Design Of Lattice Structures Research Articles

Mechanical design and energy absorption performances of novel plate-rod hybrid lattice structures

Hybrid lattice structures, integrating diverse structural components from fundamental lattice topologies, have attracted significant attention for their exceptional mechanical properties encompassing elastic modulus, yield stress, and energy absorption. To amalgamate the lightweight characteristics of rod structures with the robust mechanical properties of plate structures, a novel plate-rod hybrid lattice (PRHL) with controllable geometrical parameters and higher energy absorption was proposed and fabricated via the Selective Laser Sintering technique. In the PRHL design, the hybrid rod structure, interlinked with the center of each surface of the semi-open Octet plate lattice (SOPL), mutually provides support and deformation constraints. To identify the mechanical properties of PRHL, quasi-static uniaxial compression tests of PRHL samples sintered by Polylactic Acid powder were carried out. In comparison to SOPL, the newly proposed PRHL demonstrates an approximate 13.4% improvement in initial crush stress and an 18.5% increase in specific energy absorption capacity. Furthermore, numerical simulations incorporating the effect of printing orientation were performed to analyze the deformation mechanism of the PRHL structures. The present study also underscores the capacity to fine-tune the mechanical properties of PRHLs by regulating the plate thickness, rod diameter and excavated hole diameter.

Rational design and additive manufacturing of grain boundary-inspired, multi-architecture lattice structures

The advent of additive manufacturing has facilitated the design and fabrication of hybrid lattice structures with multiple morphologies. These structures combine multiple distinct architectures into a single structure with an exceptional performance that far exceeds that of each constituting architecture. However, combining strut-based lattices poses serious challenges in establishing effective connections, primarily due to complications in formulating mathematical expressions. Here, we introduce a novel approach, inspired by the connections observed in the grain boundaries of polycrystalline materials, to design the interconnections of hybrid structures. This strategy involves shrinking the unit cell linkage, thereby addressing the difficulty of forming efficient connections at arbitrary spatial interfaces within strut-based lattice structures. We then use the relevant design theories to tune the performance of these connections and simplify the design process for hybrid structures – even for inexperienced designers. Our experimental observations confirm the efficacy of the proposed strategy, bridging the knowledge gap in the design of connected strut-based multi-lattice structures. Furthermore, this approach enhances the design of tailored hybrid structures and fosters the development of metamaterials with advanced, unique functionalities. The proposed approach has important implications for the development of designer materials, with applications in medical devices, (soft) robotics, and implants.

Predictive modeling of lattice structure design for 316L stainless steel using machine learning in the L-PBF process

Lattice structures in additive manufacturing of 316L stainless steel have gained increasing attention due to their well-suited mechanical properties and lightweight characteristics. Infill structures such as honeycomb, lattice, and gyroid have shown promise in achieving desirable mechanical properties for various applications. However, the design process of these structures is complex and time-consuming. In this study, we propose a machine learning-based approach to optimize the design of honeycomb, lattice, and gyroid infill structures in 316L stainless steel fabricated using laser powder bed fusion (L-PBF) technology under different loading conditions. A dataset of simulated lattice structures with varying geometries, wall thickness, distance, and angle using a computational model that simulates the mechanical behavior of infill structures under different loading conditions was generated. The dataset was then used to train a machine learning model to predict the mechanical properties of infill structures based on their design parameters. Using the trained machine learning model, we then performed a design exploration to identify the optimal infill structure geometry for a given set of mechanical requirements and loading conditions. Finally, we fabricated the optimized infill structures using L-PBF technology and conducted a series of mechanical tests to validate their performance under different loading conditions. Overall, our study demonstrates the potential of machine learning-based approaches for efficient and effective designing of honeycomb, lattice, and gyroid infill structures in 316L stainless steel fabricated using L-PBF technology under different loading conditions. Furthermore, this approach can be used for dynamic loading studies of infill structures.

Fabricating 316 L stainless steel unsupported rods by controlling the flow of molten pool via wire arc additive manufacturing

Fabricating unsupported inclined rods using additive manufacturing poses significant challenges, limiting the design and manufacturing of lattice structures. This study introduces a method for controlling molten pool flow to successfully fabricate unsupported rods with varying diameters (4.6 mm to 9.3 mm) and inclination angles (-30 degrees to 90 degrees) using wire arc additive manufacturing. The key contributions of this research lie in enabling the fabrication of negatively inclined unsupported rods and investigating the influence of arc heat input on the deposition process, molten pool behavior, microstructure, and mechanical properties. By effectively controlling the molten pool flow, this method significantly reduces constraints on structural design, facilitating the fabrication of multi-angle lattice structures. It is observed that rod diameter negatively correlates with arc heat input per volume. Tensile strength initially increases and then decreases with diameter increment. Additionally, fabricating negatively inclined rods requires additional heat input, resulting in slightly inferior mechanical properties compared to positively inclined rods. The demonstrated applicability of the proposed method through the stable fabrication of screw rods and arc-curved rods showcases its potential for various lattice structure designs. Furthermore, the limitations of minimum rod diameter and inclination angle are discussed, determined by arc energy equipment, machine tool accuracy, and torch interference. This study advances additive manufacturing techniques by enabling the fabrication of unsupported inclined rods and expanding the design space for lattice structures.

Assessment of Additive Manufacturing Technology for Rotor Fixture used in Gas turbine Assembly

Abstract: The study involves an examination of the rotor fixture assembly to understand its functionality under standard boundary conditions. The fixture components were modelled in NX CAD. To achieve the desired weight reduction and equivalent stiffness, Finite Element Analysis was conducted both before and after the Topology Optimization process using the Density-based method in ANSYS. The objective was to optimize rotor fixture design for additive manufacturing to reduce weight and lead time. Finite Element Analysis and topology optimization were used to redesign the fixture, resulting in a 16.3% mass reduction for the solid model and 27.5% for the shell model while maintaining stiffness. Metal additive manufacturing reduced lead time by 46% despite a 17% increase in cost compared to conventional machining. Future work may involve lattice structure design and part distortion prediction using Ansys additive software for further improvements.

Current trend of lattice structures designed and analysis for porous hip implants: A short review

Current hip implant materials are substantially more rigid, which can result in a phenomenon known as stress shielding. The mismatch between the stiffness of the hip implant and the surrounding bone might cause the implant to be overloaded, resulting in bone resorption, bone fracture, and revision surgery. Consequently, porous lattice structures in hip implants are employed to address the aforementioned issues. This article discusses the most recent hip implant lattice design trends. The analysis of lattice structures using finite element analysis (FEA) is also included in the review. In conclusion, lattice structure design is a promising method that can reduce stress shielding, reduce weight, and improve osseointegration.

Experimental and analytical investigation of bio-inspired lattice structures under compressive loading

The main objective of this study is to fabricate a Novel bio-inspired lattice structure for energy absorption. A lattice structure design was proposed based on the microstructure of one of the various butterfly species Papilio Xuthus. Two major parameters are chosen from the structure to make multiple designs which may cause changes in the behavior of the structure among all available parameters. The parametric values required for the designs were calculated with the help of Response Surface Methodology (RSM) using Minitab software. The proposed designs are modeled in Autodesk Fusion 360 and 3D printed specimens of size 40 × 40 × 40 (all are in mm) are fabricated by Stereolithography (SLA) process based on the chosen parameters. The 3D-printed specimens are tested under quasi-static compressive loading using Instron 8801 Universal testing machine (UTM). The test results obtained from the testing are used to construct regression equations for energy absorption (EA) and specific energy absorption (SEA). The developed equations can be used to find out EA and SEA values for any combination of the proposed parameters (x and d) for suitable energy absorption applications.

DESIGN AND OPTIMIZATION OF THE VARIABLE-DENSITY LATTICE STRUCTURE BASED ON LOAD PATHS

Lattice structure is more and more widely used in engineering by replacing solid structure. But its mechanical performances are constrained by the external shape if the unit cells are directly filled in the design domain, and the traditional topology optimization methods are difficult to give the explicitly mechanical guidance for the distribution of internal unit cells. In this paper, a novel design and optimization method of variable-density lattice structure is proposed in order to simultaneously optimize the external shape and the internal unit cells. First of all, the envelope model of any given structure should be established, and the load paths need to be visualized by the theory of load path. Then, the design criteria of external shape are established based on the principle of smoother load paths in the structure. An index of load flow capacity is defined to indicate the load paths density and to control the density distribution of unit cells, and a detailed optimization strategy is given. Finally, three examples of a cantilever plate, an L-shaped bracket and a classical three-point bending beam are used to verify the method. The results show that the models designed by the proposed method have better mechanical performances, lower material usage and less printing time.

Improving the Mechanical Properties of a Lattice Structure Composed of Struts with a Tri-Directional Elliptical Cylindrical Section via Selective Laser Melting.

In recent years, lattice structures produced via additive manufacturing have been increasingly investigated for their unique mechanical properties and the flexible and diverse approaches available to design them. The design of a strut with variable cross-sections in a lattice structure is required to improve the mechanical properties. In this study, a lattice structure design method based on a strut cross-section composed of a mixture of three ellipses named a tri-directional elliptical cylindrical section (TEC) is proposed. The lattice structures were fabricated via the selective laser melting of 316L alloy. The finite element analysis results show that the TEC strut possessed the high mechanical properties of lattice structures. Compression experiments confirmed that the novel lattice structure with the TEC strut exhibited increases in the elastic modulus, compressive yield strength, and energy absorption capacity of 24.99%, 21.66%, and 20.50%, respectively, compared with the conventional lattice structure at an equal level of porosity.

Lattice structure design optimization under localized linear buckling constraints

An optimization method for the design of multi-lattice structures satisfying local buckling constraints is proposed in this study. In order to resolve the highly nonlinear large-scale optimization problem, a consecutive numerical approach is devised: macro-field optimization and microstructure embedding. The macro-field optimization finds an optimal elasticity tensor distribution among all feasible elastic continua based on a concept of free material optimization (FMO), which largely extends the design space compared with density-based topology optimization. After this, by an inverse design approach that approximates the elasticity tensor under local buckling constraint, an appropriate lattice structure is able to be embedded within each macro-element, where the local stress tensors are considered in particular to produce more reasonable microstructures. During the process, a machine learning approach is also devised to significantly reduce the number of material/lattice types and thus the overall computational costs. Ultimately, a lattice structure under requirements of overall stiffness and local buckling resistance is produced, as demonstrated via numerical examples.

Multiscale concurrent topology optimization of hierarchal multi-morphology lattice structures

This paper proposes a multiscale concurrent topology optimization method for design of hierarchal multi-morphology lattice structures (HMMLSs), which features in the Kriging metamodel assisted Uniform Multiphase Materials Interpolation (KUMMI) model and the sigmoid function (SF) based hybrid transition strategy. Specifically, level set functions are adopted to model hierarchal lattice unit cells (LUCs). Then LUCs with different morphology are treated as distinct lattice materials (LMs) and the SF-based hybrid transition strategy is employed to realize smooth transition between multi-morphology LUCs. Besides, Kriging metamodels are constructed to predict the equivalent properties of LUCs efficiently so that the topology optimization of HMMLSs can be achieved with an affordable computational cost. Two kinds of design variables are involved in the topology optimization of HMMLSs, where discrete variables indicate the categories of lattice materials and continuous variables determine the relative densities of lattice microstructures. The proposed KUMMI model can couple the two kinds of design variables dexterously to realize concurrent optimization of relative densities of LUCs, and distribution regions and percentages of different LMs within HMMLSs. Several numerical examples are presented to demonstrate the effectiveness and applicability of the proposed method. Results indicate the optimized HMMLSs exhibit rational distribution of hierarchal multi-morphology LUCs, hence achieving superior structural performance.

Proportional Topology Optimization algorithm for two-scale concurrent design of lattice structures

In this paper, the Proportional Topology Optimization (PTO) algorithm is extended for the two-scale concurrent topology optimization, in which both the structure and material cellular micro-structure are subject to design. PTO was originally developed on the concept that the amount of material being distributed to an element would be proportional to the contribution of that element in the objective function. Sensitivity analysis is not required. In a two-scale concurrent topology optimization problem, two sets of design variables are defined, one for macro-structure and one for micro-structure. Here, the objective function is reformulated such that the contribution of each micro-scale design variable can be determined, facilitating the employment of PTO. The macroscopic effective elastic tensor is evaluated by the energy-based homogenization method (EBHM), providing a link between micro-structure and macro-structure. Feasibility and efficiency of the proposed PTO approach are demonstrated via several benchmark examples of both two and three dimensional structures.

Crashworthiness analysis and multi-objective optimization of spatial lattice structure under dynamic compression

A spatial lattice structure is proposed to improve the structural crashworthiness and energy absorption. First, a single-cell structure is proposed via a bionic honeycomb, and then the single-cell structure is arrayed to form a spatial lattice structure. The finite element model of the spatial lattice structure for crashworthiness analysis is established. The theoretical model of the plateau stress of the lattice structure under compressive conditions is derived, and its accuracy is verified by the corresponding finite element analysis. After that, the effect of geometrical parameters of single-cell structure on crashworthiness is analyzed. Then, geometrical parameters of single-cell structure and number of single-cell in the X, Y, and Z directions are used as design variables, the mass, and overall size are used as constraints, and specific energy absorption and collision peak force are used as optimization objectives. The multi-objective crashworthiness optimization of spatial lattice structure is carried out, and the optimal lattice structure design is determined via the gray relational analysis coupling entropy weight method. The validity of the finite element model and optimal design is verified by the drop weight impact test. The crashworthiness optimization of spatial lattice structures has important guiding significance for the design of energy-absorbing structures.

Design and analysis of lattice structure applied humerus semi-prosthesis

Abstract Bone tissue loss may occur in bone structures, which are one of the elements that provide the body’s endurance and movement of living things, due to situations such as falling, hitting, or cancer formation. In bad scenarios, applications such as an external plate or internal rod addition are made to regain the old durability of the structure. At the same time, full or semi-prosthesis applications can be made in cases where the original bone structure cannot be preserved. With today’s advanced possibilities, lattice structures can be produced effortlessly with the additive manufacturing (AM) method. Here, the formation of the structure that can show anisotropic behavior depending on the production and the effect of the roughness caused by the production quality should also be seen in the process plan. In this study, it was aimed to compare the durability of titanium (Ti-6Al-4V) and magnesium (ZK60) materials for humeral half prosthesis using cubic-based lattice structure and to show their differences compared to the original bone structure. Maximum stress and deformation values were obtained by performing analyses with the finite element method on the lattice semi-humerus prosthesis obtained with this aim. Reliability analysis was made on the data obtained, and parameter optimization of the lattice structure was aimed. As a result of the study, it was seen that the lattice structure with 65% porosity compared to the reference values is reliable and with the same reliability rate, magnesium provides approximately 60% lightness compared to titanium.

Optimization of the machining of metallic additive manufacturing supports: first methodological approach

Metal additive manufacturing is an active field of innovation. However, for laser power bed fusion (LPBF), supports removal is a major constraint. In this technology, supports are strongly welded to the part to tightly maintain it, avoid distortion, and evacuate thermal load. Although supports are usually optimized for manual removal, machining is often necessary, which can affect post-processing productivity. This paper proposes a comprehensive methodological approach to optimize the selection of cutting parameters, cutting tools, and support structure for LPBF. The aim is to help additive manufacturers find supports that reduce machining costs in terms of time and cutting tool degradation, from among the numerous support designs available. This approach can also optimize the design of lattice structures used inside parts. Our results show that among the 11 designs tested, honeycomb and squared pattern grid supports are the most efficiently machined using the 8-teeth tangential milling of the 3 tools tested, with a good post-machined surface roughness and tools’ health. The method considers low magnification optical analysis and an accelerometer sensor, which is easy to use even for small- and medium-sized enterprises. This paper also proposes and analyzes a new kind of porous support using this method.

Additive manufactured Triply Periodical Minimal Surface lattice structures with modulated hybrid topology

The fabrication freedom offered by additive manufacturing techniques is a unique asset to be exploited in the design of lightweight lattice structures. Adjusting topological and architectural features towards the design of multi-morphological lattice structures can offer a high potential towards obtaining fine-tuned mechanical response. Herein, to understand the role of unit cell topology and arrangement, various stacking and gradient strategies were implemented to modulate the overall mechanical response of the lattice structures under compression, using two Triply Periodical Minimal Surface (TPMS) unit cell designs. Experimental and numerical approaches were developed to reveal the deformation mechanism and failure modes and quantify stiffness, quasi-static uniaxial compressive strength, and energy absorption capacity of the structures. The topological arrangement of the selected unit cells was found to play a key role in defining the mechanical performance of the designed lattice structures. The obtained results demonstrated the high potential of various graded design elements for obtaining lattice structures with desired properties.

Design of dual-material lattice structures with compression-torsion bistability

Lattice structures with bistability can maintain additional equilibrium states after external loads are removed. While conventional bistable structures typically realize compression and torsional bistabilities under compression and twisting loads, this paper introduces a new design of bistable structures that exhibit torsional bistability under uniaxial compression. The proposed structure is composed of two co-axis polygonal prisms connected by struts. Torsional bistability is achieved by opposite rotations of two co-axial polygonal prisms under compression, which result in snap-through instabilities in the connecting struts. An analytical model and numerical simulations demonstrate that dual-material design for the inclined and connecting struts is required to induce bistability. A parameter study is conducted to illustrate the effect of the volume fractions of soft material in struts and the modulus ratios between two materials on bistability characteristics. One such design is practically fabricated by multi-material 3D printing, and experiments are conducted to demonstrate the existence of the second equilibrium state. Furthermore, a lattice structure is designed by periodically arraying the unit structures, which exhibit multiple stable states due to existence a sequence of bistable states arising in a layer-by-layer manner. This compression-torsion bistability breaks the restriction on the direction of the bistable deformation and the applied load, and provides inspiration for novel functional designs in the areas of logic gates and deformation control.

A systematic design of multifunctional lattice structures with energy absorption and phononic bandgap by topology and parameter optimization

ABSTRACT Lattice structure can realize excellent multifunctional characteristics because of its huge design space, and the cellular configuration directly affects the lattice structural performance and lightweight. A novel energy-absorbing multifunctional lattice structure with phononic bandgap is presented by topology and parameter optimization in this paper. First, the two-dimensional (2D) cellular configuration is lightweight designed by using independent continuous mapping (ICM) topology optimization method. The 2D cell is reconstructed by geometric parameters and rotated into a three-dimensional (3D) cell by using chiral shape to achieve bandgap. Subsequently, the surrogated model with energy absorption as the object and first-order natural frequency as the constraint is established to optimize a parametric 3D cell based on the Response Surface Methodology (RSM). Finally, the lattice structures are assembled with dodecagonal staggered arrangements to avoid the deformation interference among the adjacent cells. In addition, the lattice structural energy absorption and bandgap characteristics are analyzed and discussed. Compared to Kelvin lattice structure, the optimal lattice structure shows significant improvement in energy absorption efficiency. Besides, the proposed design also performs well in damping characteristics of the high-frequency and wide-bandgap. The lattice structural optimization design framework has great meaning to achieve the equipment structural lightweight and multi-function in the aerospace field.

Analysis and design of bistable and thermally reversible metamaterials inspired by shape-memory alloys

In this work, we study lattice structures that exhibit a bistable behavior, i. e., they can snap from one stable state to another, and are also completely reversible, capable of reverting back to its original state through a heat treatment. We design this behavior by constructing lattice structures using networks of nonlinear springs that display tension–compression asymmetry and have different thermal expansion coefficients. The mismatch in the thermal expansion coefficients induces residual stresses in the springs which results in the lattice structure exhibiting bistability at low temperatures and monostability at high temperatures. This behavior mimics the crystallographic phase transformations of shape memory alloys, but here artificially introduced in a structural lattice. By analyzing a representative unit cell, we quantify the effect that the stiffness and the thermal expansion coefficient of the springs have on the stability of the structural lattice. In addition, for simple 2D lattices, using the concept of universal unfoldings of singularity theory, we perform a perturbation analysis to identify the key variables of the structure where controlling defects is important, as they lead to drastic changes in the bifurcation behavior of the lattice. Finally, we verify numerically our analytical predictions in both 2D and 3D simulations using continuation techniques. The examples proposed confirm that the bistable and reversible features of the unit cell carry on to the macroscale, opening the route for the design of lattice structures for energy absorption applications that can heal with a heat treatment.

Design of central symmetric lattice structure for ocean engineering based on fluid-solid-interaction

Some structures that constitute underwater vehicles and other ocean engineering structures, such as the shell of underwater vehicles, shafting of power systems, compressor impellers and propeller hubs, all have central symmetric or rotationally symmetric cross sections. In this paper, a kind of central symmetric lattice is designed. The lightweight design of the above structure with this lattice can significantly reduce the weight of the structure on the premise of reducing the static response of the structure. Combined with the ANSYS Parameter Design Language (APDL), the homogenization method is used to analyze the static response of the rotationally symmetric lattice structure and the parallel pattern lattice structure under pressure. The fluid load (pressure) of impeller is calculated by CFX. The results show that the structural stress of the central symmetric lattice structures with the same volume fraction is smaller than that of parallel pattern lattice under the same load when the rotationally symmetric structures have the same form. The application of the homogenization method proves that the above conclusions also improve the efficiency of the static response calculation of the central symmetric lattice structure. The design and research methods in this paper provide technical support for the realization of lightweight design of small and medium-sized underwater rotationally symmetric structures.