Metal Foams: A Design Guide

198 Metal Foams: A Design Guide
Through-fasteners may be required to carry bearing loads (Figure 15.5).
Initial yield occurs when the mean bearing load exceeds the crushing strength
of the foam, that is, when
Fb D 2Rt c
t
2R
F F
2 2
Figure 15.5 A through-fastener carrying bearing loads
where c is the crushing strength of the foam, approximated by
� �3/2 c ³ 0.3
y,s
s
2R
s c
F
⊲15.6⊳
(see Chapter 4, Equation (4.2)). Once yielding has occurred the fastener is no
longer secure and fretting or local plasticity caused by tilting make its behavior
unpredictable. Equation (15.6), with an appropriate safety factor, becomes the
safe design criterion.
Displacement (mm)
10
8
6
4
2
0
−2
1
F p = 0.85N
10
F max /F p
= 0.8
10 2
0.55
10 3 10 4 10 5 10 6
Number of cycles
0.50
Figure 15.6 The accumulated displacement under tension–tension cyclic
loading of embedded fastners at various levels of peak cyclic stress
0.40