Metal Foams: A Design Guide

128 Metal Foams: A Design Guide
Bond
Failure
Core
Yield
Core
Indentation
Face
Yield
Face
Wrinkle
Failure
Modes
Figure 10.10 Failure modes in sandwich panels
Loading
Gc D Ec/2⊲1 C c⊳. The uniaxial yield strain of the core, c y /Ec, is assumed to
be no less that of the face sheets, f y /Ef. Consequently, a constraint on face
sheet yielding ensures that only shear yielding of the core need be explicitly
considered. In this example, the yield strength of the core in shear is
taken to be
c
y D ˛3⊲ s y /2⊳⊲ c/ f⊳ 3/2
where the quality factor, ˛3, is about 0.3.
The weight (in units of kg) of the sandwich plate is
c
t
p
⊲10.22b⊳
W D bℓ⊲2 ft C cc⊳ ⊲10.22c⊳
Under the uniform lateral pressure, p, the maximum stress in the face sheets is:
D ⊲p/8⊳⊲ℓ 2 /ct⊳ ⊲10.23a⊳
This maximum occurs at the middle of the plate, with tension on the bottom
and compression at the top. The maximum shear stress in the core, which
occurs near the supports, is:
D ⊲p/2⊳⊲ℓ/c⊳ ⊲10.23b⊳
The face sheet wrinkling stress is:
f
w D k⊲EfE 2 c ⊳1/3
⊲10.23c⊳