3D-printed Samples Research Articles

Three-Dimensional-Printed Sensing Samples Embedding Fiber Bragg Gratings: Metrological Evaluation of Different Sample Materials and Fiber Coatings

Embedding optical fibers with fiber Bragg grating (FBG) sensors in 3D-printed samples can effectively facilitate the systematic use of smart materials in many fields such as civil, bio-medical and soft robotics applications. The aim of the study is to analyze different combinations of filament materials and FBG coatings, and to assess their metrological characteristics. Eighteen samples are fabricated and tested under different mechanical and thermal conditions. The repeated tests allow to perform an evaluation of the measurement repeatability for each sample, along with an analysis of the samples sensitivity. The filaments employed are acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and thermoplastic polyurethane (TPU). The fiber coatings are acrylate, Ormocer® and polyimide. The fiber coating has no significative influence on the performance of the sensors. The tests for temperature sensitivity highlight a good performance of ABS (116 pm/°C) and TPU samples (32 pm/°C) up to 60 °C, whereas the fabricated PLA samples (139 pm/°C for polyimide, 55 pm/°C for acrylate, 14 pm/°C for Ormocer®) cannot be used above 40 °C. The tests for strain sensitivity in axial elongation show an average sensitivity of 3.049 nm/mm for ABS, 1.991 nm/mm for PLA, 3.726 nm/mm for TPU. The bending tests show that all specimens materials have different sensitivity to elongation (2.994 nm/mm for ABS, 0.668 nm/mm for PLA, 0.149 nm/mm for TPU). Only for acrylate in PLA samples an effective difference for bending sensitivity resulted (1.241 nm/mm for the acrylate coating vs 2.366 nm/mm for the other coatings).

Comparative physical and mechanical properties of a 3D printed temporary crown and bridge restorative material.

The objective was to compare physic-mechanical properties of different materials used for temporary restorations. Protemp 4/bisacrylic resin, Jet/acrylic resin, and Nexdent C&B/3D-printed resin samples (10mm diameter x 2mm thickness) were analyzed for surface roughness and color stability tests (baseline, after 5 thousand brushing cycles; and after artificial aging in water at 60oC for 24 hours) and Knoop microhardness. All data were checked for normality using Shapiro-Wilk test. Surface roughness and color stability were analyzed using two-way repeated measurements ANOVA, microhardness data was subjected to one-way ANOVA. All tests were followed by Tukey test and were performed with α=0.05. For roughness, material (p=.002), time points (p=.002) and interaction between both (p<.001) were significant. All groups presented similar roughness for measurements of baseline and after brushing. After artificial aging, 3D printed resin showed decreased roughness when compared with other resins, and with its baseline reading. Acrylic resin showed an increase in surface roughness (when compared with measurement after brushing cycles). Considering color stability, only the material (p=.039) and the time (p<0.001) were significant. All groups showed similar color variation before and after artificial aging. There was an increase in color alteration after artificial aging for all groups. Considering microhardness test (p<.001), the 3D printed resin showed the highest values and acrylic resin the lowest. Bysacylic resin was similar to both 3D printed and acrylic resins. The tested 3D printed resins present similar or better properties than other tested temporary materials while being integrated with the digital workflow. Key words:Disinfection methods, hydroxyl radical, environment, surfaces, dentistry.

USING TOPOLOGY OPTIMISATION TO INFLUENCE THE INFILL PLACEMENT OF FUSED DEPOSITION MODELLED PARTS

Additive manufacturing continues to see increased growth and adoption across various industries owing to technology improvements and increasing material options. This paper presents a method to optimise the infill structure placement in fused deposition modelling parts. The method uses finite element analysis and the bi-directional evolutionary structural optimisation technique to determine the optimal placement based on stress and validated through testing 3D-printed samples. The results show that multi-infill geometry outperforms traditional rectilinear infill in loading capacity and stiffness. The paper concludes with a real-world application, using this optimisation method on a railway-related part.

Digital light processing 3D printing of dynamic magneto-responsive thiol-acrylate composites.

Additive manufacturing is one of the most promising processing techniques for fabricating customized 3D objects. For the 3D printing of functional and stimuli-triggered devices, interest is steadily growing in processing materials with magnetic properties. Synthesis routes for magneto-responsive soft materials typically involve the dispersion of (nano)particles into a non-magnetic polymer matrix. Above their glass transition temperature, the shape of such composites can be conveniently adjusted by applying an external magnetic field. With their rapid response time, facile controllability, and reversible actuation, magnetically responsive soft materials can be used in the biomedical field (e.g. drug delivery, minimally invasive surgery), soft robotics or in electronic applications. Herein, we combine the magnetic response with thermo-activated healability by introducing magnetic Fe3O4 nanoparticles into a dynamic photopolymer network, which undergoes thermo-activated bond exchange reactions. The resin is based on a radically curable thiol-acrylate system, whose composition is optimized towards processability via digital light processing 3D printing. A mono-functional methacrylate phosphate is applied as a stabilizer to increase the resins' shelf life by preventing thiol-Michael reactions. Once photocured, the organic phosphate further acts as a transesterification catalyst and activates bond exchange reactions at elevated temperature, which render the magneto-active composites mendable and malleable. The healing performance is demonstrated by recovering magnetic and mechanical properties after the thermally triggered mending of 3D-printed structures. We further demonstrate the magnetically driven movement of 3D-printed samples, which gives rise to the potential use of these materials in healable soft devices activated by external magnetic fields.

Исследование прочности 3D-печатных изделий при варьировании технологических параметров в процессе печати

The technology of additive manufacturing of parts makes it possible to signifi cantly reduce the cost of machinery repair. However, the property formation laws of such parts have not been suffi ciently studied. The authors have studied the relationship between the ultimate strength of 3D-printed samples and the number of wall layers and infi ll density. Samples produced according to GOST 11262-2017 by 3D printing using FDM technology from ABS plastic were tested for static stretching. Two groups of samples, diff erent in technological parameters of 3D-printing, were made. In the fi rst group the wall of the samples was formed in four layers, the density of the sample fi ll varied in the range of 20 to 100%. In the second group, the number of wall layers varied from 2 to 10, the infi ll density of the samples corresponded to 33%. When samples were made, extruder temperature was 230°C, table temperature - 110°C, layer height - 0.15 mm, and printing speed - 60 mm/s. An analysis of the yield strength of the samples showed an increase in strength with an increase in the number of wall layers. Signifi cant diff erence of strength values was observed in samples with six layers and more. Signifi cant variation of yield strength values can be explained by the presence of defects in the samples after printing. When infi ll density exceeded 40%, a signifi cant increase in strength was observed due to the densifi cation of polymer molecule bonds. In the range of 20 to 40%, the strength index did not change, because the same structural changes occurred in this range. It was found that the number of wall layers should not exceed the number of inner perimeter layers and the infi ll density of the parts should be 100% to produce polymeric parts of agricultural machinery by 3D printing using FDM technology with maximum strength characteristics.

TPMS-based interpenetrating lattice structures: Design, mechanical properties and multiscale optimization

Compared to single-phase structures, interpenetrating lattice structures display the potential to achieve a wide range of tailorable physical and mechanical properties. Herein, we present a novel class of interpenetrating lattice structures based on triply periodic minimal surfaces. Using representative volume elements applied with the periodic boundary conditions, the contributions of the volume fraction and the interpenetrating parameter, a measure of the ratio of the two phases, on the mechanical properties and deformation behavior of the interpenetrating lattice structures are investigated. Results show that the mechanical properties are highly dependent on the interpenetrating parameter, and isotropic elasticity can be achieved at a particular value. Moreover, the uniaxial and shear deformation mechanisms (bending or stretching behavior) can be easily changed by adjusting the interpenetrating parameter. Our new interpenetrating lattice designs are experimentally validated using 3D-printed samples. Finally, a new multiscale optimization framework, based on simultaneously optimizing the distribution of the volume fraction and the interpenetrating parameter, is developed. Compared to the traditional optimized designs that only consider the volume fraction, the proposed optimized design reduces the structural compliance by more than 10.85%, confirming the effectiveness of the proposed optimization framework for lightweight applications.

Ultrasonic Welding of Additively Manufactured PEEK and Carbon-Fiber-Reinforced PEEK with Integrated Energy Directors

The thermoplastic polymer polyether ether ketone (PEEK) offers thermal and mechanical properties comparable to thermosetting polymers, while also being thermally re-processable and recyclable as well as compatible with fused filament fabrication (FFF). In this study, the feasibility of joining additively manufactured PEEK in pure and short carbon-fiber-reinforced form (CF-PEEK) is investigated. Coupon-level samples for both materials were fabricated using FFF with tailored integrated welding surfaces in the form of two different energy director (ED) shapes and joined through ultrasonic polymer welding. Using an energy-driven joining process, the two materials were systematically investigated with different welding parameters, such as welding force, oscillation amplitude and welding power, against the resulting weld quality. The strengths of the welded bonds were characterized using lap-shear tests and benchmarked against the monotonic properties of single 3D-printed samples, yielding ultimate lap-shear forces of 2.17kN and 1.97kN and tensile strengths of 3.24MPa and 3.79MPa for PEEK and CF-PEEK, respectively. The weld surfaces were microscopically imaged to characterize the failure behaviors of joints welded using different welding parameters. Samples welded with optimized welding parameters exhibited failures outside the welded region, indicating a higher weld-strength compared to that of the bulk. This study lays the foundation for using ultrasonic welding as a glue-free method to join 3D-printed high-performance thermoplastics to manufacture large load-bearing, as well as non-load-bearing, structures, while minimizing the time and cost limitations of FFF as a fabrication process.

Self-Monitoring Performance of 3D-Printed Poly-Ether-Ether-Ketone Carbon Nanotube Composites

In this paper, poly-ether-ether-ketone (PEEK) carbon-nanotube (CNT) self-monitoring composites at different levels of filler loading (i.e., 3, 5 and 10% by weight) have been extruded as 3D-printable filaments, showing gauge factor values of 14.5, 3.36 and 1.99, respectively. CNT composite filaments of 3 and 5 wt% were 3D-printed into tensile samples, while the PEEK 10CNT filament was found to be barely printable. The 3D-printed PEEK 3CNT and PEEK 5CNT composites presented piezo-resistive behavior, with an increase in electrical resistance under mechanical stress, and showed an average gauge factor of 4.46 and 2.03, respectively. Mechanical tests highlighted that 3D-printed samples have a laminate-like behavior, presenting ultimate tensile strength that is always higher than 60 MPa, hence they offer the possibility to detect damages in an orthogonal direction to the applied load wit high sensitivity.

Characterization of mechanical properties of soft tissues using sub-microscale tensile testing and 3D-Printed sample holder

Obtaining the mechanical properties of soft tissues is critical in many medical fields, such as regenerative medicine and surgical simulation training. Although various tissue-characterization methods have been developed, such as AFM, indentation, and elastography, there remain some limitations on their accuracy and validity for measuring small and fragile soft tissues. This paper presents a tensile testing technique to measure the mechanical properties of soft tissues directly and accurately. Tensile testing was chosen as the primary method because of its simple procedure and ability to derive mechanical properties without requiring many assumptions or complicated models. However, tensile testing on soft tissues presents challenges related to gripping the tissue sample without affecting its inherent properties, applying minuscule forces to the sample, and measuring the cross-section area and strain of the sample. To solve these issues, this study presents a sub-micro scale tensile testing system that uses a flexure mechanism and a novel 3D-printed sample holder for gripping the tissue samples. The system also measures tested samples' cross-section area and strain using two high-resolution cameras. The system was validated by testing standard materials and used to characterize the elastic modulus, yield stress, and yield strain of lung tissue slices from six different mice. The results from the validation tests showed a less than 2.5% error for elastic modulus values measured using the tensile tester. At the same time, results from the mice lung tissue measurements revealed qualitative findings that closely matched those seen in the literature and displayed low coefficient of variation values, demonstrating the high repeatability of the system.

Optimizing Color-Difference Formulas for 3D-Printed Objects.

Based on previous visual assessments of 440 color pairs of 3D-printed samples, we tested the performance of eight color-difference formulas (CIELAB, CIEDE2000, CAM02-LCD, CAM02-SCD, CAM02-UCS, CAM16-LCD, CAM16-SCD, and CAM16-UCS) using the standardized residual sum of squares (STRESS) index. For the whole set of 440 color pairs, the introduction of kL (lightness parametric factor), b (exponent in total color difference), and kL + b produced an average STRESS decrease of 2.6%, 26.9%, and 29.6%, respectively. In most cases, the CIELAB formula was significantly worse statistically than the remaining seven formulas, for which no statistically significant differences were found. Therefore, based on visual results using 3D-object colors with the specific shape, size, gloss, and magnitude of color differences considered here, we concluded that the CIEDE2000, CAM02-, and CAM16-based formulas were equivalent and thus cannot recommend only one of them. Disregarding CIELAB, the average STRESS decreases in the kL + b-optimized formulas from changes in each one of the four analyzed parametric factors were not statistically significant and had the following values: 6.2 units changing from color pairs with less to more than 5.0 CIELAB units; 2.9 units changing the shape of the samples (lowest STRESS values for cylinders); 0.7 units changing from nearly-matte to high-gloss samples; and 0.5 units changing from 4 cm to 2 cm samples.

Turning desert sand into building material products: An ambitious attempt of solar 3D printing

Global desertification is a significant concern, and non-renewable energy sources are scarce. To address this issue, solar three-dimensional (3D) printing can be used for desert sand to manufacture green building materials. In this study, process parameter optimization experiments for solar 3D printing were conducted, and the 3D-printed samples were analyzed by an X-ray scanning system, scanning electron microscopy, X-ray diffraction, universal testing machine, Vickers hardness tester, nanoindenter, thermal dilatometer, and laser flash analyzer. The experimental data from the tests showed that the compressive strengths of the 3D-printed samples reached 62.05 MPa and the thermal conductivities reached 1.069 W/m·K. The flexural strength, Vickers hardness, fracture toughness and coefficient of thermal expansion also reached the levels of samples obtained by the conventional process. Finally, two types of scaled building material products were 3D printed, and the interlocking self-assembly was realized. This study demonstrated that it is feasible to use direct focused sunlight to 3D print desert sand and manufacture building materials. This unprecedented method of manufacturing building materials has significance for desertification control, energy conservation and environmental protection.

Enhanced thermoelectric performance of 3D-printed Bi2Te3-based materials via adding Te/Se

Bi2Te3-based materials were prepared by direct ink writing (DIW) 3D printing and their microstructure and thermoelectric properties were investigated with an emphasis on the effect of the content of DMF and Te/Se addition. As the mass ratio of DMF in the composition increased from 6.5% to 8.0% (in mass), the electrical conductivity deteriorated because of the corresponding increased porosity and organic remains in the samples. However, the volatilization of DMF would reduce the fluidity of the slurry. Thus, thermoelectric slurry with 7.0% DMF is the most suitable mass ratio for 3D printing. Additionally, adding Te in the p-type Bi0.4Sb1.6Te3 and adding Se in the n-type Bi2Te2.6Se0.4 have significantly improved their electrical conductivity due to the increased carrier concentration and mobility. Combining with the moderate Seebeck coefficient (∼200 μV/K), high power factors with ∼802 μW·m−1·K−2 and 1266 μW·m−1·K−2 were obtained for the n-type Bi2Te2.6Se0.4+10%Se and p-type Bi0.4Sb1.6Te3+7%Te, respectively, which result in the final relatively high zT values of 0.68 at 573 K and 0.56 at 330 K for n-type and p-type 3D-printed samples.

Recycled PP for 3D Printing: Material and Processing Optimization through Design of Experiment

In this work, blends that were based on first use PP added with talc (PPt) and recycled polypropylene (r-PP) were designed and formulated, aiming at producing filaments that are suitable for 3D printing fused filament fabrication (FFF) processes. A preliminary characterization of PPt/r-PP blends at different weight ratios allowed selecting two systems showing adequate rheological behavior for FFF. The selected blends were melt compounded in a twin-screw extruder, optimizing the processing conditions through a design of experiments approach, involving the use of Taguchi’s method. The materials that were prepared with the optimized processing conditions, hence showing the best performance in terms of rheological behavior and thermal characteristics, were then selected for the production of the filament and for the subsequent FFF processing. Finally, the morphology of the filament and the mechanical properties of 3D-printed samples were assessed, demonstrating the achievement of satisfactory results in terms of performances. In general, the obtained results clearly demonstrated that a proper optimization of both material and processing conditions offers the possibility of using recycled PP-based formulations for additive manufacturing processes, hence allowing a remarkable valorization of a low added-value material through its utilization for an innovative and sustainable manufacturing approach.

Fused Filament Fabrication of Alumina/Polymer Filaments for Obtaining Ceramic Parts after Debinding and Sintering Processes.

In this paper, a hybrid commercially available alumina/polymer filament was 3D printed and thermally treated (debinding and sintering) to obtain ceramic parts. Microscopic and spectroscopic analysis was used to thoroughly characterize the green and sintered parts in terms of their mesostructured, as well as their flexural properties. The sintered samples show an α alumina crystalline phase with a mean density of 3.80 g/cm3, a tensile strength of 232.6 ± 12.3 MPa, and a Vickers hardness of 21 ± 0.7 GPa. The mean thermal conductivity value at room temperature was equal to 21.52 ± 0.02 W/(mK). The values obtained through FFF production are lower than those obtained by conventional processes as the 3D-printed samples exhibited imperfect interlayer bonding and voids similar to those found in the structures of polymeric FFFs. Nonetheless, the highly filled ceramic filament is suitable for use in affordable and easy-to-operate FFF machines, as shown by the cost analysis of a real printed and sintered FFF part.

A new methodology to efficiently test pitting corrosion: design of a 3D-printed sample holder to avoid the occurrence of crevice corrosion in chemically aggressive media

A new methodology to efficiently test pitting corrosion: design of a 3D-printed sample holder to avoid the occurrence of crevice corrosion in chemically aggressive media

Simple Preparation of Metal-Impregnated FDM 3D-Printed Structures.

Modifying the natural characteristics of PLA 3D-printed models is of interest in various research areas in which 3D-printing is applied. Thus, in this study, we describe the simple impregnation of FDM 3D-printed PLA samples with well-defined silver nanoparticles and an iron metal salt. Quasi-spherical and dodecahedra silver particles were strongly attached at the channels of 3D-printed milli-fluidic reactors to demonstrate their attachment and interaction with the flow, as an example. Furthermore, Fenton-like reactions were successfully developed by an iron catalyst impregnated in 3D-printed stirrer caps to induce the degradation of a dye and showed excellent reproducibility.

Environmental stress cracking of 3D-printed polymers exposed to concrete

Increasing demand for complex concrete shapes in architecture has triggered the use of digital fabrication methods for producing non-standard formworks. To this end, polymer extrusion 3D printing has already shown promising results in a range of research projects. However, 3D-printed polymer formworks can suffer from sudden failures during casting, which are generally associated with the pressure exerted by the wet concrete on the thin plastic formworks. Such failures can however be substantially accelerated by the corrosive effects of the wet concrete paste on some 3D-printed thermoplastics, a phenomenon that has not been studied in depth so far. This paper first reviews the state of the art of 3D-printed polymer formworks and their applications in architecture. It focuses on the failures caused by formwork pressure and synthesizes the various solutions to this problem reported in the literature. Beyond this, additional results are introduced to provide a guideline for thermoplastic selection in 3D-printed formworks. Common thermoplastics are presented, and their behaviour during concrete casting is documented. This behaviour can be analysed through ultimate strength and creep tests performed in three-point bending on 4 × 10 × 100 mm 3D-printed polymer samples, both in dry state and exposed to an alkaline solution of pH 13, typical for cementitious materials. The tests show that contact with the alkaline solution leads to a rapid strength loss in some thermoplastics. This effect is particularly pronounced with PLA and its blends, for which the strength loss over 10 min is more than 80 % compared to dry samples. Other thermoplastics, such as ABS, ASA, HIPS, Nylon, PVA and ABS/PC have shown more limited or in some cases no deterioration under the same conditions. The material-specific mechanism of deterioration is environmental stress cracking in contact with the alkaline solutions and it occurs in all 3D printing orientations and loading directions where tensile stresses occur. • Polymer extrusion 3D printing is used to fabricate complex formworks for concrete. • 3D-printed polymer formworks can suffer sudden failures during concrete casting. • High pH and hydrostatic pressure can reduce the strength of some polymers by 80 %. • This is a material-specific phenomenon known as environmental stress cracking.

Directional passive acoustic structures inspired by the ear of Achroia grisella

The need for small directional microphones is patent in the current market. From smartphones to hearing aids, a small microphone capable of rejecting ambient noise is highly desirable. Most MEMS microphones are omnidirectional and have to resort to arrays to achieve directionality, effectively counteracting the reduced size that they offer in the first place. For this reason, we use bio-inspiration and turn to nature to find examples of solutions to this problem. The female specimens of the moth Achroia grisella are capable of monoaural directional hearing, which they use to track the males’ mating calls. It is believed that they achieve directionality solely due to the morphology of their tympana. To test it, we first produce a multiphysics simulation of the structure that serves as a starting point. For experimental measurements, additive manufacturing is chosen for its ease and cost-efficiency. 3D-printed samples of the same model are examined through micro-CT scanning and then measured using laser-Doppler vibrometry to determine their frequency and directivity responses. The results of both approaches are compared, and it is found that the structure does indeed show directionality with the second eigenfrequency showing a hypercardioid-like pattern towards the front of the moth.

Effects of drying method on the stability and quality of post-processing of 3D-printed processed cheese

The three-dimensional (3D) printing of processed cheese personalizes food materials and provides a novel means of addressing the nutritional and health needs of consumers. This study used “Anjia” cheese as a raw material to explore the effects of hot air drying (AD) and freeze drying (FD) on the shape and color stability, volatile flavor compounds, casein content, and microstructure of 3D-printed samples after post-processing. Compared with AD -finished products, FD-finished products exhibited better post-processing stability in their dimensional characteristics and color, a higher casein retention rate, and a finished porosity as low as 5.7%. The drying efficiency of FD was also higher, with the drying time decreasing by 66.7% compared with that of AD. The combination of FD and 3D printing can thus yield higher quality products. This study provides useful information for developing post-processing and high-value-added 3D-printed products, especially for nutritional functional foods.

Investigation of the light output of 3D-printed plastic scintillators for dosimetry applications

Three-dimensional (3D) printing, specifically digital light processing (DLP) technique, can be used to manufacture plastic scintillators of any shape. The purpose of this study was to determine the light output of DLP 3D-printed scintillators for dosimetry applications. Two types of plastic scintillators with dimensions 10 mm × 10 mm × 10 mm were fabricated using DLP 3D-printing at Hanyang University, South Korea. The light output of these DLP 3D-printed samples was measured and compared to that of a commercial plastic scintillator of the same dimensions, RP-408, produced by casting. The 3D-printed scintillators emitting violet and blue light had a lower relative light output by 49% and 43%, respectively, compared to the RP-408 reference scintillator. We also investigated three types of scintillator surface finishing methods: the original surface made by the 3D printer, a sanded surface, and a polished surface. Furthermore, three wrapping configurations were tested: bare scintillator, diffuse-type polytetrafluoroethylene tape, and specular-type enhanced specular reflector foil. Both reflector types, diffuse and specular, reflected blue light with comparable efficiency. Additionally, emission and transmission spectra of the samples were measured. Emission maxima were located at 430 nm for RP-408, and 438 and 475 nm for two 3D-printed samples. Transmittance at the wavelength of maximum emission was equal to 89% for RP-408, and 73% and 66% for the two DLP-printed samples. Although the light output of the 3D-printed scintillators was about 50% lower than that of the commercial plastic scintillator, due to characteristics of 3D-printed plastic scintillators, i.e. fast, low-cost production, and easy customization of the printed shape, they are promising as an active part of dosimeters for use in high intensity gamma radiation fields produced by medical linear accelerators with acceptable signal-to-noise ratio level.