Design and mechanical properties analysis of a cellular Waterbomb origami structure

Cellular structures are commonly used to design energy-absorbing structures,and origami structures are becominga prevalent method of cellular structure design.This paper proposes a foldable cellular structure based on theWaterbomb origami pattern.The geometrical configuration of this structure is described.Quasi-static compressiontests of the origami tube cell of this cellular structure are conducted,and load-displacement relationship curvesare obtained.Numerical simulations are carried out to analyze the effects of aspect ratio,folding angle,thicknessand number of layers of origami tubes on initial peak force and specific energy absorption(SEA).Calculationformulas for initial peak force and SEA are obtained by the multiple linear regression method.The degree ofinfluence of each parameter on the mechanical properties of the single-layer tube cell is compared.The resultsshow that the cellular structure exhibits negative stiffness and periodic load-bearing capacity,as well as foldingangle has the most significant effect on the load-bearing and energy-absorbing capacity.By adjusting the designparameters,the stiffness,load-bearing capacity and energy absorption capacity of this cellular structure can beadjusted,which shows the programmable mechanical properties of this cellular structure.The foldability andthe smooth periodic load-bearing capacity give the structure potential for application as an energy-absorbing structure.

Full-Scale Isogeometric Topology Optimization of Cellular Structures Based on Kirchhoff-Love Shells

Cellular thin-shell structures are widely applied in ultralightweight designs due to their high bearing capacity and strength-to-weight ratio.In this paper,a full-scale isogeometric topology optimization(ITO)method based on Kirchhoff-Love shells for designing cellular tshin-shell structures with excellent damage tolerance ability is proposed.This method utilizes high-order continuous nonuniform rational B-splines(NURBS)as basis functions for Kirchhoff-Love shell elements.The geometric and analysis models of thin shells are unified by isogeometric analysis(IGA)to avoid geometric approximation error and improve computational accuracy.The topological configurations of thin-shell structures are described by constructing the effective density field on the controlmesh.Local volume constraints are imposed in the proximity of each control point to obtain bone-like cellular structures.To facilitate numerical implementation,the p-norm function is used to aggregate local volume constraints into an equivalent global constraint.Several numerical examples are provided to demonstrate the effectiveness of the proposed method.After simulation and comparative analysis,the results indicate that the cellular thin-shell structures optimized by the proposed method exhibit great load-carrying behavior and high damage robustness.

A Hybrid Level Set Optimization Design Method of Functionally Graded Cellular Structures Considering Connectivity

With the continuous advancement in topology optimization and additive manufacturing(AM)technology,the capability to fabricate functionally graded materials and intricate cellular structures with spatially varying microstructures has grown significantly.However,a critical challenge is encountered in the design of these structures–the absence of robust interface connections between adjacent microstructures,potentially resulting in diminished efficiency or macroscopic failure.A Hybrid Level Set Method(HLSM)is proposed,specifically designed to enhance connectivity among non-uniform microstructures,contributing to the design of functionally graded cellular structures.The HLSM introduces a pioneering algorithm for effectively blending heterogeneous microstructure interfaces.Initially,an interpolation algorithm is presented to construct transition microstructures seamlessly connected on both sides.Subsequently,the algorithm enables the morphing of non-uniform unit cells to seamlessly adapt to interconnected adjacent microstructures.The method,seamlessly integrated into a multi-scale topology optimization framework using the level set method,exhibits its efficacy through numerical examples,showcasing its prowess in optimizing 2D and 3D functionally graded materials(FGM)and multi-scale topology optimization.In essence,the pressing issue of interface connections in complex structure design is not only addressed but also a robust methodology is introduced,substantiated by numerical evidence,advancing optimization capabilities in the realm of functionally graded materials and cellular structures.

Influence of manufacturing process-induced geometrical defects on the energy absorption capacity of polymer lattice structures

Modern additive manufacturing processes enable fabricating architected cellular materials of complex shape,which can be used for different purposes.Among them,lattice structures are increasingly used in applications requiring a compromise among lightness and suited mechanical properties,like improved energy absorption capacity and specific stiffness-to-weight and strength-to-weight ratios.A dedicated modeling strategy to assess the energy absorption capacity of lattice structures under uni-axial compression loading is presented in this work.The numerical model is developed in a non-linear framework accounting for the strain rate effect on the mechanical responses of the lattice structure.Four geometries,i.e.,cubic body centered cell,octet cell,rhombic-dodecahedron and truncated cuboctahedron 2+,are investigated.Specifically,the influence of the relative density of the representative volume element of each geometry,the strain-rate dependency of the bulk material and of the presence of the manufacturing process-induced geometrical imperfections on the energy absorption capacity of the lattice structure is investigated.The main outcome of this study points out the importance of correctly integrating geometrical imperfections into the modeling strategy when shock absorption applications are aimed for.

Design Optimization of Irregular Cellular Structure for Additive Manufacturing

Irregularcellular structurehas great potential to be considered in light-weight design field. However, the research on optimizing irregular cellular structures has not yet been reporteddue to the difficulties in their modeling technology. Based on the variable density topology opti- mization theory, an efficient method for optimizing the topology of irregular cellular structures fabricated through additive manufacturing processes is proposed. The pro- posed method utilizes tangent circles to automatically generate the main outline of irregular cellular structure. The topological layoutof each cellstructure is optimized using the relative density informationobtained from the proposed modified SIMP method. A mapping relationship between cell structure and relative densityelement is builtto determine the diameter of each cell structure. The results show that the irregular cellular structure can be optimized with the proposed method. The results of simulation and experimental test are similar for irregular cellular structure, which indicate that the maximum deformation value obtained using the modified Solid Isotropic Microstructures with Penalization （SIMP） approach is lower 5.4× 10-5 mm than that using the SIMP approach under the same under the same external load. The proposed research provides the instruction to design the other irregular cellular structure.

Symplectic analysis for elastic wave propagation in two-dimensional cellular structures

On the basis of the finite element analysis, the elastic wave propagation in cellular structures is investigated using the symplectic algorithm. The variation principle is first applied to obtain the dual variables and the wave propagation problem is then transformed into two-dimensional （2D） symplectic eigenvalue problems, where the extended Wittrick-Williams algorithm is used to ensure that no phase propagation eigenvalues are missed during computation. Three typical cellular structures, square, triangle and hexagon, are introduced to illustrate the unique feature of the symplectic algorithm in higher-frequency calculation, which is due to the conserved properties of the structure-preserving symplectic algorithm. On the basis of the dispersion relations and phase constant surface analysis, the band structure is shown to be insensitive to the material type at lower frequencies, however, much more related at higher frequencies. This paper also demonstrates how the boundary conditions adopted in the finite element modeling process and the structures＇ configurations affect the band structures. The hexagonal cells are demonstrated to be more efficient for sound insulation at higher frequencies, while the triangular cells are preferred at lower frequencies. No complete band gaps are observed for the square cells with fixed-end boundary conditions. The analysis of phase constant surfaces guides the design of 2D cellular structures where waves at certain frequencies do not propagate in specified directions. The findings from the present study will provide invaluable guidelines for the future application of cellular structures in sound insulation.

Effect of Cellular Structure on Mechanical Properties of Polyurethane Foam Curing Materials

Based on the mechanical properties and microstructure of polyurethane foam solidified material, a two-dimensional model of polyurethane foam solidified material was constructed. Polyurethane foam was obtained by fully and uniformly mixing the two components. The research was carried out through the combination of experimental test and finite element simulation. The experimental results show that when the pore density is constant, the size of the bubble hole is an important factor affecting the mechanical properties of the model. The smaller the size of the bubble hole, the less likely it is to produce stress concentration inside the model, and the stronger the resistance to material deformation. Under the random distribution, the lower the density of the polyurethane cured material, the higher the probability of damage between the adjacent bubbles, which is not conducive to the stability of the material. The density of the cured material should not be lower than 199 kg/m^3.

Development of Composite Cellular Cores for Sandwich Panels Based on Folded Polar Quadra-Structures

An idea to develop a family of cellular cores for sandwich panels using a technology of prepreg folding is presented.Polar folded quadra-structures are regarded as a geometric basis for these cores whose standard fragment has the fourth degree of axial symmetry.The classification of the polar structures are described and a method of various quadra-structure synthesis is developed.A possibility to provide high strength of the structure due to preservation of faces reinforcement pattern is presented.Arrangement of the plane core on a bi-curvature surface is also introduced.Besides,provision of isotropy of the core in two or three directions are described.Finally,examples of cellular folded cores manufactured from basalt reinforced plastic are demonstrated.

Functionally Graded Cellular Structure Design Using the Subdomain Level Set Method with Local Volume Constraints

Functional graded cellular structure(FGCS)usually shows superiormechanical behaviorwith lowdensity and high stiffness.With the development of additivemanufacturing,functional graded cellular structure gains its popularity in industries.In this paper,a novel approach for designing functionally graded cellular structure is proposed based on a subdomain parameterized level set method(PLSM)under local volume constraints(LVC).In this method,a subdomain level set function is defined,parameterized and updated on each subdomain independently making the proposed approach much faster and more cost-effective.Additionally,the microstructures on arbitrary two adjacent subdomains can be connected perfectly without any additional constraint.Furthermore,the local volume constraint for each subdomain is applied by virtue of the augmented Lagrange multiplier method.Finally,several numerical examples are given to verify the correctness and effectiveness of the proposed approach in designing the functionally graded cellular structure.From the optimized results,it is also found that the number of local volume constraints has little influence on the convergence speed of the developed approach.

Design and Mechanical Characterization of an S-Based TPMS Hollow Isotropic Cellular Structure

Cellular structures are regarded as excellent candidates for lightweight-design,load-bearing,and energy-absorbing applications.In this paper,a novel S-based TPMS hollow isotropic cellular structure is proposed with both superior load-bearing and energy-absorbing performances.The hollow cellular structure is designed with Boolean operation based on the Fischer-Koch(S)implicit triply periodic minimal surfaces(TPMS)with different level parameters.The anisotropy and effective elasticity properties of cellular structures are evaluated with the numerical homogenization method.The finite element method is further conducted to analyze the static mechanical performance of hollow cellular structure considering the size effect.The compression experiments are finally carried out to reveal the compression properties and energy-absorption characteristics.Numerical results of the Zener ratio proved that the S-based hollow cellular structure tends to be isotropic,even better than the sheet-based Gyroid TPMS.Compared with the solid counterpart,the S-based hollow cellular structure has a higher elastic modulus,better load-bearing and energy absorption characteristics.

Modeling of solidification grain structure for Ti-45%Al alloy ingot by cellular automaton

A cellular automaton model for simulating grain structure formation during solidification processes of Ti-45%Al(mole fraction) alloy ingot was developed, based on finite differential method for macroscopic modeling of heat transfer and a cellular automaton technique for microscopic modeling of nucleation, growth, solute redistribution and solute diffusion. The relation between the growth velocity of a dendrite tip and the local undercooling, which consists of constitutional, thermal, curvature and attachment kinetics undercooling is calculated according to the Kurz-Giovanola-Trivedi model. The effect of solidification contraction is taken into consideration. The influence of process variables upon the resultant grain structures was investigated. Special moving allocation technique was designed to minimize the computation time and memory size associated with a large number of cells. The predicted grain structures are in good agreement with the experimental results.

Influence of environmental factors on corrosion damage of aircraft structure

Corrosion is one of the important structural integrity concerns of aging aircraft, and it is estimated that a significant portion of airframe maintenance budgets is directed towards corrosion-related problems for both military and commercial aircraft. In order to better understand how environmental factors influence the corrosion damage initiation and propagation on aircraft structure and to predict pre-corrosion test pieces of fatigue life and structural integrity of an effective approach, this paper uses the cellular automaton (CA) method to character the effect of electrolyte concentrations, dissolution probabilities, and temperature on the corrosion damage of a metal structure exposed to an aggressive environment, and the procedure for applying the local rules between the cells of the CA to simulate the corrosion damage evolution is formulated. The simulation results show that the different electrolyte concentrations, dissolution probabilities and temperature, the laws of the dissolution current with time are investigated and they obey the time power function.

Structured hierarchical Mn–Co mixed oxides supported on silicalite-1 foam catalyst for catalytic combustion

Silicalite-1(S1)foam was functionalized by supporting manganese-cobalt(Mn-Co)mixed oxides to develop the structured hierarchical catalyst(Mn-Co@SlF)for catalytic combustion for the first time.The self-supporting S1 foam with hierarchical porosity was prepared via hydrothermal synthesis with polyurethane(PU)foam as the template.Subsequently,Mn-Co oxide nano sheets were uniformly grown on the surface of S1 foams under hydrothermal conditions to prepare the structured hierarchical catalyst with specific surface area of 354 m^2·g^-1,micropore volume of 0.141 cm^3·g^-1 and total pore volume of 0.217 cm3·g^-1,as well as a good capacity to adsorb toluene(1.7 mmol·g^-1 at p/p0=0.99).Comparative catalytic combustion of toluene of over developed structured catalyst Mn-Co@SlF was performed against the control catalysts of bulk Mn-Co@S1(i.e.,the crushed Mn-Co@SlF)and unsupported Mn-Co oxides(i.e.,Mn-Co).Mn-Co@SlF exhibited comparatively the best catalytic performance,that is,complete and stable toluene conversion at 2480 C over 65 h due to the synergy between Mn-Co oxides and S1 foam,which provided a large number of oxygen vacancies,high redox capacity.In addition,the hierarchical porous structure also improved the accessibility of active sites and facilitated the global mass transfer across the catalyst bed,being beneficial to the catalysis and catalyst longevity.

Analysis of 13Cr bloom solidification structure using CA-FE model

Solidification structure is critical in the control of the mechanical properties and quality during the continuous casting process. The thermo-physical properties of 13 Cr steel added some rare metals, such as Mo, V, Nb, are measured to better understand the solidification structure of 13 Cr bloom. A computational model using CA-FE(cellular automation-finite element) method coupled with heat transfer model is developed to describe the solidification structure in continuous casting process. It is found that the calculated solidification structure is in good agreement with the observed data. The influence of casting speed and superheat on the solidification structure of the bloom is studied in detail. In order to obtain more equiaxed crystal ratio and low degree of the segregation in the bloom, the optimized casting speed 0.6 m/min and superheat less than 25 °C are determined for the caster. Using the optimized manufacturing parameters, these samples are 60% with the equiaxed zone ratio of 8%–10% and below the degree of segregation 1.05.

NO_3^-/NH_4^+ ratios affect plant growth, chlorophyll content,respiration rate, and morphological structure in Malus hupehensis seedlings

Malus hupehensis （Pamp.） Rehd. is a widely cultivated rootstock in China. We studied the effect of three NO3-/NH4＋ ratios （100/0, 50/50, and 0/100, molar basis） at total nitrogen （N） concentration of 8 mmoL L-1 in a nutrient solution on M. hupehensis seedlings. Plant biomass, NO3- and NH4＋concentrafion, chlorophyll con- tent, respiratory rate, and cellular structure were investi- gated. M. hupehensis seedlings at the NO3-/NH4＋ ratio of 50/50 had the highest level of fresh weight, dry weight, shoot length, and chlorophyll （a, b, and a ＋ b） content, but the lowest respiration rate in the leavesand roots. In addition, thickness and numbers of palisade and spongy tissue cells of the leaves were greater with this treatment than with other treatments. At the NO3-/NH4＋ ratio of 100/0, the leaves and roots had higher NO3- concentration and lower NH4＋ concentration. However, the opposite trend occurred at the NO3-/NH4＋ ratio of 0/100. Chloro- phyll （a, b, and a ＋ b） content was lowest at the NO3-/NH4＋ ratio of 100/0 than at the other ratios. At the NO3-/ NH4＋ ratio of 0/100, oxygen （02） consumption increased in the leaves and roots, and irregular epidermis and cortex cells were observed in the root apical meristematic and mature region. Our results indicated that the NO3-INH4＋ ratio at 50/50 was suitable for growth of M. hupehensis seedling to achieve the highest biomass production and efficiency.

Effect of process variables on grain growth in simulating solidification microstructure of Ti-45% Al alloy ingot by stochastic model

A comprehensive stochastic model for simulating microstructure formation of Ti-45%Al(mole fraction) alloy ingot during solidification process was developed, based on a finite differential method(FDM) for macroscopic heat flow calculation and a cellular automaton(CA) technique for microscopic modeling of nucleation and growth. The formation of a shrinkage cavity at the top of ingot was taken into account. The effects of process variables such as pouring temperature and mold-preheated temperature on the microstructure formation were investigated. The calculated results indicate that the columnar zone is expanded with increasing pouring temperature in the nonlinear way and the volume fraction of equiaxed zone only slightly varies with the mold-preheated temperature.

Negative compressibility property in hinging open-cell Kelvin structure

A new three-dimensional(3D)cellular model based on hinging open-cell Kelvin structure is proposed for its negative compressibility property.It is shown that this model has adjustable compressibility and does exhibit negative compressibility for some certain conformations.And further study shows that the images of compressibility are symmetrical about the certain lines,which indicates that the mechanical properties of the model in the three axial directions are interchangeable and the model itself has a certain geometric symmetry.A comparison of the Kelvin model with its anisotropic form with the dodecahedron model shows that the Kelvin model has stronger negative compressibility property in all three directions.Therefore,a new and potential method to improve negative compressibility property can be derived by selecting the system type with lower symmetry and increasing the number of geometric parameters.

Experimental Testing of Cellular Construction Materials Containing Flax Particles

The feasibility of a sustainable non-autoclaved cellular concrete,based on flax vegetable co-products,for the production of usable specimen in the lightweight construction field,has been investigated experimentally.The produced specimen,containing various volume ratios of flax particles with respect to preformulatd Tradical PF70 lime binder of 0,1,and 2,were lightened by creating a porous structure in the matrix through the addition of 0.3%wt.Aluminium powder(able to react with calcium hydroxide from the binder and result in microscopic air-bubbles).Fresh and hardened specimen properties,including hydration,fresh density,porosity,hardened density,compressive and flexural strengths,toughness energy,and dry thermal conductivity at different temperatures,were assessed for varying flax-to-binder ratios.Results have shown that the addition of Aluminum powder leads to restrain the setting time delay of binder-based lime.Moreover,the hardened material displays a significant decrease in specimen density,thereby resulting in a compressive strength level compatible with that required in the cellular construction materials sector.Results also highlighted the ability of added flax to induce a change in the specimen from brittle to ductile behavior.Moreover,a high degree of thermal insulation can be achieved,which makes the cellular specimen based on flax particle suitable as insulated-bearing walls material.

Structure-activity correlationship and folding of recombinant Escherichia coli dihydro folate reductase (DHFR) enzyme through biochemical and biophysical approaches

The design of any antagonist or inhibitor for any enzyme requires the knowledge of structure- function relationship of the protein and the optimum conformational states for maximum and minimum activities. Furthermore, designing of the inhibitors or drugs against an enzyme becomes easier if there is information available about various well characterized intermediate conformation of the molecule. In vivo folding pathway of any recombinant protein is an important parameter for understanding its ability to fold by itself inside the cell, which always dictates the downstream processing for the purification. In the present manuscript we have discussed about the in vivo and in vitro folding, and structure-function relationship of Dihydrofolate reductase enzyme. This is an important enzyme involved in the cell growth and hence inhibition or inactivation of the enzyme may reduce the cell growth. It was observed that the equilibrium unfolding transition of DHFR proceeds through the formation of intermediates having higher exposed surface hydrophobicity, unchanged enzymatic activity and minimum changes in the secondary structural elements. Because of enhanced surface hydrophobicity, and unchanged enzymatic activity, these intermediates could be a nice target for designing drugs against DHFR.

Investigation on the Fire Resistance of Cellular Steel Beam with Sinusoidal Openings

This paper investigated the fire resistance of CSBs with various parameters under high temperature rise due to fire using finite element software ABAQUS. The mechanical parameters of CSBs are analyzed, including load-bearing capacity and the temperature distribution during the heating process. Through structural analysis simulation of the entire heating process, the structural response of the CSBs is divided into five stages: elastic stage, elastic-plastic stage, self-balancing stage, catenary stage and ultimate destruction stage. The results indicate that the opening diameter-to-height ratio, opening spacing-to-height ratio and load ratio significantly affect the structural responses of CSBs in fire, followed by opening shape as secondary effects. In all the numerical analyzes, CSBs are analyzed with a uniformly distributed load and having simply supported boundary conditions.