Cell Geometrical Parameters Research Articles

Blueprints of Architected Materials: A Guide to Metamaterial Design for Tissue Engineering.

Mechanical metamaterials are rationally designed structures engineered to exhibit extraordinary properties, often surpassing those of their constituent materials. The geometry of metamaterials' building blocks, referred to as unit cells, plays an essential role in determining their macroscopic mechanical behavior. Due to their hierarchical design and remarkable properties, metamaterials hold significant potential for tissue engineering; however their implementation in the field remains limited. The major challenge hindering the broader use of metamaterials lies in the complexity of unit cell design and fabrication. To address this gap, a comprehensive guide is presented detailing the design principles of well-established metamaterials. The essential unit cell geometric parameters and design constraints, as well as their influence on mechanical behavior, are summarized highlighting essential points for effective fabrication. Moreover, the potential integration of artificial intelligence techniques is explored in meta-biomaterial design for patient- and application-specific design. Furthermore, a comprehensive overview of current applications of mechanical metamaterials is provided in tissue engineering, categorized by tissue type, thereby showcasing the versatility of different designs in matching the mechanical properties of the target tissue. This review aims to provide a valuable resource for tissue engineering researchers and aid in the broader use of metamaterials in the field.

Effects of unit cell parameters on the thermal shock resistance of auxetic honeycomb sandwich structures: Combining discrete and continuum model

The influence of unit cell geometric parameters on the thermal fracture behavior and thermal shock resistance of honeycomb ceramics sandwich structures is revealed for the first time. The present study establishes a continuum model for the thermal fracture of sandwich structures, and a discrete numerical representation model for the equivalent fracture toughness of honeycombs, respectively. A novel evaluation approach for the thermal shock resistance of porous material structures has been provided by combining the two models. The effects of temperature dependence, face sheet thickness, honeycomb orientation and honeycomb geometrical parameters on thermal shock resistance are studied. Results indicate that changing the inclined angle of honeycomb can effectively increase the critical thermal shock temperature rise. Auxetic honeycomb sandwich structures with the inclined angle of −9° can reach the peak of the critical temperature rise. The results would contribute to the application of honeycomb sandwich structures in thermal protection systems.

Compressive properties and energy absorption of 4D printed auxetic mechanical metamaterials

Auxetic mechanical metamaterials contract or expand laterally when subjected to compressive or tensile load in the axial direction and offer potential benefits in areas such as flexible electronics, aerospace, and soft actuators. Nevertheless, when metamaterials are fabricated using conventional methods, their configurations and properties are fixed, which prohibits adaptation to the specific geometric requirements of their application environment. This limits their further development. This paper proposes an auxetic mechanical metamaterial with a negative Poisson's ratio and energy absorption capability. Compression specimens are fabricated with LCD photo-curable printing technology. The deformation mechanism and in-plane compression characteristics are examined through experimental and numerical simulation methods. The influence of unit cell geometrical control parameters on Poisson's ratio and energy absorption are also explored. The results indicate the dominant deformation mechanism of metamaterial during in-plane compression is bending deformation. The negative Poisson's ratio behavior is more pronounced when compressing along the X direction than along the Y direction, and the specimens also exhibit energy absorption capacity. In addition, the metamaterials prepared by 4D printing technology can be transformed from one configuration to another under external stimuli stimulation and force, and exhibit different mechanical properties, realizing programmable and reconfigurable, further expanding their application range.

3D-Printed Twisting Tubular Metamaterials with Tunable Mechanical and Torsional Characteristics

Innovative tubular compression-torsion mechanical metamaterials with potential applications in sensors, actuators, and energy harvesting are introduced. The metamaterials are parametrically designed and fabricated through stereolithography appearance 3D printing method, and their behaviour is analyzed using experiments, finite element method, and machine learning (ML). The effects of unit cell geometrical parameters, such as the unit cell size, the struts length, the angle between the struts, and the in-plane and out-of-plane thicknesses, on the performance of the structure, are investigated. Additionally, the influence of section geometry, longitudinal and circumferential cell numbers, and the unit cell assembly layouts on the metamaterial's twisting capability and mechanical properties is studied. The results demonstrate the tunability of the metamaterial by setting the unit cell design parameters, compression-torsion conversion property, volume fraction, and effective Young's modulus. ML is employed to predict a geometric design suitable to fit known working specifications. ML facilitates tuning the proposed metamaterial based on the desired responses which are expected from the structure. The problem is addressed through a multi-target supervised regression using the Random Forest regressor algorithm with optimized hyperparameters.

3D printed octet plate-lattices for tunable energy absorption

Tunable energy absorption achieved through grading of lattice structures shows high potential to be used in lightweight cellular cores for energy absorbing structures. This study investigates structurally graded and multi-material lattices consisting of plate-based octet unit cells, under quasi-static compression, to assess their energy absorption ability. Variations in the structure and material compositions of the plate-lattice structures are achieved through changing the plate thickness and through changing the filament material along the lattice in the direction of applied compressive force. The compressive stress–strain behavior reveals a near 10% increase of specific energy absorption (SEA) in the plate thickness graded designs at higher strain compared to the baseline octet lattices. The multi-material arrangements significantly modified onset location of the structure collapse. Finite element models of the structures were developed, and good agreements with experimental results were observed. Effects of varying each of the unit cell geometric parameters were analyzed, and the high sensitivity to the plate inclination angle, which resulted in greater changes to the maximum stress values and control of the overall SEA, was identified. The results demonstrate the capacity to adapt the octet lattice structure design through additive manufacturing to better suit the expected load and application.

Applications of VAM-based equivalent beam model on effective performance of composite sandwich beam with M-shaped folded core

The issue of facesheet-core debonding is expected to be addressed by increasing the bonding platform of the M-shaped folded core. To investigate its effective performance, the three-dimensional traditional equivalent beam (3D-TEB) model and the one-dimensional equivalent beam model (1D-EBM) of the M-shaped folded sandwich beam were established based on the variational asymptotic method. The expression of the original 3D elastic problem was given in variational form. By minimizing the energy functional, the asymptotic solutions of the warping functions and the Euler beam model (zeroth-order approximation) were obtained. Through the static and dynamic analysis of a three-dimensional folded sandwich beam and two equivalent beam models, the effectiveness of the 1D-EBM instead of the original 3D-TEB for static and dynamic analysis was verified. The influences of the location and frequency of the excitation on the dynamic performance of the CSB-MFC were investigated. Compared with 3D-FEM and 3D-TEM, the novelties of cell tailorability and local field recovery within the unit cell are very important features, which significantly facilitates the parametrical analysis of the CSB-MFC. The results showed that the change in the top width of the bonding platform had a particularly significant impact on the torsional stiffness. The wall thickness mainly affected the torsional performance, and the increase in the core height primarily improved the torsional and bending stiffness, resulting in the gradual increase in the fundamental frequency. • The VAM-based 1D-EBM is established to analyze the global response. • The accuracy of the model is verified by static and dynamic examples. • The influence of cell geometric parameters is systematically analyzed. • The dynamic performance of CSB-MFC is investigated based on the equivalent model. • The reduced DOFs of 1D-EBM result in high calculation efficiency.

Numerical Investigation on Performance Optimization of Offshore Sandwich Blast Walls with Different Honeycomb Cores Subjected to Blast Loading

As an important protective facility on offshore platform, the blast wall is of great significance in resisting oil and gas explosions. Honeycomb structures are widely used due to their unique deformation and mechanical properties under dynamic impact loads. The aim of this research is to develop an optimized design for an offshore sandwich blast wall with different honeycomb cores. The uniqueness of this paper is providing the quantitative optimization scheme for topological configurations and unit cell geometric parameters of honeycomb structures according to mass consistency and the proposed synthetic evaluation index of anti-blast performance. By using the numerical simulation software ANSYS/LS-DYNA, the CONWEP algorithm was first validated and then adopted to conduct the dynamical performance analysis of the honeycomb blast wall. For comparison purposes, simulating studies on a series of different blast walls were carried out by considering various influential parameters. According to different criteria, the blast resistance of the sandwich honeycomb structures was evaluated. It is found that the sandwich plate with concave arc honeycomb core has the best anti-blast performance compared to that of arrow honeycomb core and concave hexagonal honeycomb core. For the concave arc honeycomb structure, the geometric parameters such as concave angle and aspect ratio of honeycomb unit cell have great influence on the blast-resistance performance. Moreover, the concave arc honeycomb structure with positive gradient arrangement has better anti-blast performance than the negative one. The curved blast wall with the curvature of 1/20 achieves better anti-blast performance than the flat blast wall.

Flexural and Out-of-Plane Compression Performance of Hexagonal Rubber Wood Core Sandwich with Increasing Cell Wall Thickness

This paper investigates the rubber wood honeycomb core by manipulating its cell wall thickness. Rubber wood honeycomb core was fabricated with cell walls range from 1 mm to 3 mm. The impacts of the cell geometrical parameters on the flexural and out-of-plane compression performance are studied. In the case of solid rubber wood without facesheet, the density is much higher than those rubber wood honeycomb composites. The failure can be disastrous without facesheet under bending. Rubber wood honeycomb sandwiches are able to offer the similar specific flexural strength with lower density. With increasing wall thickness from 1 mm to 3 mm, the specific flexural strength increased by 12.32 %. Meanwhile, specific compressive strength improved by 11 % from 1 mm to 2 mm. However, its specific strength dropped by 3.55 % when the wall thickness at 3 mm. Minimum improvement in the compressive strength per density has caused the decrement.

Finite Element Study on the Effect of Geometrical Parameters on the Mechanical Behavior of 3D Reentrant Auxetic Honeycombs.

Auxetic materials are a special case of cellular materials, which exhibit a negative Poisson’s ratio. This in fact is the reason behind their peculiar behavior i.e. lateral shrinkage under longitudinal compression and vice versa. Since these materials do not obey the laws of “normal” materials and go beyond common sense, they are still an emerging class which can be put to use for various purposes like self-locking reinforcing fibers in composites, controlled release media, self-healing films, piezoelectric sensors, and also be used in biomedical engineering. Their stress-strain behavior, Poisson’s ratio and impact energy absorption are controlled by bulk material as well as the unit cell geometry. Among many forms of auxetic structures available, we have chosen a three-dimensional reentrant auxetic honeycomb unit cell. The unit cell geometrical parameters were taken from literature. In this study, we try to understand the effects of strut angle through finite element simulations while keeping the bulk material, unit cell size, strut thickness and number of repetitions constant. A total of three different angles were tested, based on which we conclude that as angle increases, the Poisson’s ratio increases and Energy absorption is maximum at 30 deg.

Effect of loading rates on the in-plane compressive properties of additively manufactured ABS and PLA-based hexagonal honeycomb structures

Honeycomb structures find numerous applications in automotive, aerospace, sports, and other similar engineering fields. Such incorporation is made possible by the excellent crushing resistance and specific energy absorption capabilities. However, manufacturing such structures through conventional processes is highly laborious and expensive. Such a drawback can be largely mitigated by the adoption of additive manufacturing (AM) processes. Consequently, in this study, hexagonal honeycomb structures are subjected to experimental tests to determine their compressive strength under different loading rates. In addition to this, attempts have also been made to evaluate the effect of different materials and the unit cell dimensions on the compressive properties. The test specimens of different wall thicknesses are manufactured by fused deposition modelling (FDM) using PLA and ABS as the base materials. The samples are then subjected to compressive tests using a standard UTM to quantify the effect of the cell geometrical parameters and the loading rate on the overall compressive nature of the structures. The results show that the compression properties are primarily affected by the loading rate, material properties and the cell-wall thickness of the structures. The initial compressive yield stress and plateau stress generally increase up to a given value of loading rate, after which the strength decline. The cell-wall thickness of the structure influences the threshold loading rate. Therefore, this study provides a preliminary understanding of the compressive properties of AM hexagonal honeycomb structures to analyse the prospects for application in real-world engineering applications. It is proposed that such structures find profound applications in structural components of aerospace equipment, automotive parts, sports gear, and other similar areas of interest where high strength and energy absorption are of predominant importance.

Integration of hydrogen production and greenhouse gas treatment by utilizing nitrogen oxide as sweep gas in a solid oxide electrolysis cell

Solid oxide electrolysis cells (SOECs) for hydrogen production are generally operated at a thermoneutral voltage, a voltage at which the cell does not generate or require additional heat. When an SOEC is operated above the thermoneutral voltage, it consumes more electrical energy. However, operating below the thermoneutral voltage cools the cell and results in a temperature gradient within the electrode because of the endothermic reaction. To prevent these phenomena, an SOEC requires additional heat input to maintain a constant temperature. Recently, nitrous oxide has become a global concern because of its high global-warming potential. In this study, we propose the use of nitrogen oxide instead of air or pure oxygen as the sweep gas for SOEC operation, integrating the hydrogen production and greenhouse gas treatment. This study investigated the influence of different types of sweep gas on the heat demand of water electrolysis. To examine this SOEC system, we conducted a simulation study, and the effects of operating conditions and cell geometrical parameters on the system performance were analyzed in detail. With the heat released from the decomposition of nitrogen oxide, operation of the SOEC below the thermoneutral voltage and a higher hydrogen production efficiency are achieved.

Failure analysis of 3D woven spacer sandwich composites with woven cross-links and face sheet thickening under compressive and flexural loading

The effect of face sheet thickening on the mechanical properties of sandwich structures reinforced with 3 D woven spacer fabrics having woven cross-links has been presented in this work. Spacer fabrics forming cells of rectangular (RECT), trapezoidal (TPZ) and triangular (TR) shapes were used as reinforcement of sandwich structures with non-thickened face sheets. While for thickened face sheet structures, additional layers of 2 D fabric were integrally woven with the top and bottom face sheets of spacer fabrics, having almost similar cell geometrical parameters as that of the former structures, in a single step of weaving. Composites manufactured from these structures were characterized for their out-of-plane compressive and flexural properties. The specific compressive load was observed to be lower for thickened face sheet structures. The flexural load was higher for thickened face sheet structures; but the specific bending load decreased for the same. Flexural stress was also found to decrease with thickening of the face sheets. The results obtained could be helpful in designing sandwich composites connected woven fabric cross-links with enhanced mechanical properties.

An Egg-Box Sandwich Structure Static Behavior

There is a significant theoretical and applied value to study sandwich structures mechanical behavior in the anti-collision device due to their excellent physical and mechanical performance. A new egg-box sandwich structure device was designed. Next, the important factors (cell half-height h, cell thickness t 0 and cell width b) affecting the deformation capability and energy absorption performance of the structure were explored by the finite element method in this paper. The findings show that cell geometric parameters have a remarkable effect on structural deformation capability and energy-absorption performance. In addition, the structural displacement rises significantly with the size of cell half-height h increasing. Besides, the more quickly the cell thickness t 0 rises, the more obviously the displacement and the stress of the structure decrease. Also, with the size of cell width b gradually enlarging, the displacement and the stress increase at first and then decrease. When cell width b is 50mm, the structure has extraoridnary deformability and energy-absorption characteristics. Thus, the study of the parameters of the egg-box sandwich structure can provide some effective inspirations for the design of vehicle anti-collision device.

Research on explosion-proof characteristics and optimization design of negative Poisson’s ratio honeycomb material

In order to study in depth the structural response of the bottom protective component of the vehicles under blast loading and improve the blast resistant performance of the protective vehicles, a finite element model of the bottom protective component of a vehicle under blast loading was established, and the reliability of the finite element simulation was verified by the explosion impact bench test; the concave hexagonal negative Poisson’s ratio honeycomb material was used as the core layer of the protective component, the deformation mode of the negative Poisson’s ratio honeycomb material under blast loading was analyzed, and the blast resistant performance was compared with the other three protective components of the same mass. The results show that the protective component containing negative Poisson’s ratio honeycomb core has better resistance to blast loading. A mathematical model was established for multi-objective optimization problems with the cell size parameters of the honeycomb material as design variables, and the multi-objective genetic algorithm was used to obtain the optimal solution of the cell geometric parameters, which effectively reduces the maximum deflection and maximum kinetic energy of the protective component substrate.

Comparative analysis of mechanical behavior of 3D woven spacer sandwich composites with single and double level structures

Abstract3D woven spacer fabrics connected with woven cross‐links and forming tunnels of trapezoidal shape were produced in single and double level configuration with four different cell wall opening angles in each configuration. The sandwich composites produced from these spacer fabrics were then analyzed for their out‐of‐plane compressive and flexural properties to study their failure loads, energy absorbency, and failure modes. With an increase in the cell wall opening angles, compressive load and specific compressive load increased for single and double level structures, but the same properties were found to be poor for double level structures compared to their single level counterparts. Absorbed energy/volume was also found to be lower for double level composites. The bending load and specific bending load values increased with increase in cell wall opening angle, with double level structures performing better at each cell wall opening compared to their single level counterparts. But the flexural stress of double level structures was lower than that of their corresponding single level structures. The outcomes of this study can be used in designing and manufacturing of multilevel spacer structures with different cell geometrical parameters for specific end use requirements.

Impact energy absorption of functionally graded chiral honeycomb structures

Auxetic chiral structures with negative Poisson ratio (NPR) can contract its width along the directions perpendicular to compression loading direction, thus generate enhanced indentation resistance and enhanced impact energy absorption abilities. To enhance the dynamic mechanical performances of periodic anti-chiral structures and hybrid-chiral structures, geometrically graded ligaments are proposed, and the in-plane dynamic deformation mechanism and energy absorption capacity of the functionally graded anti-chiral and hybrid-chiral cellular structures are studied through finite element analysis (FEA). Numerical results in our work show that the crushing energy absorption performances of periodic chiral structures can be improved by introducing structural graded design, where the plateau stress and energy absorption efficiency can be optimized by means of adjusting the unit cell geometrical parameters. Our study can enrich insightful understanding of the dynamic behavior of chiral cellular materials, and can be employed for optimizing the design of automobile crash energy absorption and impact protection structures.

Optimization of the Cell Structure for Radiation-Hardened Power MOSFETs

Power MOSFETs specially designed for space power systems are expected to simultaneously meet the requirements of electrical performance and radiation hardness. Radiation-hardened (rad-hard) power MOSFET design can be achieved via cell structure optimization. This paper conducts an investigation of the cell geometrical parameters with major impacts on radiation hardness, and a rad-hard power MOSFET is designed and fabricated. The experimental results validate the devices’ total ionizing dose (TID) and single event effects (SEE) hardness to suitably satisfy most space power system requirements while maintaining acceptable electrical performance.

Characterization of laminar flow in periodic open-cell porous structures

The present work deals with the numerical simulations of 3D incompressible flow through periodic porous structures, consisting of cubic cells with different strut geometry and structure tilting with respect to the flow direction. Simulation results are obtained for different porosities, while covering a range of Reynolds numbers from laminar-steady flow (Darcy regime) up to the transition to laminar-unsteady flow (moderate Forchheimer regime). These results are post-processed in order to characterize the influence of the periodic porous structures on the flow statistics related to the Darcy-Forchheimer law. Based on this analysis, along with 3D simulation results previously obtained for different random foams, correlations for the Darcy and Forchheimmer permeability coefficients are developed from a theoretical background, being expressed only as functions of the cell geometrical parameters and tortuosity estimation. However, the influences of flow tortuosity and cell orientation on the Darcy coefficient are found to cancel each other. The proposed correlation for the Darcy coefficient performs very well for both periodic and random porous structures, when compared with recent correlations available in the literature. The performance of the correlation proposed for the Forchheimmer coefficient is found to be satisfactory, however, different correlation constants were found for periodic and random structures. The proposed correlation for the Forchheimer permeability coefficient depends on the flow tortuosity inside the porous structure, which must be estimated either through 3D fluid flow simulations or using tortuosity correlations. In this respect, a correlation is proposed for predicting the flow tortuosity inside porous structures, as an alternative for avoiding 3D simulations.

Drastic tailorable thermal expansion chiral planar and cylindrical shell structures explored with finite element simulation

Design of materials and structures with quite low coefficient of thermal expansion (CTE), even zero or negative CTE is important for industrial application where drastic temperature changes are encountered. In this paper, making use of the bending of bi-material beam and the unique deformation mechanism of chiral lattice structures, five sets of chiral lattice composite structures with tailorable CTEs are proposed, where synergic effects of rigid node rotation and bi-material ligament bending deformation are responsible for giant range of structural deformation due to temperature change, from positive CTE to negative CTE through adjusting the geometrical parameters of composite bi-material chiral unit cell, and the relationship between unit cell geometric parameters and CTEs of the structure are studied systematically through finite element analysis. Finally, design of bi-material cylindrical shells consisting of anti-tetra chiral unit cells are proposed, and its axial CTEs with different number of the unit cells along the circumferential are studied systematically, demonstrating the robust range of CTEs can be generated through adjusting the geometrical parameters of chiral bi-material unit cells. The proposed chiral structures demonstrated promising application potentials in industrial fields, such as: aerospace and microelectronics, where extremely high structural accuracy is required during harsh working temperature environment.

Analysis and design of periodic beams for vibration attenuation

This paper presents a new finite-element-based design procedure for geometrically periodic beam structures to target a specific desired attenuation frequency band. Using the “forward approach,” the effects of the cell geometric parameters on the location of the stop bands are first studied. Then using the “reverse approach,” explicit expressions for the start and end frequencies of all stop bands are derived as functions of the cell geometric parameters using a symbolic solver. These expressions are used in the design procedure to determine the cell geometric parameters that will result in vibration attenuation in the desired attenuation band. The design procedure has been validated by comparison with the results of the forward approach in different problems targeting the first or second stop bands. It was found that, depending on the frequency range of the desired attenuation band, and the stop band selected to target the desired attenuation band in the design, one, two or no solution set for the cell geometric parameters can be obtained. For the case of two available solutions, the designer will have two design options that satisfy the design requirements to choose from.