Advances In Additive Manufacturing Technologies Research Articles

Development and Comparison of Model-Based and Data-Driven Approaches for the Prediction of the Mechanical Properties of Lattice Structures

AbstractLattice structures have great potential for several application fields ranging from medical and tissue engineering to aeronautical one. Their development is further speeded up by the continuing advances in additive manufacturing technologies that allow to overcome issues typical of standard processes and to propose tailored designs. However, the design of lattice structures is still challenging since their properties are considerably affected by numerous factors. The present paper aims to propose, discuss, and compare various modeling approaches to describe, understand, and predict the correlations between the mechanical properties and the void volume fraction of different types of lattice structures fabricated by fused deposition modeling 3D printing. Particularly, four approaches are proposed: (i) a simplified analytical model; (ii) a semi-empirical model combining analytical equations with experimental correction factors; (iii) an artificial neural network trained on experimental data; (iv) numerical simulations by finite element analyses. The comparison among the various approaches, and with experimental data, allows to identify the performances, advantages, and disadvantages of each approach, thus giving important guidelines for choosing the right design methodology based on the needs and available data.

Crashworthiness Investigations for 3D-Printed Multi-Layer Multi-Topology Engineering Resin Lattice Materials

In comparison to monolithic materials, cellular solids have superior energy absorption capabilities. Of particular interest within this category are the periodic lattice materials, which offer repeatable and highly customizable behavior, particularly in combination with advances in additive manufacturing technologies. In this paper, the crashworthiness of engineering multi-layer, multi-topology (MLMT) resin lattices is experimentally examined. First, the response of a single- and three-layer single topology cubic and octet lattices, at a relative density of 30%, is investigated. Then, the response of MLMT lattices is characterized and compared to those single-topology lattices. Crashworthiness data were collected for all topology arrangements, finding that while the three-layer cubic and octet lattices were capable of absorbing 9.8 J and 7.8 J, respectively, up to their respective densification points, the unique MLMT lattices were capable of absorbing more: 19.0 J (octet-cube-octet) and 22.4 J (cube-octet-cube). These values are between 94% and 187% greater than the single-topology clusters of the same mass.

The Interaction between Oral Bacteria and 3D Titanium Porous Surfaces Produced by Selective Laser Melting-A Narrative Review.

The interaction between oral bacteria and dental implant surfaces is a critical factor in the success and longevity of dental implants. With advancements in additive manufacturing technologies, selective laser melting (SLM) has emerged as a prominent method for producing titanium implants with highly controlled microstructures and porosities. These 3D printed titanium surfaces offer significant benefits, such as enhanced osseointegration and improved mechanical properties. However, the same surface features that promote bone cell attachment and proliferation may also provide favorable conditions for bacterial adhesion and biofilm formation. Understanding the dynamics of these interactions is essential for developing implant surfaces that can effectively resist bacterial colonization while promoting tissue integration. This narrative review explores the complex interplay between oral bacteria and SLM-produced titanium porous surfaces, examining current research findings and potential strategies for optimizing implant design to mitigate the risks of infection and ensure successful clinical outcomes.

An adjustable acoustic metamaterial cell using a magnetic membrane for tunable resonance

Acoustic metamaterials are growing in popularity for sound applications including noise control. Despite this, there remain significant challenges associated with the fabrication of these materials for the sub-100 Hz regime, because acoustic metamaterials for such frequencies typically require sub-mm scale features to control sound waves. Advances in additive manufacturing technologies have provided practical methods for rapid fabrication of acoustic metamaterials. However, there is a relatively high sensitivity of their resonant characteristics to sub-mm deviations in geometry, pushing the limits of additive manufacturing. One way of overcoming this is via active control of device resonance. Here, an acoustic metamaterial cell with adjustable resonance is demonstrated for the sub-100 Hz regime. A functionally superparamagnetic membrane—devised to facilitate the fabrication process by eliminating magnetic poling requirements—is engineered using stereolithography, and its mechanical and acoustic properties are experimentally measured using laser Doppler vibrometry and electret microphone testing, with a mathematical model developed to predict the cell response. It is demonstrated that an adjustable magnetic acoustic metamaterial can be fabricated at ultra-subwavelength dimensions (≤λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\le \\lambda$$\\end{document}/77.5), exhibiting adjustable resonance from 88.73 to 86.63 Hz. It is anticipated that this research will drive new innovations in adjustable metamaterials, including wider frequency ranges.

Circuits for Printed Electronics for Flexible Displays & Sensors

Printed circuits are crucial components in the field of printed electronics, enabling the creation of flexible, lightweight, and cost-effective electronic devices. This proposal explores the fabrication techniques, materials, and applications of printed circuits in printed electronics. Various printing methods such as inkjet, screen, and flexography are discussed, along with the integration of conductive inks and substrates. The versatility of printed circuits allows for the development of diverse electronic products including wearable sensors, RFID tags, and flexible displays. Moreover, advancements in additive manufacturing technologies continue to drive innovation in printed circuit design and production, promising a future of increasingly sophisticated printed electronic devices.

Efficient design of sandwich panels with cellular truss cores and large phononic band gaps using surrogate modeling and global optimization

Recent advancements in additive manufacturing technologies and topology optimization techniques have catalyzed a transformative shift in the design of architected materials, enabling increasingly complex and customized configurations. This study delves into the realm of engineered cellular materials, spotlighting their capacity to modulate the propagation of mechanical waves through the strategic creation of phononic band gaps. Focusing on the design of sandwich panels with cellular truss cores, we aim to harness these band gaps to achieve pronounced wave suppression within specific frequency ranges. Our methodology combines surrogate modeling with a comprehensive global optimization strategy, employing three machine learning algorithms—k-Nearest Neighbors (kNN), Random Forest Regression (RFR), and Artificial Neural Networks (ANN)—to construct predictive models from parameterized finite element (FE) analyses. These models, once trained, are integrated with Particle Swarm Optimization (PSO) to refine the panel designs. This approach not only facilitates the discovery of optimal truss core configurations for targeted phononic band gaps but also showcases a marked increase in computational efficiency over traditional optimization methods, particularly in the context of designing for diverse target frequencies.

Crashworthiness investigations for 3D printed multi-layer multi-topology carbon fiber nylon lattice materials

Cellular solids have superior energy absorption capabilities as compared to monolithic materials. Within this category of materials, lattice materials are of particular interest since their periodicity offers repeatable – and thus predictable – behavior. In combination with the advancements in additive manufacturing technologies, these lattice materials can be highly customized for a desired response. In this paper, the crashworthiness of unique multi-layer, multi-topology (MLMT) lattices is investigated. First, the nylon-carbon fiber composite material properties within a developed numerical model were tuned based on strut orientation. Then, the response of single-layer and three-layer cubic and octet lattices was investigated, where all lattices were designed with a relative density of 30%. Following the characterization of single-topology lattices, the response of MLMT lattices were investigated. Stress-strain, efficiency-strain, and multiple crashworthiness parameter data was collected for all lattices to facilitate in the comparison of those lattices. It was found that, experimentally, the unique MLMT lattices did not absorb more energy than their constituent layers combined, though modifications to the interface between layers could increase the energy absorption capability; the prediction of energy absorption of the MLMT lattices based on constituent layers was similar to actual numerical results. As all lattices were designed at the same relative density, the mass-specific energy absorption of the cubic-octet-cubic MLMT lattice (1.56 x103 J/kg) outperforms the single-topology octet lattice by 19% to 36% (1.15–1.31 x103 J/kg). While the octet-cubic-octet MLMT lattice (0.71 x103 J/kg) is outperformed by the single-topology cubic lattices (1.69–3.76 x103 J/kg), they see an increase of 59% to 77% in plateau stress (5.1–9.2 MPa) as compared to the MLMT lattice (2.1 MPa).

Parametric design and modular construction of a large additive-manufactured hypar shell structure

Despite recent advances in additive manufacturing technologies, challenges remain to build 3D-printed structures at the architectural scale due to the high cost of large printing equipment. To address this challenge, modular construction has demonstrated its merit by making smaller prefabricated components and using on-site assembly. This paper presents a case study of a 3D-printed hypar shell structural art using modular construction. Guided by parametric design and structural analysis, we optimized the hypar shell to form a butterfly-like shape with a hollow-out pattern. The prefabrication of modular units was completed using commercial 3D printers to catch a limited production time. The prefabricated modular unit of the hypar shell was assembled on site for the Guangzhou International Light Festival, in which the lighting effect was added through the adjustable transparency of hollow spaces within the sandwiched panels. The 3D-printed hypar shell was also disassembled and rebuilt in the UK, showcasing the adaptability and flexibility of the modular design. The resulting 3D-printed structural art not only provides unique aesthetics for the built environment but also demonstrates the possibility of building large shell structures with a low budget by reducing complex falsework.

Characterisation of Heat Transfer within 3D Printed TPMS Heat Exchangers

Recent advances in additive manufacturing technology have enabled rapid and inexpensive prototyping of designs to explore shape effects across a range of engineering applications. In this work, we measure the heat transfer performance of a range of heat exchangers based on triply periodic minimal surfaces (TPMS). The results showed that the sheet gyroid TPMS design produced a high rate of heat transfer and moderate pressure drop. The sheet gyroid TPMS design was further investigated to determine its performance over porosities ranging from 40% to 85%, hydraulic diameters from 2 to 10 mm, and wall thicknesses from 0.4 to 2.6 mm. Our results show that all correctly parameterised TPMS of the same type have results positioned on the same Nusselt versus Reynolds number curves. A correlation was developed for the purpose of designing micro-channel heat exchangers over the operating range 100<ReH<2500. At equal pumping power, the Nusselt number was improved by 13% through the use of the gyroid TPMS, as compared to a straight tube heat exchanger.

Challenges in two‐scale computational homogenization of mechanical metamaterials

AbstractThanks to the advancement of additive manufacturing technologies, mechanical metamaterials have attracted a great deal of attention in recent years. With the employment of such technologies, materials with exceptional or tailored mechanical properties can be easily manufactured mainly by 3D printing of different microstructures rather than by changing the material composition. These lattice materials can provide remarkable material properties in spite of being significantly lighter than typical bulk materials. Due to the large number of degrees of freedom for engineering structures, single‐scale numerical simulation of such cellular materials is computationally demanding. Therefore, two‐scale computational homogenization approaches, such as FE2 and FE‐FFT, can perform a key role in the cost‐effective numerical modeling of metamaterials. Two‐scale computational homogenization methods rely on solving a boundary value problem (BVP) for each of the macroscopic and microscopic scales in a nested procedure. Although representative homogenization techniques have been widely used to study materials with heterogeneous microstructures, there still exist some challenges in their employment for lattice materials. This study addresses main challenges in two‐scale‐based computational homogenization methods for numerical modeling of mechanical metamaterials. High dependence of convergence rate and accuracy on phase contrast for fast Fourier transform (FFT) solvers and comparable macro and micro characteristic lengths in metamaterials (i.e. the applicability of the principle of scale separation) are some examples of such challenges.

Generalized yield surface for sheet-based triply periodic minimal surface lattices

Triply periodic minimal surfaces (TPMS), which are a class of architected cellular materials, have attracted significant attention lately, due to their prevailing mechanical, electrical and chemical properties, to name a few, and due to the advancements in additive manufacturing technologies that make it possible to print such materials. However, simulating the elastic-plastic mechanical behavior of structural systems (e.g., beams, plates, cores of sandwich panels, structural systems with various levels of geometric complexity) that are latticed with thousands of TPMS lattices are computationally expensive to model explicitly, and hence the need to develop accurate yield surfaces in order to capture their plastic behavior in a homogenized approach. In this work, a generalized initial yield criterion is proposed for sheet-based TPMS lattices, which incorporates the Lode parameter L. The initial yielding of five different sheet-based TPMS lattices are investigated in five different loading conditions. These lattices are Schoen's I-WP (IWP-s), Gyroid (GYR-s), Diamond (DIA-s), F-RD (FRD-s) and Primitive (PRIM-s). The proposed yield criterion accurately predicts the initial yielding of all these lattices in all the loading conditions considered, outperforming other yield criteria currently proposed in literature.

Multiscale Design of Graded Stochastic Cellular Structures for the Heat Transfer Problem

Advancesin additive manufacturing technology have expanded the development prospect of structures with complex configurations. Cellular structures have been a hot research topic in recent years for their superior performance and characteristics, such as being lightweight and having high specific strength and good permeability. With a high specific surface area, cellular structures perform noticeably well in heat transfer applications when subjected to a body heat source. In this paper, a scale-separated multiscale design of theVoronoi graded stochastic cellular structure (Voronoi-GSCS) that considers the heat transfer problem is proposed. The design method is composed of three steps: the offline calculation on the microscale, the online optimization on the macroscale, and geometry reconstruction on the full scale. Numerical examples are given to show the effectiveness and superiority of the developed method for designing the Voronoi-GSCS. The results obtained by the solid isotropic material with penalization (SIMP) approach are used for comparison. The size effect analysis was conducted to research the influence of the size of the microstructure on the Voronoi-GSCS. It should be stressed that the smallest struts were larger than the minimum print size of the additive manufacturing so that the Voronoi-GSCS could be conveniently exploited in heat transfer applications.

Data-Efficient Deep Generative Model with Discrete Latent Representation for High-Fidelity Digital Materials

The rapid advancement of additive manufacturing technologies enables a pixelated or voxelated structure consisting of multiple materials in 2D or 3D, respectively, called digital materials. It maximizes design flexibility without constraints in geometry and material, realizing unprecedented physical properties and functionalities that cannot be realized by conventional manufacturing processes. However, the enormous design space of digital materials has become a significant challenge for maximizing the availability of digital materials. In this study, we developed a novel deep generative model with discrete representations of the latent space for designing digital materials. The proposed model, inspired by the discrete nature of digital materials, retains reconstruction and prediction accuracies with one-third of the data usage compared to the conventional generative model. The physical insight of discrete representations of latent space is rigorously interpreted, proving that certain discrete representations are strongly related to the mechanical behavior of digital materials, such as auxeticity. It was also confirmed that the proposed model is an excellent tool for generating functionally graded structures as well as the unseen auxetic structures.

Liquid-Based 4D Printing of Shape Memory Nanocomposites: A Review

Significant advances have been made in recent years in the materials development of liquid-based 4D printing. Nevertheless, employing additive materials such as nanoparticles for enhancing printability and shape memory characteristics is still challenging. Herein, we provide an overview of recent developments in liquid-based 4D printing and highlights of novel 4D-printable polymeric resins and their nanocomposite components. Recent advances in additive manufacturing technologies that utilise liquid resins, such as stereolithography, digital light processing, material jetting and direct ink writing, are considered in this review. The effects of nanoparticle inclusion within liquid-based resins on the shape memory and mechanical characteristics of 3D-printed nanocomposite components are comprehensively discussed. Employing various filler-modified mixture resins, such as nanosilica, nanoclay and nanographene, as well as fibrous materials to support various properties of 3D printing components is considered. Overall, this review paper provides an outline of liquid-based 4D-printed nanocomposites in terms of cutting-edge research, including shape memory and mechanical properties.

Utilizing ultrafast lasers for postprocessing to improve mechanical properties of 3D-printed parts

Recent advances in additive manufacturing technologies have already led to the wide-scale adoption of 3D-printed parts in the aerospace, medical, automotive, tooling, and electronics industries. The expansion in choice of materials that can be processed, in particular, using fused deposition modeling (FDM), selective laser sintering/melting, and stereolithography, and the steady advancements in dimensional accuracy control, have extended the range of applications beyond rapid prototyping. However, additive manufacturing still has considerable limitations compared to traditional and subtractive manufacturing processes. This work addresses limitations associated with the as-deposited surface roughness of 3D-printed parts. The effects of roughness-induced stress concentrations on the mechanical strength were studied, and ultrafast laser postprocessing was utilized to reduce the surface roughness of 3D-printed parts. The samples were manufactured using a commercial desktop FDM system and standard ASTM flat dogbone geometries. The samples were then postprocessed with a high-repetition-rate ultrafast Yb-fiber laser using a multi-layer scan approach. This novel postprocessing method enables high-efficiency material removal without inducing excessive thermal residual stresses into the material and, therefore, is suitable for postprocessing thermally sensitive materials, such as PLA and other polymers as well as parts with engineered porosity. In this work, we vary laser process parameters, such as average power and number of laser-processed layers, to achieve various levels of surface roughness. Values of tensile strength of the specimens were compared between 3D-printed samples featuring initial roughness and laser postprocessed samples with different values of surface roughness. The results indicate that the laser-processed samples exhibit an almost 10% increase in tensile strength depending on specific laser processing parameters.

Impact of compression and bending behavior on fused deposition modeling of 3D printed components

The fast-prototyping technology known as additive manufacturing (AM) was first created as a tool for developing and analyzing ideas. Fast manufacturing is being facilitated by the recent advancement of AM technologies like Fused Deposition Modelling (FDM). In this paper, the material used as PLA biodegradable material which is made up of plant starch, cost also less when compared to other materials, and process parameters are considered Infill Percentage, Raster Angle, and Layer Thickness. Infill percentages are 20, 40, 60, 80, and 100, Layer heights are 120 µm, 180 µm, and 300 µm and raster angles are angles (00,00) (450,00) and (900,00). By using the selected parameters, 90 samples are constructed by using FDM and tested by using Flexural and Impact. The PLA material properties of each component were examined and components of 300 µm underwent SEM and examined whether the external surface was deposited correctly or if any imperfections are there. Examining all tested PLA components mechanically and SEM reports concluded that compression, flexural tests, and microstructural behavior are good at raster angles (00,00), 80% infill, and 120 µm this reduces material deposition and the time of printing sample.

Rodent Model for Orthotopic Implantation of Engineered Liver Devices.

This study presents a novel surgical model developed to provide hematological support for implanted cellularized devices augmenting or replacing liver tissue function. Advances in bioengineering provide tools and materials to create living tissue replacements designed to restore that lost to disease, trauma, or congenital deformity. Such substitutes are often assembled and matured in vitro and need an immediate blood supply upon implantation, necessitating the development of supporting protocols. Animal translational models are required for continued development of engineered structures before clinical implementation, with rodent models often playing an essential early role. Our long-term goal has been generation of living tissue to provide liver function, utilizing advances in additive manufacturing technology to create 3D structures with intrinsic micron to millimeter scale channels modeled on natural vasculature. The surgical protocol developed enables testing various design iterations in vivo by anastomosis to the host rat vasculature. Lobation of rodent liver facilitates partial hepatectomy and repurposing the remaining vasculature to support implanted engineered tissue. Removal of the left lateral lobe exposes the underlying hepatic vasculature and can create space for a device. A shunt is created from the left portal vein to the left hepatic vein by cannulating each with separate silicone tubing. The device is then integrated into the shunt by connecting its inflow and outflow ports to the tubing and reestablishing blood flow. Sustained anticoagulation is maintained with an implanted osmotic pump. In our studies, animals were freely mobile after implantation; devices remained patent while maintaining blood flow through their millifluidic channels. This vascular anastomosis model has been greatly refined during the process of performing over 200 implantation procedures. We anticipate that the model described herein will find utility in developing preclinical translational protocols for evaluation of engineered liver tissue. Impact statement Tissue and organ transplantation are often the best clinically effective treatments for a variety of human ailments. However, the availability of suitable donor organs remains a critical problem. Advances in biotechnology hold potential in alleviating shortages, yet further work is required to surgically integrate large engineered tissues to host vasculature. Improved animal models such as the one described are valuable tools to support continued development and evaluation of novel therapies.

Patient-Specific Stent Fabrication Using a Seven-Degree-Of-Freedom Additive Manufacturing System

With advances in additive manufacturing technologies, the creation of medical devices which are tailored to the geometry of a patient’s unique anatomy is becoming more feasible. The following paper details the capabilities of a seven-degree-of-freedom fused filament deposition modeling system which enables a wide variety of user-control over previously restricted parameters, such as nozzle angle, print bed rotation, and print bed tilt. The unique capabilities of this system will be showcased through the production of a patient-specific tracheal stent using three different methods: segmented overmolding, transverse rastering, and longitudinal rastering. The resulting opportunities and time savings demonstrated by the prints will provide a case for greater implementation of seven-degree-of-freedom manufacturing technologies.

One-shot additive manufacturing of robotic finger with embedded sensing and actuation

A main challenge in the additive manufacturing (AM) field is the possibility to create structures with embedded actuators and sensors: addressing this requirement would lead to a reduction of manual assembly tasks and product cost, pushing AM technologies into a new dimension for the fabrication of assembly-free smart objects. The main novelty of the present paper is the one shot fabrication of a 3D printed soft finger with an embedded shape memory alloy (SMA) actuator and two different 3D printed sensors (strain gauge and capacitive force sensor). 3D printed structures, fabricated with the proposed approach, can be immediately activated after their removal from the build plate, providing real-time feedback because of the embedded sensing units. Three different materials from two nozzles were extruded to fabricate the passive elements and sensing units of the proposed bioinspired robotic finger and a custom-made Cartesian pick and place robot (CPPR) was employed to integrate the SMA spring actuator into the 3D printed robotic finger during the fabrication processes. Another novelty of the present paper is the direct integration of SMA actuators during the 3D printing process. The low melting thermoplastic polycaprolactone (PCL) was extruded: its printing temperature of 70 °C is lower than the SMA austenitic start temperature, preventing the SMA activation during the manufacturing process. Two different sensors based on the piezoresistive principle and capacitive principle were studied, 3D printed and characterized, showing respectively a sensitivity ratio of change in resistance to finger bending angle to be 674.8 frac{Omega }{^circ mathrm{Angle}} and a capacitance to force ratio of 0.53 frac{mathrm{pF}}{mathrm{N}}. The proposed manufacturing approach paves the way for significant advancement of AM technologies in the field of smart structures with embedded actuators to provide real-time feedback, offering several advantages, especially in the soft robotics domain.

Computational homogenization of additively manufactured lightweight structures with multiscale topology optimization

Abstract Topology optimization (TO) is an optimal design method to obtain an efficient structure with minimal usage of material by satisfying two conflicting objectives of weight reduction and structural safety. Owing to the recent advances in additive manufacturing technology, TO has been developed in connection with the use of microscale lattices, of which complicated geometries require considerable computational loads to verify their structural performance. This study aims to develop an efficient computational method to analyze a complex TO model. Computational homogenization was then developed for efficient computation of the TO model that contains a number of microscale lattices. The proposed homogenization scheme was then applied to perform three-dimensional (3D) finite element analysis (FEA) on various TO models with three scales (i.e., macroscale, microscale, and multiscale TOs). The homogenized FEAs were conducted to verify the static and dynamic deformation behaviors of three optimized meta-sandwich beams, and their results and computational efficiency were compared with those from full solid FEAs. Experimental verification revealed that the proposed homogenized FEA provided more reliable results and better computational efficiency for the microscale and multiscale TO models, whereas the conventional solid FEA was advantageous for the macroscale TO model. To apply the proposed simulation strategy to a more complex 3D geometry, three TO models were calculated for a 3D block under a compression load. The simulation strategy combining the full solid and homogenized FEAs was then applied to analyze the static and dynamic deformation behaviors of various TO models, which provided reliable predictions of the experimentally observed behaviors within an acceptable computational time.