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As a promising energy absorbing structure, reentrant honeycomb (RH) structures have been focus of interest in recent years. By reasonably adjusting the geometric configuration of the honeycomb cell, advanced structures with unique mechanical properties and deformation behaviors can be designed flexibly and novely. In this work, inspired by the composite laminates, a novel laminated reentrant honeycomb (LRH) structure is developed by controlling the orientations of RH layers for achieving excellent energy absorption capacity. Mechanical and deformation characteristics of the proposed structures under static and dynamic loadings are investigated experimentally and numerically. By comparing with single-layer RH structure with the same thickness, the results demonstrate that LRH structures have better energy absorption capacity. The deformation modes of RH and LRH structures are also discussed and it is noted that the LRH structure with ±30° honeycomb sublayers shows zero Poisson's ratio effect. It is worth emphasizing that LRH with 0° and 90° sublayers presents similar negative Poisson's ratio effect with RH by analyzing the equivalent Poisson's ratio-strain curves. In addition, it is found that the latter structure has the best energy absorption capacity when the thickness of single-layer 0° RH structure equals to 5 mm. This work provides a new and reliable thought to design the advanced protective structures under compression and impact loadings. [ABSTRACT FROM AUTHOR]

Sandwich structure is one of the blasts protecting and energy absorbing materials with different types of light weight cores. This article aimed at investigating blast response of hexagonal honeycomb sandwich structure having perforations along the cell height of core over conventional honeycomb cores. The study discussed the mechanics of deformation behavior of perforated sandwich structure to improve the energy absorption characteristics of the bare honeycomb core sandwich structure. Detailed numerical analysis is conducted to accurately produce the deformation process with finite element analysis using explicit software LS-DYNA®. Blast load resulting from 1 kg TNT on the sandwich structure is applied using Conventional Weapons Effects Program (ConWep) function available in LS-DYNA. Several different parameters consisting of varying sizes of perforation by changing d/l ratio, shape, number of perforations and different facesheet and backsheet thicknesses, and different scaled distances are investigated in detail. The results indicated that both size and shape and number of perforations have significant influence on reduction of blast impulse. The variation of facesheet and backsheet thicknesses without changing the overall thickness of the structure also has evident effect in blast resistance capability of perforated honeycomb sandwich structure. The blast mitigation and energy absorption capacity of honeycomb core sandwich structure can be improved with the provision of perforations and optimizing the arrangement of holes. The perforated honeycomb core is further investigated based on analytical formulation developed using single degree of freedom (SDOF) system analysis approach. Optimization study is done further to get the best configuration based on different design variable limits. [ABSTRACT FROM AUTHOR]

With the increase of demands for anti-collision performance in many fields, the negative Poisson's ratio structure has attracted the attention of researchers due to its light weight and high shear stiffness. Therefore, a new negative Poisson's ratio (NPR) structure named three-beam star honeycomb (TBSH) is proposed based on the classical star honeycomb (CSH). The stress equation of TBSH is derived by energy method, and its deformation characteristics and mechanical properties are studied. The results show that the structural deformation modes are different under different impact velocities, and TBSH has more obvious NPR effect. In addition, the influence of geometrical parameters on energy absorption of structures is also investigated. Finally, the thickness gradient is introduced into this structure, and the thickness gradient is optimized by multi-island genetic algorithm (MIGA). After optimization, the specific energy absorption (SEA) of the structure is significantly improved, while the initial peak stress (IPS) is decreased. The new structure proposed in this paper is expected to provide a novel design thinking and optimization idea for superstructure design. [ABSTRACT FROM AUTHOR]

In this study, impact behavior and deformation mechanism of triply periodic minimal surface (TPMS) sheet (Schwarz' P, Schoen's I-WP, and Neovius) were numerically investigated. The convergence study of mesh size, sensitivity of cell number, and parametric investigation of shell thickness were performed. Three different collapse modes " ⋁ + ⋀ = X , " " / + \ = X , " and "Whole-X" were experienced corresponding to Schwarz' P, Schoen's I-WP, and Neovius sheets, respectively. Comparison between the anisotropic 2D circular honeycomb and isotropic 3D TPMS were conducted. The results show that TPMS sheets perform excellent mechanical properties due to their isotropic smooth surface transitions and open-cell connectivity. Cell number sensitivity of TPMS structures is investigated and Mesh size convergence study of TPMS structure is performed. Systematic regular TPMS patterns are obtained and collapse mechanisms related to deformation mode are revealed. Comparison between TPMS structure and the representative 2D cellular circular honeycomb structure is conducted, better performance in withstanding uniaxial compression is confirmed. [ABSTRACT FROM AUTHOR]

The dynamic response of honeycomb sandwich panels under aluminum foam projectile impact was investigated. The different configurations of panels were tested, and deformation/failure modes were obtained. Corresponding numerical simulations were also presented to investigate the energy absorption and deformation mechanism of sandwich panels. Results showed that the deformation/failure modes of sandwich panels were sensitive to the impact velocity and density of aluminum foam. When the panel was impacted by the aluminum foam projectile with the back mass of nylon, the “accelerating impact” stage can be produced and may lead to further compression and damage of the sandwich structures. [ABSTRACT FROM AUTHOR]

The purpose of this study is to develop tools dedicated to the design of sandwich panels involving Nomex® honeycomb cores. Special attention is paid to the ability to perform full three dimensional calculations up to failure of such structures. In the first part, the determination of effective elastic properties of Nomex® honeycomb cores is carried out thanks to strain based periodic homogenization technique. Using an equivalence in energy between a real honeycomb and a fictitious continuous medium, it becomes possible to evaluate the elastic behavior of Nomex® cores, starting from the knowledge of the behavior of the constitutive paper. Next, relying on experimental observations, the strengths of Nomex® honeycomb cores are evaluated with a linear Euler's buckling analysis. Results are compared with data coming from manufacturers, and give satisfaction. In order to carry out these two first studies, the NidaCore software has been developed using the finite element code Cast3M from CEA. The last part deals with the modeling of the nonlinear compressive response of Nomex® cores. A model based on the thermodynamics of irreversible process is proposed and the identification technique detailed. Good agreement between experimental data and computed values is obtained. [ABSTRACT FROM AUTHOR]