Open-cell Foams Research Articles

Enhanced sound absorption characteristic of aluminum-polyurethane interpenetrating phase composite foams

Open-cell aluminum foams with large pore size (4.41 mm), large pore opening size (1.45 mm) and low thickness (10 mm) exhibit unsatisfied sound absorption characteristic in the low-middle frequency range. To improve this characteristic, novel aluminum-polyurethane interpenetrating phase composite foams (Al/PU IPC foams) were successfully prepared by producing polyurethane foams in the internal cavities of open-cell aluminum foams. The sound absorption coefficient of the Al/PU IPC foams is above 0.3 in the frequency range of 670–1600 Hz and shows a maximum value of 0.67 at about 1150 Hz, which is ∼ 10 times higher than that of the open-cell Al foams with equal thickness, attributing to the small pore size, fine pore opening size and high sound absorption characteristics of internal polyurethane foams.

Negative Pressure Wound Therapy for Extremity Open Wound Management: A Review of the Literature.

Negative pressure wound therapy (NPWT) with reticulated open cell foam is used commonly in orthopaedic trauma, particularly in the management of complex open fracture wounds. This article reviews the literature to date regarding this adjunctive treatment, particularly in regard to removal of infectious material, temporary management of wounds pending soft tissue reconstruction, combat wounds, and over split-thickness skin grafts. Mechanism of action is also reviewed, including stabilization of the wound environment, edema control, macrodeformation, and microdeformation effects. Use of NPWT as an adjunct in management of open fractures along with operative debridement, systemic antibiotics, and early soft tissue reconstruction are the highest yield interventions for managing open fracture wounds with infection. NPWT as an adjunct therapy in the protocol for open fractures seems to add additional clinical benefit for patients with severe open fracture wounds not amenable to primary, immediate closure.

Numerical studies on ballistic limit and cellular dispersion of aluminium foam sandwich panel under hypervelocity impact

This study presents the ballistic limit and cellular dispersion analysis for open cell aluminum foam sandwich panel. Systematic simulation of cell-based open-cell aluminum foam sandwich models is completed and a numerical method for determining ballistic limit is developed. The validity of the simulation technique can be verified by comparing the simulated ballistic limits with the experimental results and this approach can be used to get the ballistic limit of foam materials with arbitrary cellular parameters. It is found that the ballistic limit of foam core sandwich exhibits dispersion characteristics. A comparative analysis of protection performance of aluminum foams with different cellular parameter was carried out, and aluminum foam with smaller cell size has better protection performance under the same relative density condition; in addition, the topology of the foam also had a significant influence on the shielding performance.

Ru/Al2O3 on Polymer-Derived SiC Foams as Structured Catalysts for CO2 Methanation

The catalytic methanation of CO2 via the strongly exothermic equilibrium Sabatier reaction requires the development of structured catalysts with enhanced mass- and heat-transfer features to limit hot-spot formation, avoid catalyst deactivation, and control process selectivity. In this work, we investigated the use of polymer-derived SiC open-cell foams as structured carriers onto which γ-Al2O3 was applied by either dip-coating or pore-filling methods; eventually, Ru was dispersed by impregnation. The formation of an undesired insulating SiO2 layer on the surface of the SiC struts was prevented by a pyrolysis treatment under an inert atmosphere at temperatures varying from 800 up to 1800 °C. SiC foam substrates and their corresponding structured catalysts were characterized by SEM, XRD, N2 physisorption, and compressive strength measurements, and their CO2 methanation activity was tested at atmospheric pressure in a fixed bed flow reactor operated in the temperature range from 200 to 450 °C. SiC foams obtained at intermediate pyrolysis temperatures (1000–1200 °C) showed good mechanical strength and high compatibility with the Ru/Al2O3 active catalytic overlayer.

Prediction of spectral radiative property based on the microscopic ligament morphology and pore-level structure of open-cell alumina foam

In this work, based on the complete structure model consisting of microscopic ligament morphology and pore-level structure, a trans-scale analysis method is presented for accurately predicting the spectral radiative properties of open-cell ceramic foams. The characteristic models of microscopic ligament morphologies are obtained by the SEM technique, while the network structure of ligaments is reconstructed by the μ-CT technique. According to the SEM data, the microscopic statistical models are developed for the rough surfaces and the internal porous media of ligaments. Additionally, based on the statistical models, the FDTD method is employed to analyze the spectral radiative transfer behaviors on the surfaces and inside the ligament media. The spectral directional-hemispherical reflectivity and specularity parameter for the ligament surface, as well as the extinction coefficient, the scattering albedo and the scattering phase function for the ligament medium are extracted from the FDTD simulations. The above parameters are used as the input data for the pore-level simulations of spectral radiative transfer inside the ligament network, where the Monte Carlo method is conducted. The apparent spectral absorptivity and reflectivity, as well as the equivalent volumetric spectral radiative properties of alumina foam sheets are predicted by the presented trans-scale analysis method. The trans-scale predicting method is verified and compared with the single pore-level simulations of radiative transfer inside alumina foams. The spectral radiative characteristics of alumina foams are analyzed for various wavelengths and incident angles. From the analysis, only when the specularity parameter is properly chosen, the pore-level simulation is also reliable for predicting the spectral radiative properties of ceramic foams.

Radial heat transport in a fixed-bed reactor made of metallic foam pellets: Experiment and particle-resolved computational fluid dynamics

Open-cell metallic foams in the shape of pelletized catalysts are regarded as potential catalyst substrates for the application in fixed-bed reactors. This work reports an experimental study and a detailed Computational Fluid Dynamics (CFD) model to investigate the heat transfer performance of a fixed-bed reactor made of open-cell metallic foam pellets. The steady-state heat transfer behavior of a hot gas flowing through such a packed bed under wall-cooled conditions was examined. The proposed CFD model is in line with the particle-resolved CFD (PRCFD) approach that accounts explicitly for the random packing structure, so that the transport processes in the interstitial regions are fully resolved. The momentum and energy transports inside the highly porous foam particles are considered by closure equations based on the porous-media model. The Rigid Body Dynamics (RBD) method is adopted to create the packing geometry. The axial temperature and the pressure drop obtained by the CFD simulations show good agreement with experimental data. To evaluate the thermal performance, effective heat transport parameters in a packed bed such as the effective radial thermal conductivity and the apparent wall-fluid heat transfer coefficient are determined, with the aid of a 2D pseudo-homogenous plug-flow reactor model. The correlations for heat transport characteristics as a function of particle Reynolds number for the metallic foam packed bed are also presented.

A Predicting Model for the Effective Thermal Conductivity of Anisotropic Open-Cell Foam

The structural anisotropy of open-cell foam leads to the anisotropy of effective thermal conductivity (ETC). To quantitatively analyze the effect of structural anisotropy on the anisotropy of ETC, a new predicting model for the ETC of anisotropic open-cell foam was proposed based on an anisotropy tetrakaidecahedron cell (ATC). Feret diameters in three orthogonal directions obtained by morphological analysis of real foam structures were used to characterize the anisotropy of ATC. To validate our proposed anisotropic model, the ETCs of real foam structures in three orthogonal directions predicted by it were compared with the numerical results, for which the structures of numerical models are reconstructed by X-ray computed tomography (X-CT). Using the present anisotropic model, the influences of the thermal conductivity ratio (TCR) and porosity of the foams on the anisotropic ratios of ETCs are also investigated. Results show that there is good consistency between the ETCs obtained by the anisotropic model and the numerical method. The maximum relative errors between them are 2.84% and 13.57% when TCRs are 10 and 100, respectively. The present anisotropic model can not only predict the ETCs in different orthogonal directions but also quantitatively predict the anisotropy of ETC. The anisotropies of the ETCs decrease with porosity because the proportion of the foam skeleton decreases. However, the anisotropies of ETCs increase with TCR, and there exist asymptotic values in anisotropic ratios of ETCs as TCR approaches infinity and they are equal to the relative Feret diameters in different orthogonal directions.

Experimental Set-Up of the Production Process and Mechanical Characterization of Metal Foams Manufactured by Lost-PLA Technique with Different Cell Morphology

A flexible and versatile method for manufacturing open-cell metal foams, called lost-PLA, is presented in this work. With a double extruder 3D printer (FDM, Ultimaker S3, Utrecht, The Netherlands), it is possible to make polymer-based samples of the lost model. Through CAD modeling, different geometries were replicated so as to get black PLA samples. This method combines the advantages of rapid prototyping with the possibility of manufacturing Al-alloy specimens with low time to market. The production process is articulated in many steps: PLA foams are inserted into an ultra-resistant plaster mix, after which the polymer is thermally degraded. The next step consists of the gravity casting of the EN-6082 alloy in the plaster form, obtaining metal foams that are interesting from a technological point of view as well as with respect to their mechanical properties. These foam prototypes can find application in the automotive, civil and aeronautical fields due to their high surface/weight ratio, making them optimal for heat exchange and for the ability to absorb energy during compression. The main aspects on which we focus are the set-up of the process parameters and the characterization of the mechanical properties of the manufactured samples. The main production steps are examined at first. After that, the results obtained for mechanical performance during static compression tests with different geometry porosities are compared and discussed. The foam with truncated octahedron cells was found to show the highest absorbed energy/relative density ratio.

Effect of base materials and pore grades on mechanical properties of open-cell aluminum foam fabricated by investment casting

As a structural and functional integration material, open-cell aluminum foam has been widely applied in many fields. It is of significance to study its fabrication and properties. In this article, the compression properties of ultralight open-cell aluminum foam are studied in terms of base materials and pore grades. The base materials are divided into pure aluminum and 6061 aluminum alloy, while the pore grades range from 10 to 40 according to PPI (Pores Per Inch). Results show that better compression properties appear in aluminum foam with 6061 aluminum alloy as the base material, compared to the pure aluminum. Besides, the plateau stress decreases with the increase in pore grades. Reasons for the variation of the mechanical properties are also analyzed.

From μCT data to CFD: an open-source workflow for engineering applications

The generation of high-quality volume meshes out of µCT data can be a challenging task that is mandatory to perform CFD simulations of fluid flows within or around scanned objects. Despite the growing relevance of CT-based CFD simulations, there is still a lack of a standardized, free-to-use workflow. In this work, an open-source based workflow is presented, which covers all steps from the CT image stack to a volume mesh in the end. The software packages ImageJ, ParaView, and Blender are used for surface reconstruction and processing of µCT data; resulting meshes are evaluated regarding geometric parameters, surface fidelity, and used memory. For volume meshing, the mesh generator snappyHexMesh implemented in OpenFOAM is used. A detailed description of this workflow is provided in the Supplementary Materials. We demonstrate how potential pitfalls and shortcomings can be avoided and how surface smoothing is especially important to preserve the surface area of scanned objects. We use CT data of a 10 ppi open cell foam to illustrate that data decimation can reduce the required time for the volume meshing by up to 45% and RAM up to 75%. The resulting meshes are used to simulate flow fields and heat transport with a surface heat source. The resulting temperature fields show that differences in the surface area and recesses in an unsmoothed mesh can affect the outcome of heat transport simulations, highly relevant for reactive CFD simulations. The results highlight the quality of our workflow’s outcome, which can help engineers that rely on CT reconstruction processes, also for other applications.

Special Issue on Experimental Solid Mechanics

In the present special volume, the German Association of Applied Mathematics and Mechanics (GAMM) Expert Committee “Experimental Solid Mechanics” was again given the opportunity to summarize the current scientific activities of individual participating working groups in Germany. Both optical measurement methods from surface information as well as radiation-based methods for detecting the internal states present in material bodies are receiving increasing interest. Nowadays, the required measurement systems can simply be purchased, or they can be developed in-house. In addition, there are still many scientific questions left open in the evaluation of the found measurement data. In the meantime, image correlation methods are often used to determine the surface deformation of components, the discrete data of which are now evaluated using proprietary software tools, or are coupled with infrared thermography systems, in particular to determine the dissipating energy of mechanically loaded components. In the first issue of this special volume, four contributions are compiled proposing (1) a shear evaluation tool using digital image correlation (DIC) for plane problems [5], the coupling of infrared thermography (IRT) and 3D DIC for both (2) identifying material parameters in metal plasticity [6] as well as (3) applicability studies of foams and auxetic materials [3], and, finally, (4) identifying the heat conductivity parameters in transversal isotropy using IRT [8]. The second issue treats distance measurements of laminate layers using microscopical images [4], and three further contributions on μ-CT measurements. First, new in-situ measurements in granular media using μ-X-ray computer tomography (CT) combined with ultrasonic wave propagation is investigated [7]. A further contribution treats the influence of the pores on the fatigue properties of particular additively manufactured parts [2], and, finally, a study on the micro-structural characterization and stochastic modeling of open-cell foam using μ-CT image analysis [1]. All articles contribute to contact-less measurement sensing and evaluation in the field of solid mechanics. We gratefully acknowledge the German Association of Applied Mathematics and Mechanics (GAMM) for scientific support of the expert committee in the last years.

Data-driven finite element computation of open-cell foam structures

This paper presents a model-free data-driven strategy for linear and non-linear finite element computations of open-cell foam. Employing sets of material data, the data-driven problem is formulated as the minimization of a distance function subjected to the physical constraints from the kinematics and the balance laws of the mechanical problem.The material data sets of the foam are deduced here from representative microscopic material volumes. These volume elements capture the stochastic characteristics of the open-cell microstructure and the properties of the polyurethane material. Their computation provides the required stress–strain data used in the macroscopic finite element computations without postulating a specific constitutive model. The paper shows how to derive suitable material data sets for the different cases of (non-)linear and (an-)isotropic material behavior efficiently.Exemplarily, we compare data-driven finite element computations with linearized and finite deformations and show that in a data-driven computation the linear kinematic is sufficiently accurate to capture the material’s non-linearity up to 50% of straining. The numerical example of a rubber sealing illustrates possible areas of application, the expenditure, and the proposed strategy’s versatility.

Pore-scale direct numerical simulation of fluid dynamics, conduction and convection heat transfer in open-cell Voronoi porous foams

The pore-scale analysis includes the pore network simulation and direct numerical simulation, which the latter is more accurate and provides more details about the problem. This study presents a pore-scale direct numerical simulation of flow and convection-conduction heat transfer in open-cell metal foams with a complex structure. First, using the Laguerre–Voronoi tessellations (LVT) algorithm, three foam samples with various porosities (76.6%, 84.4%, and 93.8%) and a constant pore density of 20 pores per inch (PPI) are generated. Next, the open-source library of OpenFOAM is employed to perform heat transfer and flow analysis in Darcy and non-Darcy regimes. Results were verified through comparison with available experimental and numerical data. The effects of foams' porosity, solid material, and Reynolds number on flow characteristics and heat transfer are investigated. Results are presented in terms of the permeability, Forchheimer coefficient, the volumetric and average heat transfer coefficient, and temperature and velocity distribution. By decreasing porosity, the flow complexity increases with subsequent increments in heat transfer and pressure drop. Also, the conductive heat transfer through the foam plays a vital role in the total heat transfer rate. These pore-scale outcomes could be used in macro-scale thermo-fluid models to perform more accurate simulations with less computational costs.

Heat transfer characteristics of ceramic foam/molten salt composite phase change material (CPCM) for medium-temperature thermal energy storage

Molten salts have been widely used as energy storage materials in medium- and high-temperature thermal energy storage. However, pure salt commonly suffers from low thermal conductivity and many conventional methods of heat transfer enhancement do not apply due to the serious corrosion and the extremely high temperature. In the current study, the open-cell SiC ceramic foam was integrated with solar salt (60wt% NaNO3 + 40wt% KNO3) to enhance the heat transfer of salt and avoid severe corrosion issues. A visualised experiment was for the first time conducted to investigate the melting phase change heat transfer in the ceramic foam/molten salt composite phase change material (CPCM). A representative elementary volume (REV)-scale simulation was simultaneously performed and the computational results were compared with experimental data. It is found that the conduction-friendly ceramic skeleton remarkably enhances the heat transfer in molten salt, especially in the region far away from the heat source. The spatial temperature difference across the composite is decreased in both horizontal and vertical directions and the local superheating is mitigated. The enhancement of heat conduction is greater than the suppression of natural convection; as a result, the melting rate of the CPCM is increased by 41.3%. This study provides crucial benchmark data of phase change heat transfer for medium-temperature thermal energy storage and paves the way for system design and optimization.

New model of pressure drop for the foam trays with dynamic bubbling process analysis

Open-cell foams as the column tray are promising candidates for the purpose of process intensification in the distillation process. In this paper, the real foam porous structure is obtained based on Micro Computed Tomography (µ-CT), and the bubble formation process on pore-scale foam tray is discussed based on the VOF-CSF model (volume of fluid method-continuous surface force). The results show that the wettability (CA), superficial gas velocity (Ug), porous structure, and clear liquid layer height (HCL) all affect a crucial factor of the foam tray - the liquid holdup in the porous channels (LHPC). It determines the effective porosity, which in turn affects the bubbling frequency and pressure drop. Meanwhile, the evolutionary mechanism of instantaneous pressure drop is analyzed based on the flow patterns, force analysis and interfacial phenomena. Moreover, the new model to predict pressure drop is proposed based on LHPC, which shows good consistency with experiments.

Experimental investigation of the pressure-drop characteristics of open-cell metal foam with air-gaps under non-Darcy flow regimes

Multi-layer metal foam with discrete air gaps between neighbored layers can have wide engineering applications, and its pressure drop characteristic is the crucial performance that needs to be predicted precisely. Experimental studies were carried out to investigate the influences of the air gaps and their layouts on the pressure drop characteristics of the multi-layer open-cell metal foam within a wide flow velocity range to develop efficient models for pressure drop predictions. The accumulated metal foam thickness and air gap distance were kept unchanged in the tests, and four sets of test sections with different air gap layouts were tested. The varying airflow speed across the metal foam was realized by adjusting the inlet pressure level of the test section to reveal the relations of the pressure drop versus the mass flow rate. Results indicate that in the multi-layer and multi-gap configurations, the Forchheimer model in the transition regime and bilinear model in the turbulent regime is still applicable for predicting the pressure drop; however, the insertion of air gaps between the metal foam slices leads to an increased pressure drop coefficient. Meanwhile, the first air gap leads to a higher pressure drop compared to the subsequent air gaps and shifts the flow regime transition point towards an even more minor flow rate operating point, while the subsequent air gaps present almost the same influences on the metal foam pressure drop characteristics and transition point. With the experimental study, two models for predicting the pressure drop characteristics of open-cell metal foam with and without air gaps in the transition and turbulent flow regimes with a broadened range are presented.

Investigation on laser forming of open cell aluminum foam

Open cell aluminum foam having high porosity has the potential to increase the efficiency of a heat exchanger and also to be used for diverse other functions. However, being prone to fail easily under tensile mechanical load, their thermal forming using a laser has been proposed in the literature. This work investigates the effect of laser parameters, orientation-position-curvature of scan path, the number of scans, and foam thickness on the bending angle achieved while forming 95% porous pure aluminum (99.7% aluminum) open cell foam plates using a diode laser. Furthermore, the capability of laser forming to produce developable and nondevelopable surfaces out of this foam has been demonstrated. Higher line energy gave a higher bending angle. Under the same line energy, the combination of higher power-higher scan speed produced a higher bending angle. In contradiction to laser forming of the sheet metal, no saturation or reduction in bending angle per scan pass was observed with an increase in scan pass number. This observation could be explained with the help of cell densification by previous scan passes leading to an increase in the coupling of more thermal energy for subsequent scan passes. Scan paths with increased curvature (or less radius) also produced higher bending due to a higher amount of cell collapse in the irradiated region.

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

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

A hybrid shape memory polymer filled metallic foam composite: shape restoring, strain sensing, Joule heating, strengthening, and toughening

In this paper, an open-cell metallic foam was filled in by a tough shape memory polymer (SMP), to form a hybrid metal/polymer composite with multifunctionalities and enhanced mechanical properties. This work aims to study the positive composite actions between the metallic skeleton and the SMP filler. Mechanical, thermal, and conductive properties of the resulting hybrid composite were evaluated and compared to the individual components. Uniaxial compression tests and shape memory effect tests were conducted. Results demonstrated an improvement in the compressive strength and toughness. The hybrid composite also exhibited excellent shape recovery and high recovery stress of 1.76 MPa. Infrared thermography has been used to verify the free shape recovery by Joule heating. Sandwich structures with the hybrid composite as the core were studied through low velocity impact test and three-point bending test. The sandwich structures with the composite foam core showed significant performance improvement in both tests. Electrical resistivity study during the three-point bending test validates the possible application of this multifunctional polymer-aluminum open cell foam composite as strain sensor. This type of hybrid composites can be beneficial in many industrial sectors that search for an ideal combination of high strength, high toughness, low weight, damage sensing, and excellent energy absorption capabilities.

Open-cell bio-polyurethane foams based on bio-polyols from used cooking oil

Used cooking oil is a widely available and inexpensive waste with a high application potential as a feedstock for the bio-based polyurethane production. Usually, bio-polyols from vegetable oils have higher viscosity and lower hydroxyl values compared to commercial petrochemical polyols, which limits their usefulness. This article reports on the development of open-cell polyurethane foam systems wherein 100% of the polyol components were bio-polyols obtained from used cooking oil. What is particularly considered is the effect of bio-polyol properties (molecular weight, viscosity and hydroxyl value) on the properties of the final open-cell polyurethane systems - apparent density, thermal conductivity coefficient, content of closed cells, mechanical strength, brittleness and short-term water absorption. It was found that the key step in the synthesis of bio-polyols designed for open-cell polyurethane foams is the epoxidation reaction. The epoxy value has a significant effect on the occurrence of side reactions (mainly oligomerization) during the oxirane ring-opening process determining the properties of bio-polyols. The resulting open-cell foams were characterized by apparent densities from 12.4 to 13.3 kg/m3, thermal conductivity coefficients from 36.6 to 38.2 mW/m∙K, and closed cell contents below 10%, which makes them comparable to commercial products. The results demonstrate that used cooking oil-based polyols can provide an alternative starting material for open-cell polyurethane foam production.