In this study, a series of in-plane hexagonal honeycombs with different Poisson's ratio induced by topological diversity are studied, considering re-entrant, semi-re-entrant and convex cells, respectively. The crushing strength of honeycomb in terms of Poisson's ratio is firstly presented. In the previous research, we have studied the compression performance of honeycomb with different negative Poisson's ratio. In this study, a comparative study on the local impact resistance of different sandwich panels is conducted by considering a spherical projectile with low to medium impact speed. Some critical criteria (i.e. local indentation profile, global deflection, impact force and energy absorption) are adopted to analyze the impact resistance. Finally, an influential mechanism of Poisson's ratio on the local impact resistance of sandwich panel is studied by considering the variation of core strength and post-impact collapse behavior.

The influence of in-plane and out-of-plane element array effects of honeycomb on the impact characteristics of sandwich panels was studied under different local impact speeds. The numerical model is calibrated by air cannon impact experiment and used to conduct the investigations. It is demonstrated that the sandwich panel with in-plane honeycomb core (SPIH) exhibits a response mode with larger local indentation and smaller overall deflection, and also shows superior energy absorption as compared to the sandwich panel with out-of-plane honeycomb core (SPOH). When facing more severe impact conditions, SPIH shows better anti-penetration capability. When the impact radius is 20 mm and the impact velocity is 83 m/s, the SHOP is penetrated while the SHIP is not. When the impact radius is 20 mm and the impact velocity is 100 m/s, the total absorbed energy of SHIP is 59.79% higher than that of SPOH, and the impact residual velocity is 32.67% lower. Furthermore, the impact mitigation performances of SPIH with different density gradient cores are investigated by comparing their deformation modes and energy absorption characteristics. The results indicate that different gradient schemes enable sandwich panels to perform multiple functions. The positive gradient design in the cell stretching direction is beneficial to reduce the overall deflection and improve the energy absorption effect.

This study examines a hierarchical vertex-based structure that improves the crashworthiness of the conventional multi-cell square, a biological hierarchy of natural origin with exceptional mechanical properties. The vertex-based hierarchical square structure (VHS) is explored for its geometric properties, including infinite repetition and self-similarity. The cut-and-patch method is used to derive an equation for the material thicknesses of different orders of the VHS based on the principle of the same weight. A thorough parametric study of VHS was conducted using LS-DYNA, which examined the effects of material thickness, orders, and various structural ratios. The results were evaluated based on common crashworthiness criteria and demonstrated that the total energy absorption (TEA), specific energy absorption (SEA), and mean crushing force ($P_m$) of VHS exhibited similar monotonicity concerning the orders. SEA of the first-order VHS with ${\lambda }_1=0.3$ and the second-order VHS with ${\lambda }_1=0.3$ and ${\lambda }_2=0.1$ are improved by at most 59.9% and 102.4% respectively; the second-order VHS with $0.2\le {\lambda }_1\le 0.4$ and $0.1\le {\lambda }_2\le 0.15$ have the better overall performance of crashworthiness. Then, the half-wavelength equation of VHS and $P_m$ of each fold was established based on the Super-Folding Element method. Meanwhile, a comparative analysis with the simulation results reveals three different out-of-plane deformation mechanisms of VHS. The study indicated that material thickness had a greater impact on crashworthiness. Finally, the comparison with conventional honeycombs demonstrated that VHS holds great promise as a structure for crashworthiness. These results provide a solid foundation for further research and development of new bionic energy-absorbing devices.

To study the aging mechanism of air springs, the effect of aging time on the vertical static stiffness of an air spring was systematically analyzed by means of an accelerated aging test and finite element simulation. Accelerated aging tests were carried out on the entire air spring, rubber material, and cord material, and the vertical static stiffness and elastic moduli of the rubber and cord materials of the entire air spring were obtained with aging time. The finite element simulation model of the air spring was established. Based on the experimental data, the influences of the elastic moduli of the rubber and cord materials, aged for different times, and the cord angle on the vertical static stiffness of an air spring were simulated and analyzed, and the law of the influence of aging on the vertical static stiffness characteristics of air springs was revealed.

MnZn ferrite precursor powders were prepared by the nano in situ composite method. Three surfactants, which include polyethylene glycol 400 (PEG-400), cetyltrimethyl ammonium bromide (CTAB), and sodium dodecyl sulfate (SDS), were usedM and the impact of the surfactants on the precursor sol solutions and precursor powders was studied. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, a field emission scanning electron microscope (FE-SEM), a transmission electron microscope (TEM), a Zeta potential meter, a BET surface analyzer, and a vibrational sample magnetometer (VSM) were used to characterize the precursor sol solutions and the precursor powders. The results showed that these surfactants can improve the dispersion state and Zeta potentials of sol particles and increase the specific surface areas of the precursor powders. Moreover, the precursor powders were composed of MnZn ferrite, and some were amorphous. CTAB was the optimum surfactant and the zeta potential of the sol particles and the specific surface area of the precursor powders named P-0.1CTAB are 10.7 mV and 129.07 m²/g, respectively. In addition, the nano-particles that were made up of the P-0.1CTAB precursor powders had smaller sizes and more uniform particle distributions than the others. The magnetic properties’ improvement was attributed to the addition of surfactants, and CTAB is the optimal type. In addition, the novel nano in situ composite method will inspire fresh thinking and investigation into the research of ferrite.