Metals

Research

783 KiB

Open AccessArticle

Permeability of Aluminium Foams Produced by Replication Casting

by Eugeny L. Furman, Arcady B. Finkelstein and Maxim L. Cherny

Metals 2013, 3(1), 49-57; https://doi.org/10.3390/met3010049 - 28 Dec 2012

Cited by 30 | Viewed by 11490

The replication casting process is used for manufacturing open-pore aluminum foams with advanced performances, such as stability and repeatability of foam structure with porosity over 60%. A simple foam structure model based on the interaction between sodium chloride solid particles poorly wetted by [...] Read more.

The replication casting process is used for manufacturing open-pore aluminum foams with advanced performances, such as stability and repeatability of foam structure with porosity over 60%. A simple foam structure model based on the interaction between sodium chloride solid particles poorly wetted by melted aluminum, which leads to the formation of air pockets (or “air collars”), is proposed for the permeability of porous material. The equation for the minimum pore radius of replicated aluminum foam is derived. According to the proposed model, the main assumption of the permeability model consists in a concentration of flow resistance in a circular aperture of radius r_min. The permeability of aluminum open-pore foams is measured using transformer oil as the fluid, changing the fractions of initial sodium chloride. Measured values of minimum pore size are close to theoretically predicted ones regardless of the particle shape. The expression for the permeability of replicated aluminum foam derived on the basis of the “bottleneck” model of porous media agrees well with the experimental data. The obtained data can be applied for commercial filter cells and pneumatic silencers. Full article

(This article belongs to the Special Issue Selected Papers from the 7th International Conference on Porous Metals and Metallic Foams (MetFoam 2011))

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493 KiB

Open AccessArticle

Characterization of Steel Foams for Structural Components

by Brooks H. Smith, Stefan Szyniszewski, Jerome F. Hajjar, Benjamin W. Schafer and Sanjay R. Arwade

Metals 2012, 2(4), 399-410; https://doi.org/10.3390/met2040399 - 1 Nov 2012

Cited by 28 | Viewed by 10412

Abstract

Experimentally measured mechanical properties of hollow sphere steel foam are the subject of this paper. The characterization of the hollow sphere foam encompasses compressive yield stress and densification strain, compressive plastic Poisson’s ratio, and compressive unloading modulus, as well as tensile elastic modulus, [...] Read more.

Experimentally measured mechanical properties of hollow sphere steel foam are the subject of this paper. The characterization of the hollow sphere foam encompasses compressive yield stress and densification strain, compressive plastic Poisson’s ratio, and compressive unloading modulus, as well as tensile elastic modulus, tensile unloading modulus, tensile yield stress, and tensile fracture strain. Shear properties are also included. These tests provide sufficient information to allow calibration of a macroscopic, continuum constitutive model. Calibrated foam plasticity parameters are tabulated, and unique feature of foam plasticity are explained. Also, initial development of mesoscale simulations, which explicitly model voids and sintered hollow spheres, is reported. This work is part of a larger effort to help the development of steel foam as a material with relevance to civil engineering applications. Full article

(This article belongs to the Special Issue Selected Papers from the 7th International Conference on Porous Metals and Metallic Foams (MetFoam 2011))

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667 KiB

Open AccessArticle

3D Microstructure Modeling of Porous Metal Filters

by Vladimír Hejtmánek and Pavel Čapek

Metals 2012, 2(3), 344-352; https://doi.org/10.3390/met2030344 - 10 Sep 2012

Cited by 1 | Viewed by 8003

Abstract

The contribution presents a modified method of stochastic reconstruction of two porous stainless-steel filters. The description of their microstructures was based on a combination of the two-point probability function for the void phase and the lineal-path functions for the void and solid phases. [...] Read more.

The contribution presents a modified method of stochastic reconstruction of two porous stainless-steel filters. The description of their microstructures was based on a combination of the two-point probability function for the void phase and the lineal-path functions for the void and solid phases. The method of stochastic reconstruction based on simulated annealing was capable of reproducing good connectivity of both phases, which was confirmed by calculating descriptors of the local porosity theory. Theoretical values of permeability were compared with their experimental counterparts measured by means of quasi-stationary permeation of four inert gases. Full article

(This article belongs to the Special Issue Selected Papers from the 7th International Conference on Porous Metals and Metallic Foams (MetFoam 2011))

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517 KiB

Open AccessArticle

Preparation and Characterization of Directionally Freeze-cast Copper Foams

by Aurelia I. Cuba Ramos and David C. Dunand

Metals 2012, 2(3), 265-273; https://doi.org/10.3390/met2030265 - 9 Aug 2012

Cited by 36 | Viewed by 8506

Abstract

Because of their excellent thermal and electric conductivities, copper foams are ideally suited for applications such as heat exchangers, catalyst supports and EMI-shields. Here, we demonstrate the preparation of copper with ~80% aligned, elongated, interconnected pores via directional freeze casting, a well established [...] Read more.

Because of their excellent thermal and electric conductivities, copper foams are ideally suited for applications such as heat exchangers, catalyst supports and EMI-shields. Here, we demonstrate the preparation of copper with ~80% aligned, elongated, interconnected pores via directional freeze casting, a well established processing technique for porous ceramics. First, an aqueous slurry of 40−80 nm cupric oxide powders was directionally solidified, resulting in a preform consisting of elongated, aligned dendrites of pure ice separated by interdendritic ice walls with high oxide powder content. Oxide rather than metallic nanometric particles are used, as the latter would oxidize rapidly and uncontrollably when suspended in the aqueous solution used during directional casting. The preforms were then freeze-dried to sublimate the ice and sintered in a hydrogen-bearing atmosphere to reduce the copper oxide to metallic copper particles and densify these copper particles. Microstructural analysis of the copper foams shows that three types of porosities are present: (i) aligned, elongated pores replicating the ice dendrites created during the freeze-casting process; (ii) micro-porosity in the partially sintered copper walls separating the elongated pores; and (iii) cracks in these copper walls, probably created because of shrinkage associated with the reduction of the oxide powders. Full article

(This article belongs to the Special Issue Selected Papers from the 7th International Conference on Porous Metals and Metallic Foams (MetFoam 2011))

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653 KiB

Open AccessArticle

Rate Dependence of the Compressive Response of Ti Foams

by Petros Siegkas, Vito L. Tagarielli, Nik Petrinic and Louis-Philippe Lefebvre

Metals 2012, 2(3), 229-237; https://doi.org/10.3390/met2030229 - 29 Jun 2012

Cited by 8 | Viewed by 6544

Abstract

Titanium foams of relative density ranging from 0.3 to 0.9 were produced by titanium powder sintering procedures and tested in uniaxial compression at strain rates ranging from 0.01 to 2,000 s⁻¹. The material microstructure was examined by X-ray tomography and Scanning [...] Read more.

Titanium foams of relative density ranging from 0.3 to 0.9 were produced by titanium powder sintering procedures and tested in uniaxial compression at strain rates ranging from 0.01 to 2,000 s⁻¹. The material microstructure was examined by X-ray tomography and Scanning Electron Microscopy (SEM) observations. The foams investigated are strain rate sensitive, with both the yield stress and the strain hardening increasing with applied strain rate, and the strain rate sensitivity is more pronounced in foams of lower relative density. Finite element simulations were conducted modelling explicitly the material’s microstructure at the micron level, via a 3D Voronoi tessellation. Low and high strain rate simulations were conducted in order to predict the material’s compressive response, employing both rate-dependant and rate-independent constitutive models. Results from numerical analyses suggest that the primary source of rate sensitivity is represented by the intrinsic sensitivity of the foam’s parent material. Full article

(This article belongs to the Special Issue Selected Papers from the 7th International Conference on Porous Metals and Metallic Foams (MetFoam 2011))

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1433 KiB

Open AccessArticle

Dynamic Behavior of Hybrid APM (Advanced Pore Morphology Foam) and Aluminum Foam Filled Structures

by Joachim Baumeister, Michele Monno, Massimo Goletti, Valerio Mussi and Joerg Weise

Metals 2012, 2(2), 211-218; https://doi.org/10.3390/met2020211 - 20 Jun 2012

Cited by 19 | Viewed by 7693

Abstract

The aim of this work is to evaluate the effect of different densities of hybrid aluminum polymer foam on the frequency behavior of a foam filled steel structure with different ratios between steel and foam masses. The foam filled structure is composed of [...] Read more.

The aim of this work is to evaluate the effect of different densities of hybrid aluminum polymer foam on the frequency behavior of a foam filled steel structure with different ratios between steel and foam masses. The foam filled structure is composed of three steel tubes with a welded flange at both ends bolted together to form a portal grounded by its free ends. Structure, internal and ground constraints have been designed and manufactured in order to minimize nonlinear effects and to guarantee optimal constraint conditions. Mode shapes and frequencies were verified with finite elements models (FEM) to be in the range of experimental modal analysis, considering the frequency measurement range limits for instrumented hammer and accelerometer. Selected modes have been identified with suitable modal parameters extraction techniques. Each structure has been tested before and after filling, in order to compute the percentage variation of modal parameters. Two different densities of hybrid aluminum polymer foam have been tested and compared with structures filled with aluminum foams produced using the powder compact melting technique. All the foam fillings were able to suppress high frequency membrane modes which results in a reduction of environmental noise and an increase in performance of the components. Low frequency modes show an increase in damping ratio only when small thickness steel frames are filled with either Hybrid APM or Alulight foam. Full article

(This article belongs to the Special Issue Selected Papers from the 7th International Conference on Porous Metals and Metallic Foams (MetFoam 2011))

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317 KiB

Open AccessArticle

Noise Reduction Potential of Cellular Metals

by Björn Hinze, Joachim Rösler and Nicolas Lippitz

Metals 2012, 2(2), 195-201; https://doi.org/10.3390/met2020195 - 12 Jun 2012

Cited by 9 | Viewed by 6296

Abstract

Rising numbers of flights and aircrafts cause increasing aircraft noise, resulting in the development of various approaches to change this trend. One approach is the application of metallic liners in the hot gas path of aero-engines. At temperatures of up to 600 °C [...] Read more.

Rising numbers of flights and aircrafts cause increasing aircraft noise, resulting in the development of various approaches to change this trend. One approach is the application of metallic liners in the hot gas path of aero-engines. At temperatures of up to 600 °C only metallic or ceramic structures can be used. Due to fatigue loading and the notch effect of the pores, mechanical properties of porous metals are superior to the ones of ceramic structures. Consequently, cellular metals like metallic foams, sintered metals, or sintered metal felts are most promising materials. However, acoustic absorption depends highly on pore morphology and porosity. Therefore, both parameters must be characterized precisely to analyze the correlation between morphology and noise reduction performance. The objective of this study is to analyze the relationship between pore morphology and acoustic absorption performance. The absorber materials are characterized using image processing based on two dimensional microscopy images. The sound absorption properties are measured using an impedance tube. Finally, the correlation of acoustic behavior, pore morphology, and porosity is outlined. Full article

(This article belongs to the Special Issue Selected Papers from the 7th International Conference on Porous Metals and Metallic Foams (MetFoam 2011))

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824 KiB

Open AccessArticle

Mitigation of Blast Effects on Protective Structures by Aluminum Foam Panels

by Changsu Shim, Nuri Yun, Robin Yu and Doyeon Byun

Metals 2012, 2(2), 170-177; https://doi.org/10.3390/met2020170 - 11 Jun 2012

Cited by 21 | Viewed by 8846

Abstract

Aluminum foams have low density and are attractive materials to mitigate high-speed pressure by blast loads due to high-energy absorption capabilities. In order to develop nonlinear material models for the aluminum foam with different density, mechanical properties of the foam and foam panels [...] Read more.

Aluminum foams have low density and are attractive materials to mitigate high-speed pressure by blast loads due to high-energy absorption capabilities. In order to develop nonlinear material models for the aluminum foam with different density, mechanical properties of the foam and foam panels under compression, tension, shear and bending moment were obtained by numerous tests. Through the explicit analyses of the foam panels by LS-DYNA, the derived models were verified. Performance of the foam panels with different scaled distances was evaluated by blast tests. Thickness, density and skin plate properties of the panel are the most important parameters to estimate the transmitted pressure to protective structures. Because the pressure of close range blast loading is not uniform, the skin plays an important role in the behavior of the foam. Numerical simulations considering the parameters provided basic design guidelines for the protective structures with sacrificial foam panels. Properly designed panels for the required blast loads can control the transmitted pressure to the target structure under a certain pressure on the yield strength of the foam. Full article

(This article belongs to the Special Issue Selected Papers from the 7th International Conference on Porous Metals and Metallic Foams (MetFoam 2011))

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281 KiB

Open AccessArticle

Molding of Aluminum Foams by Using Hot Powder Extrusion

by Masanori Shiomi and Yoshitaka Tanino

Metals 2012, 2(2), 136-142; https://doi.org/10.3390/met2020136 - 5 Jun 2012

Cited by 8 | Viewed by 8385

Abstract

In order to form aluminum foams directly from powder, a combined process of hot powder extrusion and molding is proposed. Aluminum powder mixed with a foaming agent is extruded into the mold through the die heated to a temperature higher than the melting [...] Read more.

In order to form aluminum foams directly from powder, a combined process of hot powder extrusion and molding is proposed. Aluminum powder mixed with a foaming agent is extruded into the mold through the die heated to a temperature higher than the melting point, and the mold is filled with the aluminum foam. When a stainless steel pipe is used for a simple mold, an aluminum foam bar is obtained of which the relative density varies between 0.2 and 0.3. The molding of aluminum foam by using three types of mold shape shows the influence of gravity and friction. The effect of gravity is significant when a large step exists at the connection between the mold inlet and the die outlet, and friction is dominant in cases where foam is mold in a narrow space. Full article

(This article belongs to the Special Issue Selected Papers from the 7th International Conference on Porous Metals and Metallic Foams (MetFoam 2011))

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2828 KiB

Open AccessArticle

Characterisation and Mechanical Testing of Open Cell Al Foams Manufactured by Molten Metal Infiltration of Porous Salt Bead Preforms: Effect of Bead Size

by Appichart Jinnapat and Andrew Kennedy

Metals 2012, 2(2), 122-135; https://doi.org/10.3390/met2020122 - 1 Jun 2012

Cited by 23 | Viewed by 8866

Abstract

Preforms made from porous salt beads with different diameters (0.5–1.0, 1.4–2.0 and 2.5–3.1 mm) have been infiltrated with molten Al to produce porous structures using pressure-assisted vacuum investment casting. Infiltration was incomplete for preforms with high densities. At higher infiltration pressures, penetration of [...] Read more.

Preforms made from porous salt beads with different diameters (0.5–1.0, 1.4–2.0 and 2.5–3.1 mm) have been infiltrated with molten Al to produce porous structures using pressure-assisted vacuum investment casting. Infiltration was incomplete for preforms with high densities. At higher infiltration pressures, penetration of molten Al occurred into beads of all sizes and was predicted using a simple model. The yield strength of the porous structures increased with increasing density and decreasing pore (bead) size. Despite the non-optimum distribution of metal in the porous structure, due to partial infiltration within the beads, the magnitude and density dependence of the yield stress were comparable with those for pure Al foams reported in similar studies. The structural efficiency was improved for structures produced at lower infiltration pressure, where the metal is predominantly distributed in the cell walls. The rate of salt dissolution from the preforms was high, in particular for high density preforms, large beads and preforms infiltrated at low pressures, owing to the ability of the porous beads to collapse as well as dissolve. Full article

(This article belongs to the Special Issue Selected Papers from the 7th International Conference on Porous Metals and Metallic Foams (MetFoam 2011))

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339 KiB

Open AccessArticle

Thermal Conductivity Computations of Sintered Hollow Sphere Structures

by Christoph Veyhl, Thomas Fiedler, Tobias Herzig, Andreas Öchsner, Timo Bernthaler, Irina V. Belova and Graeme E. Murch

Metals 2012, 2(2), 113-121; https://doi.org/10.3390/met2020113 - 30 May 2012

Cited by 7 | Viewed by 8505

Abstract

The thermal conductivity of sintered hollow sphere structures (HSS) is investigated within the scope of this paper. For this purpose, finite element analyses based on micro-computed tomography images are performed on HSS structures. The complex geometry of the real sintered HSS sample is [...] Read more.

The thermal conductivity of sintered hollow sphere structures (HSS) is investigated within the scope of this paper. For this purpose, finite element analyses based on micro-computed tomography images are performed on HSS structures. The complex geometry of the real sintered HSS sample is accurately captured with this new hybrid method. The numerical computations are investigated in three perpendicular directions (i.e., x, y and z) in order to examine the anisotropic material behaviour. The results indicate that sintered HSS reveals quasi-isotropic behaviour in terms of effective thermal conductivity. For the first time, the influence of the sphere wall thickness of real HSS is investigated. To this end, the computed tomography data is carefully manipulated by changing the thickness of the hollow sphere wall. The variation of the wall thickness alters the relative density and has a significant influence on the thermal conductivity. The influence of the relative density on the thermal conductivity reveals a linear dependency. Full article

(This article belongs to the Special Issue Selected Papers from the 7th International Conference on Porous Metals and Metallic Foams (MetFoam 2011))

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