Axially loaded pressurized thin-walled circular tubes used as adaptive energy absorbers

By filling compressed air into cellular materials, honeycombs or thin-walled structures, their energy absorption can be greatly enhanced, while this enhancement can be controlled by the applied pressure. This concept shines a light on the possibility of achieving adaptive energy absorption. To investigate the effect of the internal pressure on the response of the structures under impact loadings, the present paper reports our study on the axial crushing behavior of pressurized thin-walled circular tubes. Three groups of thin-walled circular tubes with the radius/thickness ratio between 120 and 200 were employed in the experiments and two working modes were studied: mode-I (with constant internal pressure) and mode-II (closed tubes with finite leakage). In the tests of mode-I, the influences of internal pressure on the deformation mode and energy absorption of the tubes were investigated. The results show that with the increase of internal pressure, the deformation mode switches from diamond mode with sharp corners to that with round corners, and eventually to ring mode. In diamond mode, the mean force of the tubes increases linearly with the internal pressure. The enhancement comes from two mechanisms: direct effect of the pressure and indirect effect due to the interaction between the pressure and the tube wall. After the deformation switches to ring mode, the enhancement resulted from the second mechanism becomes weaker. Based on the results of mode-I, the mode-II was experimentally investigated both quasi-statically and dynamically. The results are compared with the predictions obtained from a semi-empirical formula, showing good agreements.