Lightweight Cellular Structures Research Articles

Fabrication of Cellular Composite Structures with Continuous Fiber Reinforcement and Different Infill Patterns Using Fused Filament Fabrication

Additive manufacturing (AM), also known as 3D printing, is a process of creating three-dimensional objects with complex geometries that is utilized in various engineering applications. Continuous carbon fiber (CCF) is a high-performance material that offers a range of benefits in terms of strength, weight, and durability. Fused filament fabrication (FFF) is a type of AM that uses a thermoplastic filament as a material with which to create a three-dimensional object, and it has been widely used in various applications, as it enables the faster, cheaper, and more customizable production of parts and products. Lightweight cellular composite structures consists of small, repeating unit cells that are interconnected to form a larger structure, and they are employed in high engineering applications. In this study, cellular composite structures were fabricated using FFF technology, considering two types of infill paths design (grid and triangular) manufactured at three infill density levels (20%, 40%, and 60%). After the fabrication process, tensile and flexural properties were experimentally investigated, and the influence of the infill pattern and density on the cellular composite parts were studied. The achieved results demonstrated that the infill design pattern and its density had great influence on the mechanical properties of the cellular structure. The obtained results also showed that the lightweight cellular composite parts had great potential for use in structural applications.

3D auxetic cementitious-polymeric composite structure with compressive strain-hardening behavior

A composite can have properties much better than the components it is made of. This work proposes a three-dimensional auxetic cementitious-polymeric composite structure (3D-ACPC) which incorporates 3D printed polymeric shell with cementitious mortar. Uniaxial compression experiments are performed on the 3D-ACPC to study their quasi-static stress-strain response. Experimental results show that the created composite structure can simultaneously overcome the brittleness of conventional cementitious material and the low compressive strength of 3D printed polymeric cellular shell. Therefore, the 3D-ACPC exhibit compressive strain-hardening behavior ensuring high energy absorption ability. In addition, it is found that structural anisotropy and the shell printing direction have significant impact on the stress-strain response of the 3D-ACPC. Moreover, due to the lightweight cellular structure, the 3D-ACPC shows significantly enhanced specific energy absorption compared to conventional cementitious materials and polymeric cellular materials. To this end, the developed 3D-ACPC has great potential to be used in engineering practice, such as protective structures.

Quasi-static compressive performance of 3D printed polymer composite cellular cubic structures-An experimental study

Light weight cellular structures have gained extensive attention in the impact energy absorption applications owing to their superior specific strength and excellent crashworthiness characteristics. The main objective of the present research work is to utilize this benefit to tailor and to improve the structural design and material type of cellular structures for crashworthiness applications. Cubic structures with four different types of design patterns such as concave, convex, hyperbola, and hexagon were proposed and fabricated through three-dimensional (3D) printing technique. Four polymeric filament materials such as Poly lactic acid (PLA), Acrylonitrile butadiene styrene (ABS), PLA mixed carbon fiber (PLA/CF), and Polyethylene terephthalate glycol (PETG), mixed carbon fiber (PETG/CF) were utilized. Accordingly, the compression tests were performed on the fabricated cellular cubic structures under quasi-static loading to examine the effect of design pattern, and material types on the compressive behavior and energy absorbing characteristics. The results revealed that the convex design pattern of 3D printed PETG/CF cubic structure showed the significant energy absorbing characteristics compared to the other three design patterns. It is emphasized that the proposed 3D printed cubic cellular structures have great prospective to substitute the traditional energy absorbing structures in automotive vehicles and high speed trains.

Bio-inspired-based structures optimization for additive manufacturing using metaheuristic Kriging

Lightweight cellular structures are investigated intensively in additive manufacturing and require optimization strategies to distribute both patterns, cross-sections sizes and type, and even materials. There exist several parametric optimization techniques that permit not only obtaining lightweight structures but also ensuring maintaining the rigidity. Among these techniques, design of experiments is time-consuming, and the values of the optimal parameters are estimated based on their possible range rather than being determined precisely. An original scientific strategy is to use the Kriging swarm optimization technique to achieve the global optimum using a minimal amount of computer simulations. Therefore, the objective of this paper is to determine the optimal cross-sections of structures using bio-inspired “L-systems”. These L-systems-based structures were created and distributed along the directions of the principal stress lines (PSLs), then mimicking material growth and distribution inside biological structures. Two PSLs directions were separately investigated for each load case; the first direction is used as a guide for the growth of L-systems and the second one serves for branch extensions and limitations. To do so, a metamodel is used upon particle swarm optimization technique (PSO) and several case studies are conducted to improve the stiffness-to-weight ratio while respecting the additive manufacturability.

3D-printing of ceramic filaments with ductile metallic cores

The additive manufacturing of composite structures can open possibilities in the design and fabrication of devices but also demands new approaches. In this work, we use thermally reversible pastes to fabricate ceramic matrix (Al2O3) composites reinforced with continuous metallic fibres (steel). The approach is based on the micro-extrusion of ceramic–metal filaments with core–shell and layered arrangements. These filaments are employed in the additive manufacturing of dense and light-weight cellular structures that combine the stiffness and strength of the ceramic shell with the fracture resistance and energy absorption capabilities provided by the metal core. The approach can be used to extrude filaments with thin porous interlayers separating the core and the shells to create a weak fibre/matrix interphase. The cellular structures fabricated with these filaments exhibit higher compressive strengths and energy absorption capabilities than those fabricated from pure ceramics. The works of fracture of the dense composites are one to two orders of magnitude above those of the ceramic matrix (103 J/m2) while the bending strengths remain comparable to those of 3D printed alumina (200–350 MPa). The technique could be easily extended to other material combinations opening new opportunities in the additive manufacturing of multi-material parts and devices.

Mechanical performance of fractal-like cementitious lightweight cellular structures: Numerical investigations

Cellular structures with tunable mechanical properties are promising lightweight structures for prefabricated construction. In this study, a 3D fractal structure named Menger-Sponge (MS) cube is analysed. Besides, six other alternative fractal-like structures are designed with respect to different shapes of their associated hollow sections. Finite element method (FEM) is employed to predict the structure's mechanical behaviours under a uniaxial compression load. The numerical model is validated by experimental results obtained from author's previous publication. Comparisons are made between triply periodic minimal surface (TPMS-Primitive) and the second-order MS cementitious structure, and also among other fractal structures with different hierarchies. Results indicate that the MS and Primitive blocks have similar mechanical responses. The fractal-square (FS) structures exhibit better structural performances, especially for the first and second fractal orders. Overall, this numerical investigation shows the effect of the shaped holes and thinnest cross-section area on the hierarchically porous structure.

Modeling and analysis of material anisotropy-topology effects of 3D cellular structures fabricated by powder bed fusion additive manufacturing

For lightweight cellular structures fabricated via powder bed fusion additive manufacturing (PBF-AM), both the material anisotropy and the cellular topology design are both important design factors. In this work, a direct stiffness matrix-based analytical modeling approach was employed for the evaluation of material anisotropy-topology effects on three representative 3D cellular structures (auxetic, BCC and octahedral). The established models were verified via experimentation with samples fabricated by EB-PBF using Ti6Al4V as material, using the material anisotropy information established experimentally using single struts with different build orientations (0°, 15°, 30°, 45°, 60°, 75° and 90°). The predicted mechanical properties of the Ti6Al4V cellular structures showed good agreement with experimental results. It was shown that both the strength and elastic modulus anisotropy of the materials affect the strength of the cellular structures, which must be determined based on the topology design. In addition, the material anisotropy-topology effects on cellular structures of varying cellular pattern sizes were also investigated in order to quantify the pattern size effects. It was found that the pattern size effects and the material anisotropy effects can be decoupled during the design of the mechanical properties of these cellular structures.

Compression behavior and energy absorption of 3D printed continuous fiber reinforced composite honeycomb structures with shape memory effects

Three-dimensional (3D) printing is a potential rapid prototyping process that may replace traditional manufacturing processes to fabricate lightweight cellular structures with superior energy absorption performance. In the present work, continuous fiber reinforced composite honeycomb structures (CFRCHSs) with excellent shape memory properties were manufactured through a fused filament fabrication (FFF) technology, and their out-of-plane/in-plane compression behaviors and energy absorption characteristics were experimentally investigated. The results reveal that the failure process of the 3D printed CFRCHSs under in-plane loading is that the honeycomb cells collapse layer by layer along the loading direction，accompanied by the formation of a localized band. The crashworthiness analysis indicates that the 3D printed CFRCHSs outperform several competitive cellular topologies in the compression strength and specific energy absorption. A simplified analytical model for the in-plane compression strength of CFRCHSs was derived, and good agreement between measurements and predictions was observed. Additionally, the shape recovery tests demonstrate that the 3D printed CFRCHSs possess the potential as key elements of lightweight intelligent systems and adjustable energy absorbing devices.

Structural Performance Analysis of a Novel Pyramidal Cellular Core Obtained through a Mechanical Expansion Process.

Stiff and strong yet lightweight cellular structures have become widely designed and used as cores for the construction of sandwich panels to reach high stiffness and strength to weight ratios. A low-density pyramidal cellular core has been proposed for investigation in this work. The novel core is manufactured from stainless steel sheet type 304 through a mechanical expansion procedure which is described in detail. The out-of-plane stiffness and strength performance is estimated by an analytical model which is successfully validated through experimental tests. A comparative study with other existing cellular core configurations made from other materials indicates an average performance behavior for the investigated structure. However, potential for a further structural performance increase is observed and discussed

Characterisation and modeling of additively-manufactured polymeric hybrid lattice structures for energy absorption

Lightweight cellular materials and structures are widely used in load-bearing and energy absorption applications, because of favorable mechanical properties such as high compressibility and low relative density. Recent progress in additive manufacturing techniques has enabled specific architectural geometries of unit cells in cellular structures to be tailored for particular needs. Numerous metallic and polymeric cellular lattices comprising different unit cell topologies have been manufactured and examined in terms of their energy absorption performance. In this study, two designs of hybrid three-dimensional cubic lattices which combine the advantages of an octet and a bending-dominated structure were established, and fabricated via the Fused Deposition Modeling technique. To validate the energy absorption capability of these new hybrid lattices, quasi-static uniaxial compression tests were conducted on samples made from Polylactic Acid. Numerical simulations were also performed to facilitate analysis of the deformation modes of the specimens tested in experiments. Tensile tests on solid dog-bone samples printed at various angles with respect to the build plate reveal fabrication-angle-dependent anisotropy. Consequently, material properties that depend on cell strut inclination were incorporated into the simulations. Compared with a conventional octet that possesses a high stiffness but a fluctuating post-yield response, the experimental results show that the new designs are capable of producing a relatively stable post-yield stress plateau without sacrificing stiffness and strength significantly. The present study indicates the potential for further enhancement of the energy absorption performance of lattice structures by tuning their topological architectures appropriately.

Nature-Inspired Cellular Structure Design for Electric Vehicle Battery Compartment: Application to Crashworthiness

This paper discusses the potential of using lightweight nature-inspired cellular structured designs as energy absorbers in crashworthiness applications for electric vehicles (EV). As EVs are becoming popular with their increased battery capacity, these lightweight cellular structures have regained research interest as they may increase mileage by reducing vehicle mass in addition to protecting the battery during collisions. In this paper, a novel lightweight cellular structure for EV battery protection and crashworthiness is designed and simulated. In designing the cellular structure, four different ways of applying the shell thickness have been considered that affects the collapse behavior and the crashworthiness. A numerical study was conducted on 45 samples with varying length, shell thicknesses, and thickness application methods. Four types of shell thickness application methods were investigated: Uniform thickness, strut-wall thickness, gradient thickness, and alternate thickness. Force-displacement curves, energy absorption, specific energy absorption, and collapse behaviors are some of the metrics used for evaluating the crashworthiness of the structures. Shell thickness is found to affect both the collapse behavior and energy absorption capabilities. Energy absorption results are similar to other studies on designed cellular structures. The highest performing cellular structure is reported to have a specific energy absorption of 35kJ/kg, which is comparable to cellular structures reported in the literature.

Bioinspired cellular cementitious structures for prefabricated construction: Hybrid design & performance evaluations

Lightweight cellular structures with porous architectures and controllable mechanical characteristics are promising candidates for a broad range of prefabricated engineering applications. A triply periodic minimal surface (TPMS) structure that is a naturally inspired continuous non-self-intersecting surface is a bioinspired cellular structure. In this work, we investigate a novel approach based on a combination of primitive-TPMS cells and cubic blocks along with lattice and gyroid-TPMS cells achieving 50% volume fraction cellular structures. Lightweight cellular specimens made of cement mortar with 3D printed sacrificial thermoplastic Polylactic Acid (PLA) moulds are subjected to uniaxial compressive loadings. Compression tests are carried out on the cement cubes, while tensile behaviours follow the simplified damage plasticity model, which is used to obtain the material properties for the input model data. Finite element (FE) analysis is employed to predict mechanical performances such as stress distributions, stress-strain curves, and the damage mechanisms of three representative cellular structures (primitive, lattice, and gyroid). Compressive experiment tests are conducted on these blocks and validated by the FE model. Results indicate that the mechanical responses of the cellular structure, wherein primitive cellular structures yield the highest compressive strength, could be predicted accurately through the FE analysis, and outcomes from both numerical models and experimental tests are validated.

Pin on disc vizsgálatok zártcellás alumíniumhabokon

Metal foams have a lightweight cellular structure with excellent mechanical and physical properties and are at the forefront of materials development for the automotive and other industries. Although metal foams are popular, they are still not sufficiently characterized thanks to their extremely complex structure. The aim of the research is the tribological investigation of closed cell metal foams with different production technologies and different cell sizes. The paper introduces the closed cell aluminium foams produced by direct foaming and gas injection and those raw materials. The Pin on Disc instrument and the most important parameters of the experiments are also presented.

Graphene-based 3D lightweight cellular structures: Synthesis and applications

Ultralight three-dimensional (3D) cellular architectures are both a challenge and an opportunity for those academic and industrial applications involved with high performance material design. The challenges have been accessed by employing a variety of materials. Accordingly, graphene has shown greatest potential by virtue of its unique chemical, thermal, electronic, and mechanical properties for applications ranging from structural materials to energy storage/conversion devices. In this review, we highlight recent efforts and advances made in the implementation of graphene-based 3D cellular architectures, especially focusing on the ultralight density region (<10 mg·cm−3). First, we reviewed the synthetic approaches for generating graphene-based 3D lightweight cellular structures according to the criteria of closed-cellular structures (CCSs) or open-cellular structures (OCSs) whether cell faces between constituent unit cells exist or not, respectively. These structural differences could lead to discerning physical properties, such as in mass transport across pores, heat/electron transfer through graphene framework, and various modes in mechanical deformation. We then collectively introduce recent achievements for representative applications utilizing different types of cellular structures such as flexible electronics, energy storage/conversion systems, fluid absorption, mechanical dampers, and sensors. Finally, we highlight the future perspectives of graphene-based lightweight cellular structures to surpass existing technological challenges.

Experimental study and modeling of melt pool in laser powder-bed fusion of thin walls

Laser powder-bed fusion (L-PBF) is promising for manufacturing of lightweight cellular structures. A thin wall is the key element of such structures. Heat and mass transfer in the melt pool formed on the top of a thin wall is essentially two-dimensional. That is why L-PBF process parameters adapted for thin walls strongly differ from those necessary for bulk material. In the present work, a high speed camera records a side view of the melt pool formed on the top of a thin metallic wall due to a laser beam scanning along the wall edge. The melt pool profile and the position of the keyhole are observed. The results are compared with a two-dimensional model of coupled heat conduction and Marangoni convection in the laser-interaction zone. In the studied conditions, the best agreement between the experiment and the modeling implies that a keyhole is formed with the depth comparable with that of the melt pool.

Numerical and experimental investigations on the mechanical properties of cellular structures with open Kelvin cells

In this article, the response of lightweight cellular structures with open cells is investigated through finite element analysis and mechanical testing in compression. The structures consist of tessellations of Kelvin cells (tetrakaidecahedron), which were designed having three parameters that determine their relative density: strut thickness, strut length and fillet radius. The aim of the study is to determine the optimal configuration in terms of the stiffness and the strength of the structures and to validate the results of the numerical analyses with experimental procedures.

Quality control of closed-cell metal foam produced by direct foaming

Metal foams have a lightweight cellular structure with excellent mechanical and physical properties. Although metal foams are popular, they are still not sufficiently characterized thanks to their extremely complex structure which is highly stochastic in nature. In this paper the influence of the technological parameters on the structure is analyzed. In laboratorial circumstances the production of closed cell aluminum foams depends on several factor. The purpose of the paper is to analyze the human factor on the quality of the metal foam specimens.

Dynamic responses and energy absorption of hollow sphere structure subjected to blast loading

Closed-cell and open-cell hollow spheres were designed to develop lightweight cellular structures with excellent blast resistance, and the mechanical response of the hollow sphere structure (HSS) under blast loading was investigated numerically using ANSYS®/LS-DYNA®17.0. In this paper, the blast wave pressure decay rate was served as the main index of blast resistance while areal specific energy absorption and frame deformation were used as auxiliary indexes. The results indicated that the weight of HSS was reduced by 37.7%–69.8% compared to solid structures with the same physical size, and the blast resistance of HSS was significantly affected by the hollow sphere diameter and wall thickness, frame length and width, opening size and opening density. Closed-cell HSS with smaller hollow sphere diameters and thicker wall, or smaller frame lengths and widths would achieve the optimal blast resistance. Meanwhile, the blast resistance of HSS could be improved by adopting a smaller opening size, but the effect of opening density did not follow any rule, which was affected by the number and position of openings. Comprehensively, the blast resistance of HSS was enhanced when there was opening only at the face blast surface rather than at both the face blast surface and back blast surface.

Design and Optimization of Graded Cellular Structures With Triply Periodic Level Surface-Based Topological Shapes

Periodic cellular structures with excellent mechanical properties widely exist in nature. A generative design and optimization method for triply periodic level surface (TPLS)-based functionally graded cellular structures is developed in this work. In the proposed method, by controlling the density distribution, the designed TPLS-based cellular structures can achieve better structural or thermal performances without increasing its weight. The proposed technique can be divided into four steps. First, the modified 3D implicit functions of the triply periodic minimal surfaces are developed to design different types of cellular structures parametrically and generate spatially graded cellular structures. Second, the numerical homogenization method is employed to calculate the elastic tensor and the thermal conductivity tensor of the cellular structures with different densities. Third, the optimal relative density distribution of the object is computed by the scaling laws of the TPLS-based cellular structures added optimization algorithm. Finally, the relative density of the numerical results of structure optimization is mapped into the modified parametric 3D implicit functions, which generates an optimum lightweight cellular structure. The optimized results are validated subjected to different design specifications. The effectiveness and robustness of the obtained structures is analyzed through finite element analysis and experiments. The results show that the functional gradient cellular structure is much stiffer and has better heat conductivity than the uniform cellular structure.

Topology optimization for lightweight cellular material and structure simultaneously by combining SIMP with BESO

This paper presents a hybrid algorithm for topology optimization of lightweight cellular materials and structures simultaneously by combining solid isotropic material with penalization (SIMP) and bi-directional evolutionary structural optimization (BESO). Microstructure of the lightweight cellular material is assumed unique in the structure to make the proposed method feasible. A new sensitivity analysis formula with respect to the discrete variable is derived by a principal submatrix stiffness matrix, by which the material can be effectively removed from or added to cellular. Moreover, the validity of the proposed method is then demonstrated through two numerical examples (a simple supported beam and a cantilever beam), which can be easily applied in a variety of practical situations.