Re-entrant Honeycomb Research Articles

Modulating poisson’s ratio in flexible honeycombs by density and architecture gradations

Zero Poisson’s ratio structures are a new class of mechanical metamaterials wherein the absence of lateral deformations allows the structure to adapt and conform their geometries to desired shapes with minimal interventions. These structures have gained attention in large deformation applications where shape control is a key performance attribute, with examples including but not limited to shape morphing, soft robotics, and flexible electronics. The present study introduces an experimentally driven approach that leads to the design and development of (near) zero Poisson’s ratio structures with considerable load-bearing capacities through concurrent density and architecture gradations in hybrid honeycombs created from hexagonal and re-entrant cells. The strain-dependent Poisson’s ratios in hexagonal and re-entrant honeycombs with various cell wall thicknesses have been characterized experimentally. A mathematical approach is then proposed and utilized to create hybrid structures wherein the spatial distribution of different cell shapes and densities leads to the development of honeycombs with minimal lateral deformations under compressive strains as high as 0.7. Although not considered design criteria, the load-bearing and energy absorption capacities of the hybrid structures are shown to be comparable with those of uniform cell counterparts. Finally, the new hybrid structures indicate lesser degrees of instability (in the form of cell buckling and collapse) due to the self-constraining effects imposed internally by the adjacent cell rows in the structures.

Three-point bending response and energy absorption of novel sandwich beams with combined re-entrant double-arrow auxetic honeycomb cores

The response and energy absorption of novel sandwich beams with combined re-entrant double-arrow auxetic honeycomb (RDAH) cores subjected to three-point bending were studied experimentally and numerically. Two typical sandwich beams loaded at different loading positions were considered. Quasi-static three-point bending experiments were conducted to obtain the failure modes and force–displacement curves. The reliable numerical simulation models were further established based on experimental validations. The results indicate that when the loading roller is located directly above the re-entrant cell, the RDAH core sandwich beam has better load-carrying and energy absorption capacity. Subsequently, the influence of face sheet distribution, cell-wall thickness, impact velocity and cell configuration on the structural response were explored. For the sandwich beams with same total mass, the arrangement where the thickness of the front face sheet is larger than that of the back face sheet is beneficial for improving the load-carrying and energy absorption capacity. In addition, the cell-wall thickness has an influence on the local deformation mode of the sandwich beam, and increasing its value can produce more stable deformation and improve the load-carrying capacity. Increasing impact velocity has a significant influence on the initial deformation but little influence on the final deformation of the sandwich beams. As the impact velocity increases, the total energy absorption of the sandwich beam gradually increases, and the negative Poisson's ratio characteristic of the core still exists. Compared to the traditional re-entrant honeycomb (RH) core sandwich beams, RDAH core sandwich beams have better energy absorption capacity and bending resistance.

In-plane crashing behavior and energy absorption of re-entrant honeycomb reinforced by arched ribs

Arched structures have increased in importance over the last few years due to their high efficiency in bearing loads. This paper introduces arched ribs to the classical re-entrant honeycomb (RH) as reinforced structures, and then its energy absorption is improved by simultaneously utilizing the reinforced structures and the auxetic deformation of RHs. Herein, the in-plane crashing response of reinforced RHs (RRH) under different impact velocities is investigated with finite element methods verified against the quasi-static compression experiment of 3D-printed RRH specimens. By introducing arched structures, the deformation of RHs becomes more stable and regular, and two plateau stresses are produced in the stress-strain curves of RRHs. Benefiting from the stacking deformation of RRHs and pure compression characteristic of catenary arches, the second plateau stress of all-reinforced RHs (ARH) is 3.8 times higher than the first one. Two plateau stresses of ARHs are derivated theoretically with a relative error of less than 7 %. Furthermore, a parametric study is performed to explore the effect of impact velocities, thicknesses, and the height of arched ribs on the crashing response of RRHs. The present investigation paves a new way toward strengthening the energy absorption of conventional honeycombs.

The Effect of Design and Fabrication Parameters on the Mechanical Properties of 3D Re-Entrant Honeycomb Auxetic Structures

In recent years, the potential of application of auxetic structures, with negative Poisson's ratio, is gaining interest due to the increasingly widespread use of additive manufacturing. Additive technologies allow the manufacture of lightweight and complex shapes, and among them, auxetic cellular three-dimensional structures stand out for their unique behavior and with applications of interest in fields such as aerospace, medical or construction engineering. In the present work, 3D re-entrant honeycomb auxetic structures are designed and manufactured with Stereolithography (SLA) and Fused Filament Fabrication (FFF) with different geometrical parameters to analyse their impact in the mechanical behaviour of these complex structures. To this aim, an Ultimaker S5 and a Formlabs Form3 printer, respectively, have been used. Design variations are approached considering the following parameters: the length of the vertical strut (H), the length of the re-entrant strut (L), the re-entrant angle between the re-entrant and the vertical strut (θ) and the diameter of the struts cross sections (d). The designed structures shape behavior is evaluated with mechanical tests including compression tests and digital image correlation technique, and numerical simulations, The results show that lower Poisson ratio’s values are identified with slimmer profiles and with higher effective lengths and, therefore, corresponds to slender struts. On the other hand, lower angles between vertical and oblique struts show lower Poisson ratios, associated to the load distribution and its effect on the structure’s node displacements.

Finite element simulation of femoral stems lightweighted with re-entrant honeycomb lattice structure

Artificial hip joints are used to replace damaged or diseased natural joints. When the stress that is typically applied to the bone changes because the implant and bone are different in stiffness, a phenomenon known as stress shielding occurs. Stress shielding can lead to bone weakening through reduced density and aseptic loosening in the long term. Studies are ongoing to overcome this phenomenon through geometric design, the use of materials with a low modulus of elasticity, or latticed implants. In this study, the effect of lightening the hip prosthesis with lattice structures on stress shielding is investigated using finite element simulation. The femoral stem of a solid hip prosthesis was lightweighted, with a re-entrant honeycomb auxetic cellular lattice structure, and structural analysis was performed. Two different lattice orientations were used, and it was observed that the stress distribution was more homogeneous in both orientations. In these femoral stems, which can be easily produced using additive manufacturing methods, a volume reduction of up to 16% was achieved. The stress transmitted to the bone increased by more than 36%, depending on the orientation, which is a promising result for reducing the stress shield effect.

A bio-inspired auxetic metamaterial with two plateau regimes: Compressive properties and energy absorption

Auxetics are a unique class of materials that exhibit a negative Poisson's ratio (NPR) owing to their distinguish deformation behavior. However, some auxetics are either weak in their in-plane directions and/or deform non-uniformly under quasi-static compression, resulting in inferior mechanical performance. This study aims to develop an auxetic metamaterial with relatively uniform deformation pattern and superior energy absorption capability. Inspired by the geometry of a butterfly, a novel auxetic metamaterial, namely, butterfly-shaped auxetic metamaterial (BSAM), was developed. The in-plane compressive performances of the proposed metamaterial were experimentally and numerically investigated. Polyamide11 specimens were 3D printed using Multi Jet Fusion (MJF). NPRs were observed during the compression along both directions. The compressed BSAM revealed two distinctive plateau regimes in its nominal stress-strain curves. Influences of specific parameters on the mechanical performance and energy absorption of the BSAM were numerically examined. Moreover, when BSAM was compressed along the Y direction, the specific energy absorption outperformed that of BSAM compressed along the X direction. A comparative study was carried out using the validated numerical models between the proposed metamaterial (BSAM) and two other popular auxetic honeycombs: re-entrant and anti-tetrachiral. Young's moduli and plateau stresses of the BSAM were significantly surpasses those of the two honeycombs. Moreover, the specific energy absorption per unit mass (SEA) were 2.4 and 3.2 times that of re-entrant honeycomb when they were compressed along the X and Y directions, respectively. Meanwhile, the SEA of the BSAM in the X and Y directions were 2.1 and 2.7 times that of the anti-tetrachiral honeycomb. The exquisite geometric configurations of the BSAM revealed distinguished and controllable mechanical properties which could sheds light on the possibility to design bio-inspired metamaterial with multi plateau regimes and energy absorption capacities for specific applications.

A novel elliptical annular re-entrant auxetic honeycomb with enhanced stiffness

Auxetic structures have sparked a lot of interest due to their excellent mechanical characteristics and unusual negative Poisson's ratio influence. However, the large porosity property results in low stiffness, which limits their application scope. Current approaches to augment stiffness often result in diminished auxetic performance. Therefore, it is challenging to simultaneously enhance the auxetic, stiffness and energy absorption capacity of auxetic structures. To address this issue, this paper proposes a novel elliptical annular re-entrant honeycomb (EARE) by introducing an elliptical annular structure into a conventional re-entrant honeycomb (RE) cell, which can provide extra longitudinal support without hindering lateral deformation. The plateau stress, Poisson's ratio and energy absorption properties of the EARE are investigated by quasi-static compressive tests and finite element modeling. The results show that the EARE honeycomb has two plateau stages due to the supporting effect of the elliptical annular structure. Compared with the conventional RE honeycomb with the same wall thickness, the EARE honeycomb not only exhibits a stronger auxetic effect embodied in the Poisson's ratio reduced by 5.19%, but also has a higher average plateau stress and a higher specific energy absorption of 171.63% and 28.03%, respectively, which significantly improves the stiffness and energy absorption performance. The parameterized analysis reveals that by appropriately adjusting the geometric parameters, the stiffness, energy absorption, and auxetic effect of the EARE honeycomb can be enhanced. The research findings address the conflict between auxetic performance and honeycomb stiffness, providing new insights into the optimization of honeycomb structure design.

Additive Manufacturing of Continuous Fiber-Reinforced Polymer Composite Sandwich Structures with Multiscale Cellular Cores

The use of composite sandwich structures with cellular cores is prevalent in lightweight designs owing to their superior energy-absorbing abilities. However, current manufacturing processes, such as hot-press molding and mold pressing, require multiple steps and complex tools, thus limiting the exploration of advanced sandwich structure designs. This study reports a novel multi-material additive manufacturing (AM) process that allows the single-step production of continuous fiber-reinforced polymer composite (CFRPC) sandwich structures with multiscale cellular cores. Specifically, the integration of CFRPC-AM and in situ foam AM processes provides effective and efficient fabrication of CFRPC panels and multiscale cellular cores with intricate designs. The cellular core design spans three levels: microcellular, unit-cell, and graded structures. Sandwich structures with a diverse set of unit-cell designs, that is, rhombus, square, honeycomb, and re-entrant honeycomb, were fabricated and their flexural behaviors were studied experimentally. The results showed that the sandwich structure with a rhombus core design possessed the highest flexural stiffness, strength, and specific energy absorption. In addition, the effect of the unit-cell assembly on the flexural performance of the CFRP composite sandwich structure was examined. The proposed design and fabrication methods open new avenues for constructing novel and high-performance CFRPC structures with multiscale cellular cores that cannot be obtained using existing approaches.

Optimizing the performance of auxetic square tubes under uniaxial compression

Thin-walled tubes are widely used as energy absorbers to increase the crash resistance and safety while maintaining lightness. There has been an increase in interest in the integration of auxetic structures into these tubes. This is due to the better mechanical strength displayed by auxetic structures with negative Poisson’s ratio, particularly in terms of compressive behavior and energy absorption. In this study, a group of square-section tubes with different types of cell structures on their side faces was examined. Under quasi-static compression, the behaviors of thin-walled square tubes with reentrant auxetic and conventional honeycomb were examined numerically and experimentally. In addition, geometric optimization of reentrant cell shape was performed to maximize the compressive loading of the square tubes. First, the compression behaviors of thin-walled square tubes made of polylactic acid (PLA) were examined; these tubes’ side surfaces have both conventional and reentrant auxetic honeycomb cellular patterns. The reentrant auxetic and conventional honeycomb cell architectures were applied together and separately on the side faces of the thin-walled tube, with the identical cell parameters. In order to better understand the deformations, force-displacement curves were examined for four different types of thin-walled square tubes, including tubes with reentrant auxetic and honeycomb cell structures on all side faces and tubes with these structures on opposite sides and adjacent. Using the ANSYS finite element software package and Digimizer image processing programs, the Poisson’s ratio of the reentrant auxetic and conventional honeycomb configurations as well as the maximum compression force of the tubular structures were determined numerically and experimentally. After obtaining the result that the use of the reentrant auxetic structure on the side surfaces of the square tube significantly increased the compression resistance and energy absorption capability of the tube, the optimization of the square tube with the reentrant auxetic structure on all surfaces was examined. The effect of the geometrical parameters such as ligament length, reentrant angle, and cell thickness of the unit-cell on the compression load of the square tube was investigated using an integrated methodology combining numerical simulation and DoE (Design of Experiments) method. The findings show that the tubes combined reentrant auxetic structure exhibits better energy absorption than the conventional honeycomb tubes. It also reveals that the optimum geometric parameters of the reentrant auxetic unit cell are to be the ligament length of 16.358 mm, the ligament angle of 80°, and the ligament thickness of 3 mm.

In-plane crushing behavior of a novel re-entrant diamond-shaped honeycomb and its variant structures

In this paper, different polygonal structures are employed to improve the inclined cell walls of the well-known re-entrant honeycomb (REH) to obtain a series of novel REHsto proposed enhancement energy absorption capacity. The energy absorption effect and platform stress of this series of novel REHs and classical REHs were compared by quasi-static experiments. A significant negative Poisson's ratio effect was observed in all the new honeycombs. The crushing behaviors of these honeycombs under different crushing velocities were further simulated using the finite element (FE) software ABAQUS/Explicit. Both experimental and numerical results show that this series of novel REHs constructed herein have stronger crushing strength and energy absorption capacity compared to the original REH.

Experimental investigation on 4D printed intelligent assembly cushion with adjustable pre-tightening force

In order to design an intelligent assembly cushion with an adjustable pre-tightening force, a reentrant honeycomb structure was printed by additive manufacturing to realize the active and intelligent assembly process of filling gaps. The thermo-mechanical deformation experiments of the reentrant honeycomb structure were conducted at different pre-compressions, constrained displacements, and recovery temperatures. The recovery force and the force recovery ratio under semi-constrained conditions are explored emphatically. The results show that pre-compression, constrained displacement, and recovery temperature affect the recovery force and force recovery ratio under semi-constrained conditions. The recovery force and force recovery ratio increase with pre-compression, decrease with constrained displacement, and increase with recovery temperature below the glass transition temperature. Based on these results, the adjustability of the recovery force of a reentrant honeycomb cushion can be controlled by changing the thermo-mechanical deformation processes. Finally, the reentrant honeycomb cushion is applied to the mimetic assembly environment for corresponding testing, achieving the design of an active and intelligent assembly cushion with an adjustable pre-tightening force.

DESIGNING PROGRAMMABLE FERROMAGNETIC SOFT METASTRUCTURES FOR MINIMALLY INVASIVE ENDOVASCULAR THERAPY.

Minimally invasive endovascular therapy (MIET) is an innovative technique that utilizes percutaneous access and transcatheter implantation of medical devices to treat vascular diseases. However, conventional devices often face limitations such as incomplete or suboptimal treatment, leading to issues like recanalization in brain aneurysms, endoleaks in aortic aneurysms, and paravalvular leaks in cardiac valves. In this study, we introduce a new metastructure design for MIET employing re-entrant honeycomb structures with negative Poisson's ratio (NPR), which are initially designed through topology optimization and subsequently mapped onto a cylindrical surface. Using ferromagnetic soft materials, we developed structures with adjustable mechanical properties called magnetically activated structures (MAS). These magnetically activated structures can change shape under noninvasive magnetic fields, letting them fit against blood vessel walls to fix leaks or movement issues. The soft ferromagnetic materials allow the stent design to be remotely controlled, changed, and rearranged using external magnetic fields. This offers accurate control over stent placement and positioning inside blood vessels. We performed magneto-mechanical simulations to evaluate the proposed design's performance. Experimental tests were conducted on prototype beams to assess their bending and torsional responses to external magnetic fields. The simulation results were compared with experimental data to determine the accuracy of the magneto-mechanical simulation model for ferromagnetic soft materials. After validating the model, it was used to analyze the deformation behavior of the plane matrix and cylindrical structure designs of the Negative Poisson's Ratio (NPR) metamaterial. The results indicate that the plane matrix NPR metamaterial design exhibits concurrent vertical and horizontal expansion when subjected to an external magnetic field. In contrast, the cylindrical structure demonstrates simultaneous axial and radial expansion under the same conditions. The preliminary findings demonstrate the considerable potential and practicality of the proposed methodology in the development of magnetically activated MIET devices, which offer biocompatibility, a diminished risk of adverse reactions, and enhanced therapeutic outcomes. Integrating ferromagnetic soft materials into mechanical metastructures unlocks promising opportunities for designing stents with adjustable mechanical properties, propelling the field towards more sophisticated minimally invasive vascular interventions.

Impact response analysis of stiffened sandwich functionally graded porous materials doubly-curved shell with re-entrant honeycomb auxetic core

Owing to unique deformation behavior and high capacity of energy absorption, auxetic structures have garnered significant research attention. To reveal the energy-absorbing properties of the auxetic structure, the impact response of stiffened sandwich functionally graded porous materials (FGPM) doubly-curved shell with re-entrant honeycomb auxetic core is studied by the established analytical model in the present work. The material properties in the thickness direction of FGPM face sheets are adjusted according to the volume fraction of constituents by power law and exponential law, while the core layer is made of the re-entrant honeycomb auxetic core with negative Poisson's ratio. On the basis of the Hertz theory for elastic impacts and the first-order shear deformation theory (FSDT), an analytical model is developed to study its impact phenomenon. Equations of motion are derived using Hamilton's principle, which are further solved analytically using Navier's technique of assuming unknown variables in the double trigonometric series. The time-dependent contact force is obtained by applying the spring-mass (SM) model consisting two-degrees-of freedom. Afterward, the transverse central displacements of the stiffened sandwich FGPM doubly-curved shell are calculated by adopting the Duhamel integration. The impact force and transverse displacements are compared with the previously published results, indicating that the theoretical results agree with the previously published results.Parametric analyses have been carried out to investigate the effect of variation of various parameters such as volume fraction exponents, radii of principal curvatures, porosity volume fraction, core layer inclined angle on the impact response of the sandwich shell. Additionally, the results show that compared with the traditional hexagonal honeycomb core type, the stiffened sandwich FGPM doubly-curved shell with re-entrant honeycomb core type has significant advantages in impact energy absorption. This work may provide an extensive reference and valuable guidance in the impact design and application of auxetic sandwich shell structures.

Re-entrant honey comb meta-materials configuration and its application in buckling restrained braces: A numerical study

Evens came up with the term "auxetics" in the 1990s. It is used to describe materials and structures with a negative Poisson's ratio (NPR) that shrink or grow in an unusual way when put under uniaxial compression and tension. These materials have different mechanical properties, such as a high shear bearing capacity, resistance to breaking, ability to absorb energy, and resistance to falling apart. But because auxetics often have holes in them, they are often much less stiff than solid structures. Although these shapes should function well under both static and dynamic loading conditions as energy-absorbing components, the behavior of auxetic metamaterials has been rarely investigated in the field of seismic protection. In this paper, a parametric study was conducted using a metallic damper, such as a buckling restrained brace (BRB) equipped with an auxetic steel core and re-entrant honeycomb cells, with the aim of exploring the performance dissipative of these types of metamaterials. The proposed model of BRB with an auxetic core was modeled and analyzed under cyclic loading using a finite element method. The repetitive re-entrant honeycomb cells are controlled by four parameters: hole ratio (porosity), section weakening rate, concave angle, and angle chamfering radius. Hysteresis behavior and vos mises distribution under large deformation were extracted and discussed. As seen in the results, it was found that the local buckling of the steel core could be improved by the auxetic behavior. The values of 75° angle and 0.5 corner chamfer radius were selected to have the largest effect on the hysteresis curves of BRB model specimens when the axial strain exceeds 1.2%. The dissipative performance of these metamaterials under cyclic tests provides a good basis for further investigations about applying auxetic structures in the field of protective structures.

Mechanical and bandgap properties of 3D bi-material triangle re-entrant honeycomb

In the aerospace industry, precision components need to serve in a comprehensive environment of severe temperature changes, vibrations, and noise. Therefore, it is necessary to design a multifunctional mechanical metamaterial that integrates a tunable coefficient of thermal expansion (CTE), Poisson's ratio (PR), and bandgap. Here, a 3D bi-material triangle re-entrant honeycomb (3D-BTRH) with adjustable Poisson's ratio is proposed. Due to the geometric symmetry, the 3D-BTRH realizes the isotropy of mechanical properties in the three coordinate axes. The intrinsic mechanisms of tunable CTE and PR of the 3D-BTRH are revealed by building theoretical models. The accuracy of the theoretical analysis of PR and Young's modulus is verified by simulation and experiment. The finite element analysis is used to calculate the band structures and width of the total effective bandgap utilizing Bloch's theorem and Bloch's periodic boundary conditions. The accuracy of the band structure calculations is verified by calculating the transmission characteristic curve. The parametric analysis shows that the 3D-BTRH can achieve tunable CTE and PR in the directions of the three axes, and has a large width of the total effective bandgap. Moreover, this work provides a design idea for 3D metamaterials to simultaneously regulate CTE, PR, and the bandgap, which offers opportunities for better engineering practice.

In‐Plane Crushing Behaviors of Hexagonal Honeycombs with Hollow‐Circle Joint under Different Compressive Velocities

The in‐plane crushing behaviors of hierarchical hexagonal honeycombs, structured by replacing every three‐wall vertex of both the conventional and reentrant hexagonal honeycombs with a small hollow‐circle, are investigated herein. The finite element (FE) models are first verified by an empirical formula from the literature and then further used to simulate the in‐plane crushing behaviors of the honeycombs under different compressive velocities. The deformation mode, plateau stress, and specific energy absorption (SEA) are studied based on the FE simulations. With respect to the conventional hierarchical honeycombs, the reentrant hierarchical honeycombs, in most instances, are found to exhibit higher plateau stress but lower SEA. It is remarkable that the hierarchical hexagonal honeycombs exhibit higher plateau stress and SEA than the basic hexagonal ones, which indicates that the hierarchical design is effective in improving both the impact resistance and energy absorption capabilities of the honeycombs.

Dynamic Compressive and Flexural Behaviour of Re-Entrant Auxetics: A Numerical Study.

Re-entrant auxetics offer the potential to address lightweight challenges while exhibiting superior impact resistance, energy absorption capacity, and a synclastic curvature deformation mechanism for a wide range of engineering applications. This paper presents a systematic numerical study on the compressive and flexural behaviour of re-entrant honeycomb and 3D re-entrant lattice using the finite element method implemented with ABAQUS/Explicit, in comparison with that of regular hexagonal honeycomb. The finite element model was validated with experimental data obtained from the literature, followed by a mesh size sensitivity analysis performed to determine the optimal element size. A series of simulations was then conducted to investigate the failure mechanisms and effects of different factors including strain rate, relative density, unit cell number, and material property on the dynamic response of re-entrant auxetics subjected to axial and flexural loading. The simulation results indicate that 3D re-entrant lattice is superior to hexagonal honeycomb and re-entrant honeycomb in energy dissipation, which is insensitive to unit cell number. Replacing re-entrant honeycomb with 3D re-entrant lattice leads to an 884% increase in plastic energy dissipation and a 694% rise in initial peak stress. Under flexural loading, the re-entrant honeycomb shows a small flexural modulus, but maintains the elastic deformation regime over a large range of strain. In all cases, the compressive and flexural dynamic response of re-entrant auxetics exhibits a strong dependence on strain rate, relative density, and material property. This study provides intuitive insight into the compressive and flexural performance of re-entrant auxetics, which can facilitate the optimal design of auxetic composites.

A systematic numerical and experimental study into the mechanical properties of five honeycombs

Honeycombs are engineered cellular materials that often show superior specific strength, stiffness and energy absorption compared to solid materials. As a consequence they have found numerous applications across engineering fields. The development of additive manufacturing (AM) technologies has initiated an abundance of studies into novel honeycombs as historic manufacturing constraints are lifted. Investigations have been focused on improving or tailoring a given property but very few have focused on isotropy, and little has been done to bring together different patterns under the same manufacturing and experimental conditions. In this study, AM has been used to manufacture nominally identical honeycombs based on differing unit cells, in a range of orientations and densities. Elastic and plastic properties for the hexagon, triangle, square, re-entrant and double-V honeycombs have been obtained through mechanical testing. The elastic properties of these honeycombs have been modelled for all possible in-plane loading directions using minimal computational resources. The effect of orientation and density has been presented, confirming the level of in-plane isotropy for dense honeycombs with regards to Young’s modulus, Poisson’s ratio, yield strength and compressive strength. Insights have also been gained into how these properties vary with relative density. These results provide a basis for comparison with future work on honeycombs.

Study on mechanical properties of cellular structures with negative Poisson's ratio based on the development of Abaqus plug-in tool

A parametric modeling approach is proposed based on secondary development of Abaqus and a plug-in tool is designed for emulation analysis on cellular structures through graphical user interface. Firstly, star honeycomb (SH), double-headed arrow honeycomb (DAH), and re-entrant hexagon honeycomb (RHH) are chosen, and prediction models are established to estimate their mechanical properties based on homogenization theory. Then, equivalent Poisson's ratio, elastic modulus and platform stress are verified through quasi-static compression tests and simulation analysis on DAH. Subsequently, the corresponding prediction models can be integrated into the plug-in tool to pre-analyze mechanical properties of cellular structures by inputting various geometric parameters. Secondly, parametric modeling on the three cellular structures is executed. Then, attribute assignments of material, load and constraint properties are set based on Python program. Based on this, the plug-in tool is utilized to output geometric models automatically and acquire target output data employed to draw curves by MATLAB. Then, quasi-static compression tests on RHH are performed to verify the accuracy of parametric models generated by plug-in tool. Eventually, multi-condition impact mechanical properties of RHH and the influences of structural parameters on mechanical properties of the SH are investigated based on the developed plug-in tool.

Mechanics of re-entrant anti-trichiral honeycombs with nature-inspired gradient distributions

This study focuses on the nature-inspired gradient-based approach to re-designing re-entrant anti-trichiral (REAT) honeycombs through extensive experimental quasi-static compression. Novel perspectives on REAT honeycomb are offered through the introduction of gradient distributions on two critical geometrical parameters, the cylindrical diameter (chiral) and height of the unit cell, rather than the traditional thickness-based gradient approach. Chiral-based gradient approach demonstrated clear advantages in elastic stiffness, specific energy absorption (SEA) and densification strain over uniform REAT structures of constant geometrical parameters. These advantages are exhibited in their extended and constantly increasing quasi-plateau stage, consistent specific energy absorption (SEA) especially during early stages of compression, and most importantly, the ability to maintain a relatively constant energy absorption efficiency that is 25% more than that of the Base uniform REAT structure. Height gradient-based REAT structures, on the other hand, were able to leverage on associations between the negative Poisson's ratio (NPR) effect and height of unit cell to demonstrate notable deformation patterns across various portions of the structure. The present work reveals the performance enhancements through alternative gradient-based approaches over thickness-based gradient approaches and highlighted the differences in NPR between layers as the main driver of compressive collapse apart from the commonly concluded difference in relative density.