Enhanced energy mitigation of thin-walled tube filled with liquid nanofoam under dynamic impact

Due to the intimate contact between the fluid-like liquid nanofoam (LN) filler and the tube wall, the filler-tube wall interaction in LN-filled tube (LNFT) is enhanced, leading to a much-improved performance of the composite structure. However, a comprehensive understanding of the energy mitigation performance and the underlying working mechanism of LNFT is still lacking. This study aims to explore the crushing behavior of LNFT subjected to quasi-static compression and dynamic impact and reveal the working mechanism of LNFT at different strain rates and the selection criteria for LN filler and tube wall material. A series of quasi-static compression tests are conducted on LNFTs with various LN fillers. The strengthening coefficient of LNFTs is larger than 3.5. Micro-CT images show that the LN-tube interaction improves the performance of LNFT through extended plastic deformation of the tube wall. Under dynamic impacts, the energy absorption capacity of LNFT shows 54% increase compared to that under quasi-static tests, leading to a remarkable strengthening coefficient of 8.0. The strain rate effect is due to the different energy mitigation mechanisms of the LN-filler, i.e. energy dissipation at lower strain rate and energy capture at higher strain rate. To optimize the impact mitigation performance of LNFT, the most critical system parameters are the infiltration pressure and total pore volume of the LN-filler and the stiffness and ductility of the tube wall. These findings and research outcomes expedite the understanding of the impact mitigation mechanism of LNFT and provide design guidance for the LN-based composite structures.