Lattice Infill Research Articles

Utilization of fused deposition modeling in the fabrication of lattice structural Al2O3 ceramics

This study focuses on fabricating lattice structural Al2O3 ceramics with lattice infill densities ranging from 25 % to 70 % using filament-based fused deposition modeling (FDM) technology. A specialized filament for FDM printing was developed, comprising 53 vol% Al2O3 powder and ethylene vinyl acetate (EVA) as the primary binder component. The filament demonstrated excellent flexibility as assessed by a self-designed three-point bending test. The impact of lattice infill density and sintering temperature on dimensional changes, microstructure evolution, compressive strength, and strength-to-density ratio was explored. It was found that with increasing sintering temperature, the samples became more compact, resulting in higher levels of shrinkage, bulk density, and compressive strength. At a sintering temperature of 1600 °C, the sintered parts reached their maximum density through the solid-state sintering process. The sample sintered at 1600 °C with 70 % infill density exhibited the maximum compressive strength of 31.47 MPa, with a corresponding strength-to-density ratio of 20.84 MPa/g·cm−3. These findings highlight the successful fabrication of lattice structural Al2O3 with low density and high compressive strength by FDM technology.

Investigating the effect of lattice design on sauce adhesion in 3D printed durum wheat pasta

Pasta has been one of the beloved foods for many years, and recently, attempts have been made in the industry to utilize 3D printing to create various designs of pasta noodles. This study investigated the effect of freeze-dried spinach powder on the quality of pasta dough used for 3D printing while focusing on improving the quality of 3D printing and post-processing characteristics and also the sauce adhesion capacity of pasta dough under various traditional Korean lattice infill patterns. Common durum wheat flour was substituted with 0, 4, 8, 12 and 16 g/54 g freeze-dried spinach powder. As wheat flour was progressively substituted with spinach powder, the rheological behavior of the dough ink changed from a long paste to a short paste. Pasta dough containing 12% spinach powder exhibited good resolution in the printing test while maintaining a stable network structure due to appropriate starch gelatinization with spinach granules after drying and cooking, ultimately resulting in a high-quality product. However, exceeding a certain threshold (16% spinach content) leads to adverse effects. Wanjasal, Guigapsal, and Ttisal muntin units were used as patterns for spinach-containing pasta, and increased sauce viscosity correlated with a greater retention of sauce within pattern holes. By successfully enhancing the nutritional value and printing resolution of durum wheat pasta using spinach powder, this study provides quantitative guidelines for the development of 3D printable pasta.

Meter-Scale Thin-Walled Structure with Lattice Infill for Fuel Tank Supporting Component of Satellite: Multiscale Design and Experimental Verification

Meter-Scale Thin-Walled Structure with Lattice Infill for Fuel Tank Supporting Component of Satellite: Multiscale Design and Experimental Verification

Mechanical Properties and Energy Absorption of Integrated AlSi10Mg Shell Structures with BCC Lattice Infill

Shell-infill structures comprise an exterior solid shell and an interior lattice infill, whose closed features yield superior comprehensive mechanical performance and light weight. Additive manufacturing (AM) can ensure the fabrication of complex structures. Although the mechanical behaviors of lattice structures have been extensively studied, the corresponding mechanical performances of integrated-manufactured shell structures with lattice infills should be systematically investigated due to the coupling effect of the exterior shell and lattice infill. This study investigated the mechanical properties and energy absorption of AlSi10Mg shell structures with a body-centered cubic lattice infill fabricated by AM. Quasi-static compressive experiments and corresponding finite element analysis were conducted to investigate the mechanical behavior. In addition, two different finite element modeling methods were compared to determine the appropriate modeling strategy in terms of deformation behavior. A study of different parameters, including lattice diameters and shell thicknesses, was conducted to identify their effect on mechanical performance. The results demonstrate the mechanical advantages of shell-infill structures, in which the exterior shell strengthens the lattice infill by up to 2.3 times in terms of the effective Young’s modulus. Increasing the infill strut diameter can improve the specific energy absorption by up to 1.6 times.

Flexural performance of 3D printed concrete structure with lattice infills

Large-scale 3D printed concrete structures with lattice infill will result in lightweight components with high mass-specific strength, and faster fabrication, compared to conventional casting methods. However, the effect of different infill patterns on mechanical performance is still not addressed clearly in many scientific publications. This study investigates the bending performance of 3D-printed concrete beams with four infill patterns such as lattice, triangular, lattice-triangular, and sinusoidal tested in vertical (layer deposition direction) and transverse (layer translation direction) loading directions. The load versus displacement curves and crack propagation patterns are investigated both via Finite Element (FE) simulations and experiments. The FE results corroborated by experiments indicated that the triangular patterns perform better than lattice-shaped infill counterparts particularly under the transverse loading direction exhibiting the highest flexural deformation resistance capacity. The findings of this study would be useful in latticing large-scale concrete structures for diverse applications.

An Automated Parametric Surface Patch-Based Construction Method for Smooth Lattice Structures with Irregular Topologies

Additive manufacturing enables the realization of complex component designs that cannot be achieved with conventional processes, such as the integration of cellular structures, such as lattice structures, for weight reduction. To include lattice structures in component designs, an automated algorithm compatible with conventional CAD that is able to handle various lattice topologies as well as variable local shape parameters such as strut radii is required. Smooth node transitions are desired due to their advantages in terms of reduced stress concentrations and improved fatigue performance. The surface patch-based algorithm developed in this work is able to solidify given lattice frames to smooth lattice structures without manual construction steps. The algorithm requires only a few seconds of sketching time for each node and favours parallelisation. Automated special-case workarounds as well as fallback mechanisms are considered for non-standard inputs. The algorithm is demonstrated on irregular lattice topologies and applied for the construction of a lattice infill of an aircraft component that was additively manufactured.

Multiscale topological design of coated structures with layer-wise bi-material lattice infill for minimum dynamic compliance

In this paper, a novel multiscale topological design strategy for coated structures infilled with layer-wise bi-material lattice microstructures is presented, where the objective is to minimize the dynamic compliance of the macrostructure under time-harmonic excitation frequency. The optimization of bi-material microstructures is concurrently performed with the topological design of the macrostructure to fully consider the interaction of structural evolution between the two scales. At the macroscale, the material distribution for the macrostructure is optimized using the velocity field-based level set method, which inherits the implicit geometrical representation, and smooth structural boundaries can be obtained. Due to the signed distance property, the thickness of the outer coating is able to be well-maintained during the iteration. As for the microscale, the density method is chosen to conduct topology optimization of lattice microstructures. The lattice infill for coated structures is designed to be layer-wise by dividing it uniformly (or near-uniformly) into different layers, and each layer is composed of periodic and uniform bi-material microstructures, which can enlarge the design space and generate various microscale structural patterns to better resist the vibration response. The sensitivity analysis for the dynamic compliance with respect to the design variables at different scales is carefully performed and the influences of the number of divided layers, excitation frequency, coating thickness, damping coefficients, element meshes, static constraint, and division direction for the lattice infill on the optimized macroscale and microscale structures are studied by several numerical examples. Moreover, a body-fitted mesh for a Computer-Aided Design (CAD) model is constructed and the finite element analysis results further verify the effectiveness of the proposed approach.

Investigation of lattice infill parameters for additively manufactured bone fracture plates to reduce stress shielding

BackgroundStress shielding is a detrimental phenomenon caused by the stiffness mismatch between metallic bone plates and bone tissue, which can hamper fracture healing. Additively manufactured plates can decrease plate stiffness and alleviate the stress shielding effect. MethodsRectilinear lattice plates with varying cell sizes, wall thicknesses, and orientations are computationally generated. Finite element analysis is used to calculate the four-point bending stiffness and strength of the plates. The mechanical behaviors of three different lattice plates are also simulated under a simple diaphyseal fracture fixation scenario. ResultsThe study shows that with different combinations of lattice infill parameters, plates with up to 68% decrease in stiffness compared to the 100% infill plate can be created. Moreover, in the fixation simulations, the least stiff lattice plate displays 53% more average stress distribution at the healing callus region compared to the 100% infill plate. ConclusionsUsing computational techniques, it has been demonstrated that additively manufactured stiffness-reduced bone plates can successfully address stress shielding with the strategic modulation of lattice infill parameters. Lattice plates with design versatility have the potential for use in various fracture fixation scenarios.

Additive Manufacturing for Lightweighting Satellite Platform

Lightweight structures with an internal lattice infill and a closed shell have received a lot of attention in the last 20 years for satellites, due to their improved stiffness, buckling strength, multifunctional design, and energy absorption. The geometrical freedom typical of Additive Manufacturing allows lighter, stiffer, and more effective structures to be designed for aerospace applications. The Laser Powder Bed Fusion technology, in particular, enables the fabrication of metal parts with complex geometries, altering the way the mechanical components are designed and manufactured. This study proposed a method to re-design the original satellite structures consisting of walls and ribs with an enclosed lattice design. The proposed new structures must comply with restricted requirements in terms of mechanical properties, dimensional accuracy, and weight. The most challenging is the first frequency request which the original satellite design, based on traditional fabrication, does not satisfy. To overcome this problem a particular framework was developed for locally thickening the critical zones of the lattice. The use of the new design permitted complying with the dynamic behavior and to obtain a weight saving maintaining the mechanical properties. The Additive Manufacturing fabrication of this primary structure demonstrated the feasibility of this new technology to satisfy challenging requests in the aerospace field.

Three-dimensional strength and stiffness optimization of coated structures with lattice infill

Additive manufacturing (AM) offers a design freedom to fabricate high performance parts, such as a solid outer shell with a porous infill (coated structure), to enhance strength-to-weight ratio. The goal of this article is to describe and analyze how to develop a strength-based optimization to design the topology and infill microstructures density by minimizing the failure load subjected to weight constraint. To establish the coated structure, the material and coating indicators are obtained using double smoothing and projection of design variable. Additionally, three characteristic parameters are utilized to represent the lattice geometry. Two lattices, including octet-truss lattice and cubic lattice, are considered for the infill region. The strength-based optimization is developed based on Hill’s yield criterion, and the element failure indices are aggregated to a single function using the p-mean approach. The proposed design methodology has been successfully applied to different numerical test cases, which showed that performing strength-based optimization led to a smoother boundary at the re-entrant corner, achieving a lower failure load. Numerical evaluation also demonstrated that, in contrast to solely considering characteristic parameters to design lattice, considering additional material and coating indicators during the design process resulted in optimized topology as well as infill microstructures material distribution. • Development of homogenization-based optimization for coated structures with lattice infill. • Sensitivity analysis for the strength-based objective function • Comparison study between strength and stiffness-based designs • Comparison study between two lattice types optimized designs • Comparison study between lattice structures with and without coating

Investigation of the Performance of Ti6Al4V Lattice Structures Designed for Biomedical Implants Using the Finite Element Method

The development of medical implants is an ongoing process pursued by many studies in the biomedical field. The focus is on enhancing the structure of the implants to improve their biomechanical properties, thus reducing the imperfections for the patient and increasing the lifespan of the prosthesis. The purpose of this study was to investigate the effects of different lattice structures under laboratory conditions and in a numerical manner to choose the best unit cell design, able to generate a structure as close to that of human bone as possible. Four types of unit cell were designed using the ANSYS software and investigated through comparison between the results of laboratory compression tests and those of the finite element simulation. Three samples of each unit cell type were 3D printed, using direct metal laser sintering technology, and tested according to the ISO standards. Ti6Al4V was selected as the material for the samples. Stress–strain characteristics were determined, and the effective Young’s modulus was calculated. Detailed comparative analysis was conducted between the laboratory and the numerical results. The average Young’s modulus values were 11 GPa, 9 GPa, and 8 GPa for the Octahedral lattice type, both the 3D lattice infill type and the double-pyramid lattice and face diagonals type, and the double-pyramid lattice with cross type, respectively. The deviation between the lab results and the simulated ones was up to 10%. Our results show how each type of unit cell structure is suitable for each specific type of human bone.

Topology optimization of coated structures with layer-wise graded lattice infill for maximizing the fundamental eigenfrequency

Combining the advantages of lattice infill and coating, coated structures with lattice infill are widely used in engineering to achieve light-weight structural characteristic or certain functionalities. This paper presents a novel concurrent multiscale topology optimization (TO) framework to maximize the fundamental eigenfrequency of structures with a uniform outer coating and layer-wise graded lattice infill microstructures. The macroscale topology optimization is conducted by using the velocity field-based level set method, which inherits the implicit geometrical representation and signed distance property of the conventional level set method (smooth and clear boundaries and well-maintenance of the uniform thickness of the coating). Besides, the employment of general mathematical programming algorithms enables the velocity field-based level set method to handle multiple constraints in an easier way. At microscale, the popular density-based method is used to design layer-wise graded lattice structures. The effective material properties of microstructures are computed by using the asymptotic homogenization method, which bridges macroscale and microscale designs. With higher design flexibility, it is found that coated structures with layer-wise graded lattice infill have higher eigenfrequencies than those with periodic and uniform lattice infill microstructures. The influence of layers of lattice infill and coating thickness on the concurrent optimization of macrostructures and microstructures are carefully studied by showcasing several numerical examples, and the effectiveness of the proposed method is also confirmed, as well as the manufacturability of optimization results.

Lattice infill structure design of topology optimization considering size effect

The vigorous development of additive manufacturing technology promotes the tendency of lattice infill design to be miniaturized. The representative scale of the deformation field becomes equivalent to the length scale of the microstructures when the characteristics size of the lattice infill design is down to micron or nanoscale, and strain gradient effects or size effects arise in the structure. Due to the lack of microscopic material properties, the typical topology optimization framework based on classical mechanics for lattice infill structure cannot represent the performance difference induced by the size effect. Therefore, single-scale lattice infill structure design and couple stress theory are combined to explore the size effect on topology optimization. Numerical examples show that when the size ratio of the macroscopic feature size to the material characteristic length is reduced to a comparable range, the topological configurations and the target compliance values exhibit a significant size effect.

Design optimization of functionally graded lattice infill total hip arthroplasty stem for stress shielding reduction.

Reducing stress shielding of stem-inserted femurs in total hip arthroplasty caused by the high stiffness of the stem is an emerging medical engineering issue. In this study, a numerical design optimization methodology lattice infill stem was developed to realize a stem, balancing the low stiffness and strength requirements. Two pairs of models and loading conditions were introduced for the stress shielding and strength criteria. The objective function was set as the weighted sum of the criteria. Its effective density distribution was optimized by handling the representative size of the lattice as a design variable, assuming that the so-called body-centered cubic lattice was the base shape of the lattice. In the optimization, the approximated model of the lattice was handled as a solid material with the effective physical properties of the lattice derived by the homogenization method. After optimization, the detailed lattice stem geometry was modeled based on the obtained optimal lattice distribution, and the actual performance was numerically evaluated. The developed stem increased the stress applied to the remaining femur by 32.4% compared with the conventional stem.

Multiscale topology optimization of coated structures with layer-wise graded lattice infill for maximum fundamental eigenfrequency

Coated structures with lattice infill have attracted great interest from academia to industry. Functionally, the outer coating can protect its inner substrate and lattice infill structures exhibit great ability to improve certain structural performance. In this research, we propose a novel concurrent multiscale topology optimization method to design structures with layer-wise graded lattice infill covered by an outer coating of uniform thickness. The fundamental eigenfrequency is selected as the design objective to be maximized. At the macroscale, the velocity field-based level set (VFLS) method is used to achieve optimal macroscale structures with clear and smooth boundaries. Besides, making use of the signed distance property, the thickness of the outer coating can be well-maintained. At the microscale, the substrate area of coated structures is uniformly (or near-uniformly) divided into several layers to have different microstructural configurations and the popular solid isotropic material with penalization (SIMP) method is used to perform microscale topology optimization. Two different scales are bridged using the asymptotic homogenization method. Numerical results show that coated structures with layer-wise graded lattice infill we design own higher fundamental eigenfrequency than those with periodic and uniform lattice infill microstructures, due to the enlargement of the design freedom.

Infill topology and shape optimization of lattice‐skin structures

AbstractLattice‐skin structures composed of a thin‐shell skin and a lattice infill are widespread in nature and large‐scale engineering due to their efficiency and exceptional mechanical properties. Recent advances in additive manufacturing, or 3D printing, make it possible to create lattice‐skin structures of almost any size with arbitrary shape and geometric complexity. We propose a novel gradient‐based approach to optimizing both the shape and infill of lattice‐skin structures to improve their efficiency further. The respective gradients are computed by fully considering the lattice‐skin coupling while the lattice topology and shape optimization problems are solved in a sequential manner. The shell is modeled as a Kirchhoff–Love shell and analyzed using isogeometric subdivision surfaces, whereas the lattice is modeled as a pin‐jointed truss. The lattice consists of many cells, possibly of different sizes, with each containing a small number of struts. We propose a penalization approach akin to the SIMP (solid isotropic material with penalization) method for topology optimization of the lattice. Furthermore, a corresponding sensitivity filter and a lattice extraction technique are introduced to ensure the stability of the optimization process and to eliminate scattered struts of small cross‐sectional areas. The developed topology optimization technique is suitable for nonperiodic, nonuniform lattices. For shape optimization of both the shell and the lattice, the geometry of the lattice‐skin structure is parameterized using the free‐form deformation technique. The topology and shape optimization problems are solved in an iterative, sequential manner. The effectiveness of the proposed approach and the influence of different algorithmic parameters are demonstrated with several numerical examples.

Enhancing Design for Additive Manufacturing Workflow: Optimization, Design and Simulation Tools

In the last few decades, complex light-weight designs have been successfully produced via additive manufacturing (AM), launching a new era in the thinking–design process. In addition, current software platforms provide design tools combined with multi-scale simulations to exploit all the technology benefits. However, the literature highlights that several stages must be considered in the design for additive manufacturing (DfAM) process, and therefore, performing holistic guided-design frameworks become crucial to efficiently manage the process. In this frame, this paper aims at providing the main optimization, design, and simulation tools to minimize the number of design evaluations generated through the different workflow assessments. Furthermore, DfAM phases are described focusing on the implementation of design optimization strategies as topology optimization, lattice infill optimization, and generative design in earlier phases to maximize AM capabilities. In conclusion, the current challenges for the implementation of the workflow are hence described.

Multicomponent topology optimization of functionally graded lattice structures with bulk solid interfaces

AbstractThis article presents a topology optimization method for structures consisting of multiple lattice components under a certain size, which can be manufactured with an additive manufacturing machine with a size limit and assembled via conventional joining processes, such as welding, gluing, riveting, and bolting. The proposed method can simultaneously optimize overall structural topology, partitioning to multiple components and functionally graded lattices within each component. The functionally graded lattice infill with guaranteed connectivity is realized by applying the Helmholtz PDE filter with a variable radius on the density field in the solid isotropic material with penalization (SIMP) method. The partitioning of an overall structure into multiple components is realized by applying the discrete material optimization (DMO) method, in which each material is interpreted as each component, and the size limit for each component imposed by a chosen additive manufacturing machine. A gradient‐free coating filter realizes bulk solid boundaries for each component, which provide continuous mating surfaces between adjacent components to enable the subsequent joining. The structural interfaces between the bulk solid boundaries are extracted and assigned a distinct material property, which model the joints between the adjacent components. Several numeral examples are solved for demonstration.

Projection-Based Implicit Modeling Method (PIMM) for Functionally Graded Lattice Optimization

We propose a projection-based implicit modeling method (PIMM) for functionally graded lattice optimization, which does not require any homogenization techniques. In this method, a parametric projection function is proposed to link the implicit function of functionally graded lattice with the finite element background mesh. To reduce the number of design variables, the radial basis function is utilized to interpolate the implicit design field. The triply periodic minimal surface lattice is employed to demonstrate the proposed method. Several two- and three-dimensional lattice design examples are presented to solve the compliance problems. The proposed PIMM method is flexible and can potentially be extended to design graded irregular porous scaffold and non-periodic lattice infill designs.

3D Printing Improved Testicular Prostheses: Using Lattice Infill Structure to Modify Mechanical Properties

Patients often opt for implantation of testicular prostheses following orchidectomy for cancer or torsion. Recipients of testicular prostheses report issues regarding firmness, shape, size, and position, aspects of which relate to current limitations of silicone materials used and manufacturing methods for soft prostheses. We aim to create a 3D printable testicular prosthesis which mimics the natural shape and stiffness of a human testicle using a lattice infill structure. Porous testicular prostheses were engineered with relative densities from 0.1 to 0.9 using a repeating cubic unit cell lattice inside an anatomically accurate testicle 3D model. These models were printed using a multi-jetting process with an elastomeric material and compared with current market prostheses using shore hardness tests. Additionally, standard sized porous specimens were printed for compression testing to verify and match the stiffness to human testicle elastic modulus (E-modulus) values from literature. The resulting 3D printed testicular prosthesis of relative density between 0.3 and 0.4 successfully achieved a reduction of its bulk compressive E-modulus from 360 KPa to a human testicle at 28 Kpa. Additionally, this is the first study to quantitatively show that current commercial testicular prostheses are too firm compared to native tissue. 3D printing allows us to create metamaterials that match the properties of human tissue to create customisable patient specific prostheses. This method expands the use cases for existing biomaterials by tuning their properties and could be applied to other implants mimicking native tissues.