Honeycomb Materials Research Articles

Study on passive momentum exchange landing gear using two-dimensional analysis

This paper discusses a landing response control system based on the momentum exchange principle for planetary exploration spacecraft. In the past, landing gear systems with cantilever designs that incorporate honeycomb materials to dissipate shock energy through plastic deformation have been used, but once tested before launch, the system cannot be used in a real mission. The sky crane system used for the Mars Science Laboratory by NASA can achieve a safe and precise landing, but it is highly complex. This paper introduces a momentum exchange impact damper (MEID) that absorbs the controlled object׳s momentum with extra masses called damper masses. The MEID is reusable, which makes it easy to ensure the landing gear׳s reliability. In this system, only passive elements such as springs are needed. A single-axis (SA) model has already been used to verify the effectiveness of MEIDs through simulations and experiments measuring the rebound height of the spacecraft. However, the SA model cannot address the rotational motion and tipping of the spacecraft. This paper presents a two-landing-gear-system (TLGS) model in which multiple MEIDs are equipped for two-dimensional analysis. Unlike in the authors׳ previous studies, in this study each MEID is launched when the corresponding landing gear lands and the MEIDs do not contain active actuators. This mechanism can be used to realize advanced control specifications, and it is simply compared with previous mechanisms including actuators, in which all of the MEIDs are launched simultaneously. If each MEID works when the corresponding gear lands, the rebound height of each gear can be minimized, and tipping can be prevented, as demonstrated by the results of our simulations.

A fast numerical method for the analysis of the heat transfer performance of graded metallic honeycomb materials

Abstract A fast numerical method that combines the finite element and finite difference methods (FE–FDM) is proposed to analyze the forced convection heat transfer performance of graded honeycomb heat exchangers. The temperature distribution in the cross-section of the graded honeycomb perpendicular to the direction of flow is described using discrete finite elements that include the convective heat transfer of the two side surfaces. The temperature distribution in the flow direction is obtained by the finite different method. The most important difference with previous methods is the assumption of Constant Cross-sectional Fluid Temperature (CCFT) is relaxed. The fluid temperature of every individual channel is assumed constant and the different channels may have different temperatures in the same cross-section. Comparison with the results by the CFD model shows that FE–FDM has high precision and efficiency. The results of examples illustrate that its precision is similar to CFD model, but its calculation efficiency is increased 102–104 times as compared to CFD simulation. The assumption of CCFT is only suitable for heat transfer analysis of uniform honeycombs.

Electrical Control of Edge Magnetism in Two-Dimensional Buckled Honeycomb Lattice

We theoretically study indirect spin coupling strength between two magnetic impurities located on honeycomb Kane—Mele zigzag ribbon (KMZR) with periodic and open boundary (PB and OB). We show that spin interaction J in PB ribbons displays an AFM-FM oscillating behavior with increasing the staggered potential and electron density, and approaches to maximum at the edges. While the spin coupling in OB KMZR shows a trivial smooth AFM coupling with varying staggered potential. Such a novel J(Δ) behavior is the combining effect of finite size, topological edge states and inversion symmetry breaking induced by the staggered potential. We propose that one could control the edge magnetism electrically in two-dimensional buckled honeycomb materials, e.g., silicence, germanene and stanene.

Phase diagram of the Kane-Mele-Coulomb model

We determine the phase diagram of the Kane-Mele model with a long-range Coulomb interaction using an exact quantum Monte Carlo method. Long-range interactions are expected to play a role in honeycomb materials because the vanishing density of states in the semimetallic weak-coupling phase suppresses screening. According to our results, the Kane-Mele-Coulomb model supports the same phases as the Kane-Mele-Hubbard model. The nonlocal part of the interaction promotes short-range sublattice charge fluctuations, which compete with antiferromagnetic order driven by the onsite repulsion. Consequently, the critical interaction for the magnetic transition is significantly larger than for the purely local Hubbard repulsion. Our numerical data are consistent with $SU(2)$ Gross-Neveu universality for the semimetal to antiferromagnet transition, and with 3D XY universality for the quantum spin Hall to antiferromagnet transition.

Numerical simulation of an open sorption thermal energy storage system using composite sorbents built into a honeycomb structure

Abstract A new composite mesoporous honeycomb material was developed to be a thermal energy storage medium that can contact the functional fluid directly. In our previous study, this honeycombed composite material acted as a promising sorption thermal energy storage medium in an open system, exhibiting a lower regeneration temperature as 80 °C, high volumetric heat storage density, and high stability. In the present study, a one-dimensional transient model was used to predict both the heat storage process (desorption process) and heat release process (sorption process) occurring in the open sorption thermal energy storage unit. Our model was validated using the experimental results obtained in our previous experiments, and a close agreement was observed for the sorption process. Some discrepancy was observed in the desorption process, but it has been explained. The sorption and desorption processes were simulated repeatedly for 20 cycles, whose result was also compared with the experimental result. The operating parameters of the open thermal energy storage system were evaluated to determine its operation performance. Finally, our open thermal energy storage system was assumed to be incorporated into a paint-drying system, within which the heat storage unit is regenerated for 10 h by the exhaust heat produced by a blower in the daytime and releases its stored heat during the nighttime for 14 h. The simulation result shows that almost 51.3% of the blower’s waste heat can be reutilized if the proposed thermal energy storage system is incorporated.

Modeling of axial and shear stresses in multilayer sandwich beams with stiff core layers

In order to optimize the load-bearing behavior of sandwich structures and adapt it to specific requirements, their core may be composed of layers of different materials with tailored properties. These layers may consist not only of soft foam or honeycomb materials but also comprise stiff materials, e.g. timber, or even very stiff laminates in the case of fiber-reinforced polymer (FRP) materials. In this paper, new analytical models for predicting axial and shear stresses in multilayer sandwich structures composed of stiff core layers and intermediate laminates are presented. The models are based on new formulations for calculating the bending and shear stiffness of multilayer sandwiches. They have been validated by finite element modeling (FEM) and the results from four-point bending experiments on GFRP-balsa sandwich beams with complex core assembly. In contrast to existing models, e.g. the high-order sandwich panel theory (HSAPT), the new models are able to accurately predict axial and shear stresses in stiff cores and intermediate FRP laminate layers.

The Effect of Face and Side Panels of Honeycomb Core on its Equivalent In-Plane Elastic Properties

The effect of the face and side panels of honeycomb cores on their equivalent in-plane elastic properties is studied by the numerical simulation in this paper. The numerical results show that the deformation pattern of the honeycomb core constrained by either face panels or side panels is totally different from that of pure honeycomb materials. As a result, both the face panels and the side panels of honeycomb cores significantly increase the equivalent in-plane moduli of honeycombs. The commonly used prediction model of honeycombs cannot be used for the evaluation of the additional in-plane tensile stiffness contributed from the honeycomb core. However, the prediction model for the equivalent in-plane moduli of honeycombs with the periodic displacement condition yields much better results.

Valley polarization in magnetically doped single-layer transition-metal dichalcogenides

We demonstrate that valley polarization can be induced and controlled in semiconducting single-layer transition-metal dichalcogenides by magnetic doping, which is important for spintronics, valleytronics, and photonics devices. As an example, we investigate Mn-doped ${\mathrm{MoS}}_{2}$ by first-principles calculations. We study how the valley polarization depends on the strength of the spin orbit coupling and the exchange interaction and discuss how it can be controlled by magnetic doping. Valley polarization by magnetic doping is also expected for other honeycomb materials with strong spin orbit coupling and the absence of inversion symmetry.

A new approach for determining the hidden material parameters of a honeycomb

An optimization method to obtain the cell wall properties of Nomex honeycomb material is presented. There, the outcomes of physical experiments and micromechanical simulations are compared in an effort to identify the geometric or/and material parameters for the best match. Only the cell wall thickness and Young’s modulus, called here as the hidden parameters, are used in the matching as the Young’s modulus is difficult measure reliably. The mean values and standard deviations of the geometric parameters of the cell structure model are obtained through image analysis. In the micromechanical model used, the cell walls are considered as linearly elastic Bernoulli beams. The optimum hidden parameter values for the Nomex case turn out not to be unique but they appear in a combination known as the bending stiffness.

Design of an Ultrasonic Pointed Cutter

Ultrasonic cutting technique is an advanced processing method of cutting honeycomb materials. An ultrasonic pointed cutter was designed. Combined with the principle of ultrasonic cutting, the mathematical model of the tool was established. Modal analysis of the tool was calculated with the finite element software to study the effects of tool geometry on the natural frequency. The results show that the natural frequency increases as the tool thickness increases, but it decreases as the tool length increases. And it obtained the modal shapes and natural frequencies of the tool which meet design requirements. The optimal geometry of the tool was also determined. Finally, it verified the rationality of tool design by amplitude measurement experiment of the tool.

Performance-properties and fabrication of the reaction sintered Si/SiC honeycomb materials for solar absorber application

Performance-properties and fabrication of the reaction sintered Si/SiC honeycomb materials for solar absorber application

Non-symmetric deformation of lattices under quasi-static uniaxial compression

The response of planar lattices is usually investigated based on symmetric deformation modes , although non-symmetric deformations are often observed in experiments and numerical simulations. In this work, the influence of this non-symmetric deformation mechanism on the quasi-static uniaxial compression behavior of four kinds of lattices is investigated through theoretical analyses. For bending-dominated lattices, such as hexagonal and rhombus lattices, this non-symmetric deformation mechanism does not affect the average stress which is an indicator of energy absorption capacity of honeycomb materials. But for the membrane-dominated lattices, i.e., the square and Kagome lattices, the average stress of non-symmetric deformations is obviously lower than that of symmetric deformation modes, indicating that the energy absorption capability of membrane-dominated lattices with non-symmetric deformation modes are much lower than those with symmetric deformation modes. • Non-symmetric deformation mechanisms are proposed for four kinds of lattices under quasi-static uniaxial compression. • Non-symmetric deformation does not affect the average stress and yield strength for bending-dominated lattice. • For membrane-dominated lattices under non-symmetric deformation, the yield strength and average stress is much lower than symmetric case. • The post yielding property is not stable for membrane-dominated structures.

Mechanical properties of a hollow-cylindrical-joint honeycomb

In this paper, we constructed a new honeycomb by replacing the three-edge joint of the conventional regular hexagonal honeycomb with a hollow-cylindrical joint, and developed a corresponding theory to study its mechanical properties, i.e., Young’s modulus, Poisson’s ratio, fracture strength and stress intensity factor. Interestingly, with respect to the conventional regular hexagonal honeycomb, its Young’s modulus and fracture strength are improved by 76% and 303%, respectively; whereas, for its stress intensity factor, two possibilities exist for the maximal improvements which are dependent of its relative density, and the two improvements are 366% for low-density case and 195% for high-density case, respectively. Moreover, a minimal Poisson’s ratio exists. The present structure and theory could be used to design new honeycomb materials.

Char Structure and Combustion Kinetics of a Phenolic-Impregnated Honeycomb Material

The combustion behavior of a honeycomb material used for the core in sandwich panels, consisting of aramid fiber sheets (Nomex) dipped in a phenolic resin, is studied. Char, produced from pyrolysis of thick samples at 950 K, preserves the honeycomb structure, but the total volume is highly reduced in spite of an increase in the wall thickness. Following softening, the more internal fibers lose their shape, giving rise to a highly porous swelled char. Instead, the more external ones, trapped by the resin char, still show their original shape but with evident shrinkage. Thermogravimetric curves in air are used to formulate a combustion mechanism. It consists of three reactions for the stage of oxidative decomposition of the honeycomb material and one reaction for combustion of the resulting char. Activation energies for the various steps vary in a narrow range of high values (190–256 kJ/mol), testifying low reactivity.

Dual Scaled Stochastic FEM Simulation of Porous Honeycomb Material

In this paper, a dual-scaled method is introduced to simulate the nonlinear property of porous honeycomb material. In microscopic scale, stochastic analysis upon a detailed representation of the hexagonal cells is applied. In macroscopic scale, coupled fluid-solid PDEs with a modified stochastic item are used to describe the rheology of non-Newtonian property of honeycomb. Semi-discrete finite element method (FEM) is applied to solve the PDEs. Comparison of stochastic dynamic system with definite dynamic system is introduced. Numerical Results of Euler explicit time scheme and Crank-Nicolson semi-implicit time scheme are presented.

Testing and modeling of Nomex™ honeycomb sandwich Panels with bolt insert

Nomex™ honeycomb core sandwich panels with a bolt insert were load tested and modeled. The objective was to predict the honeycomb local buckling load and to identify a Nomex™ honeycomb constituent material model. Sandwich specimens were subjected to bolt pull-out load tests. The same sandwich structure was also tested in flat-wise tension with strain gages installed on the honeycomb walls. Finite element models of the flat-wise tension and bolt pull-out tests were built. The honeycomb geometry and strain gages were modeled with shell elements. An orthotropic honeycomb material model was identified by comparing the two test models to the experimental data. The material parameters identified are in the mid-range of previously published values. The pull-out test model was used to predict honeycomb wall buckling with a nodal rotation vector sum criterion. The buckling loads predictions closely corresponded to the start of the experimental load/displacement slope transition zone.

Numerical assessment of the impact behavior of honeycomb sandwich structures

Composite sandwich structures are widely used in the high-performance applications where weight reduction is one of the most attractive design parameters. However, structural sandwich components have low resistance to out-of-plane impact due to the thin outer composite skins and the highly deformable cores. The present paper deals with a finite element study on the impact response of sandwich panels, obtained combining phenolic resin-based glass fiber reinforced plastics as skins and phenolic resin-impregnated aramid paper honeycomb structure (Nomex) as core. The numerical analysis has been performed using the LSDYNA software enabling to account for the main sandwich failure modes occurring during impact. The honeycomb core structure and composite skins have been modeled by means of solid and shell elements respectively. The properties of the finite element model have been calibrated on a series of experimental outcomes in order to achieve numerical parameters for both composite facesheet and orthotropic honeycomb material models. The major concerns are related to damage mechanisms, influence of strain-rate effects and energy absorbing capability. The model is validated using the results from experimental impact tests performed on different initial impact conditions. Good agreement was obtained between numerical and experimental results in terms of impact damage and force–displacement trend.

STATISTICAL STRENGTH ANALYSIS FOR HONEYCOMB MATERIALS

In the present study, a statistical strength model is proposed, which aims at describing how the strength of geometrically irregular honeycomb material is affected by the scale. Hence, the samples are designed based on the selected geometrical irregularity and the number of the cells/scale. Simulation experiments are conducted on these samples under different loading combinations. The experiment results are linked to possible failure mechanisms in order to obtain the critical loads which are expressed in terms of cumulative distribution functions. The discrete distribution data of the critical loads are then fitted to analyze the effect of scale on different strength percentiles by virtue of the least squares function and closed quadric surface fitting. Eventually, the outcome is expressed in terms of ellipsoid surface representing the honeycomb material strength in three-dimensional stress space.

Impact damage characteristics in reinforced woven natural silk/epoxy composite face-sheet and sandwich foam, coremat and honeycomb materials

This research is interested in the impact toughness of a reinforced composite face-sheet and cores materials used in lightweight sandwich panels. It investigated the degrees of damage inflicted on the contact surface, through thickness and rear surface of the sandwich panels. The sandwich specimens were prepared in configurations of natural silk (NS)/Epoxy/Foam, NS/Epoxy/Coremat, NS/Epoxy/Honeycomb and reinforced NS/Epoxy serving as referral. For all experiments, drop weight impact test was carried out under low velocity impact energies of 32 J, 48 J and 64 J. Parameters measured were load bearing capability, energy absorption capability and damage fragmentation of the specimen with regards to increasing impact loads. Dominant deformation modes were seen as upper face-sheet compression failure, lower face-sheet delamination and lower face-sheet tensile failure.

Honeycomb Structures: Facile Synthesis of Biomimetic Honeycomb Material with Biological Functionality (Small 4/2013)

Honeycomb Structures: Facile Synthesis of Biomimetic Honeycomb Material with Biological Functionality (Small 4/2013)