<p>Thin-walled structures are widely used as energy absorbers in many industrial and aerospace applications to mitigate the adverse effect of impact. While its energy absorption mechanism is the progressive tube wall buckling, the post-buckling stress buckling is much lower than the buckling initiation stress, leading to a much-reduced energy absorption efficiency of thin-walled structures. To address this problem, a novel energy absorption material liquid nanofoam (LN) is employed as the filling material in thin-walled tubes. The LN is a mixture of hydrophobic nanoporous particles and liquid. As the LN is subjected to a hydrostatic pressure and the pressure reaches a critical value, the liquid is intruded into the hydrophobic nanopores. Massive incident energy is converted into the liquid-solid interfacial energy and then mitigated as heat. It is hypothesized that by using LN as a filler, the energy absorption performance of thin-walled tube can be significantly improved.</p><p>First, small-scale LN-filled tubes (LNFTs) are prepared and their crush response is evaluated by both quasi-static compression tests (2 mm/min) and dynamic impact tests (~3 m/s). Results show that the average post-buckling strength of LNFTs is increased by more than 260% compared to empty tubes. Also, the post-buckling stress increases with increasing incident speed. The strengthening coefficient of LNFT is 3.8, much higher than that of solid foam-filled tube. This promoted strengthening effect of LNFTs is due to the enhanced liquid-solid interaction between LN and tube wall, resulting from extended plastic deformation of the tube wall. Second, large scale LNFTs are prepared and characterized by quasi-static compression tests (2 mm/s) and gas gun impact tests (6.7 m/s). The strengthening coefficient is also larger than 3.5. The extended plastic deformation of the tube wall due to liquid-solid interaction is confirmed by Micro-CT imaging. Compared to the LNFT under quasi-static tests, the energy absorption capacity of LNFT shows 54% increase under dynamic impacts, leading to a remarkable strengthening coefficient of 8.0. This 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. It is also found that to optimize the energy mitigation capacity of LNFTs, the tube wall should be stiff and ductile, while the working pressure of LN should match the fracture strength of tube wall. These findings suggest that LNFTs have great promise in energy mitigation applications and provide guidance on the design of LN-based composite structures.</p>

Axial Impact Behavior of Liquid Nanofoam Filled Thin-Walled Tubes

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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