The in-plane dynamic crushing behaviors and energy-absorbed characteristics of honeycombs with negative Poisson’s ratio (NPR) have been studied by means of explicit dynamic finite element analysis (DFEA) using ANSYS/LS-DYNA. First, the honeycomb models filled with different reentrant cells by the variation of micro-cell configuration parameters (cell-wall angle and shape ratio) are established. The respective influences of micro-structure and impact velocities on the deformation behaviors, the dynamic plateau stresses and the absorbed energy of reentrant honeycombs are explored in detail. It is shown that owing to the variation of cell micro-structure, reentrant honeycombs display different macro-/micro- deformation properties during the crushing. For the given impact velocity, the dynamic plateau stresses are related to the shape ratio by a power law and to the cell-wall angle by least-square curves. And they are also proportional to the square of impact velocities for a high impact velocity. Based on the finite element simulated results and one-dimensional shock wave theory, an empirical formula for auxetic honeycomb to predict the dynamic plateau stress is derived in terms of relative density and impact velocity.
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.
The in-plane dynamic crushing behavior and energy absorption capacity of self-similar hierarchical honeycombs under different impact velocities are numerically studied using ANSYS/LS-DYNA. First, the hierarchical honeycomb models with uniform cell-wall thickness are constructed by replacing every three-edge structure nodes of a regular honeycomb with smaller self-similar hexagons of the same orientation. The respective influences of hierarchical parameters, bulk materials, and impact velocities on the macro-/micro-deformation behaviors, the dynamic strength, and the specific absorbed energy of hierarchical honeycombs are explored in detail. The results show that the crushing strengths and energy-absorbing capacities of honeycombs significantly improve when adding the hierarchy into conventional cellular structures. The variation of hierarchical parameter changes the local dynamic evolution of stress waves, which further results in different macro-/micro-deformation properties. Through the proper choice of hierarchical parameters and bulk materials, the optimal crushing strength and the maximum absorbing energy could be obtained.
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