while the convection effect has a remarkable influence on a single phase change process. A temperature difference is found between the aluminum foams and phase change materials. Phase transitions in pored aluminum with different porosity are also simulated to validate the feasibility of the enthalpy model at the pore scale. [ABSTRACT FROM AUTHOR]

In this study, finite element (FE) modeling of open-cell aluminum foams in tension was performed based on laboratory X-ray tomography scans of the materials at two different scales. High-resolution stitching tomography of the initial state allowed local intermetallic particles to be distinguished from internal defects in the solid phase of the foam. Lower-resolution scans were used to monitor the deformation and fracture in situ during loading. 3D image-based FE models of the foams were built to simulate the tensile behavior using a new microstructure-informed Gurson–Tvergaard–Needleman model. The new model allows quantitative consideration of the local presence of brittle intermetallic particles in the prediction of damage. It performs well in the discrimination of potential fracture zones in the foam, and can be easily adapted to any type of architectured material where both the global architecture and local microstructural details should be taken into account in the prediction of damage behavior.

In this research work, the effect of lateral loading (LL) on the crushing performance of empty tubes (ETs) and ex situ aluminum foam-filled tubes (FFTs) was investigated at 300 °C. The cylindrical thin-walled steel tube was filled with the closed-cell aluminum alloy foam that compressed under quasi-static loading conditions. During the compression test, the main mechanical properties of the ETs improved due to the interaction effect between the cellular structure of the foam and the inner wall of the empty tube. In addition, the initial propagated cracks on the steel tubes reduced considerably as a result of such interaction. Furthermore, the obtained results of the LL loading were compared with the axial loading (AL) results for both ETs and FFTs at the same temperature. The findings indicated that the application of loading on the lateral surface of the composite causes the lower mechanical properties of both ETs and FFTs in comparison with the axial loading conditions.

The present study investigated the accuracy of micro-scale finite element modeling for simulating broadband ultrasound propagation in water-saturated trabecular bone-mimicking phantoms. To this end, five commercially manufactured aluminum foam samples as trabecular bone-mimicking phantoms were utilized for ultrasonic immersion through-transmission experiments. Based on micro-computed tomography images of the same physical samples, three-dimensional high-resolution computational samples were generated to be implemented in the micro-scale finite element models. The finite element models employed the standard Galerkin finite element method (FEM) in time domain to simulate the ultrasonic experiments. The numerical simulations did not include energy dissipative mechanisms of ultrasonic attenuation; however, they expectedly simulated reflection, refraction, scattering, and wave mode conversion. The accuracy of the finite element simulations were evaluated by comparing the simulated ultrasonic attenuation and velocity with the experimental data. The maximum and the average relative errors between the experimental and simulated attenuation coefficients in the frequency range of 0.6−1.4 MHz were 17% and 6% respectively. Moreover, the simulations closely predicted the time-of-flight based velocities and the phase velocities of ultrasound with maximum relative errors of 20 m/s and 11 m/s respectively. The results of this study strongly suggest that micro-scale finite element modeling can effectively simulate broadband ultrasound propagation in water-saturated trabecular bone-mimicking structures. [ABSTRACT FROM AUTHOR]

Light aluminum closed-cell foams (4% relative density to solid aluminum) were experimentally studied in order to determine the added dynamic compressive strength facilitated by the trapped gas. A compression machine, an impact pendulum, and a shock tube were used to compress foam samples in strain rates varying from 10 −3 s −1 to 700 s −1 . Very similar results were recorded from the compression machine and the impact pendulum experiments. The shock tube results exhibited a significantly higher compressive strength. An experiment was designed to isolate the compressive strength contribution from the gas trapped inside the foams. It was shown that, in light aluminum foams, gas compression contributes the additional dynamic stress. It was also shown that, in the samples used in this study, gas compression caused as much as 50% of the dynamic compressive strength. An isentropic model was used to analytically explain the gas contribution to the dynamic compression stress recorded in the experiments. [ABSTRACT FROM AUTHOR]

An increasing interest in lightweight metallic foams for automotive, aerospace, and other applications has been observed in recent years. This is mainly due to the weight reduction that can be achieved using foams and for their mechanical energy absorption and acoustic damping capabilities. An accurate knowledge of the mechanical behavior of these materials, especially under dynamic loadings, is thus necessary. Unfortunately, metal foams and in general "soft" materials exhibit a series of peculiarities that make difficult the adoption of standard testing techniques for their high strain-rate characterization. This paper presents an innovative apparatus, where high strain-rate tests of metal foams or other soft materials can be performed by exploiting the operating principle of the Hopkinson bar methods. Using the pre-stress method to generate directly a long compression pulse (compared with traditional SHPB), a displacement of about 20 mm can be applied to the specimen with a single propagating wave, suitable for evaluating the whole stress-strain curve of medium-sized cell foams (pores of about 1-2 mm). The potential of this testing rig is shown in the characterization of a closed-cell aluminum foam, where all the above features are amply demonstrated. [ABSTRACT FROM AUTHOR]

The processing of aluminum (Al) foams with maximum porosity of around 70%, regular pore size and interconnected pores were successfully produced by means of the powder metallurgy method of Sintering Dissolution Process (SDP). The metal powder used for the present study was Al powder with 99.5% of purity and diameters between 75 μm and 200 μm. The chosen Space Holder Particles (SHP) were spherical carbamide CH4N2O particles with diameters ranging from 1 to 2 mm. The optimum sinterization temperature was found at 620°C, at this temperature, a number of necks between Al particles surfaces were observed; indicating a good cohesion between Al particles, while keeping the porous structure of the green compact. The level of porosity was dependent of the carbamide content and the voids formed within the Al particles after the sinterization process. The sample with 60 wt.% of carbamide showed the lowest yield stress value than those for the samples with 40 and 50 wt.%. The strain values significantly increased when the carbamide content increased from 40 to 60 wt.%. Finally, the results obtained from a new sintering device for producing metallic foams at temperatures below 900°C are also discussed. [ABSTRACT FROM AUTHOR]

The effects of microstructure on the thermal conductivity of open-cell structures are investigated using a numerical approach. They include sample size, cell arrangement, and non-uniformity of strut cross-sectional area. The approach combines the Laguerre–Voronoï tessellation method for generating volumetric digitalized foam samples and the finite-element method for solving the heat transfer problem and thus for computing thermal properties. It is shown that ( i ) the apparent thermal conductivity is size dependent for small sample volumes. The size effect becomes negligible when the volume element representing the sample contains more than nine cells along the edge side and we can refer to effective thermal conductivity. ( ii ) The non-uniformity of axial strut cross-sectional area causes a strong thermal resistance along the strut axis and consequently, a decrease of the effective thermal conductivity. And ( iii ) From comparison between regular Kelvin's cells and random monomodal cell structures, the arrangement of cells has little influence on the effective thermal conductivity of open-cell foams. This is explained by the similarity of their tortuosity values (skeleton tortuosity about 1.4). The suitability of the current approach for predicting effective thermal conductivity of open-cell foams is confirmed by the satisfactory agreement between numerical calculations and measurements over the porosity range 75–96%. [ABSTRACT FROM AUTHOR]

Metal foams are a new kind of materials with low densities and novel physical, mechanical, thermal, electrical and acoustic properties. They can be divided into closed and open cell structures. In this paper the open cell structures, called sponges, were treated. A new technique to manufacture sponges by plaster investment casting was described. Experimental results show that it is essential to make a sound plaster mould by casting plaster slurry into the polyurethane foams and infiltrate the open channels of the baked plaster mold by molten metal. The optimal processes include plaster slurry preparation, plaster mold baking, and molten metal infiltration. The sponge sample with porosity of 97% is presented.

• Ultrasonic technique was used to fabricate composite foam. • A small volume of MgAl 2 O 4 can satisfy the foaming and stability. • MgAl 2 O 4 p/Al composite foams have good energy absorption capacity. Composite aluminum foams, which are reinforced with submicron MgAl 2 O 4 generated in situ using different weight percentages of SiO 2 precursor (0.3, 0.5, and 0.7 wt%), were fabricated by stir casting and ultrasonic treatment (UT). Experimental results indicated that the microstructural constitution of all the foams prepared was composed of α -Al, MgAl 2 O 4 and Fe based intermetallics. More uniform pore distribution and better stability were achieved in the foams corresponding to maximum SiO 2 addition. The mechanical properties of the MgAl 2 O 4 p/Al composite foams were investigated by the quasi-static compression test. The plateau stress and energy absorption are enhanced with increasing SiO 2 addition. These are mainly due to the presence of submicron particles in the microstructure. [ABSTRACT FROM AUTHOR]

In this paper, a series of experiments were conducted to clarify the effects of the strain rate and inertia on the deformation behavior of closed-cell aluminum foams under impact. The quartz-crystal technique was employed to analyze the stress uniformity of aluminum foam samples under split Hopkinson pressure bar (SHPB) loading. It was revealed that the condition of stress uniformity is hard to reach for a thicker foam sample, and the strength of aluminum foam is sensitive to strain rate. Two different direct-impact Hopkinson pressure bar (DHPB) methods were introduced to validate the three deformation modes, i.e. homogeneous mode, transitional mode and shock mode. Results displayed that the stress at the front surface increased dramatically than that at the back surface as the impact speeds increased from 16 m/s to 113 m/s. The axial-inertia effect became more important than the strain rate effect under high speed impact. The dynamic deformation processes were recorded by a Phantom-675 camera and were analyzed through the digital imaging correlation (DIC) method. The deformation of aluminum foam in homogeneous mode was presented by the evolution of global distributed failure, but it was dominated by the local failure in shock mode. [ABSTRACT FROM AUTHOR]

To evaluate the effects of structural parameters on sound absorption performance of the aluminum foams with semiopen cells, a generalized regression neural network (GRNN) model has been utilized. In this paper, parameters of bulk density, static flow resistivity were analyzed. Results indicate that the effects of bulk density on sound absorption properties of the semiopen-celled foams are limited. On the contrary, the effects of static flow resistivity on absorption coefficients are complicated. When frequency is 500Hz, there has no significant relationship between static flow resistivity and sound absorption coefficients. When the frequency is higher than 1000Hz, with flow resistivity increasing, absorption coefficients of the aluminum foams increased significantly from 0.2 to exceed 0.8. However, when the static flow resistivity reaches 140kPas/m2, still increasing static flow resistivity could not improve the acoustic performance. Analysis revealed that the GRNN model provides a robust method for predicting acoustic absorption properties. [ABSTRACT FROM AUTHOR]

The bubble formation process at submerged orifices with different geometry is investigated in the preparation of aluminum foams by gas injection method. The bubble profile on a horizontal plate is calculated by quasi-static analysis through Laplace equation. The bubble formation process is then distinguished into three stages: nucleation stage, growth stage and detachment stage in wetting and less wetting conditions based on the force balance analysis. In addition, the bubble size at high Reynolds number is obtained by considering the contribution of buoyancy, pressure force, inertial force, drag force and surface tension based on the three stages of bubble formation. The bubble size is confirmed to be sensitive to the equivalent contact angle, which consists of two terms including the contact angle and the wedge angle. Therefore, the wedge angle is introduced in the design of gas outlet orifices for the purpose of decreasing bubble size generated. The experimental study is conducted at three different types of stainless steel orifices under constant gas flow rates (0.05-2 L/min). It is clarified that the orifice geometry and the orifice size are both responsible for the cell size of aluminum foams. The experimental results for three different types of orifices show a consistent trend with the theoretical predictions at various gas flow rates. In the design of orifices to generate small bubbles in the melt, the wedge angle that coordinates with the contact angle is thus suggested. [ABSTRACT FROM AUTHOR]

An increasing interest in lightweight metallic foams for automotive, aerospace, and other applications has been observed in recent years. This is mainly due to the weight reduction that can be achieved using foams and for their mechanical energy absorption and acoustic damping capabilities. An accurate knowledge of the mechanical behavior of these materials, especially under dynamic loadings, is thus necessary. Unfortunately, metal foams and in general “soft” materials exhibit a series of peculiarities that make difficult the adoption of standard testing techniques for their high strain-rate characterization. This paper presents an innovative apparatus, where high strain-rate tests of metal foams or other soft materials can be performed by exploiting the operating principle of the Hopkinson bar methods. Using the pre-stress method to generate directly a long compression pulse (compared with traditional SHPB), a displacement of about 20 mm can be applied to the specimen with a single propagating wave, suitable for evaluating the whole stress-strain curve of medium-sized cell foams (pores of about 1–2 mm). The potential of this testing rig is shown in the characterization of a closed-cell aluminum foam, where all the above features are amply demonstrated.

The split Hopkinson pressure bar (SHPB) is most widely used to measure the dynamic mechanical properties of materials. Such a testing methodology implies the assumption of uniform deformation during an impact test. However, the experimental verification of this assumption for aluminum foams has, as yet, been unreported. In this paper, a test system combining the SHPB with a high-speed digital camera was designed and constructed to study the problem. In the system, the synchronization between SHPB and the high-speed digital camera, the lighting, and the surface treatment of specimen are established. The deformation of meso-structure of aluminum foams during the SHPB impact was observed successfully; furthermore, the localized strains along the specimens were measured quantitatively. Experimental results show that the deformation is non-uniform; that means the assumption of uniform deformation for aluminum foam is not well satisfied. Therefore, a need exists for some modifications to characterize the dynamic mechanical properties of aluminum foams by SHPB. [ABSTRACT FROM AUTHOR]