Dynamic Response Of Foam-filled Thin-walled Structures And High-g Impact Protection Design

When the projectile penetrates the complex protective layer,it may produce multiple high g-value overloads.The crashworthiness and survivability of the measurement and control device in extreme environments have become the key technical bottlenecks restricting the high-speed launch and deep penetration of weapons.Adding a sacrificial buffer energy-absorbing structure between the measurement and control module and the projectile can effectively enhance the impact resistance of the components.However,severe service conditions such as multiple consecutive high g-value impacts,narrow space constraints in the projectile and stable and orderly feedback load requirements put forward more stringent requirements for the dynamic response and optimization of the buffer structure under extreme dynamic loads.In this paper,based on the design of impact-resistant structures required in high g-value protection,the mechanical responses of three types of foam-filled thin-walled structures,including foam-filled cylindrical shells,cellular tubes,and foam-filled cellular tubes,under medium and high-speed impact are carried out.Simulation and theoretical research,analyze the dependence of structural crushing load,energy absorption and deformation mode on structural geometric parameters,impact velocity and other factors,study the energy absorption mechanism of foam-filled thin-walled structures,and conduct regulation and optimization.In this paper,the stress of the closed-cell aluminum foam platform prepared by the melt foaming method has a weak dependence on the impact velocity,which is mainly caused by the impact inertia.Compared with uniaxial compression,the platform stress in confining compression is increased by about 5.23 MPa and 5.72 MPa.Foam filling,increasing wall thickness and impact velocity can make thin-walled structures produce accordion folding failure modes with higher energy absorption efficiency;equal-mass clamps The MCF and SEA of the core tube are 0.29-2.72 k N and 0.38-1.69J/g higher than those of the filled tube;the average crushing loads of the FT and ST structures are more dependent on the tube wall thickness and foam density,and the loading range is 60m/s.The dynamic MCF and SEA of the two inner structures can be increased by about 2.25-3.22 k N,1.77-3k N,1.44-1.82 J/g,and1.43-2.24 J/g,respectively.The diameter analysis of the deformed structure shows that ST and FT are compressed by 60%.Compared with the cylindrical shell,the average diameter increases by 3.99%,5.97% and 3.99%,8.34%,respectively,and the radial expansion of the structure increases with the increase of the impact velocity.The analysis shows that the mechanism of coupling effect mainly includes the change of foam stress state,the friction effect between the foam and the tube wall and the radial expansion and deformation effect of the tube wall.The multicellular tube（MT）has stable feedback load and excellent energy absorption characteristics.Compared with the filling structure and the sandwich structure,it has a larger compression stroke and specific energy absorption,but the crushing load is under the impact load within 60m/s.No obvious dynamic enhancement effect.Under quasi-static loading,the outer tube of MT mainly folds in an accordion mode,while the inner tube and rib mainly produce asymmetric long-wave folding.Under impact loading,the accordion folding pattern of the outer tube is more regular,and the inner tube produces diamond short-wave folding with more petals,which increases the energy absorption of the structure.Foam-filled multicellular tubes（FMT）can effectively increase the MCF of MT.The FMT crushing load and energy absorption have obvious dependence on the loading speed,and the MCF is increased by about 26.81% within the current loading speed range.Low-density foam filling can improve the dynamic energy absorption characteristics of the structure without significantly reducing（4.07-11.13%）the specific energy absorption of the structure.The results show that increasing the foam filling and increasing the loading speed can improve the crushing deformation mode of the MT structure and improve the energy absorption of the structure.The theoretical prediction model of the average crush load of MT and FMT is constructed,but the dynamic enhancement coefficient of the crush load of thin-walled structures is positively related to the velocity.An improved foam-filled multicellular thin-walled structure OFT was designed and fabricated by combining foam filling and multicellularization.Experiments show that the structure has high specific energy absorption and dynamic energy absorption characteristics.Based on numerical simulation,the research on high-g value shock response was carried out,and the optimal solution of structural parameters under high-g value shock with 40000 g amplitude and 200 us pulse width three times was obtained through multi-objective optimization.The research on foam-filled thin-walled structures in this paper can provide a basis for in-depth understanding of the interaction mechanism of foam-thin-walled structures,and provide technical ideas for the design of high-g impact protection.