Special Issue "Selected Papers from the 7th International Conference on Porous Metals and Metallic Foams (MetFoam 2011)"
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A special issue of Metals (ISSN 2075-4701).
Deadline for manuscript submissions: closed (31 March 2012)
Special Issue Editors
Guest Editor
Prof. Dr. Bo-Young Hur
School of Materials Science and Engineering, Department of Metallurgical and Materials Engineering, Gyeongsang National University, #501, Jinju-Daero, Jinju, 660-701, Korea
E-Mail: hurby@gsnu.ac.kr
Guest Editor
Dr. Seung-Eun Kim
Korea Institute of Material Science 797 Changwondaero, Sungsanku, Changwon, Gyeongnam, 642-831, Korea
E-Mail: sek24@kims.re.kr
Guest Editor
Prof. Dr. John Banhart
Institute of Materials Science and Technology, Berlin Institute of Technology - TU Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany
Website: http://www.helmholtz-berlin.de/media/media/spezial/people/banhart/html/index.html
E-Mail: john.banhart@tu-berlin.de
Guest Editor
Dr. Francisco Garcia Moreno
Institute of Applied Materials, Helmholtz-Centre Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
E-Mail: garcia-moreno@helmholtz-berlin.de
Special Issue Information
Dear Colleagues,
This 7th International Conference on Porous Metals and Metallic Foams (MetFoam) is one of a series held regularly at two-years intervals since 1999. The previous conferences of the MetFoam series were held at Bremen (1999, 2001) and Berlin (2003) in Germany, Kyoto (2005) in Japan, Montreal (2007) in Canada and Bratislava (2009) in Slovakia. MetFoam 2011 will be held in Busan, the second largest city of Korea, from September 18 to 21, 2011. The meeting will be scheduled to provide a forum for researchers active in the fields of porous and foam materials and for industrial materials engineers and product designers seeking new materials. We cordially invite you to attend MetFoam 2011 to present and discuss your research and to obtain new information on porous metals and metal foaming technology.
Papers for this special issue should be submitted on invitation only!
Conference website: http://www.metfoam2011.org/main/
Prof. Dr. Bo-Young Hur
Dr. Seung-Eun Kim
Prof. Dr. John Banhart
Dr. Francisco Garcia Moreno
Guest Editors
Submission
Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.
Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed Open Access quarterly journal published by MDPI.
Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 300 CHF (Swiss Francs).
English correction and/or formatting fees of 250 CHF (Swiss Francs) will be charged in certain cases for those articles accepted for publication that require extensive additional formatting and/or English corrections.
Published Papers (11 papers)
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Received: 17 April 2012; in revised form: 10 May 2012 / Accepted: 14 May 2012 / Published: 30 May 2012
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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 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.
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Received: 16 April 2012; in revised form: 17 May 2012 / Accepted: 28 May 2012 / Published: 1 June 2012
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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 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.
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Received: 29 March 2012; in revised form: 9 May 2012 / Accepted: 25 May 2012 / Published: 5 June 2012
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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 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.
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Received: 13 April 2012; in revised form: 16 May 2012 / Accepted: 1 June 2012 / Published: 11 June 2012
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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 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.
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Received: 15 April 2012; in revised form: 29 May 2012 / Accepted: 7 June 2012 / Published: 12 June 2012
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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 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.
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Received: 3 May 2012; in revised form: 29 May 2012 / Accepted: 11 June 2012 / Published: 20 June 2012
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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 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.
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Received: 27 April 2012; in revised form: 22 May 2012 / Accepted: 20 June 2012 / Published: 29 June 2012
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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 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.
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Received: 2 June 2012; in revised form: 9 July 2012 / Accepted: 30 July 2012 / Published: 9 August 2012
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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 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.
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Received: 11 May 2012; in revised form: 9 August 2012 / Accepted: 15 August 2012 / Published: 10 September 2012
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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. 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.
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Received: 5 May 2012; in revised form: 30 August 2012 / Accepted: 17 October 2012 / Published: 1 November 2012
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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, 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.
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Received: 18 September 2012; in revised form: 6 December 2012 / Accepted: 20 December 2012 / Published: 28 December 2012
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Abstract: 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 rmin. 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.
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Last update: 12 October 2012
