Flexural Properties of Periodic Lattice Structured Lightweight Cantilever Beams Fabricated Using Additive Manufacturing: Experimental and Finite Element Methods

Zhang C., Zheng H., Yang L., Li Y., Jin J., Cao W., Yan C., Shi Y.

• The additive manufacturability of TPMS structures is investigated. • Defects can be eliminated by the gradient design and higher volume fraction. • Continuously graded TPMS structure show unique layer-by-layer deformation behavior. • The collapse model of TMPS structures affects the energy absorption. • Finite element method can predict the stress distribution and mechanical properties. Owing to their lightweight design, high energy absorption capacity, and excellent thermal and sound insulation properties, lattice structures have many potential applications in the fields of security, aerospace, biomedicine, and heat dissipation. In this study, a gyroid-type triply periodic minimal surface is used to design lattice structures. Gyroid uniform lattice structures and gyroid graded lattice structures are mathematically designed and fabricated using selective laser melting with a SS 316 L stainless steel powder. The mechanical properties of these structures are studied under a compression load, and the deformation differences between the graded and uniform structures are compared. The finite element method is used to simulate the compression process, and the experimental and simulation results are qualitatively compared. Results show that during plastic deformation, the stress change in the graded structure is larger than that in the uniform structure. By controlling the volume fraction, mechanical properties can be specifically tailored, which provides the design guidelines for the application of this structure.

Ali M., Nazir A., Jeng J.

The mechanical properties such as energy absorption, crushing behavior, and strength-to-weight ratio of graded density structures are significantly better when compared with uniform density counterparts. Graded density structures have been widely investigated due to recent developments in additive manufacturing (AM) technology, which can easily manufacture complex geometries. The study explores the significance of variable-dimension helical spring (VDS) to be used in shoe midsole to improve the stiffness, energy absorption, and energy return. Two novel shoe midsoles are designed using the variable-dimension helical springs and their performance was compared with a third shoe midsole designed using uniform-dimension helical spring (UDS). Variable-dimension shoe midsoles were designed according to the actual pressure distribution applied by the human foot on the midsole. The Multijet fusion AM process was employed for the fabrication of all shoe midsole samples. It is revealed that despite the same mass and bounding box, variable-dimension midsoles have significantly improved mechanical properties compared to uniform-dimension midsole. It is found that the VDS midsole has sixfolds higher force-bearing capacity, and has a lower permanent material setting phenomena when compared to UDS midsole. Moreover, a higher (45%) distortion was found in the UDS midsole after the loading-unloading experiment when compared to the VDS midsole (24%) distortion. A further comparison of the VDS midsole was carried out with the commercially available wave spring-based midsole. Despite about 2-fold higher weight of the wave spring–based midsole, the VDS polymer midsole has higher mechanical properties found in terms of flexibility and force-bearing capacity. Finally, it is concluded that the VDS structure of the midsole can enhance the mechanical properties such as force-bearing capacity, flexibility, and stability with a higher strength-to-weight ratio. This study also proves the feasibility of design and AM of customer-specific shoe midsole.

Zaharia S.M., Enescu L.A., Pop M.A.

Material Extrusion-Based Additive Manufacturing Process (ME-AMP) via Fused Filament Fabrication (FFF) offers a higher geometric flexibility than conventional technologies to fabricate thermoplastic lightweight sandwich structures. This study used polylactic acid/polyhydroxyalkanoate (PLA/PHA) biodegradable material and a 3D printer to manufacture lightweight sandwich structures with honeycomb, diamond-celled and corrugated core shapes as a single part. In this paper, compression, three-point bending and tensile tests were performed to evaluate the performance of lightweight sandwich structures with different core topologies. In addition, the main failure modes of the sandwich structures subjected to mechanical tests were evaluated. The main failure modes that were observed from mechanical tests of the sandwich structure were the following: face yielding, face wrinkling, core/skin debonding. Elasto-plastic finite element analysis allowed predicting the global behavior of the structure and stressing distribution in the elements of lightweight sandwich structures. The comparison between the results of bending experiments and finite element analyses indicated acceptable similarity in terms of failure behavior and force reactions. Finally, the three honeycomb, diamond-celled and corrugated core typologies were used in the leading edge of the wing and were impact tested and the results created favorable premises for using such structures on aircraft models and helicopter blade structures.

Malahias M., Kostretzis L., Greenberg A., Nikolaou V.S., Atrey A., Sculco P.K.

Background A number of papers have been published reporting on the clinical performance of highly porous coated titanium acetabular cups in primary and revision total hip arthroplasty (THA). However, no systematic review of the literature has been published to date. Methods The US National Library of Medicine (PubMed/MEDLINE), Embase, and the Cochrane Database of Systematic Reviews were queried for publications utilizing the following keywords: “tritanium” OR “highly-porous” AND “titanium” OR “acetabular” AND “trabecular” AND “titanium”. Results Overall, 16 studies were included in this review (11,366 cases; 60% females, 2-7 years mean follow-up). The overall survival rate of highly porous titanium acetabular components in primary cases was 99.3% (10,811 of 10,886 cases), whereas the rate of aseptic loosening was 0.1%. The overall survival rate of the highly porous titanium acetabular components in revision THA cases was 93.5% (449 of 480 cases), whereas the rate of aseptic loosening was 2.1%. Conclusion There was moderate quality evidence to show that the use of highly porous titanium acetabular components in primary and revision THA cases is associated with satisfactory clinical outcomes in the short- and medium-term, without showing any evidence of cup migration or radiolucency. Taking into consideration that there is no evidence yet regarding the long-term survivorship of these components, we feel that further research of higher quality is required to generate more evidence-based conclusions regarding the longevity of highly porous titanium acetabular implants compared with conventional titanium counterparts.

Abate K.M., Nazir A., Chen J., Jeng J.

Cellular materials with very highly regulated micro-architectures are promising applicant materials for orthopedic medical uses while requiring implants or substituting for bone due to their ability to promote increased cell proliferation and osseointegration. This study focuses on the design of an acetabular cup (AC) cellular implant which was built using a vintiles cellular structure with an internal porosity of 56–87.9% and internal pore dimensions in the range of 600–1200 μm. The AC implant was then optimized for improving mechanical performance to reduce stress shielding by adjusting the porosity to produce stiffness (elastic modulus) to match with the bone, and allowing for bone cell ingrowth. The optimized and non-optimized AC cellular implant was fabricated using the SLM additive manufacturing process. Simulation (finite element analysis, FEA) was carried out and all cellular implants are finally tested under static loading conditions. The result showed that on the finite element model of an optimized implant, cellular has shown 69% higher stiffness than non-optimized. It has been confirmed by experimental work shown that the optimized cellular implant has a 71% higher ultimate compressive strength than the non-optimized counterpart. Finally, we developed an AC implant with mechanical performance adequately close to that of human bone.

Pelanconi M., Ortona A.

This article reports on a nature-inspired, ultra-lightweight structure designed to optimize rigidity and density under bending loads. The structure’s main features were conceived by observing the scales of the butterflies’ wings. They are made of a triply periodic minimal surface geometry called gyroid and further reinforced on their outer regions with a series of ribs. In this work, the ribs were substituted with carbon fiber-reinforced bars that were connected to the main structure with an innovative concept. Stereolithography was used to print a plastic component in one piece that comprised the core and the connection system. Bending tests were performed on the structures along with a Finite Element Method optimization campaign to achieve the optimum performance in terms of stiffness and density. Results show that these architectures are among the most effective mechanical solutions in respect to their weight because of their particular arrangement of material in space.

Nazir A., Abate K.M., Kumar A., Jeng J.

Cellular structures are made up of an interconnected network of plates, struts, or small unit cells and acquire many unique benefits such as, high strength-to-weight ratio, excellent energy absorption, and minimizing material requirements. When compared with the complicated conventional processes, additive manufacturing (AM) technology is capable of fabricating geometries in almost all types of shapes, even with the small cellular structures inside, by adding material layer-by-layer directly from the digital data file. All major industries have been exploiting the benefits of cellular structures due to their prevalence over a wide range of research fields. To date, there are a few state-of-the-art reviews compiled focusing on a specific area of lattice structures, but many aspects still need to be reviewed. Therefore, this paper aims to provide a comprehensive review of the various lattice morphologies, design, and the AM of the cellular structures. Furthermore, the superior properties of the additively fabricated structure, as well as the applications and challenges, are presented. The conducted review has identified the significant limitations and gaps in the existing literature and has highlighted the areas that need further research in the design, optimization, characteristics, and applications, and the AM of the cellular structures. This review would provide a more precise understanding and the state-of-the-art of AM with the cellular structures for engineers and researchers in both academia and industrial applications.

Azzouz L., Chen Y., Zarrelli M., Pearce J.M., Mitchell L., Ren G., Grasso M.

A full mechanical characterisation of three types of 3-D printed lattice cores was performed to evaluate the feasibility of using additive manufacturing (AM) of lightweight polymer-based sandwich panels for structural applications. Effects of the shape of three selected lattice structures on the compression, shear and bending strength has been experimentally investigated. The specimens tested were manufactured with an open source fused filament fabrication-based 3-D printer. These sandwich structures considered had skins made of polypropylene (PP)-flax bonded to the polylactic acid (PLA) lattice structure core using bi-component epoxy adhesive. The PP-flax and the PLA core structures were tested separately as well as bonded together to evaluate the structural performance as sandwich panels. The compression tests were carried out to assess the in-plane and out of plane stiffness and strength by selecting a representative number of cells. Shear band and plastic hinges were observed during the in-plane tests. The shear and three-point bending tests were performed according to the standard to ensure repeatability. The work has provided an insight into the failure modes of the different shapes, and the force-displacement history curves were linked to the progressive failure mechanisms experienced by the structures. Overall, the results of the three truss-like lattice biopolymer non-stochastic structures investigated have indicated that they are well suited to be used for potential impact applications because of their high-shear and out of the plane compression strength. These results demonstrate the feasibility of AM technology in manufacturing of lightweight polymer-based sandwich panels for potential structural uses.

Bai J., Song J., Wei J.

The solid lubricant MoS 2 was used as the reinforcement filler for the Polyamide12 material for the additive manufacturing process – selective laser sintering. The tribological and mechanical properties of the laser sintered PA12/MoS 2 and PA12 were investigated by the linear reciprocating ball-on-flat wear and impact tests. Results show that by incorporating the MoS 2 filler into the PA12 matrix, the impact properties was improved. The coefficient of friction and wear rate of the laser sintered PA12/MoS 2 were reduced significantly. The worn surface formed in the wear test was shallow and smoother for the PA12/MoS 2 , where only mild wear occurred. The XPS testing suggested the involvement of the mechanical-chemical reaction, which resulted the decomposing of the MoS 2 and the enhancement of the wear properties of the PA12/MoS 2 .

Cheng L., Zhang P., Biyikli E., Bai J., Robbins J., To A.

Purpose The purpose of the paper is to propose a homogenization-based topology optimization method to optimize the design of variable-density cellular structure, in order to achieve lightweight design and overcome some of the manufacturability issues in additive manufacturing. Design/methodology/approach First, homogenization is performed to capture the effective mechanical properties of cellular structures through the scaling law as a function their relative density. Second, the scaling law is used directly in the topology optimization algorithm to compute the optimal density distribution for the part being optimized. Third, a new technique is presented to reconstruct the computer-aided design (CAD) model of the optimal variable-density cellular structure. The proposed method is validated by comparing the results obtained through homogenized model, full-scale simulation and experimentally testing the optimized parts after being additive manufactured. Findings The test examples demonstrate that the homogenization-based method is efficient, accurate and is able to produce manufacturable designs. Originality/value The optimized designs in our examples also show significant increase in stiffness and strength when compared to the original designs with identical overall weight.

Umer R., Barsoum Z., Jishi H., Ushijima K., Cantwell W.

Four all-composite lattice designs were produced using a lost-mould procedure that involved inserting carbon fibre tows through holes in a core. Following resin infusion and curing, samples were heated to melt the core, leaving well-defined lattice structures based on what are termed BCC, BCCz, FCC and F2BCC designs. Analytical and numerical models for predicting the mechanical properties of the four designs are presented and these results are compared with the experimental data from the quasi-static compression tests. Compression tests on the four lattice structures indicated that the F2BCC lattice offered the highest compression strength, although when normalized by relative density, the BCCz lattice structure out-performed other structures. Similarly, the specific compression strengths were found to be superior to those of more traditional core materials. A number of failure mechanisms were also highlighted, including strut buckling, fracture at the strut-skin joints and debonding of reinforcing members at the central nodes. Finally, it is believed that the properties of these lattices can be further increased using higher fibre volume fractions.

Gaillard R., Lustig S., Peltier A., Villa V., Servien E., Neyret P.

Despite excellent long-term outcomes, posterior stabilisation by a third condyle continues to receive unwarranted criticism regarding patellar complications and instability. Complication rates with a tri-condylar posterior-stabilised implant are similar to those with other posterior-stabilised prostheses and have diminished over time due to improvements in prosthesis design. Post-operative complications and revision rates were assessed retrospectively in a prospective cohort of 4189 consecutive patients who had primary total knee arthroplasty (TKA) using a tri-condylar posterior-stabilised implant (Wright-Tornier) and were then followed-up for at least 24 months. The analysis included 2844 knees. The prosthesis generations were HLS1 ® , n = 20; HLS2 ® , n = 220; HLS Evolution ® , n = 636; HLS Noetos ® , n = 1373; and HLS KneeTec ® , n = 595. Complications were compared across generations by applying Fisher's exact test, and survival was compared using the Kaplan-Meier method. At last follow-up, there had been 341 (12%) post-operative complications in 306 (10.8%) knees, including 168 (5.9%) related to the implant, 41 (1.4%) infections, and 132 (4.6%) secondary complications unrelated to the implant. Re-operation was required for 200 complications (7%), including 87 (3.1%) consisting in revision of the prosthesis. Implant-related complications were stiffness ( n = 67, 2.4%), patellar fracture ( n = 34, 1.2%), patellar clunk syndrome ( n = 25, 0.9%), patellar loosening ( n = 3, 0.1%), tibial/femoral loosening ( n = 15, 0.5%), polyethylene wear ( n = 3, 0.1%), and implant rupture ( n = 1, 0.04%). Significant differences across generations were found for stiffness ( P < 0.0001), patellar fracture ( P = 0.03), clunk syndrome ( P = 0.03), and polyethylene wear ( P = 0.004), whose frequencies declined from one generation to the next. Overall 10-year survival was 92% with no significant difference across generations ( P = 0.1). Outcomes of tri-condylar posterior-stabilised TKA are similar to those obtained using other posterior-stabilised implants. Neither patellar complications nor instability are more common, and improvements in implant design have contributed to correct early flaws. IV, historical cohort, retrospective assessment of prospectively collected data.

Wu J., Wang C.C., Zhang X., Westermann R.

Recent work has demonstrated that the interior material layout of a 3D model can be designed to make a fabricated replica satisfy application-specific demands on its physical properties, such as resistance to external loads. A widely used practice to fabricate such models is by layer-based additive manufacturing (AM), which however suffers from the problem of adding and removing interior supporting structures. In this paper, we present a novel method for generating application-specific infill structures on rhombic cells so that the resultant structures can automatically satisfy manufacturing requirements on overhang-angle and wall-thickness. Additional supporting structures can be avoided entirely in our framework. To achieve this, we introduce the usage of an adaptive rhombic grid, which is built from an input surface model. Starting from the initial sparse set of rhombic cells, via numerical optimization techniques an objective function can be improved by adaptively subdividing the rhombic grid and thus adding more walls in cells. We demonstrate the effectiveness of our method for generating interior designs in the applications of improving mechanical stiffness and static stability.

Shidid D., Leary M., Choong P., Brandt M.

Recent advances in medical imaging and manufacturing science have enabled the design and production of complex, patient-specific orthopaedic implants. Additive Manufacture (AM) generates three-dimensional structures layer by layer, and is not subject to the constraints associated with traditional manufacturing methods. AM provides significant opportunities for the design of novel geometries and complex lattice structures with enhanced functional performance. However, the design and manufacture of patient-specific AM implant structures requires unique expertise in handling various optimization platforms. Furthermore, the design process for complex structures is computationally intensive. The primary aim of this research is to enable the just-in-time customisation of AM prosthesis; whereby AM implant design and manufacture be completed within the time constraints of a single surgical procedure, while minimising prosthesis mass and optimising the lattice structure to match the stiffness of the surrounding bone tissue. In this research, a design approach using raw CT scan data is applied to the AM manufacture of femoral prosthesis. Using the proposed just-in-time concept, the mass of the prosthesis was rapidly designed and manufactured while satisfying the associated structural requirements. Compressive testing of lattice structures manufactured using proposed method shows that the load carrying capacity of the resected composite bone can be recovered by up to 85% and the compressive stiffness of the AM prosthesis is statistically indistinguishable from the stiffness of the initial bone.

Alzahrani M., Choi S., Rosen D.W.

Truss-like cellular structures have great potential to be applied in light-weight design applications. However, determining the appropriate designs for these truss-like cellular structures can be a challenging task due to their geometric complexities and prohibitive computational costs in the design process. In this research, a new design method is proposed which can drastically reduce computational costs and design parameters, while maintaining the performance of the targeted outcome. Furthermore, the proposed method facilitates cellular structure designs that can handle multiple loading conditions. The proposed method utilizes the relative density information obtained from a solid topology optimization to automatically determine the diameter of each individual strut in the structure, which collectively represent the set of design variables. This allows the method to produce lattice structures that can perform reliably under multiple loading conditions and also reduce the computational cost associated with the design of these structures. The efficacy of the developed method is compared to existing methods including the size matching and scaling method that combines solid-body analysis and a predefined unit–cell library. • A method for designing lattice structures for multi-loading conditions is proposed. • The method relies on the results of a continuum topology optimization process. • The structures generated by the method show good potential compared to existing methods.

Nazir A.

Lightweighting with adequate mechanical strength is one of the key objectives of Industry 4.0. Replacement of solid parts with cellular lattice structured ones is one of the alternatives to elevate performance and reduce weight, without harming sustainability and carbon neutrality goals. Lattice structured parts possess several loads including tensile as the main type of loading; however, few researchers have studied the tensile response of mechanical metamaterials. This study aims to investigate the structural properties under tensile loading of four different types of mechanical metamaterials (simple cubic, octet, face-centered cubic, and body-centered cubic) fabricated using a selective laser sintering process using polyamide material. X-ray computed tomography was employed to examine the manufacturability of strut-based structures. Effects of relative densities, material distribution, deformation behavior, and fracture of structures on mechanical responses of each structure were evaluated at various relative densities of 40%, 50%, and 60%. Results exhibit that octet and FCC structures possess more elongation at higher relative densities compared to lower relative densities of the same structures. In addition, these structures fractured in a brittle manner at lower (40%) relative densities and this trend changes from brittle to ductile at higher relative density (60%). SC structure performed best (848 N) but the BCC (348 N) is worst at constant relative density (40%); thus, performance is significantly different due to different structure morphologies. The orientation of struts has a significant effect on the tensile loading of lattice structures. The structures having zero inclined struts fractured significantly different manner compared to their counterparts having inclined struts. The octet structure is considered to have a greater amount of elongation in the tensile direction while the SC structure has the highest load-bearing capacity.

Soni N., Renna G., Leo P.

Safdar M.U., Shen X., Saheby E.B.

Vibration characteristics play a crucial role in the overall performance of Low-pressure (LP) turbine blades and different techniques are developed to enhance vibrational response by increasing natural frequencies. The present analysis aims to develop a new technique based on the investigation of improvement in natural frequencies and mass reduction of a topology-optimized blade design through location-based integration of lattice structures inside the blades. FE models are developed for three different lattice locations based on mode shape behavior obtained through modal analysis of two different nickel-based alloys at stressed and unstressed conditions. The results show that the internal BCC lattice at specific locations showed better vibrational characteristics compared to other incorporated lattice structures, and validates the location-based integration scheme for enhancement of natural frequencies and reduced mass in applied conditions. By this method, 5.7% mass reduction was achieved from an already 35% mass-reduced blade along with enhancement in the first and second natural frequencies by 8.2% and 5.9% respectively when unstressed. At stressed condition, the natural frequencies increased by ≈7.7% and ≈6.6%.

Nazir A., Waqar S., ul Haq M.R., Tanveer M.Q.

Jiang H., Liu X., Liu Z., Ren Y.

Kamarian S., Khalvandi A., Heidarizadi E., Saber-Samandari S., Song J.I.

This study pursues two primary objectives concerning sandwich structures with chiral cores. Firstly, it delves into the realm of machine learning-assisted predictions regarding the behavior of these structures under compressive loads. In this way, three key geometric parameters of the repetitive chiral unit cells-thickness, angle, and diameter-are considered as highly influential design factors. Accordingly, a custom method for designing experiments was employed, resulting in achieving 27 totally different sandwich beams. These beam structures were made up of Poly Lactic Acid (PLA) for both their face sheets and cores, employing Fused Deposition Modeling (FDM) printing technology. Subsequently, they underwent compressive loading, where the resulting mechanical responses forming the foundational dataset for training Deep Neural Networks (DNNs). Remarkably, the DNNs were trained utilizing both Bayesian and conjugate gradient algorithms. The outcomes notably demonstrated that DNNs trained with the Bayesian algorithm exhibited superior accuracy in predicting stress-strain responses of the beams. Transitioning to the study's second objective, Response Surface Methodology (RSM) was harnessed to optimize Young's modulus and Specific Energy Absorption (SEA). The application of RSM impressively showcased its robustness in attaining optimal design values for these mechanical properties over the defined range of design parameters. This comprehensive exploration effectively reveals the potential of machine learning predictions and optimization techniques, providing valuable insights into the intricate mechanical behaviors of sandwich structures featuring innovative cores.

Chouhan G., Gunji B.M., Bidare P., Ramakrishna D., Kumar R.

This research focuses on investigating the design and mechanical aspects of unique bio-inspired structures inspired by the biological elements basal body and nautilus shell. Centriole, nautilus, and cartwheel structures have been designed by CAD software and stereolithography (SLA) 3d printing was applied to manufacture these lattice structures. Finite element analysis was applied to optimize and compressive tests were carried out for the evaluation of the mechanical properties of bioinspired structures. Bio-inspired designs have a combination of qualities, which may create unique mechanical, electrical, thermal, and acoustic characteristics by controlling various factors, which have attracted a lot of study interest. The results of experiments show that the cartwheel structure is stiffer and stronger than other lattices with almost the same volume. According to the mass-to-strength ratio, both cartwheel structures are attractively lightweight and strong. Furthermore, this is the sole study that discusses centriole, nautilus, and cartwheel structure design, manufacturing, and deformation.

Menegozzo M., Cecchini A., Ogle R.C., Vaidya U.K., Acevedo-Figueroa I., Torres-Hernández J.A.

Honeycomb cores are widely used in the aerospace and automotive fields as a part of protective structures. Unfortunately, standard prismatic honeycomb cores offer a limited amount of energy absorption under lateral loads and suffer from degradation of their impact-deadening properties when their dimensional scale is increased. In this work, a multiscale study on energy absorption under quasi-static load is carried out on 3D-printed honeycomb core samples constituted by a variable section and compared to the cases of standard hexagonal honeycomb samples having the same mass and external dimensions. When doubling the dimensional scale in the case of lateral loads, the novel core geometry showed a substantial absence of specific energy absorption degradation, whereas the hexagonal core suffered from a 12.2%-degradation. Furthermore, by increasing the dimensional scale, the novel core geometry shows a delay in the densification onset. The variable-core geometry showed an average increase, in terms of energy absorption under lateral loads, of 46.8% for the regular scale and 71.4% for the double scale. Under axial loads, a 12.4%-decrease in energy absorption was observed for the samples with novel geometry, which, nevertheless, showed a relatively constant profile of reaction force under compression: this property could potentially allow it to avoid pre-crushing.

Tang C., Liu J., Hao W., Wei Y.

Three-dimensional (3D) printed polymer-reinforced cementitious composites are expected to be used to improve the ductility of cement-based materials. However, research on the maximum flexural capacity and failure mode of lattice-reinforced cementitious composites remains insufficient. In this study, six types of cells with different volume fractions are designed, and mainly undergo bending and tensile deformation. According to the load characteristics during a three-point bending test, five kinds of graded lattice structures are designed. Moreover, a skin-lattice structure and uniform lattice structure are designed, and plain cement mortar is set to comprehensively evaluate the bending mechanical properties of graded lattice-reinforced cementitious composites. The crack evolution and failure mode of these composites under three-point bending load are studied using digital image correlation (DIC). The results show that compared with the uniform lattice, the graded lattice can improve the maximum bending capacity of cement-based materials, improve their cracking characteristics and failure modes during the bending process, and enhance their toughness while reducing the amount of required material. Compared with the plain cement mortar specimen, the graded lattice-reinforced specimen with the largest bending peak load is found to have a 175% increase in the bending peak load and a significant increase in the bending bearing capacity.

Gohar A., Nazir A., Lin S., Jeng J.

Nature has evolved over several billion years, optimizing structural efficiency through the use of repeating unit cells called lattice structures that have inspired researchers in mimicking such changes in real-life applications to achieve customized objects with high strength-to-weight ratios. Through additive manufacturing, such changes can be incorporated into designs providing site-specific properties enhancing mechanical performance while reducing weight. In this study, functionally graded lattices involving relative density and period change (mathematical parameters defining unit cell morphology) were designed from the fixed end to the loading end using three different triply periodic minimal surface (TPMS) structures, namely Gyroid, Schwarz-P, and Schwarz-D, for a cantilever beam. The structures were designed in a rectangular-shaped cantilever beam and additively manufactured using MultiJet fusion (MJF) technology. Flexure tests were performed on the manufactured samples using specially designed cantilever beam equipment until failure to study flexure properties. In calculating the flexural properties, the moment of inertia (MOI) of the beams plays a significant part which was also found by different methods owing to limitations, and a comparison is given between how the values vary when compared by taking the MOI of the bounding box. The experimental results indicate a decrease in mechanical properties as the period of the structures is changed. Even though the properties are enhanced as a result of better distribution in the case of period change in two directions, it is not as good as variation with linearly varying thickness. In the case of structures, the Schwarz-D structure performs the best among all the structures due to better tension and compression properties, as supported by the literature. Lastly, the failure of the structures reveals that as the period changes, the structures develop areas of stress concentrations that lead to earlier failure.

Nazir A., Gokcekaya O., Md Masum Billah K., Ertugrul O., Jiang J., Sun J., Hussain S.

Extensive research on nature-inspired cellular metamaterials has globally inspired innovations using single material and limited multifunctionality. Additive manufacturing (AM) of intricate geometries using multi-materials provides additional functionality, environmental adaptation, and improved mechanical properties. Recently, several studies have been conducted on multi-material additive manufacturing (MMAM) technologies, including multi-materials, methodologies, design, and optimization. However, in the past six years, very few or no systematic and complete reviews have been conducted in this research domain. This review intends to comprehensively summarize MMAM systems and the working principles of its fundamental processes. Herein, the Multi-material combinations and their design, modeling, and analysis strategies have been reviewed systematically. In particular, the focus is on applications and opportunities for using MMAM for several industries and postprocessing MMAM fabricated parts. Furthermore, this review identified the limitations and challenges of existing software packages, MMAM processes, materials, and joining mechanisms, especially at the multi-material interfaces. Finally, we discuss the possible strategies to overcome the aforementioned technological challenges and state the future directions, which will provide insights to researchers and engineers designing and manufacturing complex nature-inspired objects.

Diosdado-De la Peña J.A., Dwyer C.M., Krzeminski D., MacDonald E., Saldaña-Robles A., Cortes P., Choo K.

Additive manufacturing technologies have facilitated the construction of intricate geometries, which otherwise would be an extenuating task to accomplish by using traditional processes. Particularly, this work addresses the manufacturing, testing, and modeling of thermoplastic polyurethane (TPU) lattices. Here, a discussion of different unit cells found in the literature is presented, along with the based materials used by other authors and the tests performed in diverse studies, from which a necessity to improve the dynamic modeling of polymeric lattices was identified. This research focused on the experimental and numerical analysis of elastomeric lattices under quasi-static and dynamic compressive loads, using a Kelvin unit cell to design and build non-graded and spatially side-graded lattices. The base material behavior was fitted to an Ogden 3rd-order hyperelastic material model and used as input for the numerical work through finite element analysis (FEA). The quasi-static and impact loading FEA results from the lattices showed a good agreement with the experimental data, and by using the validated simulation methodology, additional special cases were simulated and compared. Finally, the information extracted from FEA allowed for a comparison of the performance of the lattice configurations considered herein.