cross section crash boxes

The energy absorption of an Alporas Al foam was shown to increase
approximately 50% at dynamic strain rates (Paul and Ramamurty 2000). The effect of
strain rate on the deformation of Alporas Al foams was further studied by Mukai and his
colleagues (Mukai, et al. 1999, Mukai, et al. 2006). The increase in the aspect ratio of
cell wall thickness to the cell edge length was shown to result in higher cell face
resistance to the cell wall stretching. The strain rate sensitivity of open and closed 6061
Al foams was investigated by Dannemann and Lankford (Dannemann and Lankford
2000). The strain rate dependency of the studied foams was explained by the change of
cell shape at increasing foam densities from polyhedral to spheroidal. Ma and his
colleagues studied the strain rate effect on the crushing behavior of metallic cellular
materials,(Ma, et al. 2009). Voronoi mesoscale model was implemented to resemble
closed cell foam structure in the numerical study (Figure 2.27). Both strain rate
insensitive and sensitive material model were implemented to differentiate the inertial
affects from the strain rate effects. Voronoi and the classical continuum models with
strain rate insensitive material model showed the increases in the crushing stresses at
increasing strain rates, proving the inertial effects on the stress enhancement at high
strain rates.
The energy absorption characteristics of closed cell foam were investigated at
varying impact velocities (Lopatnikov, et al. 2007, Lopatnikov, et al. 2004). The
impact of a rigid plate on a metal foam is considered in four different deformation
regimes. The first regime is the supersonic impact velocities, which is beyond the
virtually all practical applications. In the second regime, the shock compaction occurs,
the elastic wave propagation is neglected. In the third regime, both shock wave and
elastic wave propagation occur. In the fourth regime, the wave propagation is neglected;
the deformation is considered as quasi-static. The energy efficiency in regime 2 depends
on the density of foam and base material, and the mass of the impacted plate. The
energy efficiency in regime 3 depends on the Mach number and the critical stress and
strain of foam.
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