Dynamic Mechanical Behavior Of Liquid Nanofoams And Associated Filled Porous Materials

Intensive dynamic loads such as blast impact and high-speed fragmentation are the main threats to the structural damage of ships and the safety of related equipment and personnel.Based on this,the study of impact-absorbing properties of advanced structural materials is a hot research topic in the field of new generation defense industry.Liquid nanofoam(LNF),which has the characteristics of repetitive energy absorption,ultra-high load transfer rate and high energy absorption density,has become an emerging energy absorption system with certain adjustable performance and has great prospects for application in the field of ship structure protection.In order to solve the current problem that the energy absorption mechanism of LNF is still unclear,this paper conducted a systematic experimental study on the liquid infiltration and exfiltration behavior and influence mechanism of LNF at microscopic scale,and characterized the dynamic behavior of LNF materials to reveal the mechanical response and energy absorption mechanism of LNF under dynamic impact,Based on this,the mechanical properties and energy absorption mechanism of LNF-filled porous foam metal composite energy-absorbing materials were further investigated.In this paper,firstly,based on different kinds of liquid nanofoams,the behavior of liquid molecules infiltrating into microscale nanopore channels under external pressure is systematically investigated experimentally by using different liquid types and loading rates,revealing the effect of solid-liquid properties on the infiltration pressure and clarifying the strain rate insensitivity of LNFs under quasi-static conditions.The behavior of liquid molecules infiltrating the nanopore channel is investigated by quasi-static cyclic compression experiments,which reveal the influence of gas molecules inside the microscale pore channel on the infiltration behavior of liquid molecules,and the main parameter properties affecting the energy absorption density and the repeatable usage rate of LNF are obtained.The dynamic impact experiments were carried out based on two mixed forms of LNF specimens,homogeneous and heterogeneous,by a separated Hopkinson pressure bar(SHPB)experimental setup.The strain rate effects of the mechanical response and energy absorption characteristics of LNF materials under dynamic impact were systematically analyzed to obtain the influence laws of different loading rates on the macroscopic mechanical response and microscopic infiltration behavior of LNF,and the results were compared and analyzed with the quasi-static experimental results.It is shown that although the mechanical properties of LNF under dynamic impact are still based on its nanosolid-liquid infiltration behavior,the influence mechanism is not completely consistent with that under quasi-static conditions,and it shows obvious rate correlation under dynamic conditions;in addition,the liquid infiltration rate is also adaptive to the impact energy level,which provides a mechanistic explanation for the high energy absorption efficiency of LNF under high strain rate.The results also indicate that gas molecules have a similarly significant effect on the liquid infiltration behavior and energy absorption efficiency of the LNF under high strain rate impacts.Based on the understanding of the microscopic scale liquid infiltration and exfiltration nanopore mechanism,a new liquid-solid composite energy-absorbing structural material(C-LNF)is obtained by combining LNF as a filler material with porous foam metal in this paper.The mechanical response and energy absorption mechanism of this liquid-solid composite energy-absorbing material were investigated by quasi-static and dynamic tests,and the analysis of the test data revealed that the C-LNF material has a significant rate dependence under dynamic loading conditions,but not under quasi-static loading.The strengthening effect is mainly due to the multi-layer energy absorption of C-LNF and the interaction of a large number of liquid-solid interfaces,and this composite strengthening effect increases with increasing strain rate.This composite liquid-solid energy absorption enhancement effect proves that the solid-liquid multilayer energy absorption material formed by LNF as liquid filling material has important application prospects,and this study provides experimental and theoretical basis for the development and application of new multilayer protective structures under strong dynamic loads.