210 Gasmetal eutectic solidification

Numerous metal alloy-hydrogen binary phase diagrams exhibit a eutectic these include Al-, Be-, Cr-, Cu-, Fe-, Mg-, Mn- and Ni-based alloys. The alloys are melted, saturated with hydrogen under pressure, and then direction-ally solidified, progressively reducing the pressure. During solidification, solid metal and hydrogen simultaneously form by a gas eutectic reaction, resulting in a porous material containing hydrogen-filled pores. These materials are referred to as GASARs (or GASERITE). A...

153 Joining of metal foams

Metal foams can be soldered and welded. Foams have a cellular structure resembling, in some ways, that of wood. Because of this they can be joined in ways developed for wood, using wood screws, glue joints or embedded fasteners. Figure 15.1 summarizes joining methods. Wood screws Soldering brazing Glue line n Wood screws Soldering brazing Glue line n Figure 15.1 Ways of fastening and joining metal foams Welding and brazing are best used for foams with integral skins. Studies of laser welding...

73 Postscript

Insufficient experimental data are available to be fully confident about the accuracy of the isotropic hardening law (7.18). There is some evidence that the rate of hardening for hydrostatic compression may be greater than that in simple compression. Indeed, experimental measurements of the hydrostatic and uniaxial compression responses of Alporas and Duocel suggest that the hardening rate is faster for hydrostatic compression (see Figure 7.5 for data presented...

Preface and acknowledgements

Metal foams are a new class of materials with low densities and novel physical, mechanical, thermal, electrical and acoustic properties. This Design Guide is a contribution to the concurrent development of their science and exploitation. It seeks to document design information for metal foams even as the scientific research and process development are evolving. This should help to identify promising industrial sectors for applications, guide process development and accelerate take-up. This work...

References

Antohe, B.V., Lage, J.L., Price, D.C. and Weber, R.M. (1996) Int. J. Heat Fluid Flow 17, 594-603 Bastawros, A.-F., and Evans, A.G. (1997) Proc. Symp. on the Applications of Heat Transfer in Microelectronics Packaging, IMECE, Dallas, Texas, USA. Bastawros, A.-F., Stone, H.A. and Evans, A.G. (in press) J. Heat Transfer. Holman, J.P. (1989) Heat Transfer - a Modern Approach, McGraw-Hill, New York. Kaviany, M. (1985) Int. J. Heat Mass Transfer 28, 851-858. Lu, T.J., Stone, H.A. and Ashby, M.F....

94 Creep data for metallic foams

The limited creep data for metallic foams are consistent with equation (9.3). Figure 9.3 shows log(steady-state creep rate) plotted against log(stress) and against 1 T for a Duocel 6101-T6 aluminum foam, allowing the power, n, and activation energy, Q, to be determined. The measured creep exponent n 4.5 Compression, Q 157 kJ mole a Tension, Q 174 kJ mole - Figure 9.3 Secondary creep strain rate plotted against (a) stress (T 275 C) and (b) 1 Temperature (a 0.42 MPa) for an open-cell aluminum...

Design analysis for material selection

A material is selected for a given component because its property profile matches that demanded by the application. The desired property profile characterizes the application. It is identified by examining the function of the component, the objectives which are foremost in the designer's mind, and constraints that the component must meet if it is to perform adequately. The applications in which a new material will excel are those in which the match between its property profile and that of the...

61 Constitutive equations for mechanical response

The behavior of a component when it is loaded depends on the mechanism by which it deforms. A beam loaded in bending may deflect elastically it may yield plastically it may deform by creep and it may fracture in a brittle or in a ductile way. The equation which describes the material response is known as a constitutive equation, which differ for each mechanism. The constitutive equation contains one or more material properties Young's modulus, E, and Poisson's ratio, v, are the material...

174 Optical systems for space applications

ERG, the producers of the DUOCEL range of metal foams (see Chapter 2, Section 2.5), exemplify successful applications of these materials in aerospace.* This case study and the next two describe three of these. Mirrors of all sorts play a key role in space technology. Whether the frequencies are optical, infrared or microwave, precision, low mass and freedom from long-term distortion are primary design constraints. Figure 17.6 shows the basic structure of a DUOCEL-backed composite mirror used by...

Design for fatigue with metal foams

In structural applications for metallic foams, such as in sandwich panels, it is necessary to take into account the degradation of strength with cyclic loading. A major cause of this degradation is the nucleation and growth of cracks within the foams. In a closed-cell foam, the cell faces are subject to membrane stresses while the cell edges bend predominantly. Consequently, crack initiation and growth occurs first in the cell faces and then progresses into the cell edges for a closed-cell...

163 Cost modeling

The manufacture of a foam (or of a component made from one) consumes resources (Table 16.1). The final cost is the sum of these resources. This resource-based approach to cost analysis is helpful in selecting materials and processes even when they differ greatly, since all, no matter how different, consume the resources listed in the table. Thus the cost of producing one kg of foam entails the cost Cm ( kg) and mass, m, of the materials and feedstocks from which it is made, and it involves the...

143 Electrical conductivity and relative density

Figure 14.3 shows an idealization of a low-density open cell foam. The cell edges have length i and cross-section t x t, meeting at nodes of volume t3. The relative density of an open-cell foam is related to the dimensions of the cells (omitting terms of order (t i)4) by Figure 14.3 An idealized open-cell foam consisting of cell edges of length I and cross-section t2, meeting at nodes of volume t3. In real foams the nodes are larger ('Plateau borders') and the edges thinner at their mid-points,...

54 Where might metal foams excel

Material indices help identify applications in which a material might excel. Material-selection charts like those shown in Chapters 4, 11 and 12 allow the values of indices for metal foams to be established and compared with those of other engineering materials. The comparison reveals that metal foams have interesting values of the following indices 1. The index E1 3 p which characterizes the bending-stiffness of lightweight panels (E is Young's modulus and p the density). A foam panel is...

36 Multiaxial testing of metal foams

A brief description of an established test procedure used to measure the multiaxial properties of metal foams is given below. Details are given in Deshpande and Fleck (2000) and Gioux et al. (2000). A high-pressure triaxial system is used to measure the axisymmetric compres-sive stress-strain curves and to probe the yield surface. It consists of a pressure cell and a piston rod for the application of axial force, pressurized with hydraulic fluid. A pressure p igives compressive axial and radial...

28 Hollow sphere structures

Several approaches have recently emerged for synthesizing hollow metal spheres. One exploits the observation that inert gas atomization often results in a small fraction (1-5 ) of large-diameter (0.3-1 mm) hollow metal alloy spheres with relative densities as low as 0.1. These hollow particles can then be sorted by flotation methods, and consolidated by HIPing, by vacuum sintering, or by liquid-phase sintering. Liquid-phase sintering may be the preferred approach for some alloys since it avoids...

Energy management packaging and blast protection

Ideal energy absorbers have a long, flat stress-strain (or load-deflection) curve the absorber collapses plastically at a constant stress called the plateau stress. Energy absorbers for packaging and protection are chosen so that the plateau stress is just below that which will cause damage to the packaged object the best choice is then the one which has the longest plateau, and therefore absorbs the most energy. Solid sections do not perform well in this role. Hollow tubes, shells, and metal...

Contents

Preface and acknowledgements ix List of contributors xi Table of physical constants and conversion units xiii 1.2 Potential applications for metal foams 3 1.3 The literature on metal foams 5 2.2 Melt gas injection (air bubbling) 8 2.3 Gas-releasing particle decomposition in the melt 9 2.4 Gas-releasing particle decomposition in semi-solids 11 2.5 Casting using a polymer or wax precursor as template 11 2.6 Metal decomposition on cellular preforms 14 2.8 Hollow sphere structures 16 2.9...

Appendix Catalogue of material indices

Material indices help to identify the applications in which a material might excel and those for generic components are assembled here. Their derivation and use is illustrated in Chapters 5, 11 and 12. (a) Stiffness-limited design at minimum mass (cost, energya) Function and constraintsa Maximizeb Stiffness, length, shape specified, section area free G1 2 p Stiffness, length, outer radius specified wall thickness free G p Stiffness, length, wall thickness specified, outer radius free G1 3 p...

Electrical properties of metal foams

The electrical conductivity of a metal foam is less than that of the metal from which it is made for the obvious reason that the cell interiors, if gas-filled, are non-conducting. One might guess that the conductivity should vary linearly with the relative density, but the real dependence is stronger than linear, for reasons explained below. Though reduced, the conductivity of metal foams is more than adequate to provide good electrical grounding and shielding of electromagnetic radiation. The...

81 Definition of fatigue terms

First, we need to define some standard fatigue terms. Consider a cylindrical specimen loaded uniaxially by a stress, a, which varies from a minimum absolute value amin to a maximum absolute value amax, as shown in Figure 8.1. For example, for a fatigue cycle ranging from 1MPa to 10MPa, we take Figure 8.1 (a) Definition of fatigue loading terms (b) Typical S-N curve for aluminum alloys, in the form of stress range Aa versus number of cycles to failure, Nf. The endurance limit, Aae, is defined,...

39 Indentation and hardness testing

Reproducible hardness data require that the indenter (a sphere or a flat-ended cylinder) have a diameter, D, that is large compared with the cell size, d(D di> i7). Edge effects are avoided if the foam plate is at least two indenter diameters in thickness and if the indentations are at least one indenter diameter away from the edges of the plate. Because they are compressible, the indentation strength of a foam is only slightly larger than its uniaxial compressive strength. By contrast, a...

310 Surface strain mapping

The strain field on the surface of a metallic foam resulting from thermome-chanical loading can be measured using a technique known as surface strain mapping. The surfaces of cellular metals are irregular, with the cell membranes appearing as peaks and troughs, allowing in-situ optical imaging to be used to provide a map of surface deformation. Commercial surface displacement analysis equipment and software (SDA) are available from Instron (1997). The SDA software performs an image correlation...

Product name and contact information

*AEREX Aerex Limited Specialty Foams CH-5643 Sins, Switerland Tel +0041 42 66 00 66 Fax +0041 42 66 17 07 Duralcan (Dr L.D. Kenny) Alcan International Ltd Box 8400, Kingston Ontario, K7L 5L9 Canada Tel +001 613 541 2400 Fax +001 613 541 2134 Tel +001 905 602 1100 ext 17 Fax +001 905 602 1250 e-mail cymat ican.net Web www.cymat.com Tel +001 513 772 1242 Fax +001 513 602 9080 *DUOCEL (Mr Bryan Leyda, Technical Director) ERG Materials and Aerospace Corporation 900 Stanford Avenue Oakland, CA 94608...

72 Yield behavior of metallic foams

We can modify the above theory in a straightforward manner to account for the effect of porosity on the yield criterion and strain-hardening law for a metallic foam. We shall assume the elastic response of the foam is given by that of an isotropic solid, with Young's modulus E and Poission's ratio v. Since foams can yield under hydrostatic loading in addition to deviatoric loading, we modify the yield criterion (7.8) to where we define the equivalent stress o by This definition produces a yield...

82 Fatigue phenomena in metal foams

Metal Foams

When a metallic foam is subjected to tension-tension loading, the foam progressively lengthens to a plastic strain of about 0.5 , due to cyclic ratcheting. A single macroscopic fatigue crack then develops at the weakest section, and progresses across the section with negligible additional plastic deformation. Typical plots of the progressive lengthening are given in Figure 8.2. Shear fatigure also leads to cracking after 2 shear strain. In compression-compression fatigue the behavior is...

211 Literature on the manufacture of metal foams

Metal Foams

Ampormat Porous Materials, Astro Met, Inc., Cinncinnati. Davies, G.J. and Zhen, S. 1983 Metallic foams their production, properties, and applications. Journal of Materials Science 18 1899-1911. Banhart, J. and Baumeister, J. 1988 Production methods for metallic foams. In Shwartz, D.S., Shih, D.S., Evans, A.G. and Wadley, H.N.G. eds 1998 Porous and Cellular Materials for Structural Application, Materials Research Society Proceedings, Vol. 521, MRS, Warrendale, PA, USA. a Metal -...

84 Notch sensitivity in static and fatigue loading

A practical concern in designing with metallic foams is the issue of damage tolerance in the presence of a notch or hole, does it fail in a notch-insensitive, ductile manner when the net section stress equals the uniaxial strength Or does it fail in a notch-sensitive, brittle manner, when the local stress at the edge of the hole equals the uniaxial strength We can answer this question immediately for the case of static compression of a foam containing a circular hole the large compressive...