6TH International Congress on Technology - Engineering - Kuala Lumpur3 - Malaysia (2018-07-19)

Crashworthiness Performance Of Cracked Circular Thin-walled Tube Under Oblique Impact

Circular thin-walled tubes have been widely used as energy absorbers for the protection of passengers and goods during accident and crashing damage. This geometrical energy absorbing structure has been found to be more reliable and efficient than other geometrical shape thin-walled structural absorbers. However, during high dynamic crushing process, these tubes may fail due to ductile fracture. The crack on the tubes has effect on their overall crashworthiness performance. This study investigates the crushing behavior of a conventional circular thin-walled tube subjected to various impact loading conditions and the crashworthiness parameters are evaluated. Parametric effects, deformation mode, damage morphologies, and stress-strain relationship are analyzed. The effect of crack initiation and propagation on the thin-walled tube to evaluate their crashworthiness performance can be studied. However, crack propagation of thin-walled tubes subjected to crushing conditions is a highly non-linear problem and a singular stress field which arises around the fracture end make the computation more complicated. Although, a non-propagating crack on the thin-walled tube subjected to high compressive impact loading is also non-linear, the singular stress field at the crack tip does not have any effect on the crashworthiness performance. To this end, we limit this research work to a non-propagating crack initiation on the thin-walled tube. The most crash occurrence that causes fatalities and death in real life is due to high velocity impact crushing. For this purpose, only dynamic impact crushing under oblique loading is studied. This crushing condition makes the energy absorbing material very sensitive to strain. Hence, a strain rate constitutive property is used for all the thin-walled tube configurations. Moreover, the material is typically a metal prepared from A36 steel hot rolled carbon and it is not enhanced with foams or composites. The results of the crashworthiness performance show that cracked thin-walled tube gives increased crushing force efficiency under oblique impact than their circular tube without crack when subjected to oblique impact. For tube thickness of 2.5 mm and impacting angles of 10°, 20° and 30°, the crushing force efficiency of the cracked tube are 73.36%, 74.42% and 67.04% respectively while that of the tube without crack are 72.82%, 61.85% and 57.96% respectively. The increased crushing force efficiency of the thin-walled tubes with crack is due to the ability of the tube to withstand bending during the deformation process and this also causes a reduction in the mean crushing force. Moreover, the introduction of crack on the tube causes it to be less susceptible to bending during oblique impact. However, during the dynamic impact of the cracked tube, the crashworthiness performance such as the total energy absorption and specific energy absorption, are reduced. The overall crashworthiness analysis shows the favourable and unfavourable effect of crack initiation on thin-walled tubes used as energy absorbers.
Chukwuemeke Isaac, Oluleke Oluwole