Metal Foams: A Design Guide

96 Metal Foams: A Design Guide
σ max
σ pl
σ max
σ pl
1
0.8
0.6
0.4
0.2 R = 0.1, Compression
R = 0.5, Compression
0
R = 0.1, Tension
103 102 101 104 105 106 107 108 1.4
1.2
1
0.8
0.6
10 2
Cycles
R = 0.1, Compression
R = 0.5, Compression
R = 0.1, Tension
Figure 8.5 (continued)
(c)
10 3 10 4 10 5 10 6 10 7
Cycles
(d)
Endurance
limit
the number of cycles to failure relates to specimen fracture in tension–tension
fatigue, and to the number of cycles, NI, to initiate progressive shortening
in compression–compression fatigue. Results are shown in Figure 8.5(a) for
an Alporas foam, in Figure 8.5(b) for an Alulight foam, in Figure 8.5(c) for
an Alcan foam and in Figure 8.5(d) for a Duocel foam. The following broad
conclusions can be drawn from these results:
1. The number of cycles to failure increases with diminishing stress level. An
endurance limit can usefully be defined at 1 ð 10 7 cycles, as is the practice
for solid metals.
2. The fatigue life correlates with the maximum stress of the fatigue cycle,
max, rather than the stress range 1 for all the foams considered: