Achieving variable load crushing using pressurised composite tubes to improve vehicle crashworthiness

Abstract

This thesis presents an investigation on the utilisation of carbon fibre composite elements designed into a crushing system with the aim of improving energy absorption for crashworthy structures. An experimental evaluation of the crushing behaviour of pressurised composite tubes is presented, with the intent to develop a variable load energy absorbing system in which, the crushing force can be controlled through the radius size of trigger mechanism and the use of pressurised composite tubes. The influence of plug triggering radius on the energy absorption characteristics was determined from using different trigger radii from 0 mm (sharp corner) to 6 mm. Internal pressurisation is presented as a method to vary the crushing force of the tubes. A novel sealing-crushing system was demonstrated to achieve a simultaneously crushing and maintaining constant internal pressure under dynamic impact condition. Experiments were carried out for the composite tubes crushed axially at 9 bar and 18 bar internal pressure levels. The experimental program included quasi-static testing carried out at UNSW in Australia and dynamic testing at the German Aerospace Centre (DLR) in Stuttgart, Germany. For dynamic testing, a new generation of crushing system was developed and tested. The contribution of the force due to the internal pressure was significant to the crushing force of the tubes. It was improved by a proportion of the unpressurised crushing force (up to 60% in one case). Internal pressurisation of composite tubes has been presented as a method for achieving an ideal variable load energy absorber. Explicit finite element study was also carried to simulate the experiment. The finite element analysis contributed to the understanding of the experimental results as well as providing a predictive tool to minimise the need for further testing. This investigation included the application of a stacked-shell finite element modelling methodology incorporating detailed information about trigger chamfer, different friction zones between a composite tube and crushing tool. Based on the extensive experimental work and FE simulation, this thesis has demonstrated the potential for an adaptable composite crushing element under a range of impact energy scenarios as a proposed variable load energy absorber for realistic crash conditions.