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Novel honeycombs with buckling-induced features and tailorable properties have been designed and fabricated using the fused deposition modeling (FDM) method. Quasi-static out-of-plane compression tests were carried out to investigate the topological dependence of the crushing behavior of the buckling-induced honeycombs (BIHs). The results demonstrated that the crushing performance of BIHs can be artificially controlled by altering their shape parameters. In particular, the initial peak force (IPF) and the undulation of the mechanical response of BIH can be effectively reduced by increasing the layer number or arranging the asymmetric layers. A finite element model validated against experimental results was also utilized to reveal the underlying deformation mechanism and study the corresponding displacement-crushing force responses for BIHs with different topological parameters. It was uncovered that the buckling-induced mechanism is beneficial for tuning the stiffness and mitigating local buckling resistance through the pre-determined collapse behavior of cell walls. Further, a multi-objective optimization process of BIH was performed to seek the optimal design solution for energy-absorbing structures in specific scenarios. The findings of this study provide a theoretical basis for the development of new ideas and optimization solutions for the design of lightweight and performance-tailored energy-absorbing structures. [ABSTRACT FROM AUTHOR]

Abstract The energy absorption characteristics of sandwich panels with aluminum plate as facesheet and metal hexagonal honeycomb as the core are investigated under quasi-static punch loading using two flat nose and spherical projectiles, experimentally. Failure modes are classified as plastic hinges, facesheet wrinkling, debonding of the adhesive layer between the facesheet and core, facesheet tearing, out of plane core crushing, in-plane core folding, core tearing and detachment from the support. Furthermore, the article examines the influences of six parameters including honeycomb wall thickness, sandwich core thickness, facesheet thickness, aspect ratio, adhesive layer between facesheet and core and existence of bottom facesheet. The results show that the increase in core thickness improves the energy absorption parameters of sandwich panel better than the increase in the facesheet thickness. Specific absorbed energy is increased linearly by increasing the honeycomb core thickness while it seems that the mentioned parameter has a meaningless dependence on the facesheet thickness. In addition, a 12 percent quota of adhesive layer between top facesheet and core is indicated in the energy absorption capacity of a sandwich panel for both flat nose and spherical projectiles, while its effect on the value of maximum force is 17% using flat nose projectile and 25% using the other one. Despite the major influence of the existence or non-existence of the bottom facesheet on the sandwich failure modes, its absorbed energy changes less than 3.5 percent; yet other parameters such as specific energy absorption and peak load are more dependent on the existence or non-existence of the bottom facesheet. Finally, keeping the honeycomb wall less thick improves the energy absorption characteristics of the sandwich panel. [ABSTRACT FROM AUTHOR]

Abstract The dynamic response of cylindrical sandwich panels with aluminum foam core, hexagonal honeycomb core, and auxetic honeycomb core are compared numerically. A novel curved auxetic honeycomb core is designed, and the finite element models are built by employing ABAQUS–Explicit. To calibrate the numerical models, the experiments of sandwich panels with honeycomb core and aluminum foam cores are modeled. And the numerical results have a good agreement with the experiment date. The calibrated numerical models are used to simulate the dynamic response of cylindrical panels subject to external blast loadings. It is found that the cylindrical panels with auxetic honeycomb cores have a better performance than that with aluminum foam cores and hexagonal honeycomb cores in resisting blast loadings. A material concentration effect was observed in the auxetic honeycomb core due to the negative Poisson's ratio (NPR) effect. According to parameter studies, it is concluded that with the increase of curvature and face sheet thickness the blast-resistance of panels with both auxetic honeycomb core, hexagonal honeycomb core, and foam cores increased obviously, especially the panels with auxetic honeycomb cores. For the panels with auxetic honeycomb cores, increasing the back face sheet thickness can improve the blast-resistance performance more efficiently than increasing the thickness of front face sheet, which is opposite for the panels with foam cores and hexagonal honeycomb cores. Auxetic cores with a smaller unit cell aspect ratio and a smaller unit cell length ratio has a larger Poisson's ratio, and achieves better blast resistance performance. These simulation findings can guide well the theoretical study and optimal design of cylindrical sandwich structures subject to external blast loading. [ABSTRACT FROM AUTHOR]

Auxetic honeycombs have a variety of potential applications in aerospace engineering due to their excellent mechanical and multidisciplinary properties. A novel class of auxetic honeycombs have been invented recently named as Re-entrant circular (REC) honeycombs. The REC honeycombs can be obtained by replacing the sloped cell walls of the well-known re-entrant (RE) unit honeycombs with double circular arc walls to dissipate more energy. This study aims to investigate the in-plane dynamic crushing responses of the novel REC honeycombs through numerical simulations and theoretical analyses. LS-DYNA based numerical simulations revealed the "X" and "I" combined deformation mode of the REC honeycomb under low velocity crushing, and the "I" mode under high velocity loading. The geometric parameters of unit cell and the crushing velocity were both found to have great effects on the proximal end crushing stress of the REC honeycomb. It was also shown that the REC honeycomb presents obvious negative Poisson's ratio (NPR) effect, attributed to its re-entrant characteristic. Based on the meso-scale deformation mechanisms of the representative unit cell, theoretical models have been established to predict the plateau stress of the REC honeycomb under different crushing velocities. The theoretical predictions were in good agreement with the numerical simulation results. Moreover, the dynamic sensitivity index and the deformation mode map of the REC honeycomb were obtained to evaluate its dynamic response sensitivity to the loading velocity. Finally, the in-plane crushing characteristics of the REC and the RE honeycombs were compared. The REC honeycomb was found to show higher specific energy absorption (SEA) and penetration resistance than its RE counterpart, due to the more plastic hinges formed during the dynamic crushing process. [ABSTRACT FROM AUTHOR]

Two innovative re-entrant hierarchical sandwich panels constructed by substituting the cell walls of re-entrant honeycombs with isotropic regular hexagon substructure (RHH) and equilateral triangle substructure (RHT) are proposed in this paper, and their crashworthiness performance has been investigated systematically. Based on the Euler beam theory, the Young's moduli of units of re-entrant hierarchical sandwich panels are derived. A comparison between the re-entrant hierarchical sandwich panels and re-entrant sandwich panel has been conducted to study their energy absorption ability. Furthermore, the parametric analysis based on numerical analysis has been carried out to discuss the effects of the gradient, arranged orientation of hierarchical sandwich cores and the impact velocities. Results show that both the two proposed sandwich panels can greatly improve the in-plane stiffness and the energy absorption capacity, and the energy absorption mechanisms are discussed. In addition, the graded sandwich panels can effectively reduce initial peak force under quasi-static compression, and the configuration of large- medium -small (LMS) performs the best under high impact velocity. The cross-arranged cores can significantly improve the impact resistance ability of RHT sandwich panels. This work provides a new solution for designing lightweight sandwich structures. [ABSTRACT FROM AUTHOR]