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We have developed a synchrotron-based in situ X-ray micro-tomography facility for 3D imaging of material deformation under compression and tensile loads. In this report, we have discussed the details of this experimental facility, and as a case study, the quasi-static, elasto-plastic compression behavior of open-cell aluminum (Al) alloy foam is studied under in situ load conditions. Micro-tomography images obtained at different levels of compressive strains reveal damage kinetics of the cellular microstructure, observed in the form of strut bending and fracture, cell size reduction, shape distortion, cell wall collapse, etc. These morphological and structural changes are found to be closely correlated with specific variations in the stress–strain curve, which explain its macroscopic deformation behavior. The experimental stress–strain behavior is compared to a constitutive model for metal foams, and observed deviations are discussed for structure–property relations. [ABSTRACT FROM AUTHOR]

In recent years, metal foams have gained a lot of attention due to their distinctive physical, mechanical properties, and unique applications. Here, we fabricate magnesium base foam using viscose rayon fibers (VRFs) as a source of hydrogen by casting process at atmospheric pressure via the Gasar method. The chemical composition, pyrolysis of VRFs, and structure of magnesium foams are investigated in this study. By changing the amount of foaming agent from 0.4 to 2.2 wt%, the porosity rate changes from 10 to 52%. As the amount of foaming agent rises, the percentage of porosity first increases to a maximum and then remains almost constant, which can be due to the solubility of hydrogen in the magnesium melt. The highest obtained porosity is about 52% using 1.41 wt% of the foaming agent. The average diameter of the pores (in the range of 1.01–1.06 mm) shows no considerable change when the foaming agent amount is increased. As a result of this study, VRFs may serve as an effective foaming agent in fabricating magnesium foams to be used in load-bearing, weight-saving, and impact-absorbing structures. [ABSTRACT FROM AUTHOR]

In recent years, more attention to unique and complex structures, such as nature-inspired and porous structures for medical applications, has been strongly developed. Open-cell porous metal-based ones display more benefits than rigid ones since they facilitate the transformation of load between the bone and the implants and avoid the phenomenon of stress shielding and bone resorption. By being biodegradable and non-toxic, as well as having lower density and mechanical properties close to those of natural bone, Mg and its alloys are considered promising materials for porous scaffolds. However, a high corrosion rate is the main drawback of Mg alloys. The porosity of porous structures can also worsen it as it enhances the surface area exposed to the corrosive solution and negatively impacts the performance of porous structures, that these issues have not been addressed in detail so far. Since fabrication methods of Mg-based scaffolds can significantly affect the porosity-related properties (e.g., porosity percentage, type, size, and geometry) and, consequently, scaffolds' mechanical behavior and corrosion resistance, this paper reviews and compares the fabrication methods of porous structures and how they affect the resultant properties. However, among different methods, due to the expansion of additive manufacturing as a novel and exciting manufacturing technique, the paper's central focus is on using additive manufacturing in biomedical applications, discussing its advantages over other techniques. The effect of geometrical parameters on mechanical properties and corrosion rate, which strongly affects bio-application, are also given. Moreover, different strategies are briefly introduced for tailoring the high corrosion rate of Mg and its alloys, such as alloying elements and coatings. However, there is still less information regarding the additive manufacturing of porous Mg scaffolds and the optimum way of controlling the corrosion rate of Mg-based parts. [ABSTRACT FROM AUTHOR]

In this study, functionalized MOF (Azo@MOF-199) is prepared by introducing azo molecules into the pores of MOF-199 by vacuum assisted method, and the effects of the molecular structure of MOF material and its affinity with the modified material on the SO2 permeability and SO2/N2 selectivity of the prepared mixed matrix membrane are explored. The MOF-199 with higher porosity and specific surface area introduced in Pebax matrix has constructed rich SO2 transport channel, the –NH2 as SO2-facilitated groups and open metal sites in functionalized MOF increase the affinity to SO2. The SO2 adsorption capacity of Azo@MOF-199 reached 580 mg/g at 0 °C/Vis. The SO2 permeability and SO2/N2 selectivity of the prepared mixed matrix membrane are significantly improved, which are 3204.2 Barrer and 930, respectively. The prepared membrane has a long-term stability of more than 120 h. In particular, under different light conditions (UV and Vis), Pebax/Azo@MOF-199 membrane is used to investigate the SO2 separation process with light response, and the change of membrane properties caused by the change of light conditions is reversible. [ABSTRACT FROM AUTHOR]

Metallic foams are unique engineering materials with large pore volumes and an interconnected solid-metal structures. Lightweight, high-energy absorbing capacity and low thermal conductivities are some of the distinctive characteristics of metal foam that make them the preferred choice for many structural and functional applications. Although prevalent since 1940, the commercialization of metal foams has not achieved their full potential owing to large-scale production and near-net shaping limitations. In addition to technical challenges, mass production is hindered by to high manufacturing costs compared to those of ceramic and polymer foams. Depending on the pore structure, viz. open or closed, metal foams can be multifunctional, making them suitable for several conventional and niche applications. This review details the prevailing methods for fabricating closed metal foams, as well as their advantages and limitations. Apart from established methods such as gas injection and powder compaction, other emerging unconventional techniques for making metals, alloys and intermetallic foams are also discussed. The parameters that control the physical characteristics, such as the pore size and cell structure of the foam, are also explained. The standard characterization methods used to estimate various physical, mechanical, and thermal properties were reviewed. Applications and recent developments in closed foam research are presented here. [ABSTRACT FROM AUTHOR]

TiO2 photocatalyst has been adopted to abate typical pollutants, but the loading and immobilization of TiO2 on a low-cost and lightweight support will benefit the commoditization of this technology. In this work, TiO2 nanoparticles on porous metal foams were prepared by a facile infiltration and calcination for photocatalytic NO abatement. The porous structure of the Ni foam provided a sufficient contact of the photocatalyst with gaseous pollutants without severe blocking the penetration of photons. The calcination in air at 600 °C was found to impart an interdiffusion of NiO and TiO2 to form NiTiO3 and increase the adhesion of the particles on the support. The interdiffusion enhanced the NO removal efficiency under a LED lamp with photons > 400 nm, and this enhancement was more evident under photons > 450 nm. In the meantime, the composite was found to enhance the photocatalysis stability of TiO2 under ultraviolet photons that would annihilate the surface oxygen vacancies responsible for the photocatalysis of TiO2 under visible light. This demonstration provides a guideline in designing a practical photocatalyst for serving environmental needs. The porous nickel foam supported TiO2 nanoparticles prepared by infiltration and calcination was found to impart an interdiffusion of NiO and TiO2 with the higher surface area, stronger adhesion and stable photocatalytic performance of visible light for a continuous flow reactor. [ABSTRACT FROM AUTHOR]

Simply filling the metal foam as a thermally conductive filler into the polymer matrix can improve the thermal conductivity of the polymer matrix, but it still cannot greatly improve the thermal conductivity of the composites. In this paper, the epoxy resin/copper foam-nickel (EP/CF-Ni) composite thermal conductive material was prepared by a combination of electroplating and vacuum liquid impregnation. The deposition of nickel increases the heat dissipation area of the copper foam and at the same time widens the heat conduction path of the materials. By comparing EP/CF with different pores and EP/CF-Ni with different deposition times, it was found that the thermal conductivity of EP/CF-Ni composites could reach 5.215 W/(mK) at 7.3 wt% nickel deposition, which enhanced 2507% and 75% compared to pure epoxy and copper foam matrix composites, respectively. The deposition of nickel further improves the wear resistance of the composite. This experiment reveals the synergistic effect of thermal conductivity of metallic Ni and 3D copper foam, and provides some reference opinions for the field of thermal conductivity of metallic foam. [ABSTRACT FROM AUTHOR]

This paper reports the synthesis and the performance of polymer-derived ceramic filters for molten metal filtration. Two different filter types were studied: foam filters produced from flexible polyurethane (PU) foams and additive manufacturing (AM) filters produced from thermoplastic polyurethane (TPU) cellular structure, and the results from all filter types were compared with that of the commercially used SiC foam filters. In both cases, the urethane-based polymeric template was impregnated with the preceramic solution, followed by pyrolysis. The produced ceramic components were then used to filter a molten Al alloy (A357), and the resulting Al samples were characterized for their mechanical properties. When filters were used, more reproducible and reliable mechanical properties were achieved compared to the samples obtained without any filtration. Among the different filters tested, the foam filters demonstrated better performance in comparison with the AM ceramic filters due probably to the three-dimensional interconnected porosity compared with the unidirectional cellular structure of the AM ceramic filters. [ABSTRACT FROM AUTHOR]

Nanoporous metallic foams (NMFs) of Cu, Cu–Zn, and Cu–Ni alloys with relative densities between 0.5 and 14% were created by polymer templating followed by thermal treatments for calcination and reduction. The mechanical strength of NMFs can be dominated by chemistry and morphological parameters, including the relative density, ligament size, and chemistry. An analysis by Pearson correlation coefficients found the predominant factors in the strength, as measured with nanoindentation, of the alloys NMFs were largely controlled by the relative density. The modulus of a Cu75Ni25 alloy with a relative density of 14% was 57% greater and its hardness was 64% greater than the same alloy with a 0.5% relative density. When foams with similar ligament size and relative density but different chemistries were compared, second phase particles in the form of ZnO in Cu–Zn alloys strengthened NMFs alloys significantly more than solid solution strengthening in Cu–Zn or Cu–Ni alloys. This suggests solid solution strengthening will have limited effectiveness in increasing the strength of NMFs, and precipitation hardening should be more impactful in creating stronger NMFs. [ABSTRACT FROM AUTHOR]

Porous degradable metallic biomaterials are attracting considerable attention as promising bone implant materials. Recently, the interest in developing new biomaterials with enhanced performance stimulates the widespread development of fabricating techniques for porous metals. In this work, the recent progress and novel trends on preparation methods of metallic foams for biomedicine were systematically reviewed. The common synthesis methods for porous Mg, Fe, Zn, and their alloys intended for orthopedic applications are comprehensively discussed and compared. The advantages and disadvantages of relevant manufacturing strategies are evaluated. While the modern techniques enable fabrication of complex porous structures and customized shapes, the cost-effective and easy controllable approach are major benefits of traditional methods. Main structural characteristics and properties of biomaterials fabricated using different routes are also presented. Furthermore, the future research directions and current challenges are mentioned. The ambition of this review article is to provide useful guidelines for researchers to choose suitable manufacturing technique to prepare materials with desired structural topology and mechanical, and degradation properties. [ABSTRACT FROM AUTHOR]

Liquid metallic films are the constituting elements of metallic foams and are governed by a complex interplay between the liquid—here aluminium alloys—, the film stabilising solid particles contained in the melt, and the gas phase. We use synchrotron X-ray radioscopy to study particle dynamics and analyse particle motions by applying novel image processing techniques. We find that particles move alone and as clusters. They may move permanently with the melt or can be trapped by the film surface and subsequently even de-trapped again. The aim of this work is to observe interactions between particles or particle clusters and the film surfaces, and to understand how liquid flow in films is reduced and film stability increased by such particles [ABSTRACT FROM AUTHOR]

To develop good rate capability and good cycle stability electrode, hierarchical porous coral-like ZnO/ZnCo2O4/Co3O4 coating was fabricated on a novel 3D straight-through layered copper current collector with one-step solution combustion method and used as self-supporting anode for lithium-ion batteries (LIBs). The coral-like ZnO/ZnCo2O4/Co3O4 coating facilitated the full penetration of the electrolyte and increased the activation rate of the active material. Also, the novel 3D copper current collector has an increased surface area compared to a traditional foam metal, providing an optimal structure for balancing the volume-change tolerance and the energy density of the porous electrode. In addition, the highly oriented structure favors the effective transport of electrons and Li ions within the 3D electrode. As a consequence, high reversible capacity of 1428 mAh g−1 at a current density of 200 mA g−1 after 100 cycles and excellent rate capability of 682 mAh g−1 at 1000 mA g−1 were achieved. This study provides a facile and scalable path toward high-performance self-supporting electrodes for LIBs and demonstrates that the volume density of self-supporting electrodes can be enhanced by increasing surface area of the 3D structured current collector. [ABSTRACT FROM AUTHOR]

The aluminum alloy AA5083 is a technologically important structural alloy as it is lightweight, with outstanding weldability and formability, moderate corrosion resistance and strength, making it suitable for a wide range of marine and transportation applications. In the present study, AA5083/nano-γAlO composite metal foam was fabricated using a friction stir processing route (FSP). More precisely, the paper presents a first attempt to use grooves for the integration of the foaming and stabilizing agent on the metal foam precursor by FSP. The implementation of grooves allows to control the amount of foaming, integrates the stabilizing particles within the precursor and permits the production of localized metal foams. Unlike the commonly used manufacturing processes, only one plate is required for the production of the precursor sample in the proposed process. Therefore, this process can be easily implemented in the industrial sector. Furthermore, γ-AlO nanostructured reinforcement, which is characterized by increased interfacial energy, was utilized as a stabilizing agent. The precursor specimens were manufactured by mixing blowing agent powder (0.4% w/w TiH) and stabilization agent nanopowder (2% w/w γ-AlO) into the 5083 aluminum alloy matrix using FSP. The effects of the number of FSP passes and the foaming conditions (holding temperature and time) on the pore density, morphology and distribution were investigated. The microstructure and porosity evolution of the so-obtained metal foam was also examined and analyzed. Results indicate that, following the foaming procedure, a porosity of 60% and an equivalent pore diameter ranging from 0.2 to 3.3 mm can be achieved. Moreover, the microstructure was found to be closely related to microhardness distribution perpendicular to the traversing direction of the FSP tool for both precursor and foamed specimens. [ABSTRACT FROM AUTHOR]

Honeycomb-like NiMoO with nanosheet arrays is grown on reduced graphene oxide, which is supported on Ni foam having successfully fabricated by a simple hydrothermal treatment followed by a calcined process. In the as-synthesized Ni foam@reduced graphene oxide@NiMoO, Ni foam served as 'skeleton' to support reduced graphene oxide and reduced graphene oxide directly grown on Ni foam served as the 'skin' to provide high passway of electrons and ions, which simultaneously accommodated the volume change during the process of charge-discharge and NiMoO acted as active substance to provide high areal capacitance. It shows a high areal capacitance of 2165.9 mF cm at a current density of 1 mA cm and long cycle stability with 93.8% capacitance retained over 1000 charge-discharge cycles. Moreover, an asymmetric supercapacitor has been constructed by using Ni foam@reduced graphene oxide and Ni foam@reduced graphene oxide@NiMoO as negative and positive electrodes. The energy density of this asymmetric supercapacitor is 0.579 mWh cm, and it retains 93.1% capacitance over charge-discharge 5000 cycles. Therefore, it reveals great promise for practical applications in energy storage devices. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) porous CoMnO thin films on nickel foam substrates were successfully prepared via electrostatic spray deposition (ESD) technique and then an annealing process for lithium-ion battery anodes. The CoMnO thin films exhibited high initial coulombic efficiency of 90% and excellent cycling performance with a reversible capacity of over 1366 mAh g after 100 cycles at a current density of 400 mA g. The improved electrochemical performances are attributed to the synergistic advantages of 3D porous CoMnO film and the Ni foam collector, which can provide effective void space to the large volume change during cycling, enhance reaction sites, and improve the electron transport. The ESD technique is facile and cost-effective and can be used as a promising method to synthesize 3D porous mixed transition-metal oxides materials. [ABSTRACT FROM AUTHOR]

The present study focuses on the relationship between structure and mechanical properties in nanoporous (NP) metal foams. Experimental and numerical findings suggest for NP Au and single gyroid structures similar topological features. In particular, NP Au and single gyroids are shown to exhibit almost coincident form factors, defined as a function of specific surface area and ligament thickness. Furthermore, nanoindentation of NP Au and uniaxial compression of polymeric single gyroids with comparable relative density of about 0.3 result in almost overlapping relative Young's moduli. Surface topology and elastic deformation behavior allow considering single gyroids as approximants of the NP Au structure. Consequently, it can be also expected that NP Au and single gyroids undergo similar local deformation mechanisms. These do not involve pure bending of ligaments, but rather a combination of shear and torsion components. [ABSTRACT FROM AUTHOR]

NiCoS-based nanostructured films have been grown directly onto nickel foams by a facile two-step method, involving the growth of NiCo-precursor and subsequent conversion into NiCoS via a sulfidation process, with the aid of sodium dodecyl surfactant (SDS). This synthesis method enables the fabrication of binder- and conductive additive-free electrodes for supercapacitors. The influence of the surfactant on the crystal structure, morphology, and electrochemical performance of the electrodes has been investigated. The NiCoS-SDS films exhibit a complex cellular and hierarchical porous structure, which are different from NiCoS-pure films with nanotube arrays structure. Moreover, the electrochemical tests show that the NiCoS-SDS nanostructured electrode exhibits an ultrahigh specific capacitance of 2519 F g at 0.5 A g, which doubles that of the NiCoS-pure nanotube arrays electrode. In addition, the NiCoS-SDS electrode exhibits excellent cycling stability with 90.7 % capacitance retention at 10 A g after 8000 cycles. In view of the low cost and superior electrochemical performance, the NiCoS-SDS electrodes are promising electrode materials for high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

The development of selective-wettability surfaces of porous materials is important for oil spill cleanup. A new type of oil-water separation material has been prepared through a three-dimensional (3-D) extension of a biologically inspired two-dimensional (2-D) material. In this, a simple solution-immersion method is used to construct a super-oleophilic and super-hydrophobic surface on the metallic skeleton of a copper foam, onto which a nanosheet structure is formed that differs greatly from previous nanoscale needle-based materials. This 3-D copper foam is demonstrated to be capable of supporting a maximum height of accumulated water of 5.5 cm prior to oil wetting and 1.5 cm after oil wetting. Furthermore, the foam is capable of efficient oil-water separation, despite losing its super-hydrophobicity during the process. This has given important new insight into the mechanism of separation, in that super-oleophilicity is clearly important to achieving good separation. The selective-wettability of this porous metal foam is expected to extend the range of metal-based oil-water separation materials from 2D metal meshes to more complex 3-D metal structures. [ABSTRACT FROM AUTHOR]

Aluminum-substituted α-Ni(OH) nanoflakes grown on nickel foam as electrode for application in supercapacitor were synthesized in the presence of urea through a hydrothermal route. The as-synthesized nanoflakes with ultra-thin thickness of about 12 nm presented isolated state on Nickel foam. The sample substituted with 9.8 % Al showed the highest specific capacitance of 3637 F g at scan rate of 5 mV s in 3 M KOH aqueous solution. This sample also kept high specific capacitance of 1142 F g at high charge and discharge current density of 32 A g. The excellent electrochemical performance can be ascribed to the thin thickness and isolated state of these nanoflakes. The two characteristics of nanoflakes guaranteed their full contact with electrolyte during the electrochemical reactions, therefore leading to the instant and full utilization of electroactive material. During stability test, the capacitance of material still remained 81 % after 2000 charge-discharge cycles. These results demonstrated that the nanoflakes could be applied as high performance electrode material in supercapacitor. [ABSTRACT FROM AUTHOR]

Sintered reaction-bonded silicon nitride (SRBSN) foams with very high porosity levels of up to 85 vol% and pore interconnectivity have been fabricated in this study. SRBSN foams were fabricated based on gel-casting of Si-PMMA suspensions followed by nitriding and sintering. The addition of MgO and YO-AlO as sintering additives resulted in significant changes in the foam microstructure. Small amounts of MgO completely prevented the whisker-forming reactions during nitridation while the addition of YO-AlO could not prevent whisker formation during nitridation. It was observed that regardless of the sintering aid system, SRBSN foams were whisker-free and revealed high pore interconnectivity after sintering. The SRBSN foam struts were only composed of β-SiN grains embedded in an intergranular amorphous phase. [ABSTRACT FROM AUTHOR]

Nanostructured manganese dioxide (MnO) is deposited on nickel foams by a hydrothermal synthesis route. As-deposited MnO thin films are largely amorphous. Facile post-deposition annealing significantly improves the electrochemical performance of the MnO thin films via changing their morphology, phase, and crystallinity. The specific capacitance of the MnO electrode increases with the annealing temperature and reaches an optimal value of 244 F g (at the current density of 1 A g) in a neutral 1 M NaSO electrolyte for a specimen annealed at 500 °C. Furthermore, when an alkaline 5 M KOH electrolyte is used, an exceptionally high capacitance of 950 F g is achieved at the current density of 2 A g. The cost-effective facile synthesis, high specific capacitance, and good cycle stability of these MnO-based electrodes enable their applications in high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

The low stability and complicated fabrication procedures seriously hindered practical applications of superhydrophobic and superoleophilic materials. Here, we present a simple method for preparing the novelly three-dimensional material based on commercially available nickel foams functionalized with electrodepositing of sub-micrometer polypyrrole (PPy) particles, followed by modification of low-surface-energy material such as fluoroalkylsilane (FAS), which can efficiently separate oils and organic solvents from water. The formation of nanostructured surface roughness of PPy onto the nickel foam by combination with FAS modification would contribute to the excellent superhydrophobic and superoleophilic performance, as is the evidence of the water CA of 155° and oil CA of ca. 0° for FAS-treated PPy foam. As a separating membrane, organic solvents and oils could be easily removed without obvious absorption of water, which has great potential over traditional treatment techniques and is of technological significance as a promising and efficient absorbent material for separation of organic contaminates and oils from water. [ABSTRACT FROM AUTHOR]

The influence of oxides on the stabilisation of zinc foam made by foaming-compacted powder mixtures has been investigated by varying the oxide content in the zinc powder used by oxidation and reduction. Optical, scanning electron and transmission electron microscopy as well as energy dispersive X-ray mapping were used to determine the oxide distribution, morphology and structure in the foams. The study revealed that with increase in the oxide content of the foam, the maximum expansion and expansion rate increased. Small amount of nano-sized oxide particles and their cluster, which are randomly distributed, were observed within the bulk of foam. But the major fraction of oxides is observed on the surface of pores in the form of clusters. These clusters are distributed uniformly all over the surface. Effect of these oxides on the stability of foam is discussed. The formation of satellite pores, which is characteristic signature of zinc foams, and their stability, is investigated. [ABSTRACT FROM AUTHOR]

Particle coverage ratio on bubble interface was investigated by metallographic analysis when the foam is critically stable in the gas injection foaming process. It is found that the critical coverage ratio was almost the same under different conditions, such as different particle amount, particle size, or particle wettability. The particle coverage ratio is proposed as the criterion to judge the foam stability, and a criterion equation was deduced. Adsorption coefficient of particles, effective coverage ratio of a particle and critical coverage ratio on the bubble interface are stability influencing parameters of the criterion equation. Their determination methods were presented and examined by air injection foaming of A356/AlO melt. The adsorption coefficient calculated by measuring cross-section of foam cell wall gave values agreeing with the experimental results. The effective coverage ratio, which is about 0.9 in this article, can be calculated by combining measurements on surface and on the cross-section of the foam cell wall. The critical coverage ratio, that is about 14% in this article, can be determined by measuring the cross-section as well as the surface of the foam cell wall. [ABSTRACT FROM AUTHOR]

Aluminium foams have been recently proposed as filling reinforcements to improve impact behavior of hollow components used as protection systems in vehicles. In this study, aluminium foam filled stainless steel tubes have been prepared by directly foaming metal powder compacts inside the tubes. Attention was concentrated on the interface phenomena that characterize the core–shell interaction and the process parameters determining the metallurgical reactions between the two alloys. The formation of binary and ternary intermetallic compounds was observed at the aluminium/steel interface whenever the growth of the oxide layer on the foam surface in foaming was constrained. Compression tests of the reinforced tubes confirmed a maximized energy absorption in coincidence with the formation of the interface bonding. In those cases, extended foam intrusions into compressed tube folds were observed. The microstructural investigation revealed that in the transition zone the intermetallic layer strength was comparable to that of the foamed matrix. [ABSTRACT FROM AUTHOR]

Compressive properties of a new hybrid material, fabricated through filling of an aluminum foam with a thermoplastic polymer, are investigated. Static (0.01 s−1) and dynamic (100 s−1) compression testing has been carried out to study the behavior of the hybrid material in comparison with its parent foam and polymer materials. Considering the behavior of metal foams, the point on a compressive stress–strain curve corresponding to the minimum cushion factor is defined as the “densification” point. The analysis of the stress–strain curves provides insight into the load carrying and energy absorption characteristics of the hybrid material. At both strain rates, the hybrid is found to carry higher stresses and absorb more energy at “densification” than the foam or polymer. [ABSTRACT FROM AUTHOR]

Compression testing of cellular sandwich core materials is often complicated by the presence of edge effects, in which the cells on the outside of the specimen deform at lower stresses than those in the bulk. As a result, minimum specimen length-to-cell-size ratios have been established in the literature for metallic foams. Periodic cellular metals (PCMs) are a recently developed class of materials that have received considerable interest due to their greater architectural efficiency and enhanced mechanical properties compared to conventional metal foams. In this study, edge effects of PCM core materials have been measured in compression using a new test platform which evaluates the properties of the core as a stand-alone material. This approach introduces uniform and periodically rigid boundary conditions to the PCM nodes, resulting in the same inelastic buckling failure mechanism that occurs in reference PCM sandwich panels. Edge effects were comparatively small and samples down to 2 × 2 unit cells were found to be representative of bulk-like cores. [ABSTRACT FROM AUTHOR]

The effect of artificial aging on the compression yield strength of an open-cell AA6101 foam is studied using both experimental and modeling approaches. Isothermal calorimetry is used to analyze the precipitation kinetics of the foam. The modeling work combines the established approaches for predicting the yield strength of open-cell metallic foams as a function of the relative density and normalized strength, as well as the age hardening behavior of AA6101 alloy. The foam yield strength is related to the evolution of precipitate content during aging and is modeled for artificial aging at 180 and 220 °C. It is shown that the model predictions match very well with the experimentally determined yield strength values. The overall results suggest that the presented analytical and modeling approaches can effectively be used to predict the precipitation hardening behavior and/or optimize processing and properties of AA6101 foams. [ABSTRACT FROM AUTHOR]

Taguchi methodology has been applied to the production process of aluminium foams to investigate the variability detected in several properties (including bulk density, outward appearance and density homogeneity along foaming direction), for foaming tests carried out under identical conditions. The analysis of the process has been performed separately for two different alloys, the 4045 and 6061. The results have allowed finding the main factors that influence those properties. In addition, it has been possible to establish those foaming conditions able to minimize the variability in density, to improve the outward appearance and to obtain a higher homogeneity in density, all at the same time. Different final factors have been found for the two alloys; such differences have been explained in terms of the different viscosity of the aluminium melts as well as the different content of foaming agent. [ABSTRACT FROM AUTHOR]

Sandwich panels comprising metallic foam cores fail by localized indentation when subjected to impact and blast loads. In this paper the indentation response of aluminum foams with face sheets, whose behavior represent elastic, elastic–ideally plastic and elastic–plastic strain hardening, were investigated experimentally under quasi-static loading conditions. The tests were carried out using flat and hemispherical indenters made of stiff tool steel on the blocks of aluminum foam with and without face sheets. Thickness of the face sheets was varied from 0.5 mm to 1.0 mm to evaluate the thickness effect on the indentation behavior. Competing failure modes for the initiation of failure are discussed. Results show that the indentation behavior is strongly dependent on the type and thickness of the face sheets used. [ABSTRACT FROM AUTHOR]

Military and civilian structures can be exposed to intentional or accidental blasts. Aluminum foam sandwich structures are being considered for energy absorption applications in blast resistant cargo containers, ordnance boxes, transformer box pads, etc. This study examines the modeling of aluminum foam sandwich composites subjected to blast loads using LS-DYNA software. The sandwich composite was designed using laminated face sheets (S2 glass/epoxy and aluminum foam core. The aluminum foam core was modeled using an anisotropic material model. The laminated face sheets were modeled using material models that implement the Tsai-Wu and Hashin failure theories. Ablast load was applied using the CONWEP blast equations (*LOAD_BLAST) in LS-DYNA. This paper discusses the blast response of constituent S2-glass/epoxy face sheets, the closed cell aluminum foam core as well as the sandwich composite plate. [ABSTRACT FROM AUTHOR]

The quality of thermosetting polymer foams (like polyurethane foam, used for example in automotive industry) mainly depends on the manufacturing process. At a mesoscopic scale, the foam can be modelled by the expansion of gas bubbles in a polymer matrix with evolutionary rheological behaviour. The initial bubbles correspond to germs, which are supposed quasi-homogeneously distributed in the polymer. An elementary foam volume (∼1 mm3) is phenomenologically modelled by a diphasic medium (polymer and immiscible gas bubbles). The evolution of each component is governed by equations resulting from thermodynamics of irreversible processes: the relevant state variables in gas, resulting from chemical reaction creating carbon dioxide (assimilated then to a perfect gas), are pressure, temperature and conversion rate of the reaction. The number of gas moles in each bubble depends on this conversion rate. The foam is considered as a shear-thinning viscous fluid, whose rheological parameters evolve with the curing reaction, depending on the process conditions (temperature, pressure). A mixed finite element method with multidomain approach is developed to simulate the average growth rate of the foam during its manufacture and to characterize the influence of the manufacturing conditions (or initial rheological behaviour of the components) on macroscopic parameters of the foam (cell size, heterogeneity of porosity, wall thickness). [ABSTRACT FROM AUTHOR]

SEM and EDS measurements were used to scrutinize the microstructure of Duocel open cell 6101 aluminum foam in relation to its fracture properties. In-situ SEM tensile tests on the open cell aluminum foam were performed to investigate the different fracture modes of struts and Aramis/Digital Image Correlation software was used to map the strain in individual struts. Observations during tensile tests showed that the microstructure of the struts has a great influence on the fracture behaviour of the foam. In particular AlFeSi-precipitates, which are due to the casting of the 6101 aluminum alloy, and the morphology of the foam alters the fracture mode of the struts in the foam from transgranular to intergranular. Less energy is needed for intergranular fracture of struts and the strain to failure of the foam is decreased due to weak individual struts. [ABSTRACT FROM AUTHOR]

Two closed cell aluminium foams and one open cell nickel-chromium foam were subjected to microstructural characterization, in situ fracture tests and fractography. The failure process of the open cell foam was observed to be rather ductile, while that of the closed cell foams was found to be brittle. The ductility was related to the purity of the nickel chromium alloy, resulting in necking to be the dominant source of energy dissipation during failure. The brittleness of the closed cell foams was related to the presence of precipitates and particles in the cell wall microstructure, limiting the amount of plastic dissipation. The embrittling phases were traced back to the alloy composition, viscosity enhancing additions and foaming agent. [ABSTRACT FROM AUTHOR]

Techniques for making metal cellular structures have been successfully developed to commercialize aluminium and nickel foam. Work to extend these methods to create steel and titanium foams is well advanced. The question arises: in which applications might they find success? Here we apply a general methodology for exploring potential applications to answer this question. [ABSTRACT FROM AUTHOR]

A possible classification of cellular solids can be made based on the dimension into honeycombs and foams. In numerical simulations 2D models that are employed primarily to study honeycombs can also be used to model open-cell foams. Thereby, a loss of information regarding the 3D connectivity of the microstructure is involved. To answer the question how the missing third dimension in 2D models affects the overall properties, spatially periodic 2D and 3D model foams are adopted. From the point of homogenisation, a strain-energy based scheme is used for adequately determining the effective mechanical properties at large strains. The key idea behind this method is to use directly the equivalence condition between the meso-strain energy and the macro-strain energy. In a first step a representative volume element with the given microstructure and a corresponding volume element containing the effective medium are subjected to equivalent states of deformation. Subsequently, the macroscopic stress-strain relationships are determined by volume-averaging of the stored strain energy. The results of some fundamental loading cases indicate that both model foams represent the deformation characteristics of hyperelastic solid foams like localized bending and elastic buckling. In addition, the development of anisotropy due to microstructural changes at large strains can be traced with both model foams. Nevertheless, the different cell morphology affects the stress-strain curves in a quantitative manner. [ABSTRACT FROM AUTHOR]

Computational Fluid Dynamics (CFD) was used to compute the air-flow permeability K for laminar flow, for wet Kelvin foam models, as a function of cell size and cell face hole size. The predictions were compared with experimental data for a range of open-cell polyurethane (PU) foams. This suggests that the foam permeability is a function of the area of largest hole in the cells. The predictions are almost the same as those for dry Kelvin foams, showing that the face hole size and cell size are the main factors that determines foam permeability. [ABSTRACT FROM AUTHOR]

A method of constructing the deformation mechanism maps of open-cell foams is proposed. Starting with the deformation behaviour of the constitutive material and taking account of foam geometry, we are able to determine the dominant deformation mechanisms in the foam as a function of the temperature and the applied-stress. The influences of cell-size, cell-strut shape and scales in the microstructure are studied. The model is applied successfully to the experimental results available for open-cell pure nickel foams. [ABSTRACT FROM AUTHOR]

Aluminium foams obtained by injecting a gas into the liquid metal are prone to localization of strain and damage. Under compression, crushing bands form, multiply and propagate through the whole sample. A continuum model based on a compressible plasticity framework is presented that is suitable for the simulation of such strain localization bands. The importance of accounting for strain localization phenomena in structural computations is illustrated by finite element simulations of the compression of cube and tapered specimens, and of an indentation test. A regularization procedure is proposed to obtain mesh–independent results. [ABSTRACT FROM AUTHOR]

A process has been developed for obtaining closed cell metallic foams using a ceramic foam precursor. In the present study, the major constituent of the ceramic foam precursor was iron oxide (Fe2O3), which was mixed with various foaming/setting additives. The mixture set rapidly at room temperature, stabilizing the foam generated by hydrogen release. The oxide foam was then reduced by annealing at 1240∘C in a non-flammable hydrogen/inert gas mixture to obtain a metallic foam with a relative density of 0.23 ± 0.017, and an average cell diameter of 1.32 ± 0.32 mm. The iron foams were tested in compression and yielded an average compressive strength of 29 ± 7 MPa. The compressive stress-strain curves obtained were typical of cellular metals. The normalized strengths of the metal foams obtained in the present study compare favorably with those of steel foams produced by other techniques. [ABSTRACT FROM AUTHOR]

Al foams have been manufactured via a PM route and compression tested. Testing has shown that density-properties relationships can be constructed which are then valid for the prediction of mechanical response for a sample of given density. The scatter in the density can also be used to predict, with reasonable confidence, the scatter in properties. Testing has shown that little or no difference in processing time can give rise to foams with significantly different densities and hence an undesirable, but nevertheless quantifiable and predictable, scatter in mechanical properties. This demonstrates the sensitivity of the very rapid foaming process and highlights the requirement for improving foam stability. The mechanical response of foams with similar densities is, however, reproducible suggesting that this is a more suitable way in which to control the process rather than by fixing the foaming time. [ABSTRACT FROM AUTHOR]

Metal foams were produced by means of the powder compact melting technique. Specimens were made of a wrought aluminium alloy similar in composition to AA 6061. A part of the samples was subjected to a precipitation hardening treatment after foaming, others were left in the state “as foamed”. Cyclic tests were then carried out under compressive stresses. S-N curves of untreated and heat-treated foams are compared. Values for fatigue strength were estimated and compared to the static strength found for comparable specimens. As a reference system with a brittle failure mode foams based on the aluminium casting alloy AlSi7 are examined. [ABSTRACT FROM AUTHOR]

Metallic foam-filled tubes and their empty counterparts have been tested at quasi-static and dynamic strain rates in order to determine their energy absorption capabilities. Data from the Split-Hopkinson Pressure Bar have been used to generate force vs. displacement curves that are somewhat analogous to pseudo-engineering stress-strain curves. Force balance calculations have also been made. These results indicate that, on an equal weight basis, foam-filled tubes offer greater energy absorption capability than empty tubes at quasi-static strain rates. However, the benefit of foam filling does not appear to be extended to strain rates of the order of 200–500 s−1. Force balance calculations are shown to have potential as a method for monitoring the crushing of metallic foams at high strain rate. [ABSTRACT FROM AUTHOR]

“Mimetic” molecular composites can be viewed as hybrids of conventional and “molecular” composites, and are prepared from a matrix and reinforcing fiber consisting of a single polymer composition. The aim of the work was to obtain a good chemical, physical and thermal property match at the interface for an overall excellent balance of composite properties. Kevlar® aramid 49/poly(p-phenyleneterphthalamide, an all-PPD-T† composite, was used as a model system in the work, and, in theory, should be ideal for testing the merit of the “mimetic” molecular composite concept. The key to the successful preparation of all-PPD-T infusible composites was the acid catalyzed thermal transformation of a fusible precursor, poly(N,N′-di-sec-butyl-p-phenyleneterephthalamide), into PPD-T. The composites were prepared by embedding Kevlar® aramid 49 fibers in poly(N,N′-di-sec-butyl-p-phenyl-eneterephthalamide) resin, which, on heating in the presence of benzene sulfonic acid catalyst, dealkylated to a PPD-T matrix. In this way, Kevlar® aramid 49/PPD-T(8/92 to 40/60 v/o) composites with densities in the range of 0.2 to 1.2 g cm−3 (versus ∼1.4 g cm−3 for a fully consolidated PPD-T composite) have been prepared and their thermal and mechanical properties characterized. Some of the foamed composites prepared in this work bear a remarkable resemblance to wood, a natural fiber reinforced foam composite, but with the advantages of flame and rot resistance. [ABSTRACT FROM AUTHOR]

Determines the effect of bonding strength on the comprehensive mechanical behavior of aluminum (Al) foam-filled cylindrical tube. Improvement of energy absorption in Al-Si foam-filled square tubes; Observation of a minimal difference in the flow of metal into the lobes for the foam-filled tubes with different bonding methods; Little effect of bonding strength on the energy absorbed during compression of the hybrid system despite the various fabrication methods employed.