11 This Design Guide

Metallic foams ('metfoams') are a new class of material, unfamiliar to most engineers. They are made by a range of novel processing techniques, many still under development, which are documented in Chapter 2. At present metfoams are incompletely characterized, and the processes used to make them are imperfectly controled, resulting in some variability in properties. But even the present generation of metfoams have property profiles with alluring potential, and the control of processing is improving rapidly. Metfoams offer significant performance gains in light, stiff structures, for the efficient absorption of energy, for thermal management and perhaps for acoustic control and other, more specialized, applications (Section 1.2). They are recyclable and non-toxic. They hold particular promise for market penetration in applications in which several of these features are exploited simultaneously.

But promise, in today's competitive environment, is not enough. A survey of the history of development of new material suggests a scenario like that sketched in Figure 1.1. Once conceived, research on the new material accelerates rapidly, driven by scientific curiosity and by the often over-optimistic

Implementation

Industrial

Activity

Industrial

Activity

10 Years

Figure 1.1 A development history typical of many new materials. Research into the new material grows rapidly, and then slumps when little interest is shown by industry in using it. On a longer (15-year) time scale, applications slowly emerge

10 Years

Conception

Figure 1.1 A development history typical of many new materials. Research into the new material grows rapidly, and then slumps when little interest is shown by industry in using it. On a longer (15-year) time scale, applications slowly emerge predictions of its potential impact on engineering. The engineering take-up, however, is slow, held back by lack of adequate design data, experience and confidence; the disappointing take-up leads, after some 5 or 10 years, to disillusionment and a decline in research funding and activity. On a longer time-scale (15 years is often cited as the typical gestation period) the use of the new material - provided it has real potential - takes hold in one or more market sectors, and production and use expands, ultimately pulling research and development programmes with it.

There are obvious reasons for seeking a better balance between research and engineering take-up. This Design Guide is one contribution to the effort to achieve faster take-up, to give development curves more like those of Figure 1.2. Its seeks to do this by

• Presenting the properties of metallic foams in a way which facilitates comparison with other materials and structures

• Summarizing guidelines for design with them

• Illustrating how they might be used in lightweight structures, energy-absorbing systems, thermal management and other application, using, where possible, case studies.

The Guide starts with a description of the ways in which metfoams are made (Chapter 2) and the methods and precautions that have evolved for testing and characterizing them (Chapter 3). It continues with a summary of material properties, contrasting those of metfoams with those of other structural materials (Chapter 4). Chapter 5 outlines design analysis for materials selection. This is followed in Chapter 6 by a summary of formulae for simple structural shapes

Activity

Activity

5 10 15

Years

Figure 1.2 A more attractive development history than that of Figure 1.1. Early formulation of design rules, research targeted at characterizing the most useful properties, and demonstrator projects pull the 'take-up' curve closer to the 'research' curve r'"_i_i_

5 10 15

Years

Figure 1.2 A more attractive development history than that of Figure 1.1. Early formulation of design rules, research targeted at characterizing the most useful properties, and demonstrator projects pull the 'take-up' curve closer to the 'research' curve and loadings; the ways in which the properties of metal foams influence the use of these formulae are emphasized.

Mechanical design with foams requires constitutive equations defining the shape of the yield surface, and describing response to cyclic loading and to loading at elevated temperatures. These are discussed in Chapters 7, 8 and 9. One potential application for foams is that as the core for sandwich beams, panels and shells. Chapter 10 elaborates on this, illustrating how the stiffness and strength of weight-optimized sandwich structures compare with those of other types. Chapters 11, 12 and 13 outline the use of metal foams in energy, acoustic and thermal management. Chapter 14 describes how they can be cut, finished and joined. Chapter 15 discusses economic aspects of metal foams and the way economic and technical assessment are combined to establish viability. Chapter 16 reports case studies illustrating successful and potential applications of metal foams. Chapter 17 contains a list of the suppliers of metal foams, with contact information. Chapter 18 lists Web sites of relevant research groups and suppliers. The Guide ends with an Appendix in which material indices are catalogued.

Lightweight structures Excellent stiffness-to-weight ratio when loaded in bending: attractive values of E1/3/p i/and see Chapter 5 and Appendix

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