cross section crash boxes

deformation mode transition from axisymmetric to non-symmetric depended on tube
D/t ratio and the hardening characteristics of the tube material. The simulation
deformation modes and the load-deformation curves of the tubes were found to be in
good agreement with those of experiments. The analytical model proposed by
Wierzbicki et al. (Wierzbicki, et al. 1992) for circular tube plastic hinge deformation
showed the highest correlation with the experiments. Pipkorn and Haland (Pipkorn and
Hayland 2005) studied the crash performance of tubes with smooth and variable
diameter and with internal pressure. Experimental and numeric results showed that
increasing internal pressure increased the absorb energy. Energy efficiency increased
up to 60% and 70% in smooth and variable diameter circular tubes, respectively.
Finite element simulation of square and circular tube inversion under static and
dynamic loading was performed by Webb et al.(Webb, et al. 2001). The tube wall
thickness was taken as variable. The simulations gave similar results with experiments.
Singace and El-Sobky (Singace and Elsobky 2000) investigated the deformation modes
of circular tubes and reported that concertina mode of deformation resulted in higher
mean load values, while mixed mode of deformation showed higher energy absorption
values than concertina mode. The crushing behavior of a 6060T5 circular aluminum
tube was investigated experimentally and numerically by Huang and Lu (Huang 2003).
A new theoretical model was used to predict the mean crushing force using a total work
of membrane energy dissipation in deformation zones and the required bending energy
of plastic hinges. The model could not predict the peak load values accurately, while the
mean load and the half fold length calculations showed good agreement with those of
experiments and simulations. Galib and Limam performed extensive study on the
static and dynamic crushing behavior of empty 6060T5 aluminum circular tubes, (Galib
and Limam 2004). It was found that the deformation velocity had no effect on the
deformation load capacity and deformation mode of 6060T5 circular tubes within the
strain rate range between 91 and 114 s -1 . The dynamic mean load values were found
10% higher than those of quasi-static tests. The increase in the mean load values was
attributed to micro inertial effects (the lateral movement of circular structure at the
initial stage of impact). The simulations showed that increasing the ratio of amplitude
of the surface imperfection to thickness (a/t) reverted the mixed mode of deformation of
tube into diamond mode (Figure 3.7), reducing the absorbed energy.
37