Open-cell Foams Research Articles

Modeling for silicone foam material extrusion with liquid rope coiling

This research demonstrates a Modeling idea using parametric Modeling and considering the process to predict coiling patterns effectively in open-cell foams material extrusion (MEX) with liquid rope coiling (LRC) effect. The model consists of three sub-models, including pneumatic extrusion model, liquid rope coiling model, and geometric model, considering material properties, material extrusion, falling, LRC, pattern formation process and device structure. The model uses four MEX process parameters (back pressure, moving speed, inner nozzle diameter, and nozzle height) to predict three geometric parameters of the coiling pattern. The capability to predict pattern shape (period length, width, and loop length) accurately is validated by comparing the fit of predicted and experimental values when adjusting the process parameters, with R-squared coefficients up to 0.957. Then, application value is demonstrated by printing silicone open-cell foams under the guidance of the proposed model and studying the compression properties of these foams. The obtained three-region stress-strain curves indicate the feasibility of variable stiffness foam fabrication by adjusting the process parameters according to the proposed model during the printing process. Based on the results, the proposed model demonstrates accuracy in predicting geometric parameters of translational coiling pattern, makes predictable manufacturing of complex cellular structures available, and provides a foundation for design and fabrication of load-based variable stiffness silicone open-cell foam.

A cuboidal open cell model for constitutive modeling of surface effects in fluid-saturated porous materials

Fluid-saturated porous elastic materials, made up of connected networks of solid ligaments and characteristically having open pores, are commonly found in geological, biological and engineering materials. Surface effects can affect significantly the mechanical performance of such porous materials at macro scale, especially when the solid ligaments and the pores have micro or nano scale sizes. In the present study, in order to explicitly link pore-level geometrical parameters and surface effects with effective poroelastic properties as well as constitutive equations governing poroelastic deformation, we combine the top-down homogenization approach presented a previous study (Chen et al., 2021) with the bottom-up micromechanics approach. Inspired by the Gibson-Ashby cubic cell model for open-cell foams and the cellular networks typically found in fluid-saturated porous materials, we propose a cuboidal open cell model, with surface effects and fluid compressibility accounted for. For two limiting cases, i.e., the undrained state and the drained state, we demonstrate that both the surface moduli and residual surface stress (i.e., surface tension) prevent the deformation of solid ligaments, thus stiffening the porous material with enlarged effective Young's moduli. Further, we reveal that the two surface effect parameters (i.e., residual surface stress versus surface moduli) exhibit a coupling effect on effective moduli: when one parameter is large enough, the variation of the other affects significantly the effective moduli. As applications of the proposed model, we characterize mechanical behaviors of the porous material under typical loadings (e.g., uniaxial and non-proportional multiaxial tension) in both undrained and drained states; we also describe, for the first time, the stress concentration of a compressible liquid inclusion (e.g., a cell) with surface tension embedded in a fluid-saturated porous material with surface effects. Results of this study are beneficial for understanding and investigating how surface effects influence the poroelastic parameters of fluid-saturated porous materials having sufficiently small open pores.

Hydrated behavior of multilayer polyelectrolyte-nanoclay coatings on porous materials and demonstration of shape memory effect

Layer-by-layer (LbL) assembly is a powerful technique for fabricating nanocomposite thin-film coatings with a diverse range of constituents, properties, and functionalities. Templated deposition of these coatings has enabled the translation of mechanical properties from the microscale of thin-films to the macro-scale of nanocomposite-coated porous materials and has been used to tailor the elastic modulus and porosity of coated open-cell foams for potential applications including lightweight structures and engineered tissue scaffolds. However, the presence of moisture in these application environments is expected to affect the physico-mechanical behavior of the nanocomposite coating. In this work, open-cell foams coated with nanocomposites consisting of poly(ethyleneimine), poly(acrylic acid), and Na+-montmorillonite were characterised under high relative humidity and upon complete submersion in water. The nanocomposite coating imparted a substantial increase in compressive elastic modulus when tested under ambient conditions, from 0.08 ± 0.00 MPa to 4.90 ± 0.46 MPa, but had little to no mechanical effect when hydrated, and upon drying the mechanical properties of coated foams recovered to pre-hydrated levels. Chemical crosslinking of amine groups within the polymers resulted in the retention of significant compressive elastic modulus of 2.91 ± 0.49 MPa when hydrated. Initial trials showed that un-crosslinked coated foams exhibit a hydration induced shape memory effect that could be used to enable the actuation or expansion of a previously passive open-cell foam.

Biaxial characterization of open-cell aluminum foams from macro to micro responses

This experimental work aimed to understand the effect of a biaxial combined compression-torsion loading complexity on the mechanical properties of two types of aluminum foams having porosities of 85% and 80% and nominal relative densities of 15% and 20%, respectively. In this investigation, open-cell aluminum foam of highly uniform architecture with a spherical porosity was designed and used to investigate the biaxial plastic response. These foams were tested under different quasi-static complex loading paths using a patented rig, called ACTP with different torsional component rates. The key responses to be examined were yield stress, stress plateau, energy absorption capacity, densification strain, micro-hardness, and microstructure. It was revealed that the greater the density of the foam with the higher the loading complexity, the greater the yield strength, the energy absorption capacity, and the micro-hardness. The highest foam strength was thus recorded under the most complicated loading path (i.e., biaxial 60°) for the densest foam (i.e., 80% porosity). This was due to the variation in the cell wall thickness. In addition, the effect of the loading complexity on the microstructure was studied using SEM. The loading complexity of biaxial-45° provides higher particle segregation at the grain boundary and a larger densification strain for the 85% porosity foams.

Numerical Prediction and Correlations of Effective Thermal Conductivity in a Drilled-Hollow-Sphere Architected Foam

Abstract Additive manufacturing is now a promising option to obtain porous customized structures at relatively low scales. The capability to design structures with tunable heat transfer performance compared to conventional porous materials, such as open-cell foams, is very interesting to the user. In this study, we investigated heat conduction in a drilled-hollow-sphere architected foam, inspired by Triply-Periodic Minimal Surfaces (TPMS) and foam structures, generated using perforated spherical hollow shells connected with cylindrical binders. Temperature fields and heat fluxes in the foam were predicted numerically, and the effective thermal conductivity of the foam was calculated for different sets of the binder angle, the shell thickness, and the perforation radius. The dependence of the foam porosity on the binder angle and perforation radius was also pointed out. Predictions were validated by comparing them with data available from the literature. Results showed that varying the characteristics of the investigated drilled-hollow-sphere architected foam, its predicted effective thermal conductivity can be adjusted by more than one order of magnitude larger or smaller than that of conventional foams, making architected foams promising enhancers of their heat transfer performance. Finally, new dimensionless correlations among the effective thermal conductivity and some significant morphological parameters of the foam were derived and presented for practical use.

Theoretical and experimental investigation of solubility and Young's modulus models for polyhydroxybutyrate‐based electrospun scaffolds

AbstractOver the past decades, limited strategies have been developed to study nanomechanical properties. The in‐depth study on the nanomechanical properties of electrospun scaffolds can provide better insights at greater scales. Atomic force microscopy (AFM) nanoindentation is an authoritative method that can characterize mechanical properties. In this research, theoretical solubility studies of polyhydroxybutyrate (PHB) in different solvents were initially carried out. Then, three series of PHB‐based mats were prepared, including PHB/lignin, PHB/cellulose nanofiber (CNF), and PHB/lignin/CNF. The theoretical modulus of samples was studied from two different standpoints, through the use of nanoindentation on a single nanofiber. First, scaffolds were considered as a series of short fiber reinforced nanocomposites (NCs). In the second viewpoint, the geometrical structure of each scaffold was considered similar to an open‐cell foam (OCF). Consequently, modeling outputs verified that among NC models, isotropic Halpin‐Tsai presented plausible predictions with ≃93.36 to 99.77% accuracy. In addition, Tetrakaidecahedron indicated more accurate predictions among OCF models for the mats (≃78.99 to 96.15% adaption). Indeed, the theoretical NC and OCF models were able to provide acceptable forecasts for the application range of electrospun fibers. Based on this, nanoscale investigation of mechanical properties can turn a new page to estimate the further application of mats.

A Computationally Fast Method to Simulate Microwave-Heated Monoliths

Microwave-assisted process intensification is a promising technique hindered by the unavailability of design rules for optimization and scale-up. High-throughput computational models allowing the exploration of a vast design space are imperative for the rapid development and deployment of intensified microwave reactors. Recently, structured reactors, especially monoliths, are emerging as a canonical multiphase reactor setup in the microwave-heating community. The vast separation of scales in these reactors leads to a large number of mesh elements, making the simulations time-consuming and challenging to converge. To this end, we employ volume and asymptotic averaging to represent monoliths, a multiphase system consisting of a fluid and a solid phase, as a continuum or effective medium. We rigorously verify the adequacy of the averaging techniques to predict the spatiotemporal distribution of the electric field, electromagnetic power dissipation, and temperature against fully resolved monolith simulations. The developed continuum model can replicate the three-dimensional transient behavior obtained from the multiphase simulations with an order of magnitude lower computational expense. Moreover, the continuum model allows easier mesh generation and convergence of numerical solution than the multiphase model. The developed multiscale framework can be used to simulate microwave-heated monoliths and other multiphase reactors, such as packed beds and open-cell foams.

Cellular foam-based trickle-bed DBD reactor for plasma-assisted degradation of tetracycline hydrochloride

Non thermal plasma (NTP) is a promising technology for degrading organic pollutants in water/wastewater, in which the transfer of energetic species at the interface between gas discharge and liquid phase is key to improve degradation efficiency. Herein, this work shows the development of an integrated system of dielectric barrier discharge (DBD) plasma and open-cell ceramic foam (CF) for the degradation of tetracycline hydrochloride (TCH, a model antibiotic) in liquid film. Specifically, a bespoke trickle-bed DBD reactor with liquid distributor was developed to enable the formation of uniform liquid film on the surface of the hydrophilic CF strut. Due to the improved mass transfer across the thin liquid film, the trickle-bed DBD reactor with the hydrophilic CF exhibited the comparatively highest TCH removal efficiency (>80%) and energy efficiency (viz., EETCH removal of ∼0.6 g kWh−1) among the systems under investigation such as the glass bead packed DBD. The findings showed that the presence of liquid film was beneficial to the propagation of homogeneous plasma discharge in the CF bed and promoted the mass transfer of active species from plasma discharge to liquid, and thus improved the TCH degradation efficiency. Results from quenching experiments suggested that the electron induced active species (especially O2−) played the important role in degrading TCH rather than electrons.

Multiaxial mechanical characterization of additively manufactured open-cell Kelvin foams

Multiaxial mechanical characterization of additively manufactured open-cell Kelvin foams

Open-cell mullite ceramic foams derived from porous geopolymer precursors with tailored porosity

Porous geopolymer precursors were firstly prepared by the direct foaming method using bauxite, fly ash (FA), and metakaolin (MK) as raw materials, and porous mullite ceramics were prepared after ammonium ion exchange and then high-temperature sintering. The effects of chemical foaming agent concentration, ion-exchange time, and sintering temperature on porous geopolymer-derived mullite ceramics were studied, and the optimal preparation parameters were found. Studies have shown that the concentration of blowing agent had great influence on open porosity (<i>q</i>) and porosity and cell size distributions of geopolymer samples, which in turn affected their compressive strength (<i>σ</i>). Duration of the ion exchange had no obvious effect on the sintered samples, and the amount of mullite phase increased with the increase in the sintering temperature. Mullite foams, possessing an open-celled porous structure, closely resembling that of the starting porous geopolymers produced by directly foaming, were obtained by firing at high temperatures. Stable mullite (3Al₂O₃·2SiO₂) ceramic foams with total porosity (<i>ε</i>) of 83.52 vol%, high open porosity of 83.23 vol%, and compressive strength of 1.72 MPa were produced after sintering at 1400 ℃ for 2 h in air without adding any sintering additives using commercial MK, bauxite, and FA as raw materials.

Pore-scale fluid flow and conjugate heat transfer study in high porosity Voronoi metal foams using multi-relaxation-time regularized lattice Boltzmann (MRT-RLB) method

This study aims to investigate pore-scale flow and conjugate heat transfer in high-porosity open-cell metal foams. Five representative elementary volume (REV) samples with different values of porosity (0.80, 0.85, and 0.90) and pore density (10, 20, and 30 PPI) are generated using the Laguerre-Voronoi tessellation (LVT) algorithm. To perform direct numerical simulations, a decoupled lattice Boltzmann solver is developed utilizing multi-relaxation-time (MRT) model for flow and regularized lattice Boltzmann (RLB) model for advection-diffusion. As a novelty, this solver is able to simulate advection-diffusion in the non-Darcy regime. To consider thermal conduction in REV samples more prominently, a constant high temperature is assigned to the solid ligaments on the inlet plane. The flow results show that the transition from the Darcy to the non-Darcy regime occurs at lower Reynolds numbers in foams with lower porosity, whereas the pore density does not affect the transition point significantly. According to the heat transfer results, metal foams cool down rapidly at high flow velocities while the temperature rise in the fluid is minimal. Also, increasing pore density from 10 PPI to 30 PPI and decreasing porosity from 0.90 to 0.80 increase the h-ReK slope in the non-Darcy regime by 190% and 17.5%, respectively.

Forced convection of nanofluids in metal foam: An essential review

The combination of the high conductivity of nanofluids with the huge accessible surface area of open-cell metal foam would indeed be a superb heat exchange technology. While individual ingredients of this technology have been separately investigated, the combination of the two has received only scant attention. Actually, there are only few studies that are focused on nanofluids flow and heat transfer in metal foam. This paper is intended to serve as an orientation for researchers who are interested in both nanofluids heat transfer and metal foam. The paper thus includes discussion of various aspects of nanofluids and their heat-transfer applications, as well as fundamentals of flow and heat transfer of ordinary fluids in metal foam. A section on recent heat transfer studies in metal foam is included, and another section on pore-scale modeling of transport in metal foam is provided. Nanofluids are presented in terms of their definition, brief history, preparation methods, theoretical models, properties, and engineering applications related to heat transfer. The paper then moves to describe metal foam and its morphology, as well as current understanding and theoretical treatment of flow and heat transfer in this class of highly-porous media. Key heat transfer and flow properties of the foam are outlined. The paper also presents the case for nanofluids forced convection heat transfer in open channels to serve as a background for the more complex case that involves heat transfer in porous media in general. The case of forced convection of nanofluids in metal foam in particular is presented next. Studies including complex effects, e.g. magnetism, are briefly described. Based on the above information, some key findings, conclusions and recommendations are made for interested researches.

Experimental study of heat transfer enhancement using metal foam partially filled with phase change material in a heat sink

In this paper, an experimental study on the effects of using phase change materials (PCMs) embedded in open-cell copper foam in the heat sink during the heating and cooling process is carried out. In this study, the paraffin RT55 is employed as the phase change material. The experiments are performed with four different samples (with and without PCM, with and without copper foam), electric heating to the copper plate below the heat sink, and forced air convection into the duct of the device. The effect of thermal power and inlet air velocity parameters for four heat sink samples in heating and cooling processes is investigated. The results show that in the sample with copper foam partially filled with paraffin (sample 1), the copper plate has the lowest temperature compared to other samples. In the heating process, samples 1(copper foam partially filled with paraffin), sample 2 (copper foam filled with paraffin), and sample 3 (copper foam) have a temperature decrease of 20.1 %, 7.9 %, and 11.7 %, respectively, compared to sample 4 (without copper foam and paraffin). In the cooling process, due to the latent heat of paraffin, in sample 1, the temperature of copper plate is 35.5 % lower than sample 3, and increasing the inlet air velocity has less effect on reducing the temperature in the sample with PCM.

Effect of Poisson's ratio on the indentation of open cell foam

We tested whether conventional and auxetic (negative Poisson's ratio) foam indentation response fits with classical indentation theory. We first made foam cubes with 20–25 mm sides, and Poisson's ratios spanning negative and positive values (−0.35 to 0.3). These foam cubes were compression tested, and indented by the curved face of two cylinders (10 and 50 mm diameters) and a stud (12 mm diameter), to 20% of their thickness. Full-field true strains were measured by digital image correlation, to obtain Poisson's ratios and to study foam deformation during indentation. Indentation force vs. displacement was measured and calculated using incremental Poisson's ratios and tangent moduli. Normalised root mean square errors between measured and calculated indentation forces were ∼5% of measured values. Foam densification during indentation, and compression towards sample edges, increased with the magnitude of negative Poisson's ratio; these may both increase indentation resistance beyond predictions from indentation theory.

Enhancing the multifunctionality of open-cell foams through tailoring their thermal and mechanical properties using coatings

Hybrid coated open-cell foams have been proposed as an economical solution for obtaining tailored and application-optimized properties. These hybrid foams integrate commercially available metallic foams or cellular metallic solids with metallic coatings of different constituents and thicknesses to realize tailored elastic, yield, and thermal properties that can satisfy the needs of a wide range of multifunctional applications. This work aims to explore the range of tailored properties that can be obtained using a hybrid foam system that comprises copper coatings and the widely available aluminum open-cell foams. The elastic, plastic, and thermal conductive properties of the considered hybrid foam system are determined using computational tools for a range of porosities and coating thicknesses. Results show that the hybrid foam system can deliver significantly higher stiffness, yield strength, and thermal conductivity than its aluminum foam substrate. In few of the studied configurations, the stiffness and thermal conductivity of the hybrid foam system exceeded those of its aluminum foam substrate by more than 100%. Relative improvement in the hybrid foam properties correlated nonlinearly with the porosity of its aluminum foam substrate. Semi-empirical models were developed to predict the properties of hybrid coated open-cell foams. These models can assist engineers in selecting the hybrid foam parameters, such as coating constituent material and thickness, needed to obtain tailored elastic, yield strength, and thermal conductivity.

How Loading of Co3O4-Cs on an Open-Cell Foam Influences N2O Decomposition

Co3O4 modified with Cs was deposited on an α-Al2O3 open-cell foam, characterized by X-ray diffraction (XRD), N2 physisorption, temperature-programmed reduction by hydrogen (TPR-H2), and scanning electron microscopy-energy-dispersive X-ray analysis (SEM-EDAX) and tested for the low-temperature decomposition of N2O. The aim was to study the effect of the amount of active phase on N2O conversion. Three different approaches were used: (i) the application of foam supports with different cell sizes, (ii) influencing catalyst loading using impregnation solutions with different precursor concentrations, and (iii) deposition of the active phase precursor by repeated immersion–calcination cycles. Increasing the geometric surface area of the support, and thus catalyst loading, was successfully done using the support with higher pore densities. A higher loading was also achieved by increasing the nitrate precursor concentration in the impregnation solution. In both cases, the catalyst activity increased with an increase in the amount of the active phase. Compared to that, a repeated impregnation procedure can ensure the deposition of a higher amount of active phase in comparison to that obtained with one-step impregnation, but only the last layer is used in the reaction and the rest of the active phase remains unutilized, which makes this type of preparation unfavorable. The high catalytic activity was preserved at 450 °C even in the presence of O2, H2O, and NO.

A Novel Approach to Water Softening Based on Graphene Oxide-Activated Open Cell Foams

This work focuses on exploring a new configuration for the reduction of water hardness based on the surface modification of polyurethane (PU) open cell foams by the deposition of thin graphene oxide (GO) washcoat layers. GO was deposited by the dip–squeeze coating procedure and consolidated by thermal treatment. The final washcoat load was controlled by performing consecutive depositions, after three of which, a GO inventory up to 27 wt% was obtained onto PU foams of 60 pores per inch (PPI). The GO-coated PU foams were assembled into a filter, and the performance of the system was tested by continuously feeding water with hardness in the 190–270 mgCa2+,eq·L−1 range. Remarkable results were demonstrated in terms of total adsorbing capacity, which was evaluated by measuring the outlet total hardness by titration and exhibited values up to 63 mgCa2+,eq·gGO−1 at a specific filtered water volume of 650 mLH2O·gGO−1, outperforming the actual state-of-the-art adsorbing capacity of similar GO-based materials.

Effect of cell size on the microarchitectural and physicomechanical response in open-cell Al foam made through template method

Fully open interconnected Al-foam having different PPI (Pores per inch) was fabricated through the novel template method. The morphology of the open-cell Aluminium foam (OCAF) (strut, pore, and cell size) can be easily tailored with this method. Three different PPI (10, 20, and 30) Al-foams were fabricated through the template method, and show the effect of PPIs’ on their microstructure, thermal, electrical, and mechanical properties in detail. With different PPI of the foam, the porosity lies in the range of 85–94%. Through experiments, it was found that with the increase in PPI, the density of the foam gets increases. Complete openness and uniformity in terms of the pore, strut size, and porosity throughout the samples has been easily achieved with this method, which is very difficult with previously reported methods. As the PPI of the foam changes, the properties (electrical, thermal, and mechanical) also change. According to the requirement, one can easily tailor the properties by changing the PPI of the foam. Experimentally evaluated properties were also compared with the theoretically calculated values. The open-cell aluminium foam of 30 PPI (OCAF-30) having RD-0.14 shows electrical conductivity- 0.68 × 106 S/m, thermal conductivity- 6.43 W/m.K, and compressive strength of 0.65 MPa. This study helps the research community to fabricate OCAF according to their requirement with desired thermal, electrical, and mechanical properties for the application of heat transfer, electrocatalysis, and others.

Influence of fin thickness variation on the thermal performance of metallic foam heat sink laminar condition

In recent years, open-pore metallic foams have been employed in a wide variety of applications owing to the essential qualities that they possess. In the present study, the thermal performance of a finned heat sink made from open-cell copper foam was investigated numerically under laminar forced conditions. The influence of fin thickness, air velocity, and heat fluxes on the average heat sink base temperature to ambient temperature difference, the Nusselt number, and pressure drop were investigated. Fin thickness was generally taken as 2, 5, 7, and 10 mm. Heat fluxes were taken from (600 to 3000) W/m2, while the air velocity was taken from 0.04 to 0.16 m/s. The findings of laminar flow indicate that straight fins with a thickness of 10 mm minimize the temperature difference between the heat sink's base and the surrounding air the most, followed by fins with thicknesses of 7 mm, 5 mm, and 2 mm. At 3000 W/m2, a change in velocity from 0.04 to 0.16 m/s increases the average base temperature difference (i.e. (Tbase-Tamb)) by 118.9% for a heat sink with 10 mm straight fins. . At a heat flow of 600W/m2, the Nusselt number grew by 72.6%, 60.7%, and 45.7% when fin thickness was raised from 2 mm to 10 mm, 2 mm to 7 mm, and 2 mm to 5 mm, respectively. The results also demonstrate that the pressure drop rises with increasing fin thickness.

Dynamic Response of Metallic Foams Bumper with Morphology Design Variation in ABAQUS Software Simulation

Variation design of open-cell foams located in the bumper car were investigated in this paper. A brief experimental result on the dynamic response of crash was focused on energy absorption and deformation behavior. The bumper design was based on typical design of bumper compared with gradual density of hexagonal foam type. The method used was imitate crashing real behavior dynamic explicit using ABAQUS simulation software with some extra constraint, such as: crashing object and crash direction. Results showed the design strongly affect the value of energy absorption and deformation. Energy absorption was higher using hexagon foams compare to the normal bumper structure with 4.8740 E6 Joule and 4.8572 E6 respectively. Furthermore, highest energy absorption was by simulated redesign hexagon foam into varying thickness (gradual density) – similar to cortical bone structure – with 4.950 E6 Joule. Meanwhile the deformation shows highest value on typical design of bumper with 4 cm translation after crashed. Expected design has to be safe for passengers with have high ability to absorb energy and minimize the deformation movement.