Metal Foams: A Design Guide

Sandwich structures 123
the contact size increases with increasing load. The failure modes of core
shear, face yield and indentation have been observed for sandwich beams in
a four-point bend with roller-indenters by Harte (1999), and good agreement
between the measured strengths of the beams and theoretical predictions are
observed, upon making use of the formulae given above but with a D 0.
10.4 Case study: the three-point bending of a sandwich
panel
A set of three-point bend experiments on foam-cored sandwich panels has been
performed by Bart-Smith (1999), using a foam core of Alporas aluminum alloy
(relative density / s D 0.08) and 6061-T6 aluminum alloy face sheets. The
sandwich beams were loaded by flat-bottom indenters of size a/ℓ D 0.1; the
pertinent geometric and material parameters are summarized in Table 10.1 for
two specimen designs, 1 and 2. These designs are based on the collapse load
predictions, such that Design 1 sits within the core shear regime, whereas
Design 2 lies just within the indentation regime, as marked in Figure 10.6(a).
Table 10.1 Geometric and material
parameters for Designs 1 and 2
Parameter Design 1 Design 2
ℓ, mm 79 40
t, mm 0.8 0.8
c, mm 10 10
b, mm 20 21
H, mm 18 21
a, mm 7.9 4.0
Ef, GPa 70 70
f
y
, MPa 263 263
Ec, GPa 0.236 0.263
,MPa 1.5 1.5
c
y
The measured load F versus displacement υ curves are shown in
Figure 10.8; it was found that the Designs 1 and 2 failed by core shear and
by indentation, respectively. For comparison purposes, the predicted elastic
stiffness and collapse load have been added to each plot by employing relations
(10.1), (10.13) and (10.18). Additionally, the load-deflection responses were
calculated by a finite element procedure, using the constitutive model of