cross section crash boxes

The creep and plateau stress-temperature behavior of Al foams was previously
studied by few researchers (Andrews, et al. 1999a, Andrews, et al. 1999b, Haag, et al.
2003). The secondary creep strain rate and the time to failure of Alporas closed cell Al
foam were determined (Andrews, et al. 2001). Al foam showed comparable creep
activation and power law exponent values with those of pure Al under relatively low
stresses and at low temperatures. However, at high stresses, higher activation energy
and power law number were found. This behavior was attributed to the cell wall
breakage at very high creep rates due to the high local stresses caused by the
inhomogeneous cell microstructure. The plateau stresses of Al closed cell foams
decreased with increasing ,Figure 2.18 (Haag, et al. 2003).
The energy absorbing capacity and the plateau stresses of pure Al and solution
hardened Al-10% magnesium alloy (AlMg10) foams were previously compared (Han,
et al. 1998). The solution treated AlMg10 foam showed less number of load oscillations
than untreated foams. This behavior was explained by phase of Al and Mg compound
partially or wholly dissolved in phase by solution treatment. However, as-cast
AlMg10 foams showed higher plateau stresses and energy absorption than pure Al and
solution treated AlMg10 foams (Figure 2.19).
Figure 2. 18. Plateau stress vs. temperature at a strain rate of 3.4 X 10 -4 s -1 .
(Source: Haag, et al. 2003)
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