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Additive manufacturing (AM) technologies provide significant design freedom, which is highly desirable in today's fast-paced product design processes. However, most of the parametric CAD software tools used today do not fully utilize this potential for freedom of form and design. Design mechanisms, such as topology optimization (TO), generative design (GD), and lattice structures, are available on the market to help designers minimize weight and material cost while maximizing the stiffness and flexibility of planned designs. This paper proposes a benchmarking approach for designers and engineers to select a suitable software tool for lattice structure generation for their specific applications. The approach includes preselecting software tools based on a weighted point evaluation of seven significant criteria. The tools are then evaluated based on key metrics such as computing time and file size of exported structures, as well as the following six distinctive attributes: usability, reliability, availability, performance, support, and cost. The evaluation process considers a total of 32 defined features. The investigation produced clear recommendations regarding overall performance, reliability, and user experience. The findings indicate that the option of a comprehensive support offering, as well as the initial and operational costs, are significant drivers in the decision-making process. [ABSTRACT FROM AUTHOR]

This paper investigates the energy absorption capacities of selected cellular topologies under quasi-static loading conditions. Twenty topologies with nearly identical relative densities belonging to 4 groups were examined: honeycomb, re-entrant, bioinspired and chiral. The topologies were modeled using an experimentally validated numerical ABSplus model and subsequently subjected to in-plane uniaxial compression tests. The findings revealed the topologies with the most favorable energy absorption parameters and the main deformation mechanisms. The topologies were classified by mechanism, and a parametric study of basic material properties, namely modulus of elasticity, yield stress, and ductility, was performed for a representative topology from each mechanism. The results indicated that the honeycomb group topologies were characterized by the largest average absorbed energy, and yield stress was found to have the greatest impact on energy absorption efficiency regardless of the main deformation mechanism. [ABSTRACT FROM AUTHOR]

In recent years, metal cellular structures have drawn attentions in various industrial sectors due to their design freedoms and abilities to achieve multi-functional mechanical properties. However, metal cellular structures are difficult to fabricate due to their complex geometries, even with modern additive manufacturing technologies such as the direct metal laser sintering (DMLS) process. Assessing the manufacturability of metal cellular structures via a DMLS process is a challenging task as the geometric features of the structures are complex. Besides, via a DMLS process, the manufacturability also depends on the cumulative deformation of the layers during the manufacturing process. Existing methods on Design for Additive Manufacturing (DFAM) provide design guidelines that are based on past successful printed designs. However, they are not effective in predicting the manufacturability of metal cellular structures. In this paper, we propose a semi-supervised deep learning based manufacturability assessment (SSDLMA) framework to assess whether a metal cellular structure can be successfully manufactured from a given DMLS process. To enable efficient learning, we represent the complex cellular structures as 3D binary arrays with a simple yet efficient voxelisation method. We then train a deep learning based classifier using only a small amount of experimental data by adopting a semi-supervised learning approach. By running real experiments and comparing with existing DFAM methods and machine learning models, we demonstrate the advantages of the proposed SSDLMA framework. The proposed framework can be extended to predict the manufacturability of various other complex geometries beyond cellular structure in a reliable way even with a small number of training data. [ABSTRACT FROM AUTHOR]

while choosing 3D printing in preference to traditional manufacturing methods (injection molding, CNC machining or casting), it is worth considering optimizing spatial models for mass reduction. One method of mass reduction is to implement cellular structures into the designed component. CAD software, such as NX, Catia, Creo, SolidWorks are not suitable for this type of operation, due to the fact that they use boundary representations (b-reps) to express the shapes of solid objects. The nTopology software takes a new design approach using implicit modeling techniques. Focusing on the design aspect, the paper proposes workflows to model objects consisting of cellular structures. The emphasis is on the strength test specimens, printing them in both DMLS/SLM and SLS technologies. A volumetric scanning technique was applied to validate the produced objects, thus obtaining a real solid model of the specimens. The aim of the study was to develop configured workflows for the design of the strength test specimens. [ABSTRACT FROM AUTHOR]

Lattice structures for engineering applications are patterns of unit cells designed to make a larger functional structure. Research on lattice structures ranges in many fields, from mechanical characterization and cell and pattern designs in respect of their applications, to the manufacturing process and its final shape control. From the manufacturing point of view, some kinds of lattice structures can be infeasible when approached with traditional manufacturing methods. It may offer an inevitable limitation of their adoption. However, advancements in Additive Manufacturing (AM) have solved this manufacturing issue to a great extent, allowing to obtain major complexity of the cells that can be achieved. The topology, shape of the unit cell, and the characteristics of its replication pattern allow us to obtain many kinds of structures in respect of the different engineering requirements and manufacturing constraints. Nevertheless, the necessity of new or dedicated CAD-CAE approaches arises to manage the domains of multiscale modeling. These are some of the advantages and disadvantages that may arise while approaching the design of a component using lattice structures. The aim of this paper is to provide an overview that integrates the most recent applications of lattice structures with their related design and manufacturing issues so that, from a practical design point of view, any state-of-the-art improvements may be established in respect of the related field of applications. In this article, engineers and researchers may find a practical summary of the capabilities and processes of lattice structures that are currently available from a design and development point of view. [ABSTRACT FROM AUTHOR]

The expansion of lattice-structured tubular stent causes scaffold foreshortening and artery migration during implantation. Based on stent foreshortening attitudes, studies were carried out on hybrid lattices considered Zero Poisson’s Ratio (ZPR) behaviour of arrow, auxetic, and honeycomb unit cell combinations. This paper investigates the energy performance of four ZPR tubular structures inspired by hybrid stent shapes under axial and oblique impact. At the beginning of the workflow of the study, the buckling control of tubular structures was performed using the numerical model. The compression test was performed by 3D printing of the ZPR structure, which was verified to remain uniform under axial loading. The results show that hybrid (H) tubular structures that include ZPR unit cells with different configurations have higher energy absorption and higher crushing force efficiency (CFE) under oblique impact. When the oblique angle is increased, all ZPR tubular structures are unstable from 20 to 40 mm deformation distances due to moving plate compression. H1 has a better CFE value than the other two ZPR configurations when crushed under oblique load. Furthermore, ZPR tubular structures have great advantages for axial loads without buckling behaviour. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to evaluate the behaviour of 3D printed honeycomb structures under low velocity impact loading for their use in energy absorption applications. Additive manufacturing technologies are part of a growing field that represents high interest for industries such as aerospace, automotive and naval. This paper aims to determine the mechanical properties of a 3D printed polymer - Polylactic Acid (PLA) manufactured by FDM (Fused Deposition Modelling) technology. In this regard, first the material is characterized by low velocity impact dynamic experimental tests. A finite Element Analysis (FEA) is performed in LS-Dyna software in order to validate the results. The samples were manufactured by varying the infill percent to investigate the influence of different parameters on a batch of samples for every configuration. The 3D CAD modelling for impact tests samples were performed in Catia V5. Among wide range of cellular structures, honeycomb non-auxetic hexagonal cell pattern was selected in this study, assuring high strength/weight ratio. The amount of energy absorbed during the impact, the failure and degradation of the impacted specimens were monitored, following the analysis of experimental and numerical data. A fair agreement was obtained between experimental and numerical results, showing that honeycomb developed lightweight structures exhibits a proper energy absorption capacity, with a mechanism of release similar to metal or composite materials honeycombs. [ABSTRACT FROM AUTHOR]

The paper describes the results of long-term investigations on the development of the technology of superplastic forming and diffusion bonding (SPF/DB) conducted at the Institute for Metals Superplasticity Problems, Russian Academy of Sciences for producing standard articles of aero-space engineering, such as hollow blades, wing and shell panels. The process of solid-state joint formation in titanium alloy sheets during SPF was studied. The prospects of the development of the SPF/DB technology are considered and the latest results are discussed. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is a key technology for the individualized and resource-efficient production of structural components. Recent developments in manufacturing technologies enable improved quality of additively manufactured components and therefore they become more and more important in lightweight constructions. An example is the substitution of solid material by porous lattice structures. Those embedded lattice structures lead to highly weight-efficient structures. Most recent investigations focus on numerical and experimental studies to describe the mechanical behavior of lattice structures. In this paper, a method to determine analytical expressions for the axial stiffness properties of lattice structures is presented. The displacement method and direct stiffness method are used to derive symbolic parameter-dependent formulas for the axial stiffnesses and effective Young's moduli for f2cc,z, and bcc unit cells. Furthermore, an empirical approach based on Finite Element simulations is presented to describe the stiffness reduction for non-embedded or rather free lattice structures. The results are further validated by physical experiments. Stereolithography is used for specimen production. f2cc,z, and bcc lattice structures are embedded in thin-walled rectangular aluminum tubes and tested under compression load. Furthermore, lattices without a surrounding tube are tested. The analytical and empirical solutions are in good agreement with the experimental and numerical results. [ABSTRACT FROM AUTHOR]

Mesoscale cellular structures with different desired physical properties are promising for a broad spectrum of applications. The availability of Additive Manufacturing (AM) technology has significantly relaxed the fabricating limitation of cellular structures. It enables the design of cellular structure with complex cell topologies and relative density distribution. In this paper, a multifunctional design method for heterogeneous cellular structures is proposed. To introduce this method, Function-Performance-Property-Design parameter model is proposed at first. This proposed model can help designers to analyze the complex relations between focused functions and their related design parameters. Based on the proposed F-P-P-D model, the template of compromise Decision Support Problem (DSP) is applied to generate the optimization formulation which can generally consider the performances defined for several different functions. To solve the defined optimization problem, a multifunctional design simulation infrastructure is proposed for the designed heterogeneous cellular structures. Based on this simulation infrastructure, both the value of the objective function and its gradients can be evaluated. Then, Sequential Quadratic Programming (SQP) solver can be applied to solve the defined optimization formulation. The optimal relative density of cellular structures can be achieved and converted to the heterogeneous cellular structures at the end. A case study is provided at the end of this paper. For this case study, two different cell topologies and several different combinations of optimization parameters are used. A brief discussion is made to conclude the effects of cell topologies and other optimization parameters on the optimization results. Generally, the result of this design case validates the efficiency of the proposed design method. This method provides a useful design tool for users to take advantage of heterogeneous cellular structures for multifunctional purposes. [ABSTRACT FROM AUTHOR]

Combining the additive manufacturing (AM) process of extrusion with lightweight concrete, mono-material but multi-functional elements with an internal cellular structure can be created to achieve good thermal performance of a wall at low resource consumption. The aim of this paper is to analyze and optimize the actual thermal performance of such a component. A sensitivity analysis and a parametric optimization were conducted based on a mathematical description of heat transfer in cellular structures. To investigate the thermal performance, 2D and 3D heat transfer simulations were used and validated by heat flux measurements on an existing prototype. A geometric optimization led to a further reduction of the U-value by up to 24%, reaching 0.58 W/m2 K. The ratio of solid material to air inside the cells (relative density) was identified as the main driver, in addition to cell diameter, cell height, and cell wall thickness. The comparison of analytical and numerical results showed high correspondence with deviations of 3–10%, and for the experimental results 25%. These remaining deviations can be traced back to simplifications of the theoretical models and discrepancies between as designed and as built. The presented approach provides a good basis for optimizing the thermal design of complex AM components by investigating practical thermal problems with the help of 2D and 3D simulations, and thus offers a great potential for further applications. [ABSTRACT FROM AUTHOR]

Additive manufacturing is an advanced technology used to fabricate complex geometries with unique properties like cellular structures which accommodate repeated unit cells located in the x, y and z direction. These structures can be used as infill patterns due to their self-supporting structure. Among the cellular structures, Triply Periodic Minimal Surface (TPMS) structures such as Gyroid, Diamond and Schwarz Primitive (SchwarzP) structures can be tailored to produce complex structures for various applications like tissue engineering scaffolds and replace the conventional polymeric foams. TPMS structures are designed and manufactured by using the Fused Deposition Modelling (FDM) technique using Poly-Lactic Acid (PLA) as material. Among TPMS structures, Gyroid is having a unique property like structurally symmetric which design was modified to enhance the mechanical properties. The modified Gyroid or deformed Gyroid undergone a quasi-static compression test and compare the results with Diamond and SchwarzP structures. Porosity and permeability coefficients are evaluated and an optical microscope is used to verify the fabricated components. As well as, Failure patterns of the structures were evaluated and energy absorption capabilities determined. The main objective of this paper is to evaluate the impact of design and porosity on the mechanical and morphological properties of TPMS structures. In conclusion, the deformed Gyroid has more energy absorption capability up to the 11.6% strain than other TPMS structures. After 11.6% of strain, SchwarzP structure dominates. [ABSTRACT FROM AUTHOR]

In this paper, the physical and mechanical properties of products with the geometry of a triply periodic minimal energy surfaces (TPMES) are studied by computer simulation. The calculations are performed by the FEN method (hyperelastic viscoplastic fracture with a finite deformation) for typical samples of polyamide-12 material obtained by selective laser sintering (SLS). As a result of the study using the Comsol Multiphysics program, the distribution of mechanical stresses and the appearance of deformed products at various values of the applied mechanical stress, as well as the deformation curves, were obtained. The convergence of the calculations on the mesh size of the model under study is shown. The simulation results are in close agreement with the experimental data. As a result of the study, excellent physical and mechanical characteristics of the samples with the proposed geometry are found. [ABSTRACT FROM AUTHOR]

A constant development of agricultural activities is linked inherently to generation of significant amount of chemically aggressive organic wastes. This paper outlines a synergistic opportunity for industrial metalworking and plastic wastes recovery and re-use, with clear final product - composite steel-polymer material. Experimentally obtained composite polypropyleneperforated steel material is characterized by structural strength and stiffness provided by perforated steel tapes, and corrosion resistance assured by polypropylene layers, which protect steel from aggressive environment. Authors suppose that waste-based composite material could be applied for certain agricultural constructions, and namely, for boundary construction of farm animal feed lines and storage facilities for organic wastes and minerals. [ABSTRACT FROM AUTHOR]

A review of the fatigue and fracture behaviour of cellular structures with consideration of their fabrication and characterization is presented in this paper. The review is focused on some typical and often used cellular structures, which are divided into three main groups: (1) pre designed regular cellular structures, (2) irregular cellular structures, (3) composites with cellular cores. For each group, the current manufacturing technique is presented for producing the particular cellular structure belonging this group. Furthermore, the state-of-the-art of the fatigue behaviour is explained for the analysed cellular structures. Based on the findings in this review, it can be concluded that cellular structures show a huge potential to become important light-weight structural materials of the future with further development of additive manufacturing technologies, or with introduction of some new, more cost effective manufacturing techniques. However, the knowledge of the fatigue behaviour of these structures is poor, and should be the subject of the further investigations. [ABSTRACT FROM AUTHOR]

The immense design freedom offered by additive manufacturing yields tremendous benefits, but it also raises the question of how to best go about designing components to exploit this design freedom. In early design phases, design tools need to utilize this freedom, but do so with low computational cost and with a good estimate of the final weight to correctly assess the part's influence on the overall product design. This is especially important for aerospace designs. In this paper, a design methodology is devised for cellular structures to be manufactured using additive manufacturing techniques, specifically for such early design phases. This design methodology uses adaptive meshing techniques to design the topology of the cellular structure, after which the struts of that cellular structure are optimized separately to reduce the dimensionality of the problem. The method is demonstrated for a small generic bracket and an aircraft bracket design from the literature. For these problems, our method is fast enough to evaluate many thousands of design options. This results in identifying promising candidate designs for further detailed design work. [ABSTRACT FROM AUTHOR]

This paper proposes a novel multiscale concurrent topology optimization for cellular structures with continuously varying microstructures in space to obtain a superior structural performance at an affordable computation cost. At microscale, multiple prototype microstructures are topologically optimized to represent all the microstructures within macrostructure by incorporating a numerical homogenization approach into a parametric level set method (PLSM), whose connectivity is guaranteed by a kinematical connective constraint approach. A shape interpolation technology is developed to map these optimized prototype microstructures and generate a series of nonuniform microstructures, which are considered as sample points and used to construct a kriging metamodel. The built kriging metamodel is then employed to predict the effective properties of all the nonuniform microstructures within macrostructure. At macroscale, the variable thickness sheet (VTS) method is employed to generate an overall free material distribution patterns using the predicted effective properties of all the nonuniform microstructures. With the help of shape interpolation technology, all the nonuniform microstructures within macrostructure are well connected with each other due to the similar topological features at their interfaces. Using the proposed method, the macrostructural topology as well as the locations and configurations of the spatially varying nonuniform microstructures can be simultaneously optimized to ensure a sufficiently large multiscale design space. Numerical examples are provided to demonstrate the validity and advantages of the proposed method. [ABSTRACT FROM AUTHOR]

Interest in lightweight geometries and cellular structures has increased due to the freeform capabilities of additive manufacturing technologies. In this paper, six different cellular structures were designed and parameterised with three design variables to carry out the lightweight optimisation of an initial solid sample. According to the limitations of conventional computer-aided design (CAD) software, a new parametric optimisation method was implemented and used to optimise these six types of structures. The best one in terms of optimisation time and stiffness was parameterised with nine design variables, changing the dimensions of the internal cellular structure and the reinforcement zones. These seven optimised geometries were manufactured in a Phenix ProX200 selective laser melting machine without using support. The samples obtained were tested under flexural load. The results show that the cubic cell structures have some advantages in terms of CAD definition, parameterisation and optimisation time because of their simpler geometry. However, from the flexural test results it can be concluded that this type of cell structure and those with horizontal bars experience a loss of stiffness compared to the estimates of the finite element analysis because of imperfections in the manufacturing process of hanging structures. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • This paper presents a novel multiscale concurrent topology optimization method. • The optimized macrostructure is composed of various types of microstructures. • An ordered SIMP model is employed to generate a macrostructural topology. • Macrostructure, microstructures and their distributions are simultaneously optimized. Abstract This paper presents a novel multiscale concurrent topology optimization method for cellular structures with various types of microstructures to obtain a superior structural performance at an affordable computation cost. At macroscale, different microstructures are regarded as different materials in a multi-material topology optimization. An ordered solid isotropic material with penalization (SIMP) interpolation model, which is efficient for solving multi-material topology optimization problems without introducing any new variables, is employed to generate an overall structure layout with predetermined multiple materials. At microscale, each macroscale element is viewed as an individual microstructure. All macroscale elements with the same material are represented by a unique microstructure. A parametric level set method (PLSM) is applied to evolve the shape and topology of the representative microstructures, whose effective properties are evaluated by a numerical homogenization method. The connectivity of adjacent microstructures is guaranteed by a kinematical connective constraint. Using the proposed method, the macrostructural topology as well as the locations and configurations of microstructures can be simultaneously optimized. Numerical examples are provided to test the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Thin-walled tubes have long been used as energy absorbing structures, owing to their high specific energy absorption (SEA) capacity. But, they are associated with substantial high values of peak crush force (PCF). A high PCF results in a high deceleration pulse on the critical components and/or the passengers. This poses serious safety concerns. Even the use of triggers and grooves do not reduce the PCF considerably. To achieve improvement on the safety aspect, the research on the crashworthiness of the cellular truss structures was conducted in this paper. Finite element simulation model was developed by using ABAQUS/Explicit software and validated experimentally with structures fabricated through additive manufacturing. The truss structures were compared to the thin-walled tubes on the basis of their mass, SEA and PCF values. For an equal amount of energy absorption, while the truss structures had a higher mass, the PCFs were lowered significantly. The PCFs decreased at a rate 1.5 to 4.5 times faster than the corresponding decrease in SEAs. The example of the crash box showed that the drop in PCF due to the use of truss structure resulted in a reduction of around 5g deceleration at the cost of 1 kg of additional mass. [ABSTRACT FROM AUTHOR]

In this paper, a novel three-dimensional (3D) cellular structure with negative Poisson's ratio was designed by alternating cuboid surface indents on the vertical ribs of the unit cells. The Poisson's ratio and Young's modulus of structures with different geometric parameters were determined using the finite element method (FEM) as a function of these parameters. Samples with identical geometric variables were fabricated via 3D printing, and their through-thickness direction Poisson's ratios were measured and compared with simulation results. Results showed that the Poisson's ratio of the 3D cellular structures can be tuned from positive to negative and can reach a minimal value of −0.958. Good agreement was found between the experimental results and the simulation. This lattice structure is considerably stiffer than re-entrant negative Poisson's ratio foam with the same solid phase. The design concept developed here can be optimized for specific applications via geometric parameters manipulation. [ABSTRACT FROM AUTHOR]

The study of cellular structures and their properties represents big potential for their future applications in real practice. The article aims to study the effect of input parameters on the quality and manufacturability of cellular samples 3D-printed from Nylon 12 CF in synergy with testing their bending behavior. Three types of structures (Schwarz Diamond, Shoen Gyroid, and Schwarz Primitive) were selected for investigation that were made via the fused deposition modeling technique. As part of the research focused on the settings of input parameters in terms of the quality and manufacturability of the samples, input parameters such as volume fraction, temperature of the working space, filament feeding method and positioning of the sample on the printing pad were specified for the combination of the used material and 3D printer. During the experimental investigation of the bending properties of the samples, a three-point bending test was performed. The dependences of force on deflection were mathematically described and the amount of absorbed energy and ductility were evaluated. The results show that among the investigated structures, the Schwarz Diamond structure appears to be the most suitable for bending stress applications. [ABSTRACT FROM AUTHOR]