Stereolithography 3D Printing Research Articles

Multi-material and parameter-controllable stereolithography 3D printing of graded permittivity composites for high voltage insulators

ABSTRACT Graded permittivity materials have gained significant attention due to their exceptional ability to regulate electric fields. Multi-material stereolithography (SLA) 3D printing has opened up new possibilities for creating such materials. However, conventional SLA printers typically generate graded material using fixed printing parameters and multiple feedstocks with limited differences, resulting in a constrained capacity for modulating the electric field distribution. To address this limitation, we have developed a multi-material, parameter-controllable SLA strategy, enabling us to assign varying printing parameters for each building layer and switch between feedstocks with significant differences. Solid insulators with graded permittivity are optimised through electric field distribution simulations and subsequently manufactured using our innovative multi-material SLA approach. A 4-layered graded insulator effectively decreases the maximum electric field strength from 82.5–30.8 kV/mm. Both flashover tests and partial discharge signals confirm that graded insulators outperform homogeneous ones in electrical insulation.

Investigations into 3D-printed nautiloid-inspired pressure housings

The shell of the chambered nautilus is one of the few examples in nature of a biologically derived one-atmosphere pressure housing, which the animal uses to maintain neutral buoyancy via a series of sealed chambers. Extant species such as Nautilus pompilius live at depths from 200 to 800 m, and similar depth ranges have been hypothesized for their hyper diverse but extinct relatives, the ammonoids. Given the evolutionary success of these molluscan clades, their complex shell morphologies may reveal pressure-tolerant geometries comparable to the ‘ideal’ ones currently used in deep-sea marine robotics: simple spheres and cylinders, which have minimized surface area to volume ratio and easier manufacturability. We modeled and empirically tested 3D-printed bioinspired pressure housings for deep-sea applications using high resolution stereolithography 3D printing. These designs were modeled on the shells of N. pompilius and were compared to conventional 3D-printed spheres with similar wall thicknesses and implodable volumes. Two nautilus-inspired models with internal supports designed after their septal walls (one concave, one convex) had a higher-pressure tolerance compared to hollow models, but none outperformed spherical models with the same outer-wall thickness. Although spheres outperform the nautilus-inspired housings, the methods developed here show that pressure housings with complex geometries can be printed by additive manufacturing and empirically tested. From a biological perspective, this method can be a new tool for empirically testing viable depth tolerances for extinct coiled cephalopod morphologies.

3D Printer Technology Selection in Rapid Prototyping: A Spherical Fuzzy AHP Approach

The aim of this study is to make the best technology decision for an enterprise in the automotive sector that plans to purchase a 3D printer for the purpose of obtaining rapid product prototypes. The study includes seven criteria as accuracy, complex design, surface quality, ease of use, throughput, material cost, and equipment cost, and three alternative technologies as fused deposition modeling (FDM), selective laser sintering (SLS), and stereolithography (SLA). The weighting of the criteria has been carried out by three experts in the product development department, and the evaluation of alternatives has been carried out by a team of 3D printer manufacturers. The spherical fuzzy analytic hierarchy process (SF-AHP) method is applied in the study. It’s considered important for making the right technology decision in product development processes since this study seeks a solution to a real problem. As a result of the study, while the accuracy criterion is the highest priority, the ease of use of the selected printer is the least priority criterion. On the other hand, SLA 3D printer technology has been seen as the most ideal technology in terms of many criteria for prototyping automotive plastic material parts.

Development of a semi-anthropomorphic photoacoustic calcaneus phantom based on nano computed tomography and stereolithography 3D printing.

Osteoporosis is a major public health threat with significant physical, psychosocial, and financial consequences. The calcaneus bone has been used as a measurement site for risk prediction of osteoporosis by noninvasive quantitative ultrasound (QUS). By adding optical contrast to QUS, our previous studies indicate that a combination of photoacoustic (PA) and QUS, that is, PAQUS, provides a novel opportunity to assess the health of human calcaneus. Calibration of the PAQUS system is crucial to realize quantitative and repeatable measurements of the calcaneus. Therefore, a phantom which simulates the optical, ultrasound, and architectural properties of the human calcaneus, for PAQUS system calibration, is required. Additionally, a controllable phantom offers researchers a versatile framework for developing versatile structures, allowing more controlled assessment of how varying bone structures cause defined alterations in PA and QUS signals. In this work, we present the first semi-anthropomorphic calcaneus phantom for PAQUS. The phantom was developed based on nano computed-tomography (nano-CT) and stereolithography 3D printing, aiming to maximize accuracy in the approximation of both trabecular and cortical bone microstructures. Compared with the original digital input calcaneus model from a human cadaveric donor, the printed model achieved accuracies of 71.15% in total structure and 87.21% in bone volume fraction. Inorganic materials including synthetic blood, mineral oil, intralipid, and agar gel were used to model the substitutes of bone marrow and soft tissue, filling and covering the calcaneus phantom. The ultrasound and optical properties of this phantom were measured, and the results were consistent with those measured by a commercialized device and from previous in vivo studies. In addition, a short-term stability test was conducted for this phantom, demonstrating that the optical and ultrasound properties of the phantom were stable without significant variation over 1 month. This semi-anthropomorphic calcaneus phantom shows structural, ultrasound, and optical properties similar to those from a human calcaneus in vivo and, thereby, can serve as an effective source for equipment calibration and the comprehensive study of human patients.

3D printed denture base material: The effect of incorporating TiO2 nanoparticles and artificial ageing on the physical and mechanical properties

ObjectivesTo evaluate the physical and mechanical properties of three-dimensional (3D) printed denture base resin incorporating TiO2 nanoparticles (NPs), subjected to a physical ageing process. MethodsAcrylic denture base samples were prepared by a Stereolithography (SLA) 3D printing technique reinforced with different concentrations (0.10, 0.25, 0.50, and 0.75) of silanated TiO2 NPs. The resulting nanocomposite materials were characterized in terms of degree of conversion (DC), and sorption/solubility flexural strength, impact strength, Vickers hardness and Martens hardness and compared with unmodified resin and conventional heat-cured (HC) material. The nanocomposites were reassessed after subjecting them to ageing in artificial saliva. A fractured surface was studied under a scanning electron microscope (SEM). ResultsThe addition of TiO2 NPs into 3D-printed resin significantly improved flexural strength/modulus, impact strength, Vickers hardness, and DC, while also slightly enhancing Martens hardness compared to the unmodified resin. Sorption values did not show any improvements, while solubility was reduced significantly. The addition of 0.10 wt% NPs provided the highest performance amongst the other concentrations, and 0.75 wt% NPs showed the lowest. Although ageing degraded the materials’ performance to a certain extent, the trends remained the same. SEM images showed a homogenous distribution of the NPs at lower concentrations (0.10 and 0.25 wt%) but revealed agglomeration of the NPs with the higher concentrations (0.50 and 0.75 wt%). SignificanceThe outcomes of this study suggested that the incorporation of TiO2 NPs (0.10 wt%) into 3D-printed denture base material showed superior performance compared to the unmodified 3D-printed resin even after ageing in artificial saliva. The nanocomposite has the potential to extend service life of denture bases in future clinical use.

High solid loading, low viscosity stereolithography 3D printing ceramic cores slurry

The temperature enduring capacity of turbine blades determines the thrust-weight ratio of aero-engines. The heat dissipation efficiency of blades is improved mainly through designing complex internal cooling channel. As a transitional component of blade preparation, the shape of ceramic cores has become gradually complex. The traditional process is difficult to meet the preparation requirements of ceramic core with complex structure due to the limitation of mold. Stereolithography 3D printing provides a feasible technology for the preparation of ceramic cores with complex structures. The key to high-performance ceramic core via the stereolithography 3D printing lies in the prepare ceramic slurry with high solid loading, low viscosity and uniform stability. Choosing suitable dispersant is an effective way to prepare above standard slurry. In this study, the effects of single and dual dispersants on the rheological properties of ceramic slurry were systematically investigated. The action mechanism of the dispersant was analyzed. The functional relationship between solid loading and viscosity was elucidated. The silicon-based ceramic core slurry with 70 vol% solid loading and viscosity of 10520 mPa s (12.6 s−1) was obtained. Through optimizing printing parameters, the complex structure silicon-based ceramic core was fabricated. The influence of solid loading on the microstructure and physical properties of the ceramic core was investigated. The results show that with the increase of solid loading, the shrinkage of ceramic core lowers and the flexural strength of ceramic core strengthens. The successfully preparation of complex structure ceramic core based on high solid loading slurry promotes the extensively implemented of stereolithography 3D printing technology in the field of ceramic core.

Elastic and dimensional properties of newly combined 3D-printed multimaterials fabricated by DLP stereolithography

In the field of stereolithography 3D printing, the portfolio of commercially available photopolymers has burgeoned. Each material family possesses its individual properties. However, corresponding products with specific requirements remain a major challenge. This gap could be filled by combining existing materials. This study aimed to predict Young’s modulus of the specimen manufactured by combining multiple materials using digital light processing (DLP), a subtype of stereolithography. It also aimed to investigate the effects of the printing process on the geometry and mechanical properties of such 3D-printed multimaterials. Using a DLP 3D printer, samples were produced from commercially available pure and mixed materials, and half of the samples underwent post-printing curing. Three-point bending tests were performed to determine the elastic modulus of the samples. The elastic properties have been compared to linear interpolation using the properties of the primary materials. The measurements showed that Young’s modulus ranged from 1.6 GPa to 2.2 GPa for the post-cured materials, with the mixed materials fitting well with the linear interpolation approach. For eight out of nine sample sets, the prediction was within the range of the measurements. In the case of as-printed samples, the elasticity of the primary materials ranged from 0.4 GPa to 0.9 GPa, but all of the mixed materials showed a stiffer behavior than the linear interpolation prediction, up to 57% above the prediction. The dimensions of the printed specimen were measured, and groups of different geometrical deviations were identified. These were analyzed with regard to the printer system and material mixture. In conclusion, this study shows and discusses the effects of the printing process on mechanical and dimensional properties of specimens fabricated using a stereolithographic 3D printer from multiple commercially available primary materials. It discusses a process for predicting the elastic properties of these multimaterials and selecting the mixing ratios to achieve specifically desired properties.

Monolithic affinity columns in 3D printed microfluidics for chikungunya RNA detection.

Mosquito-borne pathogens plague much of the world, yet rapid and simple diagnosis is not available for many affected patients. Using a custom stereolithography 3D printer, we created microfluidic devices with affinity monoliths that could retain, noncovalently attach a fluorescent tag, and detect oligonucleotide and viral RNA. We optimized the fluorescent binding and sample load times using an oligonucleotide sequence from chikungunya virus (CHIKV). We also tested the specificity of CHIKV capture relative to genetically similar Sindbis virus. Moreover, viral RNA from both viruses was flowed through capture columns to study the efficiency and specificity of the column for viral CHIKV. We detected ~107 loaded viral genome copies, which was similar to levels in clinical samples during acute infection. These results show considerable promise for development of this platform into a rapid mosquito-borne viral pathogen detection system.

Improving the accuracy of stereolithography 3D printed Al2O3 microcomponents by adding photoabsorber: Fundamentals and experiments

Ceramic microcomponents have a wide range of applications in microfluidic, sensors, etc. Stereolithography 3D printing technology provided a shortcut for the preparation of this small-size and complex component. With the development of device miniaturization, the existing stereolithography forms cannot meet the demand. To prepare smaller components, it is necessary to decrease the slice thickness (Cs). But during the stereolithography 3D printing, ceramic is usually easy to over-cure, leading to the key issue in the stereolithography of ceramic microcomponents: the mismatching between the curing thickness (Cp) and the slice thickness (Cs). To solve the problem above, this paper started from the stereolithography mechanism of the ceramic/resin slurry and adjusted the matching relationship between Cp and Cs theoretically by adding a photoabsorber. Then, from the experiments, the influence of different content of photoabsorber (carbon black) on curing thickness, printing accuracy, and sintering accuracy, were studied. Al2O3 ceramic microcomponents that met the design requirements were thus prepared. These results would help in the development of stereolithography 3D printing of ceramic microcomponents.

Positional trueness of three removable die designs with different root geometries manufactured using stereolithographic 3D printing

Statement of problemThree-dimensional (3D) printed casts are a suitable alternative to dental stone casts. Contemporary dental design computer programs permit designing definitive casts with removable dies with different root geometries and retention mechanisms. Studies on the positional trueness of 3D-printed removable dies with different root geometries are lacking. PurposeThe purpose of this in vitro study was to investigate the 3D displacements of three 3D-printed removable die designs with different root geometries. Material and methodsThe digital file of a dental stone alveolar cast with root-form removable dies (MOD UJ IV Fixed Prosthetics; Ivoclar AG) was used as a reference to create 3 removable die and alveolar cast designs (Root Form, RF; Conical, CON; Cylindric, CYL) with different root geometries in 2 dental design computer programs (DentalCAD 3.1 Rijeka; exocad; GmbH; InLab CAD 22.0; Dentsply Sirona). 3 equidistant Ø1-mm spheres (C, Cervical; M, Middle; O, Occlusal) were designed on the buccal surface of the coronal portion of the removable die to evaluate their displacement. A total of 45 alveolar casts with 45 removable dies were fabricated using a stereolithographic 3D printer (Form 3; Formlabs); each die group consisted of 15 specimens. After fabrication and postprocessing, the specimens were scanned, and their digital files were analyzed in a metrology-grade computer program to evaluate the displacement of the removable dies with respect to the position of the die in the master reference file. Subsequently, the data were analyzed using a 3-way analysis of variance (ANOVA) followed by step-down Bonferroni-corrected pairwise comparisons (α=.05). ResultsTwo statistically significant 2-way interactions were detected between the independent variables, die design and direction (P<.001), and location and direction (P<.001). The post hoc analysis identified significant differences between the displacement values of RF and CYL (P<.001) and RF and the CON (P<.001) designs on the Y axis. The measured displacements were statistically different between the C and O locations on the Y axis (P=.001) and the M and O locations on the Z axis (P=.006). ConclusionsThe root geometry of a 3D-printed removable die and alveolar cast can affect seating, and variable degrees of tipping of the removable die can be seen. The seating and congruence of the removable die with the interocclusal space and relationships observed intraorally should be confirmed before adjusting indirect restorations.

Validation of 3D printed MAYO tubes and stethoscope in simulated medical environment – Tools fabricated with additive manufacturing for emergency care

Emergency and disaster medical care often face resource or equipment shortages. 3D printing technology has been proven to be effective in cases with insufficient supply chains. MAYO tubes and stethoscopes are essential components of ABCDE patient examinations; however, 3D-printed variants have not been fully tested. These 3D-printed instruments were substituted and validated in a simulated pre-hospital environment.In total, 26 participants were included in this study. Fifteen clinicians or paramedics with at least 3 years of professional experience and 10 medical students. One student was excluded because he had relevant experience with emergency care. As basic tasks, the placement of MAYO tubes and auscultation with stethoscopes were performed using medical simulators. 3D printed instruments were compared with conventional clinical devices by measuring the time required for the intervention, success rate, and user satisfaction. In the study FFF (Fused Filament Fabrication (FFF), SLS (Selective Laser Sintering (SLS), and SLA (stereolithography) 3D printing were used in this study.The times required for implementation and auscultation were examined for each instrument. There was no significant difference between the MAYO tube (p = 0.798) and the stethoscope (p = 0.676). In the case of stethoscopy, the study investigated the correct diagnosis, and no significant difference was found (p = 0.239), although an interesting trend was observed. Regarding the MAYO tube, the study found no significant difference in correct position formation (p = 0.163). The experience levels of the groups did not influence these factors. However, significant differences in user satisfaction were found in both cases in favour of the conventional versions (p < 0.001).Overall, the results of this study suggest that 3D-printed devices could be suitable replacements for clinic-based devices in emergency situations. The 3D-printed devices did not perform inferiorly at any of the indicated points compared to their classical counterparts. However, the practical applicability of the devices used in this study requires further investigation.

Fabrication of flexible intracranial aneurysm models using stereolithography 3D printing

Abstract The use of 3D printing technology for medical applications is becoming increasingly popular. Recent stereolithography (SLA)-based printing methods allow the generation of complex structures with a high surface quality. This is particularly useful for applications in the neurovascular field, where sophisticated structures are involved. In this study patient-specific intracranial aneurysm models are extracted based on medical image data und printed as thin-walled vascular phantom models. For this purpose, two commercially available 3D printers are used to print flexible vascular models with three different silicone-like elastic resins (Ultracur3D FL 300, Prusament Flex80 and Formlabs Elastic 50A) of various Shore hardness. Three aneurysm models of different size and complexity are chosen. To evaluate the geometric accuracy of the flexible models, angiographic measurements are performed for an exemplary case and morphological parameters are extracted from the generated 3D models. The printed results demonstrate a successful generation of hollow aneurysm phantoms. There are dependencies regarding the print quality from the model to platform positioning for two materials. The quantitative geometric accuracy analysis shows notable differences between the materials. The extracted morphological parameter values for all materials show a mean decrease compared to the original reference model of aneurysm volume (4.5 %) and maximum diameter (1.0 %) as well as an increase of ostium area (6.0 %) and maximum height (4.9 %). However, Formlabs Elastic 50A in particular exhibits just slight reductions with respect to the reference model, with a mean decrease for all parameters of 5.7 % as well as no dependence on printing position and resulting artifacts. The study investigates the feasibility of using SLA-based 3D printing to generate realistic flexible aneurysm phantoms. In this context, the Formlabs Elastic 50A could be identified as potentially applicable for phantom creation in terms of reproducible quality and geometric validity.

3D-Printed Twisting Tubular Metamaterials with Tunable Mechanical and Torsional Characteristics

Innovative tubular compression-torsion mechanical metamaterials with potential applications in sensors, actuators, and energy harvesting are introduced. The metamaterials are parametrically designed and fabricated through stereolithography appearance 3D printing method, and their behaviour is analyzed using experiments, finite element method, and machine learning (ML). The effects of unit cell geometrical parameters, such as the unit cell size, the struts length, the angle between the struts, and the in-plane and out-of-plane thicknesses, on the performance of the structure, are investigated. Additionally, the influence of section geometry, longitudinal and circumferential cell numbers, and the unit cell assembly layouts on the metamaterial's twisting capability and mechanical properties is studied. The results demonstrate the tunability of the metamaterial by setting the unit cell design parameters, compression-torsion conversion property, volume fraction, and effective Young's modulus. ML is employed to predict a geometric design suitable to fit known working specifications. ML facilitates tuning the proposed metamaterial based on the desired responses which are expected from the structure. The problem is addressed through a multi-target supervised regression using the Random Forest regressor algorithm with optimized hyperparameters.

Engineering Lung-Inspired Flow Field Geometries for Redox Flow Batteries with Stereolithography 3D Printing

Redox flow batteries are a promising electrochemical technology for low-cost, scalable and long-duration energy storage, but their energy market penetration is hampered by elevated costs1,2. One effective strategy is to increase the overall efficiency of the electrochemical stack. At the core of the electrochemical cells, the design of the flow fields—which distribute the electrolyte through the porous electrodes—determines, in combination with the electrode microstructure, the performance of the system3. To date, current designs are inspired on fuel cell technologies but have not been engineered for redox flow cells where single-phase reactive flows are sustained4.In this work, we tailor lung-inspired flow field geometries for carbon paper electrodes using stereolithography 3D printing5,6. We propose two new lung-inspired geometries—with two and three channel levels—and compare them to a baseline interdigitated flow field. A two-step process based on stereolithography 3D printing followed by the application of a conductive coating is used to manufacture these complex flow field geometries. We employ a suite of electrochemical (i.e., polarization and electrochemical impedance spectroscopy) and fluid dynamic (pressure drop measurement) techniques together with numerical modelling to elucidate flow architecture-performance relationships. We find that lung-inspired structural patterns homogenize the electrolyte distribution into the electrode, accessing a larger electrode reaction area. These fractal geometries can outperform traditional interdigitated flow fields, providing a more favourable balance between low pressure drop and high electrochemical performance (Figure 1). In this talk, I aim to leverage lung-inspired flow field geometries as a promising prospect for engineering advanced flow cell architectures for emerging electrochemical devices. References 1 E. Sánchez-Díez, J. Power Sources, 2021, 23.2 L. F. Arenas, C. Ponce de León and F. C. Walsh, J. Energy Storage, 2017, 11, 119–153.3 R. M. Darling and M. L. Perry, J. Electrochem. Soc., 2014, 161, A1381–A1387.4 C. R. Dennison, E. Agar, B. Akuzum and E. C. Kumbur, J. Electrochem. Soc., 2016, 163, A5163–A5169.5 J. Marschewski, L. Brenner, N. Ebejer, P. Ruch, B. Michel and D. Poulikakos, Energy Env. Sci, 2017, 10, 780–787.6 M. P. Browne, E. Redondo and M. Pumera, Chem. Rev., 2020, 120, 2783–2810. Figure 1

Investigating Mass Transfer Relationships in Stereolithography-Based 3D Printed Electrodes for Redox Flow Batteries

Redox flow batteries are a promising option for large-scale energy storage but remain too costly for widespread deployment. One approach to increase cost competitiveness is to improve the power density and efficiency of the electrochemical cell. Porous electrodes determine the performance of the cell, and their three-dimensional structure determines the electrolyte transport, fluid pressure drop, and the available surface area for electrochemical reactions [1]. Conventional porous electrodes are fibrous mats assembled in coherent structures [2]; however, they are repurposed from fuel cell gas diffusion electrodes and have not been tailored for redox flow batteries. Hence, an effective means to improve the performance of redox flow batteries is by engineering porous electrode structures to sustain the requirements of liquid-phase electrochemistry. To this purpose, there is a need to develop new manufacturing techniques affording a higher degree of control over the electrode microstructure and resulting properties. Additive manufacturing, or 3D printing, can be employed to manufacture customized, controlled, and deterministic architectures, enabling the fine-tuning of the electrical and hydraulic performance of porous electrodes [3].In this study, we manufacture model grid structures using stereolithography 3D printing followed by carbonization (Figure 1a) to tune the physiochemical properties of electrodes to be used in redox flow batteries. We employ a suite of microscopy, tomography, spectroscopy, fluid dynamics, and electrochemical diagnostics to understand the impact of the electrode structure on the mass transport and hydraulic performance of ordered lattice structures in flow cells. Here, the influence of the printing direction, pillar geometry (Figure 1b), and flow field type on mass transport is investigated using an organic electrolyte. We elucidate correlations between the electrode structure and performance metrics, namely surface area, pressure drop, and mass transfer correlations. We find that the printing orientation impacts the electrode performance through a change in electrode morphology caused by resin spreading and surface roughness, affecting the shrinking direction upon carbonization, internal surface area, and thus the charge transfer, mass transfer, and hydraulic resistances. Furthermore, we find that mass transfer rates within the electrode are enhanced by using an interdigitated flow field or by altering the pillar shape to a helical or triangular design, which we hypothesize improves mixing. Compared to commercial carbon-fiber electrodes, the pressure drop is significantly reduced (Figure 1c) as expected due to larger pore sizes (~500 μm for the grids vs. 2-100 μm for the Freudenberg H23 paper electrode and 2-300 μm for the ELAT Cloth electrode). Even though the commercial electrodes feature a superior internal surface area compared to the 3D printed electrodes, their area normalized mass transfer coefficients are lower (Figure 1d). Going forward, the use of printing technologies enabling finer features in combination with carbonization at elevated temperatures can be used to manufacture multiscale electrodes simultaneously providing low hydraulic resistance and excellent electrochemical performance. Additive manufacturing in combination with emerging computational approaches in topology optimization [4] might enable the bottom-up design and manufacturing of advanced electrode materials.

Experimental investigations into nonlinear dynamic behaviours of triply periodical minimal surface structures

Natural frequency, damping ratio and dynamic stiffness are fundamental to the performance of structures subjected to dynamic loads. Triply Periodic Minimal Surface (TPMS) composite structures, celebrated for their superior energy absorption capacity and specific strength, represent some of the most promising meta-structures. However, their dynamic properties are yet to be fully understood, thereby hindering their practical applications within civil engineering domains. Damping properties, crucial to vibration reduction, remain particularly elusive; previous studies have not successfully established a connection between these properties and the force excitation amplitude in TPMS structures. This study aims to compare the damping properties of different TPMS structures and to investigate their potential for adoption within civil engineering fields. Three types of TPMSs, including Schoen I-graph-wrapped package surface (IWP), Schwarz primitive (Primitive) and Schoen Gyroid (Gyroid), have been adopted to design solid and sheetal TPMS composite structures with identical relative density (50%) to compare their damping properties under varying excitation amplitudes. These TPMS structures are manufactured from photosensitive resin (UV resin) using stereolithography 3D printing technology. Owing to the lack of previous research into the damping properties and dynamic stiffness of TPMS structures as support structures, we have conducted single-freedom modal tests to determine the modal parameters, including natural frequency and damping ratios. Our novel results indicate that the natural frequency and damping ratio of the TPMS structures vary with the excitation amplitude. Additionally, the dynamic stiffness of TPMS structures reveals a similar decreasing trend to frequency when load amplitude escalates. As the excitation amplitude increases, the TPMS structures demonstrate softening and are capable of offering a higher vibration damping coefficient. Notably, the SS-Gyroid structure exhibits higher stiffness and damping ratio compared to other TPMS structures. These fresh insights pave the way for the integration of 3D printed smart TPMS structures within civil engineering, particularly for vibration reduction and efficient material usage. A judicious TPMS structure design can provide relatively high stiffness and damping ratio without excessive material use.

Optimization of mechanical properties of bio-inspired Voronoi structures by genetic algorithm

Numerous patterns in nature comprise aesthetics structures and intriguing geometries. The geometric factors behind these patterns include area, aspect ratio, circularity, orientation, and regularity. In this study, the quasi-3D porous structures with varying regularities were systematically described and generated by the Voronoi segmentation. Then, genetic algorithms were applied to optimize the mechanical properties of these structures under tension condition. The image-based finite element simulation could calculate each structure's fitness value (strength). Afterward, structures with higher fitness values were selected and underwent the replication process, including crossover and mutation. New structures were generated based on the input structures. The above steps driven by the genetic algorithms were repeated 30 iterations until the tensile strength of the structures was improved and converged. Both simulation and tensile testing results as well as digital image correlation of specimens fabricated by stereolithography 3D printing showed that the Voronoi structures optimized by the genetic algorithm could enhance their stiffness, strength, and toughness values by ∼30%. This research has the potential to be applied in the fields of structural materials and biomimetic micro-aerial vehicles, which require lightweight, strength, and toughness simultaneously.

Precision Control in Vat Photopolymerization Based on Pure Copper Paste: Process Parameters and Optimization Strategies.

Vat photopolymerization (VPP) presents new opportunities for metals to achieve the design freedom of components. However, the material properties of copper powder and the inherent defects of the technology seriously hinder its application in high-precision metal additive manufacturing. Precision control is the key to obtaining minimal precision metal parts when copper is prepared by reduction photopolymerization. This paper employed variance analysis (ANOVA) and root mean square deviation (RMSD) to determine the significant parameters affecting dimensional accuracy and their optimal regions. The results show that printing accuracy is improved by optimizing exposure time, intensity, layer thickness, and sweeper moving speed. When the exposure time is 21 s, and the exposure intensity is 220 mW/cm2, a hole with a height of 1 mm and a diameter of 200 μm can be printed with a minimum size deviation of 51 μm. In addition, RMSD and ANOVA provide an effective method for realizing high-precision stereolithography 3D printing metal copper, expanding the material adaptation in the 3D printing metals field. The study highlights the potential of VPP as a method for preparing metals in future studies.

Stereolithography 3D Printed Carbon Microlattices with Hierarchical Porosity for Structural and Functional Applications.

Hierarchically porous carbon microlattices (HPCMLs) fabricated by using a composite photoresin and stereolithography (SLA) 3D printing is reported. Containing magnesium oxide nanoparticles (MgO NPs) as porogens and multilayer graphene nanosheets as UV-scattering inhibitors, the composite photoresin is formed to simple cubic microlattices with digitally designed porosity of 50%. After carbonization in vacuum at 1000°C and chemical removal of MgO NPs, it is realized that carbon microlattices possessing hierarchical porosity are composed of the lattice architecture (≈100µm), macropores (≈5µm), mesopores (≈50nm), and micropores (≈1nm). The linear shrinkage after pyrolysis is as small as 33%. Compressive strength of 7.45 to 10.45MPa and Young's modulus of 375 to 736MPa are achieved, proving HPCMLs a robust mechanical component among reported carbon materials with a random pore structure. Having a few millimeters in thickness, the HPCMLs can serve as thick supercapacitor electrodes that demonstrate gravimetric capacitances 105 and 13.8 Fg-1 in aqueous and organic electrolyte, reaching footprint areal capacitances beyond 10 and 1 Fcm-2 , respectively. The results present that the composite photoresin for SLA can yield carbon microarchitectures that integrate structural and functional properties for structural energy storages .

Electrically assisted stereolithography 3D printing of graded permittivity composites for in-situ encapsulation of insulated gate bipolar transistors (IGBTs)

Insulated gate bipolar transistors (IGBTs) find applications in diverse fields, such as integrated motor drives, controllable power systems, and electric vehicles. However, traditional IGBT encapsulation materials are unsuitable for high-voltage applications due to the excessive electric field stress generated at the triple junction; an insulation-enhanced encapsulation material is therefore necessary. Here, using an electrically assisted stereolithography (SLA) 3D printing strategy, we fabricate an encapsulation material with graded permittivity that can uniform the electric field stress distribution in IGBTs. Compared with pure resin and uniform-dispersed BaTiO3-resin composite encapsulation, the graded BaTiO3-resin composite reduces the generated maximum electric field stress (Emax) from 190.2 to 108.3 kV/mm (nearly a 50% decrease). Regarding the partial discharge inception voltage, the devices packaged with graded BaTiO3-resin composite (4.07 kV) also performed better than devices packaged with resin (1.96 kV) and uniform-dispersed BaTiO3-resin composite (2.51 kV). This novel electrically assisted SLA 3D printing strategy will open a new window for the in-situ encapsulation of IGBTs and other microelectronics.