Metal Foams: A Design Guide

Stress (MPa)
Characterization methods 29
between 5% and 30% of the mean while that in the compressive strength is
typically between 5% and 15%. Data for the compressive strength of metallic
foams are presented in Chapter 4.
3.4 Uniaxial tension testing
Uniaxial tension tests can be performed on either waisted cylinder or dogbone
specimens. The specimens should be machined to the shape specified in ASTM
E8-96a, to avoid failure of the specimen in the neck region or at the grips.
The minimum dimension of the specimen (the diameter of the cylinder or the
thickness of the dogbone) should be at least seven times the cell size to avoid
specimen/cell size effects. Gripping is achieved by using conventional grips
with sandpaper to increase friction, or, better, by adhesive bonding.
Displacement is best measured using an extensometer attached to the
waisted region of the specimen. A typical tensile stress–strain curve for an
aluminum foam is shown in Figure 3.4. Young’s modulus is measured from the
unloading portion of the stress–strain curve, as in uniaxial compression testing.
The tensile strength is taken as the maximum stress. Tensile failure strains are
low for aluminum foams (in the range of 0.2–2%). The standard deviation in
the tensile strengths of aluminum foams, like that of the compressive strength,
is between 5% and 15% of the mean. Typical data for the tensile strength of
metallic foams are given in Chapter 4.
1.5
1.0
0.5
Unload/Reload
0.0
0 0.005
Strain
0.010
Figure 3.4 Stress–strain curve from a uniaxial tension test on a dogbone
specimen of a closed-cell aluminum foam (8% dense Alporas) (from Andrews
et al., 1999a)