Engineering Reversible Lattice Structure for High-Capacity Co-Free Li-Rich Cathodes with Negligible Capacity Degradation.

Co-free Li-rich Mn-based cathode materials are garnering great interest because of high capacity and low cost. However, their practical application is seriously hampered by the irreversible oxygen escape and the poor cycling stability. Herein, a reversible lattice adjustment strategy is proposed by integrating O vacancies and B doping. B incorporation increases TM─O (TM: transition metal) bonding orbitals whereas decreases the antibonding orbitals. Moreover, B doping and O vacancies synergistically increase the crystal orbital bond index values enhancing the overall covalent bonding strength, which makes TM─O octahedron more resistant to damage and enables the lattice to better accommodate the deformation and reaction without irreversible fracture. Furthermore, Mott-Hubbard splitting energy is decreased due to O vacancies, facilitating electron leaps, and enhancing the lattice reactivity and capacity. Such a reversible lattice, more amenable to deformation and forestalling fracturing, markedly improves the reversibility of lattice reactions and mitigates TM migration and the irreversible oxygen redox which enables the high cycling stability and high rate capability. The modified cathode demonstrates a specific capacity of 200 mAh g-1 at 1C, amazingly sustaining the capacity for 200 cycles without capacity degradation. This finding presents a promising avenue for solving the long-term cycling issue of Li-rich cathode.

Theoretical search for heterogeneously architected 2D structures.

Architected 2D structures are of growing interest due to their unique mechanical and physical properties for applications in stretchable electronics, controllable phononic/photonic modulators, and switchable optical/electrical devices; however, the underpinning theory of understanding their elastic properties and enabling principles in search of emerging structures with well-defined arrangements and/or bonding connections of assembled elements has yet to be established. Here, we present two theoretical frameworks in mechanics-strain energy-based theory and displacement continuity-based theory-to predict the elastic properties of 2D structures and demonstrate their application in a search for novel architected 2D structures that are composed of heterogeneously arranged, arbitrarily shaped lattice cell structures with regulatory adjacent bonding connections of cells, referred to as heterogeneously architected 2D structures (HASs). By patterning lattice cell structures and tailoring their connections, the elastic properties of HASs can span a very broad range from nearly zero to beyond those of individual lattice cells by orders of magnitude. Interface indices that represent both the pattern arrangements of basic lattice cells and local bonding disconnections in HASs are also proposed and incorporated to intelligently design HASs with on-demand Young's modulus and geometric features. This study offers a theoretical foundation toward future architected structures by design with unprecedented properties and functions.

Mechanical properties of additively manufactured variable lattice structures of Ti6Al4V.

Engineered micro- and macro-structures via additive manufacturing (AM) or 3D-Printing can create structurally varying properties in part, which is difficult via traditional manufacturing methods. Herein we have utilized powder bed fusion-based selective laser melting (SLM) to fabricate variable lattice structures of Ti6Al4V with uniquely designed unit cell configurations to alter the mechanical performance. Five different configurations were designed based on two natural crystal structures - hexagonal closed packed (HCP) and body-centered cubic (BCC). Under compressive loading, as much as 74% difference was observed in compressive strength and 71% variation in elastic modulus, with all samples having porosities in a similar range of 53 to 65%, indicating the influence of macro-lattice designs alone on mechanical properties. Failure analysis of the fracture surfaces helped with the overall understanding of how configurational effects and unit cell design influence these samples' mechanical properties. Our work highlights the ability to leverage advanced manufacturing techniques to tailor the structural performance of multifunctional components.

Mechanical properties and fluid permeability of gyroid and diamond lattice structures for intervertebral devices: functional requirements and comparative analysis.

Current intervertebral fusion devices present multiple complication risks such as a lack of fixation, device migration and subsidence. An emerging solution to these problems is the use of additively manufactured lattice structures that are mechanically compliant and permeable to fluids, thus promoting osseointegration and reducing complication risks. Strut-based diamond and sheet-based gyroid lattice configurations having a pore diameter of 750 µm and levels of porosity of 60, 70 and 80% are designed and manufactured from Ti-6Al-4V alloy using laser powder bed fusion. The resulting structures are CT-scanned, compression tested and subjected to fluid permeability evaluation. The stiffness of both structures (1.9-4.8 GPa) is comparable to that of bone, while their mechanical resistance (52-160 MPa) is greater than that of vertebrae (3-6 MPa), thus decreasing the risks of wither bone or implant failure. The fluid permeability (5-57 × 10-9 m2) and surface-to-volume ratios (~3) of both lattice structures are close to those of vertebrae. This study shows that both types of lattice structures can be produced to suit the application specifications within certain limits imposed by physical and equipment-related constraints, providing potential solutions for reducing the complication rate of spinal devices by offering a better fixation through osseointegration.

Lattice Structure and Bandgap Control of 2D GaN Grown on Graphene/Si Heterostructures.

2D group-III nitride materials have shown a great promise for applications in optoelectronic devices thanks to their thickness-dependent properties. However, the epitaxial growth of 2D group-III nitrides remains a challenge. In this work, epitaxial growth of 2D GaN with well-controlled lattice structures and bandgaps is achieved by plasma-enhanced metal organic chemical vapor deposition via effective regulation of plasma energy and growth temperature. The structure of graphene/2D GaN/Si heterostructures is carefully investigated by high-resolution transmission electron microscopy. The formation mechanism of the 2D GaN layer is clearly clarified by theoretical calculations. Furthermore, a bandgap for 2D GaN ranging from ≈4.18 to ≈4.65 eV varying with the numbers of layers is theoretically calculated and experimentally confirmed. 2D GaN with well-controlled lattice structure and bandgap holds great potential for the development of deep ultraviolet light-emitting diodes, energy conversion devices, etc.

Gate-Voltage Control of Borophene Structure Formation.

Boron nanostructures are easily charged but how charge carriers affect their structural stability is unknown. We combined cluster expansion methods with first-principles calculations to analyze the dependence of the preferred structure of two-dimensional (2D) boron, or "borophene", on charge doping controlled by a gate voltage. At a reasonable doping level of 3.12×1014  cm-2 , the hollow hexagon concentration in the ground state of 2D boron increases to 1/7 from 1/8 in its charge-neutral state. The numerical result for the dependence of hollow hexagon concentration on the doping level is well described by an analytical method based on an electron-counting rule. Aside from in-plane electronic bonding, the hybridization among out-of-plane boron orbitals is crucial for determining the relative stability of different sheets at a given doping level. Our results offer new insight into the stability mechanism of 2D boron and open new ways for the control of the lattice structure during formation.

Progress toward the Definition of X-ray Computed Tomography Accuracy in the Characterization of Polymer-Based Lattice Structures.

Lattice structures have become an innovative solution for the improvement of part design, as they are able to substitute solid regions, maintain mechanical capabilities, and reduce material usage; however, dimensional quality control of these geometries is challenging. X-ray computed tomography (XCT) is the most suitable non-destructive metrological technique as it is capable of characterizing internal features and hidden elements. Uncertainty estimation of XCT is still in development, and studies typically use high-resolution calibrated devices such as focal variation microscopes (FVMs) as a reference, focusing on certain parts of the lattice but not the whole structure. In this paper, an estimation of the accuracy of XCT evaluation of a complete lattice structure in comparison to a higher-resolution reference device (FVM) is presented. Experimental measurements are taken on ad hoc designed test objects manufactured in polyamide 12 (PA12) using selective laser sintering (SLS), optimized for the evaluation on both instruments using different cubic-based lattice typologies. The results confirm higher precision on XCT evaluation in both qualitative and quantitative analysis. Even with a lower resolution, XCT is able to characterize details of the surface such as re-entrant features; as well, standard deviations and uncertainties in strut diameter evaluation remain more stable in all cells in XCT, identifying on the other hand reconstruction problems on FVM measurements. Moreover, it is shown that, using XCT, no additional evaluation errors were found in inner cells, suggesting that the measurement of external elements could be representative of the whole structure for metrological purposes.

Mechanical properties of additively manufactured lattice structures composed of zirconia and hydroxyapatite ceramics.

Ceramic lattices hold great potential for bone scaffolds to facilitate bone regeneration and integration of native tissue with medical implants. While there have been several studies on additive manufacturing of ceramics and their osseointegrative and osteoconductive properties, there is a lack of a comprehensive examination of their mechanical behavior. Therefore, the aim of this study was to assess the mechanical properties of different additively manufactured ceramic lattice structures under different loading conditions and their overall ability to mimic bone tissue properties. Eleven different lattice structures were designed and manufactured with a porosity of 80% using two materials, hydroxyapatite (HAp) and zirconium dioxide (ZrO2). Six cell-based lattices with cubic and hexagonal base, as well as five Voronoi-based lattices were considered in this study. The samples were manufactured using lithography-based ceramic additive manufacturing and post-processed thermally prior to mechanical testing. Cell-based lattices with cubic and hexagonal base, as well as Voronoi-based lattices were considered in this study. The lattices were tested under four loading conditions: compression, four-point bending, shear and tension. The manufacturing process of the different ceramics leads to different deviations of the lattice geometry, hence, the elastic properties of one structure cannot be directly inferred from one material to another. ZrO2 lattices prove to be stiffer than HAp lattices of the same designed structure. The Young's modulus for compression of ZrO2 lattices ranges from 2 to 30GPa depending on the used lattice design and for HAp 200MPa to 3.8GPa. The expected stability, the load where 63.2% of the samples are expected to be destroyed, of the lattices ranges from 81 to 553MPa and for HAp 6 to 42MPa. For the first time, a comprehensive overview of the mechanical properties of various additively manufactured ceramic lattice structures is provided. This is intended to serve as a reference for designers who would like to expand the design capabilities of ceramic implants that will lead to an advancement in their performance and ability to mimic human bone tissue.

The Beneficial Effect of a TPMS-Based Fillet Shape on the Mechanical Strength of Metal Cubic Lattice Structures.

The goal of this paper is to improve the mechanical strength-to-weight ratios of metal cubic lattice structures using unit cells with fillet shapes inspired by triply periodic minimal surfaces (TPMS). The lattice structures here presented were fabricated from AA6082 aluminum alloy using lost-PLA processing. Static and dynamic flat and wedge compression tests were conducted on samples with varying fillet shapes and fill factors. Finite element method simulations followed the static tests to compare numerical predictions with experimental outcomes, revealing a good agreement. The TPSM-type fillet shape induces a triaxial stress state that significantly improves the mechanical strength-to-weight ratio compared to fillet radius-free lattices, which was also confirmed by analytical considerations. Dynamic tests exhibited high resistance to flat impacts, while wedge impacts, involving a high concentrated-load, brought out an increased sensitivity to strain rates with a short plastic deformation followed by abrupt fragmentation, indicating a shift towards brittle behavior.

Exploring the mechanical properties of 3D-printed multilayer lattice structures for use in accommodative insoles.

Full-contact insoles fabricated from multilayer foams are the standard of care (SoC) for offloading and redistributing high plantar pressures in individuals with diabetes at risk of plantar ulceration and subsequent lower limb amputation. These devices have regional variations in total thickness and layer thickness to create conformity with a patient's foot. Recent work has demonstrated that metamaterials can be tuned to match the mechanical properties of SoC insole foams. However, for devices fabricated using a multilayer lattice structure, having regional variations in total thickness and layer thickness may result in regional differences in mechanical properties that have yet to be investigated. Three lattices, two dual-layer and one uniform-layer lattice structure, designed to model the mechanical properties of SoC insoles, were 3D-printed at three structure/puck thicknesses representing typical regions seen in accommodative insoles. The pucks underwent cyclic compression testing, and the stiffness profiles were assessed. Three pucks at three structure/puck thicknesses fabricated from SoC foams were also tested. Initial evaluations suggested that for the latticed pucks, structure thickness and density inversely impacted puck stiffness. Behaving most like the SoC pucks, a dual-layer lattice that increased in density as structure thickness increased demonstrated consistent stiffness profiles across puck thicknesses. Identifying a lattice with constant mechanical properties at various structure thicknesses may be important to produce a conforming insole that emulates the standard of care from which patient-specific/regional lattice modulations can be made.

Multidisciplinary design optimisation of lattice-based battery housing for electric vehicles.

Batteries with high energy densities become essential with the increased uptake of electric vehicles. Battery housing, a protective casing encapsulating the battery, must fulfil competing engineering requirements of high stiffness and effective thermal management whilst being lightweight. In this study, a graded lattice design framework is developed based on topology optimisation to effectively tackle the multidisciplinary objectives associated with battery housing. It leverages the triply periodic minimal surfaces lattices, aiming for high mechanical stiffness and efficient heat dissipation considering heat conduction and convection. The effectiveness of the proposed framework was demonstrated through the battery housing design, showcasing its ability to address multidisciplinary objectives as evidenced by the analysis of the Pareto front. This study identifies the potential of lattices in lightweight applications incorporating multiphysics and offers an efficient lattice design framework readily extended to other engineering challenges.

A 3D printed ultra-short dental implant based on lattice structures and ZIRCONIA/Ca2SiO4 combination.

Additive Manufacturing (AM) enables the generation of complex geometries and controlled internal cavities that are so interesting for the biomedical industry due to the benefits they provide in terms of osseointegration and bone growth. These technologies enable the manufacturing of the so-called lattice structures that are cells with different geometries and internal pores joint together for the formation of scaffold-type structures. In this context, the present paper analyses the feasibility of using diamond-type lattice structures and topology optimisation for the re-design of a dental implant. Concretely, a new ultra-short implant design is proposed in this work. For the manufacturing of the implant, digital light processing additive manufacturing technique technology is considered. The implant was made out of Nano-zirconia and Nano-Calcium Silicate as an alternative material to the more common Ti6Al4V. This material combination was selected due to the properties of the calcium-silicate that enhance bone ingrowth. The influence of different material combination ratios and lattice pore sizes were analysed by means of FEM simulation. For those simulations, a bio-material bone-nanozirconia model was considered that represents the final status after the bone is integrated in the implant. Results shows that the mechanical properties of the biocompatible composite employed were suitable for dental implant applications in dentistry. Based on the obtained results it was seen that those designs with 400 µm and 500 µm pore sizes showed best performance and led to the required factor of safety.

Experimental and Numerical Investigation of Polymer-Based 3D-Printed Lattice Structures with Largely Tunable Mechanical Properties Based on Triply Periodic Minimal Surface.

Triply periodic minimal surfaces (TPMSs) have demonstrated significant potential in lattice structure design and have been successfully applied across multiple industrial fields. In this work, a novel lattice structure with tunable anisotropic properties is proposed based on two typical TPMS types, and their mechanical performances are studied both experimentally and numerically after being fabricated using a polymer 3D printing process. Initially, adjustments are made to the original TPMS lattice structures to obtain honeycomb lattice structures, which are found to possess significant anisotropy, by utilizing numerical homogenization methods. Based on this, a continuous self-twisting deformation is proposed to change the topology of the honeycomb lattice structures to largely tune the mechanical properties. Quasi-static compression experiments are conducted with different twisting angles, and the results indicate that self-twisting can affect the mechanical properties in specific directions of the structure, and also enhance the energy absorption capacity. Additionally, it mitigates the risk of structural collapse and failure during compression while diminishing structural anisotropy. The proposed self-twisting strategy, based on honeycomb lattice structures, has been proven valuable in advancing the investigation of lattice structures with largely tunable mechanical properties.

Effect of density grading on the mechanical behaviour of advanced functionally graded lattice structures.

Lattice structures have found significant applications in the biomedical field due to their interesting combination of mechanical and biological properties. Among these, functionally graded structures sparked interest because of their potential of varying their mechanical properties throughout the volume, allowing the design of biomedical devices able to match the characteristics of a graded structure like human bone. The aim of this works is the study of the effect of the density grading on the mechanical response and the failure mechanisms of a novel functionally graded lattice structure, namely Triply Arranged Octagonal Rings (TAOR). The mechanical behaviour was compared with the same lattice structures having constant density ratio. Electron Beam Melting technology was used to manufacture titanium alloy specimens with global relative densities from 10% to 30%. Functionally graded structures were obtained by increasing the relative density along the specimen, by individually designing the lattice's layers. Scanning electron and a digital microscopy were used to evaluate the dimensional mismatch between actual and designed structures. Compressive tests were carried out to obtain the mechanical properties and to evaluate the collapse modes of the structures in relation to their average relative density and lattice grading. Open-source Digital Image Correlation algorithm was applied to evaluate the deformation behaviour of the structures and to calculate their elastic moduli. The results showed that uniform density structures provide higher mechanical properties than functionally graded ones. The Digital Image Correlation results showed the possibility of effectively designing the different layers of functionally graded structures selecting desired local mechanical properties to mimic the different characteristics of cortical and cancellous bone.

Performance domains of bio-inspired and triangular lattice patterns to optimize the structures' stiffness.

Mass reduction of mechanical systems is a recurrent objective in engineering, which is often reached by removing material from its mechanical parts. However, this material removal leads to a decrease of mechanical performances for the parts, which must be minimized and controlled to avoid a potential system failure. To find a middle-ground between material removing and mechanical performances), material must be kept only in areas where it is necessary, for example using stress-driven material removal methods. These methods use the stress field to define the local material removal based on two local parameters: the local volume fraction vf and the structural anisotropy orientation ß. These methods may be based on different types of cellular structure patterns: lattice-based or bio-inspired. The long-term objective of this study is to improve the performance of stress-driven methods by using the most efficient pattern. For this purpose, this study investigates the influence of vf and ß on the mechanical stiffness of three planar cellular structures called Periodic Stress-Driven Material Removal (PSDMR) structures. The first, taken from the literature, is bio-inspired from bone and based on a square pattern. The second, developed in this study, is also bio-inspired from bone but based on a rectangular pattern. The third is a strut-based lattice pattern well documented in the literature for its isotropic behavior. These three patterns are compared in this study in terms of relative longitudinal stiffness, obtained through linear elastic compressive tests by finite element analysis. It is highlighted that each PSDMR pattern has a specific domain in which it performs better than the two others. In future works, these domains could be used in stress-driven material removal methods to select the most adequate pattern or a mix of them to improve the performances of parts.

Thermal, Microstructural, and Mechanical Analysis of Complex Lattice Structures Produced by Direct Energy Deposition.

Lattice structures have gained attention in engineering due to their lightweight properties. However, the complex geometry of lattice structures and the high melting temperature of metals present significant manufacturing challenges for the large-scale fabrication of these structures. Direct Energy Deposition (DED) methods, such as the Wire Arc Additive Manufacturing (WAAM) technique, appear to be an interesting solution for overcoming these limitations. This study provides a detailed analysis of the manufacturing process of carbon steel lattice structures with auxetic geometry. The study includes thermal analysis using infrared thermography, microstructural characterization through metallography, and mechanical evaluation via hardness and mechanical testing. The findings reveal the significant impact of heat input, thermal cycles, and deposition sequence on the morphology and mechanical properties of the lattice structures. Fast thermal cycles are related to areas with higher hardness values, smaller strut diameters, and porous formations, which shows that controlling heat input and heat dissipation is crucial for optimizing the properties of lattice structures produced using WAAM.

Mechanical Properties and Microstructure of Inconel 718 Lattice Structures Produced by Selective Laser Melting Process.

This article presents the results of an analysis regarding the microstructure, mechanical strength, and microhardness of two kinds of samples built through selective laser melting with Inconel 718, the most frequently used alloy in metal additive manufacturing due to its excellent mechanical properties. The sample geometry was made up of two types of lattice structures with spherical and hyperbolical stiffness elements. The goals of these studies are to determine how homogenization heat treatment influences the microhardness and the mechanical properties of the specimens and to identify the structure with the best mechanical properties. The analysis showed that heat treatment was beneficial because the regular dendritic structure disappears, the δ phase precipitates at the grain boundaries, and both the γ and γ″ phases dissolve. It has also been shown that the structures with hyperbolical stiffness elements have better compressive strength than the structures with the elliptical structures, with a 47.6% increase for the as-fabricated structures and an approximate 50% increase for the heat-treated structure.

Development of a density-based topology optimization of homogenized lattice structures for individualized hip endoprostheses and validation using micro-FE.

Prosthetic implants, particularly hip endoprostheses, often lead to stress shielding because of a mismatch in compliance between the bone and the implant material, adversely affecting the implant's longevity and effectiveness. Therefore, this work aimed to demonstrate a computationally efficient method for density-based topology optimization of homogenized lattice structures in a patient-specific hip endoprosthesis. Thus, the root mean square error (RMSE) of the stress deviations between the physiological femur model and the optimized total hip arthroplasty (THA) model compared to an unoptimized-THA model could be reduced by 81 % and 66 % in Gruen zone (GZ) 6 and 7. However, the method relies on homogenized finite element (FE) models that only use a simplified representation of the microstructural geometry of the bone and implant. The topology-optimized hip endoprosthesis with graded lattice structures was synthesized using algorithmic design and analyzed in a virtual implanted state using micro-finite element (micro-FE) analysis to validate the optimization method. Homogenized FE and micro-FE models were compared based on averaged von Mises stresses in multiple regions of interest. A strong correlation (CCC > 0.97) was observed, indicating that optimizing homogenized lattice structures yields reliable outcomes. The graded implant was additively manufactured to ensure the topology-optimized result's feasibility.

Compressive Behavior of Novel Additively Manufactured Ti-6Al-4V Lattice Structures: Experimental and Numerical Studies.

This paper presents novel configurations for additively manufactured lattice structures, including helical and elliptic designs, in addition to the pyramid base model. Functionally graded versions of the pyramid and elliptic lattice structures are developed by considering desirable relative densities in each layer. The lattice structures were manufactured using Ti-6Al-4V powder in a three-dimensional selective laser melting printer. The averaged porosities are 0.86, 0.91, 0.916, 0.93 and 0.74 for pyramid, functionally graded pyramid, elliptic, functionally graded elliptic and helical, respectively. The mechanical behavior of the lattice structures was characterized through compression tests using a universal testing machine and computationally analyzed using finite element code. The results indicate that the elliptic and functionally graded elliptic lattices have elastic moduli of 0.76 and 0.67 GPa, while the yield strengths are 41.32 and 32.24 MPa, respectively, in comparison to cancellous bone. Moreover, pyramid, functionally graded pyramid, and helical lattices show relatively lower elastic moduli of 0.57, 0.65 and 0.41 GPa and higher yield strengths of 54.1, 52.15 and 61.02 MPa, respectively. This could be an indication that they are fit for cortical bones. All samples have low elastic moduli coupled with high yield strengths. This could reduce or eliminate stress shielding, making them suitable for some load-bearing bio-inspired applications. A comparative study utilizing experimental and numerical models was conducted to evaluate the performance of the proposed designs.

In-Plane Compression Properties of Continuous Carbon-Fiber-Reinforced Composite Hybrid Lattice Structures by Additive Manufacturing.

Continuous-fiber-reinforced composite lattice structures (CFRCLSs) have garnered attention due to their lightweight and high-strength characteristics. Over the past two decades, many different topological structures including triangular, square, hexagonal, and circular units were investigated, and the basic mechanical responses of honeycomb structures under various load conditions, including tension, compression, buckling, shear, and fatigue were studied. To further improve the performance of the honeycombs, appropriate optimizations were also carried out. However, the mechanical properties of a single lattice often struggle to exceed the upper limit of its structure. This paper investigates the effect of permutation and hybrid mode on the mechanical properties of CFRCLSs by comparing five structures: rhomboid (R-type), octagon orthogonal array (OOA-type), octagon hypotenuse array (OHA-type), octagon nested array (ONA-type), and rhomboid circle (RC-type), with the conventional hexagonal structure (H-type). CFRCLS samples are fabricated using fused filament fabrication (FFF), with carbon-fiber-reinforced polylactic acid (PLA) as the matrix. The in-plane compression properties, energy absorption characteristics, and deformation behaviors of the hybrid structures were studied by experimental tests. The results demonstrate that different permutation and hybrid modes alter the deformation behaviors and mechanical properties of the structures. Taking elastic modulus as an example, the values of H-type, R-type, OOA-type, OHA-type, ONA-type, and RC-type are, respectively, 6.08 MPa, 5.76 MPa, 19.0 MPa, 10.3 MPa, 31.7 MPa, and 73.2 MPa, while the ratio of their masses is 1:1:1.10:1.52:1.66. Furthermore, hybrid lattice structures exhibit significantly improved mechanical properties compared to single lattice structures. Compared to the single structure R-type, the RC-type increases elastic modulus, yield strength, and energy absorption, respectively, by 12.7 times, 5.4 times, and 4.4 times.