Metal Foams: A Design Guide

42 Metal Foams: A Design Guide
by structure too. This influence, imperfectly understood at present, is a topic of
intense current study. Better understanding will lead to greater process control
and improved properties. But for now we must accept the structures as they
are, and explore how best to design with the present generation of foams.
With this in mind, we document here the properties of currently available,
commercial, metal foams.
4.2 Foam properties: an overview
The ranges of properties offered by currently available metal foams are documented
in Table 4.1. Many suppliers offer a variety of densities; the properties,
correspondingly, exhibit a wide range. This is one of the attractive aspects of
such materials: a desired profile of properties can be had by selecting the
appropriate foam material with the appropriate density.
Nomenclature and designation
It is important to distinguish between the properties of the metfoam and
those of the solid from which it is made. Throughout this Guide, properties
subscripted with s refer to the solid from which the foam is made (e.g.
solid density: s); properties without the subscript s are those of the metfoam
(foam density: ).
Data sources
Data can be found in the literature cited in Section 1.4, and in recent publications
in leading materials journals. The most comprehensive data source is
the CES (1999) database and associated literature; it draws on manufacturers’
data sheets, on published literature, and on data supplied by research groups,
worldwide (Evans, 1997/1998/1999; Banhart, 1999; Degisher, 1999; Simancik,
1999). The CES database has been used to create the material property charts
showninSection4.3 andlater chapters.
Mechanical properties
Figures 4.2 and 4.3 show a schematic stress–strain curve for compression,
together with two sets of real ones. Initial loading apears to be elastic but
the initial loading curve is not straight, and its slope is less than the true
modulus, because some cells yield at very low loads. The real modulus E, is
best measured dynamically or by loading the foam into the plastic range, then
unloading and determining E from the unloading slope. Young’s modulus, E,