The commercial explicit crash code Virtual Performance Solution
(VPS) is used for the numerical analysis. An overview of the
finite element model of the cell, punches and bearings is provided
in Fig. 6.The jelly roll is secured by a 1 mm thick cylindrical stainless
steel housing. The housing is represented by shell elements (approximately 5 5mm2), whereas the jelly roll is represented by
volume elements (approximately 5 5 5mm3). The inner hole of
the jelly roll is neglected in the simulation model, as well as discretization
of the pole connectors on each end of the jelly roll. The
bearings and the punches are modelled as rigid bodies. A penaltyspring
based contact definition is applied between housing and
jelly roll, assuming a Coulomb friction coefficient of 0.1. Another
contact is applied between the punch, the cell housing and the
bearings, using a friction coefficient of 0.1.
The explicit simulations were performed using a time step of
one micro-second, which corresponds to a typical value used for
full scale vehicle crash simulations. The density of the jelly roll was
then trimmed in order to represent the real cell weight of 1.5 kg in
the simulation run. The punch intrusion velocity was set to
a significantly higher value (vSim ¼ 0.5 mm ms1) than the actual
test speed (vExp ¼ 0.1 mm s1), in order to reduce the computation
time. At any time during the simulation, the difference of punch
force and bearings force was less than 0.2 kN (0.04% of the
maximum load), indicating that existing mass inertia forces in the
simulation are still negligible in the simulated configuration. All
material models used in the subsequent sections are rate independent,
so that the increased simulation speed does not influence
the model behaviour at all.