Conventional energy absorbing materials and structures for impact loadings have been studied extensively in the past decades. However, most conventional energy absorbers are passive and designed to work efficiently only for normal working conditions. To overcome these disadvantages and further improve their energy absorption characteristics, the concept of adaptive energy absorption is proposed....[ Read more ]

Conventional energy absorbing materials and structures for impact loadings have been studied extensively in the past decades. However, most conventional energy absorbers are passive and designed to work efficiently only for normal working conditions. To overcome these disadvantages and further improve their energy absorption characteristics, the concept of adaptive energy absorption is proposed.

A typical adaptive energy absorbing system should consist of a sensor, a controller and an adjustable energy absorber, while the last item is crucial. In this project, three types of adaptive or adjustable energy absorbers are investigated. The first type employs buckling initiators to reduce the initial peak force of axially crushed thin-walled tubes, which function slightly before the impact happens. Experimental and theoretical analyses show that for both square and circular tubes, a reduction up to 30% in the peak force could be achieved without any sacrifice of their stiffness under normal working conditions. In the second type, thin-walled circular tubes were pressurized by compressed air or explosives and their energy absorbing behaviors under axial crushing are studied. It is revealed that by adjusting the initial pressure or the mass of explosive, the energy absorption of the pressurized tubes can be effectively controlled. For the third type, the application of electro-rheological (ER) fluids in impact scenarios is investigated by using an ER fluid cylinder. The results show that controllability of ER devices greatly depends on the impact velocity and it becomes weaker when the impact velocity increases.

After comparison, the first type is more suitable for high-velocity impacts, while the pressurized and ER fluid energy absorbers are effective for medium and low velocities, respectively. Based on the conceptual study in this thesis, some principles and guidelines for the design of adaptive energy absorbers are proposed which will be helpful for their further development.