cross section crash boxes

Figure 3.12. Folding in square tubes of ASTM A36, A513, AISI 316 and 304
(Source: DiPaolo and Tom 2006)
Impact energy absorption of extruded 6061 Al tubes with different cross-
sections were investigated by Dong-Kuk Kim and Sunghak Lee (Kim and Lee 1999).
The tubes with rectangular and circular cross-section were tested with and without
welded top and bottom plate. SEA values of the impacted tubes of both geometries
increased with increasing thickness to width and thickness to diameter ratios. The
number of symmetric folds tended to increased with increasing thickness to width and
thickness to diameter ratios, in both tube geometries. It was noted that circular
specimens showed higher specific energy absorption than rectangular ones due to higher
tendency of circular tubes for symmetric fold formation. In addition, the edge tip radius
was found to be effective on the deformation load values of rectangular tubes. When the
edge tip radius was very small, compressive load was concentrated on the edges and
caused an early crack opening. The cracks propagated quickly and resulted in
considerably lower values of energy absorption.
Experimental and numerical energy absorption of an axially crushed square
6063T5 tube were determined with a buckling initiator (Figure 3.13(a)) by Zhang et
al.(Zhang, et al. 2009). During the impact test, a striker impinged the pre-hit column
and forced the steel strip to pull the opposite tube walls inwards. The folding initiated
when the striker contacted with the top edges of tube itself. Adopted folding initiator
resulted in 30% reduction in the initial buckling load level without effecting the
subsequent progressive crushing mode (Figure 3.12(b)).
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