Mechanical and FEA-Assisted Characterization of Fused Filament Fabricated Triply Periodic Minimal Surface Structures

Optimization of functionally graded solid-network TPMS meta-biomaterials

The current study enhances the performance of solid-network triply periodic minimal surface (TPMS) cellular materials through using cell size grading along with the Taguchi method. Cell size grading is a novel technique used to control the size of pores and the surface area without changing the relative density. In this context, experimental compression testing was conducted on six distinct geometries of cell size graded TPMS structures (Diamond, Fischer-Koch S, Gyroid, IWP, Primitive, and Schoen-F-RD) manufactured with dental resin using a masked stereolithography (MSLA) printer. The findings indicated that mean total energy absorption was greater for smaller initial cell sizes (4 and 6 mm) compared to larger sizes (12 mm). Consistent patterns were also observed with respect to final cell sizes. Upon examination of the stress-strain relationships between D and I-WP, it is evident that D exhibits a higher initial peak stress point. However, subsequent to a significant decline, it exhibits a tremendous degree of volatility before recovering. Conversely, I-WP demonstrated greater stability throughout the experiments, with a notably greater maximum stress effect. A significant influence was observed from the initial cell size on stress, with larger sizes leading to a reduction in absorbed energy. The acquired results serve as an essential basis for the identification of optimized designs that may be implemented to enhance the structures' durability.

Researching on the Effect of Input Parameters on the Quality and Manufacturability of 3D-Printed Cellular Samples from Nylon 12 CF in Synergy with Testing Their Behavior in Bending

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.

Prediction of Mechanical Properties for Carbon fiber/PLA Composite Lattice Structures Using Mathematical and ANFIS Models

This study investigates the influence of design, relative density (RD), and carbon fiber (CF) incorporation parameters on mechanical characteristics, including compressive modulus (E), strength, and specific energy absorption (SEA) of triply periodic minimum surface (TPMS) lattice structures. The TPMS lattices were 3D-printed by fused filament fabrication (FFF) using polylactic acid (PLA) and carbon fiber-reinforced PLA(CFRPLA). The mechanical properties of the TPMS lattice structures were evaluated under uniaxial compression testing based on the design of experiments (DOE) approach, namely, full factorial design. Prediction modeling was conducted and compared using mathematical and intelligent modeling, namely, adaptive neuro-fuzzy inference systems (ANFIS). ANFIS modeling allowed the 3D printing imperfections (e.g., RD variations) to be taken into account by considering the actual RDs instead of the designed ones, as in the case of mathematical modeling. In this regard, this was the first time the ANFIS modeling utilized the actual RDs. The desirability approach was applied for multi-objective optimization. The mechanical properties were found to be significantly influenced by cell type, cell size, CF incorporation, and RD, as well as their combination. The findings demonstrated a variation in the E (0.144 GPa to 0.549 GPa), compressive strength (4.583 MPa to 15.768 MPa), and SEA (3.759 J/g to 15.591 J/g) due to the effect of the studied variables. The ANFIS models outperformed mathematical models in predicting all mechanical characteristics, including E, strength, and SEA. For instance, the maximum absolute percent deviation was 7.61% for ANFIS prediction, while it was 21.11% for mathematical prediction. The accuracy of mathematical predictions is highly influenced by the degree of RD deviation: a higher deviation in RD indicates a lower accuracy of predictions. The findings of this study provide a prior prediction of the mechanical behavior of PLA and CFRPLA TPMS structures, as well as a better understanding of their potential and limitations.

Low Impact Velocity Modeling of 3D Printed Spatially Graded Elastomeric Lattices

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.

Development of an architecture-property model for triply periodic minimal surface structures and validation using material extrusion additive manufacturing with polyetheretherketone (PEEK)

Additively manufactured structures designed from triply periodic minimal surfaces (TPMSs) have been receiving attention for their potential uses in the medical, aerospace, and automobile industries. Understanding how these complex geometries can be designed to achieve particular architectural and mechanical properties is essential for tuning their function to certain applications. In this study, we created design tools for visualizing the interplay between TPMS design parameters and resulting architecture and aimed to validate a model of the relationship between structure architecture and Young's modulus. A custom MATLAB script was written to analyze structural properties for families of Schoen gyroid and Schwarz diamond structures, and a numerical homogenization scheme was performed to predict the effective Young's moduli of the structures based on their architecture. Our modeling methods were validated experimentally with polyetheretherketone (PEEK) structures created using material extrusion additive manufacturing. The architectural characteristics of the structures were determined using micro-computed tomography, and compression testing was performed to determine yield strength and Young's modulus. Two different initial build orientations were tested to determine the behavior both perpendicular and parallel to the layer deposition direction (referred to as z-direction and xy-direction, respectively). The z-direction Young's modulus ranged from 289.7 to 557.5 MPa and yield strength ranged from 10.12 to 20.3 MPa. For the xy-direction, Young's modulus ranged from 133.8 to 416.4 MPa and yield strength ranged from 3.8 to 12.2 MPa. For each initial build orientation, the mechanical properties were found to decrease with increasing porosity, and failure occurred due to both strut bending and interlayer debonding. The mechanical properties predicted by the modeling agreed with the values found for z-direction samples (difference 2-11%) but less so for xy-direction samples (difference 27-62%) due to weak interlayer bonding and print path irregularities. Ultimately, the findings presented here provide better understanding of the range of properties achievable for additive manufacturing of PEEK and encouraging results for a TPMS architecture-property model.

Architected Materials for Additive Manufacturing: A Comprehensive Review

One of the main advantages of Additive Manufacturing (AM) is the ability to produce topologically optimized parts with high geometric complexity. In this context, a plethora of architected materials was investigated and utilized in order to optimize the 3D design of existing parts, reducing their mass, topology-controlling their mechanical response, and adding remarkable physical properties, such as high porosity and high surface area to volume ratio. Thus, the current re-view has been focused on providing the definition of architected materials and explaining their main physical properties. Furthermore, an up-to-date classification of cellular materials is presented containing all types of lattice structures. In addition, this research summarized the developed methods that enhance the mechanical performance of architected materials. Then, the effective mechanical behavior of the architected materials was investigated and compared through the existing literature. Moreover, commercial applications and potential uses of the architected materials are presented in various industries, such as the aeronautical, automotive, biomechanical, etc. The objectives of this comprehensive review are to provide a detailed map of the existing architected materials and their mechanical behavior, explore innovative techniques for improving them and highlight the comprehensive advantages of topology optimization in industrial applications utilizing additive manufacturing and novel architected materials.

Design and Development of a Multi-Functional Bioinspired Soft Robotic Actuator via Additive Manufacturing

The industrial revolution 4.0 has led to a burst in the development of robotic automation and platforms to increase productivity in the industrial and health domains. Hence, there is a necessity for the design and production of smart and multi-functional tools, which combine several cutting-edge technologies, including additive manufacturing and smart control systems. In the current article, a novel multi-functional biomimetic soft actuator with a pneumatic motion system was designed and fabricated by combining different additive manufacturing techniques. The developed actuator was bioinspired by the natural kinematics, namely the motion mechanism of worms, and was designed to imitate the movement of a human finger. Furthermore, due to its modular design and the ability to adapt the actuator’s external covers depending on the requested task, this actuator is suitable for a wide range of applications, from soft (i.e., fruit grasping) or industrial grippers to medical exoskeletons for patients with mobility difficulties and neurological disorders. In detail, the motion system operates with two pneumatic chambers bonded to each other and fabricated from silicone rubber compounds molded with additively manufactured dies made of polymers. Moreover, the pneumatic system offers multiple-degrees-of-freedom motion and it is capable of bending in the range of −180° to 180°. The overall pneumatic system is protected by external covers made of 3D printed components whose material could be changed from rigid polymer for industrial applications to thermoplastic elastomer for complete soft robotic applications. In addition, these 3D printed parts control the angular range of the actuator in order to avoid the reaching of extreme configurations. Finally, the bio-robotic actuator is electronically controlled by PID controllers and its real-time position is monitored by a one-axis soft flex sensor which is embedded in the actuator’s configuration.

Mechanical Strength of Triply Periodic Minimal Surface Lattices Subjected to Three-Point Bending

Sandwich panel structures (SPSs) with lattice cores can considerably lower material consumption while simultaneously maintaining adequate mechanical properties. Compared with extruded lattice types, triply periodic minimal surface (TPMS) lattices have light weight but better controllable mechanical properties. In this study, the different types of TPMS lattices inside an SPS were analysed comprehensively. Each SPS comprised two face sheets and a core filled with 20×5×1 TPMS lattices. The types of TPMS lattices considered included the Schwarz primitive (SP), Scherk’s surface type 2 (S2), Schoen I-graph-wrapped package (I-WP), and Schoen face-centred cubic rhombic dodecahedron (F-RD). The finite element method was applied to determine the mechanical performance of different TPMS lattices at different relative densities inside the SPS under a three-point bending test, and the results were compared with the values calculated from analytical equations. The results showed a difference of less than 21% between the analytical and numerical results for the deformation. SP had the smallest deformation among the TPMS lattices, and F-RD can withstand the highest allowable load. Different failure modes were proposed to predict potential failure mechanisms. The results indicated that the mechanical performances of the TPMS lattices were mainly influenced by the lattice geometry and relative density.

Computational Design and Characterisation of Gyroid Structures with Different Gradient Functions for Porosity Adjustment

Triply periodic minimal surface (TPMS) structures have a very good lightweight potential, due to their surface-to-volume ratio, and thus are contents of various applications and research areas, such as tissue engineering, crash structures, or heat exchangers. While TPMS structures with a uniform porosity or a linear gradient have been considered in the literature, this paper focuses on the investigation of the mechanical properties of gyroid structures with non-linear porosity gradients. For the realisation of the different porosity gradients, an algorithm is introduced that allows the porosity to be adjusted by definable functions. A parametric study is performed on the resulting gyroid structures by performing mechanical simulations in the linear deformation regime. The transformation into dimensionless parameters enables material-independent statements, which is possible due to linearity. Thus, the effective elastic behaviour depends only on the structure geometry. As a result, by introducing non-linear gradient functions and varying the density of the structure over the entire volume, specific strengths can be generated in certain areas of interest. A computational design of porosity enables an accelerated application-specific structure development in the field of engineering.

Nylon lattice design parameter effects on additively manufactured structural performance

Lattice structures are used in a multitude of applications from medical to aerospace, and their adoption in these applications has been further enabled by additive manufacturing. Lattice performance is governed by a multitude of variables and estimating this performance may be needed during various phases of the design and validation process. Numerical modeling and constitutive relationships are common methodologies to assess performance, address risks, lower costs, and accelerate time to market for innovative and potentially life altering products. These methods are usually accompanied by engineering rationales to justify the methods appropriateness. However, engineering analyses and numerical models should be validated using experimental data when possible to quantify the accuracy of their predictions under conditions relevant to their planned use. In this work, a set of lattice design parameters are evaluated using numerical modeling and experimental methods under quasi-static tensile, compressive, and shear modalities. Regular body centered cubic (BCC) and stochastic Voronoi Tessellation Method (VTM) lattices are constructed with three different cell lengths (2.5 mm, 4.0 mm, 5.0 mm) and various strut diameter thicknesses (ranging from 0.536 mm-1.3506 mm) while maintaining the lattice's relative density (0.2 and 0.3). Some strut diameters were selected to challenge the AM process limits. Specimens were fabricated in nylon 12 on a laser powder bed fusion system. Optical microscopy showed up to a 28.6% difference between as-designed and fabricated strut diameters. Simulated reaction loads revealed up to a 4.6% difference in BCC lattices within a constant relative density at a 1.4 mm displacement boundary condition while the VTM samples had up to a 19.5% difference. Errors between the experimental and simulated lattice reaction loads were as high as 97.0%. This error magnitude appears to strongly correlate with lattice strut diameter. These results showcase that a computational estimation, even one with reasonable assumptions, may erroneously characterize the performance of these lattice structures, and that these assumptions should be challenged by experimentally evaluating and validating critical quantities of interest.

Experimental and Computational Investigation of Lattice Sandwich Structures Constructed by Additive Manufacturing Technologies

Additive Manufacturing (AM) technologies offer the ability to construct complex geometrical structures in short manufacturing lead time coupled with a relatively low production cost when compared to traditional manufacturing processes. The next trend in mechanical engineering design is the adaption of design strategies that build products with lightweight lattice geometries like sandwich structures. These structures possess low mass, large surface area to volume ratio, high porosity, and adequate mechanical behavior, which are properties of great importance in scientific fields such as bioengineering, automotive, and aerospace engineering. The present work is focused on producing sandwich structures with complex lattice patterns like the Triply Periodic Minimal Surface (TPMS) Schwarz diamond structure. The specimens were manufactured with two different Additive Manufacturing procedures employing various relative densities. More specifically, Material Jetting Printing (MJP) and Fused Filament Fabrication (FFF) processes were employed to investigate the performance of Acrylonitrile Butadiene Styrene (ABS) lightweight lattice structures. These structures were examined using digital microscopy in order to measure the dimensional accuracy and the surface characteristics of the utilized AM technologies. Furthermore, three-point bending tests and finite elements analyses have been applied to investigate the mechanical performance of the proposed technologies and designs as well as the influence of the relative density on the Schwarz diamond TPMS structure. The experimental results demonstrate that the investigated structure possesses a remarkable performance in respect to its weight due to the specific distribution of its material in space.

Geometrical Degrees of Freedom for Cellular Structures Generation: A New Classification Paradigm

Cellular structures (CSs) have been used extensively in recent years, as they offer a unique range of design freedoms. They can be deployed to create parts that can be lightweight by introducing controlled porous features, while still retaining or improving their mechanical, thermal, or even vibrational properties. Recent advancements in additive manufacturing (AM) technologies have helped to increase the feasibility and adoption of cellular structures. The layer-by-layer manufacturing approach offered by AM is ideal for fabricating CSs, with the cost of such parts being largely independent of complexity. There is a growing body of literature concerning CSs made via AM; this presents an opportunity to review the state-of-the-art in this domain and to showcase opportunities in design and manufacturing. This review will propose a novel way of classifying cellular structures by isolating their Geometrical Degrees of Freedom (GDoFs) and will explore the recent innovations in additively manufactured CSs. Based on the present work, the design inputs that are common in CSs generation will be highlighted. Furthermore, the work explores examples of how design inputs have been used to drive the design domain through various case studies. Finally, the review will highlight the manufacturability limitations of CSs in AM.