Search

• Innovative metamaterial design approach proposed to improve energy absorption capacity. • Varying the structural parameter (D/d) enhanced the metamaterial auxetic effect. • HPH metamaterials absorb energy effectively horizontally with their honeycomb structure. • HPH metamaterials show excellent reusability at lower compression ratios. Hexagonal perforated honeycomb (HPH) metamaterials were designed, fabricated and investigated in this work. Initially, the mechanical properties and deformation modes of various proposed HPH metamaterials (HPH-U, HPH-1 L and HPH-3 L) under quasi-static vertical compression were analyzed using experimental and finite element methods. The findings reveal significant improvements in mechanical properties and energy absorption due to the honeycomb and hierarchical expandable design. Notably, the auxetic effect is diminished. Subsequently, the impact of key dimensional parameters on the mechanical properties and Poisson's ratio behavior was explored. The results highlighted that an increase of elliptical perforation major axis to minor axis ratio enhanced the auxetic effect but compromised load-bearing and absorptive capacity. Additionally, HPH metamaterials displayed exceptional performance under quasi-static horizontal compression, with their honeycomb structure enabling them to withstand both vertical and horizontal impacts while exhibiting excellent energy absorption capabilities. The study also identified relative density as a crucial factor influencing horizontal impact performance. Finally, the study subjected the HPH metamaterials to multiple quasi-static vertical repetitive compressions, meticulously analyzing variations in mechanical properties under diverse compression ratios. Due to distinctive structural design and impressive mechanical properties, HPH metamaterials demonstrate immense potential for applications in automotive engineering and sports protection fields. [Display omitted] [ABSTRACT FROM AUTHOR]

• The combined effects of bending curvature, loading angle, and thickness on the crushing response of curved honeycombs were clarified in detail. • A macroscopic yield criterion for the initial yield stress of curved honeycombs was presented. • A novel inverse parameter identification method was proposed for the macroscopic yield criterion of curved honeycombs. This paper investigated the initial yield behavior of curved honeycombs under combined shear-compression loads with particular attention to the curvature, loading angle, and honeycomb thickness effects. A detailed finite element model was introduced to analyze the mechanical response and deformation mechanism of curved honeycombs and then verified through experiments using a specially designed set-up. It was found that the curvature had a significant effect on the crushing response. As the curvature increased, the initial peak stress reduced by 16.20%. The out-of-plane loading angle ranging from 0º to 15º had little effect on the crushing behavior, whereas it became more pronounced for the angles larger than 15º. In comparison, the effect of in-plane loading angle fluctuating between 0º and 60º was more significant. Based on the obtained data, a macroscopic yield criterion for the initial yield stress of curved honeycombs was proposed. A novel inverse parameter identification approach for curved honeycombs was proposed to determine the induced parameters conveniently. The current study gave insight into the performance change of honeycombs with specific curvature and could be used to develop its constitutive models under complex loads. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper the dynamics of crush band initiation and wave trapping that result from in-plane impact on a honeycomb are analysed using finite element simulations. The honeycomb structures were loaded in compression at the top surface with a prescribed velocity. Two different boundary conditions were considered; these produced an approximation to a state of uniaxial stress or uniaxial strain at an early state of deformation. The simulations proved that elastic wave propagation had an important effect on crush band initiation, since loading and unloading parts of the compressive wave can reinforce or delay crushing, respectively. Stress enhancement with increasing impact speed is mainly due to translational micro-inertia and not due to micro-rotational inertia. This effect is stronger for uniaxial strain than for uniaxial stress. For the specific case examined here, stress enhancement begins for uniaxial strain at an impact speed of about 1.0 m/s whereas for uniaxial stress it begins at about 10.0 m/s. For the analysed honeycomb the simulation showed for both boundary conditions the existence of a critical impact velocity, so that for impact speeds larger than this critical speed a crush band initiated at the impact surface. For much smaller speeds the location of the initial crush band was determined by the distribution and extent of initial imperfections. In the case of uniaxial stress an analytical estimate of the critical impact speed was derived using the theory of wave trapping. The critical speed depends only on the ratio of the length of the ribbon wall to the length of the thinner inclined wall and the material properties of the constituent material. For the aluminium honeycomb investigated in this paper, wave trapping is predicted to occur for impact speeds greater than 7.6 m/s which is close to the critical speed calculated with the finite element simulations. [Copyright &y& Elsevier]