Dynamic crushing behavior and energy absorption of honeycombs with density gradient

Abstract

This paper presents an analytical study of the in-plane dynamic crushing and energy absorption of hexagonal honeycombs with density gradients under different impact loading. Explicit dynamic finite element method simulations are carried out by using ANSYS/LS-DYNA. Firstly, under the assumption that the cell wall length is the same, a density-graded honeycomb mode is established by the variation of the cell wall thicknesses along the crushing direction. The effects of density gradient and impact velocity on the crushing deformation modes, plateau stresses and energy absorption characteristics of the specimens are explored in detail. Numerical results show that except for the impact velocity, the dynamic crushing performance and energy absorption abilities of honeycombs also rely on the density/strength gradients. The weakest layer is suggested to be placed at the impact end or the output end, and the strongest layer at the intermediate stage to achieve higher energy absorbing efficiency. According to the one-dimensional shock wave theory, the simple empirical formulae for graded honeycombs to predict the plateau stress are given under high-impact velocities. These results will provide some useful guides in the multi-objective optimization dynamic design and shock energy absorbing control of sandwich structures.

Numerical Investigation on Dynamic Crushing Behavior of Auxetic Honeycombs with Various Cell-Wall Angles

“…The quadrature rule is set as Gauss. Numerical results have shown that the shell element is sufficient to produce reliable results [19][20][21][22]29]. Five integration points along the cell-wall thickness are adopted with the aim of providing sufficient accuracy.…”

“…This is followed by a long collapse plateau and the final compressive densification regime. It is the plateau stress in the second regime that is important in characterizing the dynamic crushing of honeycombs, which has been widely used in the energy-absorbed design and analysis of cellular solid [3,[19][20][21][22][29][30][31]. The plateau stress is defined as the average nominal stress between the first stress peak and the compressive stress corresponding to the densification strain, and its expression is shown as…”

“…So the friction coefficient is 0.02 in this paper. More details on the numerical simulations were described in our previous work [20,29].…”

“…As for the weight sensitive applications, another key indicator index in characterizing the energy absorption capacity of cellular materials is the specific absorbed energy, which is defined as [29] where Δ is the relative density of the honeycomb and is the density of the bulk material. Based on (7), the absorbed energy per mass of auxetic honeycombs with different cell-wall angles under different impact velocities is plotted in Figure 14.…”

Numerical Study on the Projectile Impact Resistance of Multi-Layer Sandwich Panels with Cellular Cores

“…Cellular materials, especially cellular sandwich structures, can effectively lighten and strengthen structural component (Wadley, et al, 2003) and also meet multi-functional requirements (Evans, et al, 2001) including energy absorption (Zhu, et al, 2010;Zhang, et al, 2014), shock cushioning (Xue and Hutchinson, 2004), heat dissipation (Queheillalt, et al, 2008) and sound insulation (Xin and Lu, 2010) due to their unique structure configuration.…”