Deformation characteristics of press-formed cylindrical tubes with shallow and hemispherical caps for frontal crash protective structures

Thin-walled cylindrical tubes have been extensively used as energy absorbing structures in vehicular frontal structures owing to their superior energy absorption characteristics and effective crashworthiness performance. However, these tubes often exhibit extreme initial peak crushing force under impact, which in turn cause severe harm to the occupants. The present research study examines the effectiveness of harnessing shallow and hemispherical caps over the cylindrical tubes to mitigate the initial peak crushing force of a conventional cylindrical tube under static and impact crushing situations. Through experiments, the effect of caps on the initial peak crushing force and energy absorption characteristics of combined geometry tubes were assessed. Subsequently, coupled finite element simulations for both deep drawing and static crushing events were developed to provide additional insight using LS-DYNA finite element code. The crashworthiness characteristics of the proposed combined geometry tubes were compared with the bare cylindrical tubes and spherical caps and a significant reduction of about 20%–40% in the initial peak crushing force was witnessed. The overall results revealed the possibility of reducing the initial peak crushing force without incriminating the energy absorbing capacity using the combined geometry tubes. Hence, both the proposed cylindrical tubes with caps could be used as impact energy absorbing structures in automotive vehicles.