Printing Direction Research Articles

Biomimetic design and fabrication of PEEK and PEEK/CF cage with minimal surface structures by fused filament fabrication

The interbody fusion cages are critical implants in spinal fusion surgeries, which stabilize the spine and treat pains resulting from degenerative disc disease. The commercial used poly (ether-ether-ketone) (PEEK) cages are non-porous and manufactured by machining, which cause material waste and insufficient bioactivity. Fused filament fabrication (FFF) technology provides opportunities to fabricate fusion cages with specific shape and intricate porous architectures for bone ingrowth and nutrient exchange. Herein, PEEK-based lattice structures are designed and firstly fabricated by FFF based on three minimal surfaces including Schwarz P (P), Diamond (D) and Gyroid (G). The effects of cellular architecture and unit cell on the compressive properties are investigated. The results demonstrate that D and G surfaces possess superior load-carrying and energy absorption capacity. The prototyping defects in PEEK lattices were lesser than those in PEEK/CF samples. Also, it is notable that the compression performance of FFF-printed samples exhibited a strong anisotropy depending on the printing direction. After printing, annealing is an effective post treatment to further improve the crystallinity and compressive strength of PEEK lattice surfaces. Therefore, the novel PEEK porous structures with optimized mechanical performance show great potentials in the applications as fusion cage implants.

Bayesian inference of high-dimensional finite-strain visco-elastic–visco-plastic model parameters for additive manufactured polymers and neural network based material parameters generator

In this work, the parameters of a finite-strain visco-elastic–visco-plastic formulation with pressure dependency in both the visco-elastic and visco-plastic parts are identified using as observations experimental data obtained from tension and compression tests at different strain rates ranging from 10−4s−1 to 103s−1. Because of the high number of parameters of the model, a sequential Bayesian Inference (SBI) framework with data augmentation, which presents several advantages, is developed. First the sequential nature reduces the difficulty of selecting the appropriate prior distributions by considering only parts of the observations at a time. Second, the sequential nature prevents dealing with low likelihood values by considering only a part of the experimental observations at a time, but also subsets of the material parameters to be identified, improving the convergence of the Markov Chain Monte Carlo (MCMC) random walk. Third, the data augmentation allows considering different number of experimental tests in tension and in compression while preserving the identified model accuracy for both loading modes.This SBI is carried out to infer the properties of Polyamide 12 (PA12) processed by Selective Laser Sintering (SLS) for two different printing directions and it is shown that the models fed by their respective set of inferred parameters can reproduce the different experimental tests.Finally, in order for upcoming structural simulations to benefit from the information related to the uncertainties due to the measurement errors, the identification process and the model limitations, we introduce a Generative Adversarial Network (GAN), which is trained using the data obtained from the MCMC random walk. This generator can then serve to produce a synthetic data-set of arbitrary size of the material parameters to be used in finite-element simulations.

Evaluation of the mechanical properties of polyamide 12 regarding different percentages of reused material in the selective laser sintering process

PurposeAdditive manufacturing (AM) has been one of the most highlighted processes of the last few years. AM prints complex parts and items from 3D files regarding different materials, such as polymers. Moreover, there are different AM techniques available for polymers, such as selective laser sintering. In the SLS technology, polyamides 11 and 12 lead 88% of the market. These materials are high-cost and use an average of 50% of virgin material at each printing. It is possible to use lower rates of virgin material, but at least 30% is recommended. Low rates of virgin material decrease mechanical properties.Design/methodology/approachThis study aims to evaluate the influence on the mechanical properties of the percentage of reused PA12 in parts manufactured by the SLS process. The specimens of PA12 were manufactured with a percentage of virgin/reused polymer of 50/50, 40/60, 30/70, 20/80 and 10/90. We considered three distinct printing directions to compare the mechanical properties of the specimens: horizontal, perpendicular and vertical.FindingsThe results showed that when the percentage of reused material increases, the tensile strength limit (TSL), flexural strength limit and Shore D hardness decrease. Another aspect visualized was the fragile behavior presented in the vertical specimens. In addition, DSC analysis indicated a 2% reduction of crystallinity. Scanning electron microscopy images revealed spherical voids and unfused particles of PA12 at the fracture of tensile test specimens. The material thermal history and unfused particles could decrease the material properties.Originality/valueWe observed that the mechanical properties, such as the TSL, flexural strength limit and hardness, decrease as the percentage of reused material increases. In addition, the process presented a printing-direction dependence, where the vertical direction presented as the more brittle between the ones used.

Controlling Shear Rate for Designable Thermal Conductivity in Direct Ink Printing of Polydimethylsiloxane/Boron Nitride Composites.

Efficient heat dissipation is vital for advancing device integration and high-frequency performance. Three-dimensional printing, famous for its convenience and structural controllability, facilitates complex parts with high thermal conductivity. Despite this, few studies have considered the influence of shear rate on the thermal conductivity of printed parts. Herein, polydimethylsiloxane/boron nitride (PDMS/BN) composites were prepared and printed by direct ink writing (DIW). In order to ensure the smooth extrusion of the printing process and the structural stability of the part, a system with 40 wt% BN was selected according to the rheological properties. In addition, the effect of printing speed on the morphology of BN particles during 3D printing was studied by XRD, SEM observation, as well as ANSYS Polyflow simulation. The results demonstrated that increasing the printing speed from 10 mm/s to 120 mm/s altered the orientation angle of BN particles from 78.3° to 35.7°, promoting their alignment along the printing direction due to the high shear rate experienced. The resulting printed parts accordingly exhibited an impressive thermal conductivity of 0.849 W∙m-1∙K-1, higher than the 0.454 W∙m-1∙K-1 of the control sample. This study provides valuable insights and an important reference for future developments in the fabrication of thermal management devices with customizable thermal conductivity.

Effects of solution treatment on microstructure and mechanical properties of (SiC+TiB2)/Al–Zn–Mg–Cu composite fabricated by laser powder bed fusion

This study investigated the effects of solution treatment (ST) on the microstructure and mechanical properties of (SiC+TiB2)/Al–Zn–Mg–Cu composite produced using laser powder bed fusion (LPBF). Microstructural analysis reveals that the grid-like distribution of eutectic precipitates within the as-printed composite disappeared, giving way to the formation of uniformly distributed precipitates. As the ST temperature increased, the content of spherical Si particles decreased, while the content of elongated Al4SiC4 precipitates increased. Matrix grains recrystallization occurred, resulting in a gradual increase in the average grain size from 3.79 μm to 5.23 μm. The preferred crystallographic orientation features along the printing direction, <001> {001} plate texture, were weakened, gradually exhibiting a more disordered growth. The microhardness and tensile strength of the composites exhibited a slight decrease and exhibited a trend of initially increasing and then decreasing with increasing ST temperature. Additionally, the heterogeneity in microhardness along different directions has been reduced. When the ST temperature was 460 °C, the elongation of the composite experienced a significant increase, escalating from 6.12 ± 0.36% to 10.3 ± 0.25%. However, with the increase in ST temperature, it displayed an obvious downward trend. The maximum tensile strength was 449 ± 8 MPa, and the elongation was 9.6 ± 0.4% with the ST temperature of 500 °C. The variations in mechanical properties were primarily attributed to the elimination of grid-like substructure, the uniform distribution of precipitates, and the gradual coarsening of grains. This research was expected to contribute to developing advanced lightweight materials with improved performance, opening up new opportunities for their application in various industries.

Behavior of 3D-printed HPC plates with FRP grid reinforcement under bending

High-performance concrete (HPC) has become increasing popular in structural engineering. Capitalizing the advanced construction technology of 3D concrete printing (3DCP) and merits of HPC, structures with various profiles could be designed and constructed easily. As the mechanical properties of 3D printed concrete may be worse than the corresponding concrete cast by the conventional technology, this study proposes to evolve flexible fiber-reinforced polymer (FRP) grid as reinforcement for 3D printed HPC plates. Twelve plates were tested to explore the effects of the loading direction and fabrication type on the flexural behavior of FRP grid reinforced HPC plates. The results showed that the performance of the 3D printed HPC plates can be considerably enhanced owning to the FRP grid reinforcement. Additionally, the μCT-scanned images show that the pores between deposition layers were elongated due to the movement of the nozzle during printing, and the pores were stretched in the printing direction. The flexible FRP reinforcement may allow 3D printing of FRP reinforced concrete elements in the future.

Toughness Enhancement of PLA-Based Filaments for Material Extrusion 3D Printing

Poly(lactic acid) (PLA) is one of the most popular biodegradable thermoplastics in the market of 3D printing filaments used in the material extrusion (ME) technique. This is because it can be printed easily at low temperatures. However, its inherent brittleness limits its use in many applications. In this work, the toughness of PLA filament was improved by blending with various types of rubbers including natural rubber (NR), acrylic core–shell rubber (CSR), and thermoplastic polyurethane (TPU) in the amount of 15% by weight. PLA/TPU filament was found to have the smoothest surface with the best shape and dimension stability, while PLA/NR filament rendered the highest tensile toughness. In term of the effect of printing temperature, the highest printing temperature in this study (210°C) provided the highest smoothness with the best shape stability and dimension accuracy. Interestingly, the tensile toughness and elongation at break of 3D printed specimens were found to be higher than those of compression-molded specimens for all filament types. This could be explained by the ability of the 3D printing technique to produce specimens that aligned in the printing direction in a fiber-like pattern.

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

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

Anisotropy in Additively Manufactured Concrete Specimens under Compressive Loading-Quantification of the Effects of Layer Height and Fiber Reinforcement.

This paper analyzes the effect of print layer heights and loading direction on the compressive response of plain and fiber-reinforced (steel or basalt fiber) 3D printed concrete. Slabs with three different layer heights (6, 13, and 20 mm) are printed, and extracted cubes are subjected to compression (i) along the direction of printing, (ii) along the direction of layer build-up, and (iii) perpendicular to the above two directions. Digital image correlation (DIC) is used as a non-contact means to acquire the strain profiles. While the 3D printed specimens show lower strengths, as compared to cast specimens, when tested in all three directions, this effect can be reduced through the use of fiber reinforcement. Peak stress and peak strain-based anisotropy coefficients, which are linearly related, are used to characterize and quantify the directional dependence of peak stress and strain. Interface-parallel cracking is found to be the major failure mechanism, and anisotropy coefficients increase with an increase in layer height, which is attributable to the increasing significance of interfacial defects. Thus, orienting the weaker interfaces appropriately, through changes in printing direction, or strengthening them through material modifications (such as fiber reinforcement) or process changes (lower layer height, enables attainment of near-isotropy in 3D printed concrete elements.

Impact of printing orientation on inter and intra-layer bonds in 3D printed thermoplastic elastomers: A study using acoustic emission and tensile tests

The use of the Material Extrusion technique with Thermoplastic Elastomers is currently growing because of the large number of benefits of this family of materials. They are processable materials with high flexibility, which makes them very useful, for example, in biomedical applications that require flexible objects with complex geometries. This study aims to characterize a specific polymer, namely polyether-block-amide-based polymer (PEBA), by analyzing its anisotropic behavior in printed samples and investigating the mechanical properties based on different printing orientations. Three orientations (X, Y, and Z) were used to relate the printing orientation to the type of bonds formed in the samples: intra-layer bonds, inter-layer bonds, and the deposited filament. Tensile tests following ASTM D638 were conducted to measure sample rigidity, while Acoustic Emission, an advanced Non-Destructive Technique, was employed to examine the trend of the failure process. The presence of voids was also observed to assess printing quality, which is influenced by the printing orientation and alters the quality of bonds. The results revealed that samples printed horizontally exhibited higher Young’s Modulus values and fewer voids in the inner parts. Vertically printed samples displayed inferior mechanical properties and a greater number of voids. Consequently, the intra-layer yielded better bond formation and minimized voids. Acoustic Emission analysis corroborated these findings by demonstrating distinct energy distribution patterns among the different printing orientations. Hits were concentrated at maximum stresses, primarily observed in the vertically printed samples, which experienced macroscopic failure. Furthermore, this particular specimen exhibited a vertical asymptote near the maximum stress level. The analysis of the energy of Acoustic Emission hits demonstrated a reasonably good fit with the Gutenberg-Richter (GBR) law based on the printing direction.

Multi-material additive manufacturing of electronics components: A bibliometric analysis

The study presents a bibliometric analysis of studies conducted on multi-materials printing of electronic components via additive manufacturing technologies. Using the R package and the associated biblioshiny, the study analyzed publications from Web of Science and Scopus. The study analyzed 405 research articles after removing 104 duplicates. The study applied performance analysis, keyword analysis, and network analysis. The performance analysis showed that the publications on multi-materials additive manufacturing are multi-disciplinary. Whilst the publications span almost three decades, most contributions started after 2015. The United States of America is the country with the highest production. The keyword analysis showed a changed focus before and after 2015. The trending topics show that the most recent trend is in the ‘aerospace industry’. Finally, the thematic analysis shows that the emerging themes in the area are interfaces, moisture, diffusion, microstructure, mechanical properties, and powder metallurgy. These emerging themes are discussed as they are conceived as the future directions of multi-materials printing of electronic components and devices. The current trend of research focuses on understanding and improving the interfacial bonding between the various multi-material interfaces. Overcoming the weak interfacial bonding issues would improve the mechanical properties of multi-materials electronic components.

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

AbstractPorous electrodes govern the electrochemical performance and pumping requirements in redox flow batteries, yet conventional carbon‐fiber‐based porous electrodes have not been tailored to sustain the requirements of liquid‐phase electrochemistry. 3D printing is an effective approach to manufacturing deterministic architectures, enabling the tuning of electrochemical performance and pressure drop. In this work, model grid structures are manufactured with stereolithography 3D printing followed by carbonization and tested as flow battery electrode materials. Microscopy, tomography, spectroscopy, fluid dynamics, and electrochemical diagnostics are employed to investigate the resulting electrode properties, mass transport, and pressure drop of ordered lattice structures. The influence of the printing direction, pillar geometry, and flow field type on the cell performance is investigated and mass transfer vs. electrode structure correlations are elucidated. It is found that the printing direction impacts the electrode performance through a change in morphology, resulting in enhanced performance for diagonally printed electrodes. Furthermore, mass transfer rates within the electrode are improved by helical or triangular pillar shapes or by using interdigitated flow field designs. This study shows the potential of stereolithography 3D printing to manufacture customized electrode scaffolds, which could enable multiscale structures with superior electrochemical performance and low pumping losses.

Combining parallelized emulsion formation and sequential droplet splitting for large‐scale polymer microgel production

AbstractWith the rise of particle‐based material systems in life and materials sciences over the past years, high‐throughput microfluidics has gained tremendous interest as a simple fabrication method for large quantities of tailored emulsions and microparticles. Here, we present the fabrication of microfluidic systems that combine parallelized droplet formation with sequential droplet splitting by 3D printing via projection‐microstereolithography for large‐scale production of water‐in‐oil emulsions and polymer microparticles. The process of droplet splitting is investigated in a 3D‐printed single‐channel, flow‐focusing device and then integrated into a microfluidic system with N = 3 × 20 parallelized channels with individual channel cross‐sections of 60 μm. The arrangement of the integrated functional microfluidic elements is evaluated for different orientations to the 3D printing direction. Furthermore, emulsion droplet size adjustment for flow‐focused and parallelized microfluidic systems is studied. For a proof‐of‐concept, the 3D‐printed microfluidic system is used to fabricate water‐in‐oil emulsions and fluorescently labeled, thermally crosslinked poly(acrylamide) microparticles. With that, our platform provides a straightforward and time‐efficient path toward microgel production in the size range of 140–170 μm on a milliliter‐per‐hour scale combining droplet formation parallelization and three integrated droplet splitting stages.

Recent Advancements in 3-D Printing in Medical Applications

The field of three-dimensional (3D) printing has witnessed significant advancements in recent years, and its potential for revolutionizing medical applications is rapidly emerging. This review aims to provide an overview of the current state and scope of 3D printing in the medical field. The review begins by highlighting the various 3D printing technologies currently employed in healthcare settings, including stereolithography, selective laser sintering, fused deposition modeling, and inkjet printing. Each technology's advantages and limitations are discussed, shedding light on their suitability for different medical applications. Next, the review delves into the diverse range of medical applications where 3D printing has shown promise. These applications include the fabrication of patient-specific anatomical models for preoperative planning, surgical guides and tools, customized implants and prosthetics, tissue engineering scaffolds, and drug delivery systems. The potential benefits of using 3D printing in these areas, such as enhanced surgical accuracy, improved patient outcomes, reduced surgery time, and personalized medicine, are explored. Furthermore, the review addresses the challenges and limitations associated with implementing 3D printing in medical settings. These challenges include regulatory concerns, standardization of processes, material biocompatibility, cost-effectiveness, and scalability. The ongoing efforts to overcome these barriers and the future directions of 3D printing in medicine are also discussed. In conclusion, 3D printing holds immense potential for transforming various aspects of medical practice. While considerable progress has been made, there are still challenges to be addressed before widespread adoption can be achieved. With continued research and development, coupled with regulatory support and collaboration between academia, industry, and healthcare professionals, 3D printing is poised to International Journal of Scientific Research in Engineering and Management (IJSREM) Volume: 07 Issue: 07 | July - 2023 SJIF Rating: 8.176 ISSN: 2582-3930 © 2023, IJSREM | www.ijsrem.com DOI: 10.55041/IJSREM24845 | Page 2 make a substantial impact in the field of medicine, improving patient care and treatment outcomes. Key words: Additive manufacturing (AM); Bio-medical; Fused Deposition Modelling (FDM); Selective Laser Sintering (SLS); Stereolithography (SLA); Digital Light Processing (DLP); Binder Jetting; Material Jetting; Direct Energy Deposition (DED).

A Review of the Residual Stress Generation in Metal Additive Manufacturing: Analysis of Cause, Measurement, Effects, and Prevention.

Metal additive manufacturing (AM) is capable of producing complex parts, using a wide range of functional metals that are otherwise very difficult to make and involve multiple manufacturing processes. However, because of the involvement of thermal energy in the fabrication of metallic AM parts, residual stress remains one of the major concerns in metal AM. This residual stress has negative effects on part quality, dimensional accuracy, and part performance. This study aims to carry out a comprehensive review and analysis of different aspects of residual stress, including the causes and mechanisms behind the generation of residual stress during metal AM, the state-of-the-art measurement techniques for measuring residual stress, various factors influencing residual stress, its effect on part quality and performance, and ways of minimizing or overcoming residual stress in metal AM parts. Residual stress formation mechanisms vary, based on the layer-by-layer deposition mechanism of the 3D printing process. For example, the residual stress formation for wire-arc additive manufacturing is different from that of selective laser sintering, direct energy deposition, and powder bed fusion processes. Residual stress formation mechanisms also vary based on the scale (i.e., macro, micro, etc.) at which the printing is performed. In addition, there are correlations between printing parameters and the formation of residual stress. For example, the printing direction, layer thickness, internal structure, etc., influence both the formation mechanism and quantitative values of residual stress. The major effect residual stress has on the quality of a printed part is in the distortion of the part. In addition, the dimensional accuracy, surface finish, and fatigue performance of printed parts are influenced by residual stress. This review paper provides a qualitative and quantitative analysis of the formation, distribution, and evolution of residual stress for different metal AM processes. This paper also discusses and analyzes both in situ and ex situ measurement techniques for measuring residual stress. Microstructural evolution and its effect on the formation of residual stress are analyzed. Various pre- and post-processing techniques used to countermeasure residual stress are discussed in detail. Finally, this study aims to present both a qualitative and quantitative analysis of the existing data and techniques in the literature related to residual stress, as well as to provide a critical analysis and guidelines for future research directions, to prevent or overcome residual stress formation in metal AM processes.

Shape memory polymers structure with different printing direction: Effect of fracture toughness

The direction in which three-dimensional (3D) printing is carried out strongly affects the mechanical properties of the resultant printed part due to differences in interface bonding strengths between layers. In this work, we study the effect of printing direction (e.g., 0°, 30°, 45°, 60° and 90°) on the fracture toughness of the UV-curable specimen fabricated by digital light process (DLP) 3D printing. A compact tension specimen was used to measure the fracture toughness for different print directions. The digital image correlation(DIC) technique was used to characterize the full strain fields of the specimens. The crack pattern and crack surface were investigated using optical and scanning electron microscopy. The obtained results indicate that samples prepared at 0° and 90° exhibited higher crack resistance compared with that of other directions. DIC analysis indicated that the tendency of the crack path was consistent with the actual crack path. The reported fracture test results for computerized tomography of a specimen prepared with different directions provide a means to reveal the fracture mechanism of a DLP 3D printed structure.

Modeling the fracture behavior of 3D-printed PLA as a laminate composite: Influence of printing parameters on failure and mechanical properties

Additively Manufactured parts are known to be heavily affected by the 3D-printing parameters, and their layered morphology represents a challenge in the mechanical design analysis for engineering applications. In this work, the fracture mechanics of 3D-printed polylactic acid (PLA) samples along different printing directions was simulated as a laminate composite using different numerical approaches, i.e. extended Finite Element (XFEM) and cohesive method. Tensile specimens were 3D-printed via Fused Filament Fabrication in different directions and tested to build the stiffness matrix needed to define the constitutive behavior of the 3D-printed material. Moreover, the influence of different printing parameters (i.e. printing direction, infill, nozzle temperature and perimeter) on the mechanical response was investigated using the statistical approach analysis of variance (Anova). The statistical analysis has shown a strong influence of the printing direction and the perimeters on the resulting mechanical properties, with tensile strength ranging from 52 MPa in the best case to 4 MPa in the worst. The performed FEM analysis correctly predicts the fracture behavior of the 3D-printed samples, with an error on the predicted failure load well below 7%. The investigated model, thus, represents a useful analysis approach to broader the use of 3D printing in engineering applications.

Microstructure evolution and mechanical properties strengthening in laser powder bed fusion of high-strength SiC and TiB2 co-reinforced Al-Zn-Mg-Cu composites

A SiC and TiB2 particles reinforced Al-Zn-Mg-Cu matrix composite was designed and fabricated using laser powder bed fusion (LPBF). This study investigated the effects of ceramic reinforcements on the phase composition, microstructures, grain crystallization, and mechanical properties. The mechanisms of microstructure evolution and mechanical strengthening were discussed. Results show that a multi-level microstructure with ceramic reinforcements and nanoprecipitates has been developed. The ceramic reinforcements exhibited a uniform distribution within the matrix, while the eutectic precipitates formed a network substructure along the grain boundaries. A novel interfacial bonding mechanism, SiC/Al4C3 +eutectics/Al, has been developed through an in-situ reaction between SiC and Al. Ceramic reinforcements provided sufficient nucleation sites for grain nucleation, transforming from coarse columnar growing along the [001] direction parallel to the printing direction to fined equiaxed grains with random growth. The mechanical properties were enhanced, and the microhardness heterogeneity along different directions was reduced. The ultimate tensile strength and elongation were 516 ± 12 MPa and 6.12 ± 0.36%, respectively. The enhancement of mechanical properties was attributed to superior interfacial bonding strength, fine grain strengthening, solution strengthening, second phase strengthening, and substructural strengthening. This work could demonstrate the potential for fabricating AMCs using LPBF with Al-Zn-Mg-Cu alloy as the matrix.

Effects of platelet addition and loading direction on the mechanical properties of textured alumina fabricated by ceramic mask stereolithography

In order to simultaneously enhance the bending strength and fracture toughness of alumina, this research incorporated different amounts of alumina platelets into the ceramic slurry. Based on the shear force generated by the slurry flow during platform positioning, the platelets in the slurry were aligned. The green bodies were then sintered to prepare textured alumina. The results showed that the addition of 5 vol% alumina platelets in the slurry yielded the highest mechanical performance for the textured alumina. When the load was perpendicular to the printing direction, the bending strength and fracture toughness were measured to be 272 MPa and 4.41 MPam1/2, respectively, demonstrating an increase of 132 MPa and 1.25 MPam1/2 compared to non-textured alumina ceramics. Similarly, When the load was parallel to the printing direction, the bending strength and fracture toughness were 318 MPa and 3.4 MPam1/2, respectively, displaying improvements of 149 MPa and 0.65 MPam1/2 compared to non-textured alumina ceramics. The combination of ceramic mask stereolithography additive manufacturing technology and ceramic texturing techniques in alumina fabrication not only shortened the preparation cycle but also improved the bending strength and fracture toughness of alumina, thus expanding their potential applications.

Effect of anisotropy on permeability index and water absorption of 3D printed metakaolin-based geopolymer concrete

3D-printed geopolymer concrete (3DPGPC) is being showcased as a potential alternative to ordinary Portland cement concrete in digital construction. However, the widespread application is limited due to the unknown long-term durability properties of the material, which could also be influenced by the anisotropic behaviour of the prints. The durability index (DI) of metakaolin (MK) based 3DPGPC and mould-cast specimens from mixes modified with 0% and 5% slag and reinforced with 0.5% polypropylene fibre by volume are investigated using the oxygen permeability index (OPI) and water absorption test. 70 mm diameter by 30 mm thick specimens were cored perpendicular (D3-horizontal and D2-vertical) to the printing direction. OPI specimens were cured for 28 and 90 days, respectively, in the climate-controlled room at 23 (±2°C) and 65 (±5%) relative humidity. 7 days before curing elapsed, specimens were placed in the oven and maintained at 50 ℃. Specimens were removed from the oven and cooled to 23 (±2°C) in the desiccator for 2 h before placing them in the permeameter cell for testing at 28 and 90 days of curing following SANS-3001-CO3-3 (2015). The OPI test comprised the supply of oxygen at the pressure of 120 kPa to the permeameter cell and testing terminated when the pressure dropped to 50 kPa. Also, the water absorption of mould cast and 3DPGPC specimens were determined following ASTM D570. The water absorption and permeability coefficients of 3DPGPC are compared with mould-cast to contextualise the durability of 3DPGPC. Slag inclusion reduced the permeability index of mould-cast and 3DPGPC at 28-and 90-day curing ages. However, mould-cast specimens had better OPI performance than 3DPGPC. D3 specimens are less permeable than D2. Also, mould-cast specimens exhibited lower water absorption characteristics than printed specimens. The OPI and water absorption tests indicate different migration characteristics under one-dimensional ingress in 3DPGPC in orthogonal directions.