The safety of occupants in case of impact has become increasingly important. In crash scenarios, damage to the cargo and components of the system should also be minimized. A large amount of kinetic energy is present in the collision between two or more systems. Proper management of this energy is important to improve the safety of the structure. In many systems, deformable structures are used to absorb energy. Thin walled tubes are widely used in energy absorbing applications due to their high strength to weight ratio. Thin wall energy absorbers are used in automotive applications such as bumper systems and in aerospace applications such as aircraft subfloor systems. In the current study, energy absorption characteristics of different configurations of thin wall energy absorbers subjected to axial loading are investigated.
An experimental investigation is conducted on square thin walled tube made of aluminium alloy. The compression of specimens was carried out at a constant displacement rate. The crushing of single tubes is investigated first. Double wall tube configurations with parallel and diamond arrangements are examined. Unequal length double wall tube was analysed for different inner and outer tube length. Polymer foam was used as filler material in the cavity between two tubes. Double wall foam filled tubes are examined with three different density of foam filling in parallel and diamond configurations. 2D and 3D images obtained from X-ray computed tomography scan of specimens are used to investigate the crushing characteristics of inner and outer tubes in different configurations. Numerical analysis on different empty and foam filled configurations is conducted using nonlinear explicit finite element code LS-Dyna. Results obtained from numerical analysis are validated with experimental.
From force vs. displacement curves of crushing, energy absorption parameters for different configurations are calculated and compared. Symmetric progressive buckling mode is observed in all the configurations. Due to interaction effects, a double wall tube absorbs more energy compared to the sum of energy absorbed by single-wall tubes. The diamond double wall tube absorbs more energy compared to parallel. Unequal length configurations have higher efficiency of energy absorption compared to double wall tube. Compared to double wall tube, double wall foam filled configuration exhibit 55% more energy absorption and 17% higher specific energy absorption. The effect of density of foam filling on the folding of inner and outer tubes is investigated. In numerical analysis, energy absorbed by an individual constituent in the different configurations is examined. The effect of interaction between different components of the structure is investigated in this study.