LCD stereolithography of ceramics allows the creation of ceramic parts with unprecedented resolution for various applications from medical tooling to archeological restoration. However, the ...manufacturing of a delamination cracks-free sintered part using LCD stereolithography has been an arduous challenge in both industrial and academic research. This contribution is a guide for the elimination of such delamination cracks. Photo-rheology, instrumented indentation tests, UV/Vis spectrophotometry and multiple microscopy techniques were used to analyze the formation of delamination cracks and to identify their culprits. It was found that proper particle dispersion, sufficient air extraction, optimized slurry formulation, optimized printing parameters and sound design principles jointly contribute to the manufacturing of a delamination cracks-free ceramic part using LCD stereolithography. This research addresses each of the aforementioned factors, with the goal of improving the quality of ceramic parts and increasing their functionality for various applications.
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Additive manufacturing of bio-ceramics using LCD stereolithography allows the creation of ceramic parts with unprecedented resolution for various medical applications. However, the potential of this ...technology can only be fully harnessed if the manufacturability of critical geometries is accurately characterized. Thus, this contribution provides a guide with examples for the characterization and analysis of the printability of β-tricalcium phosphate-filled resins using LCD stereolithography. Characterized features include the minimum bore diameter, the minimum wall thickness of free-standing walls and cylindrical pins, the maximum unsupported bridging and overhang and the maximum abrupt thickness changes of cylindrical components. The analysis addresses limitations and factors affecting manufacturability of bio-ceramic-filled resins, and gives recommendations for design and processing parameters. In addition, TGA analysis is presented as a guide for the selection of suitable debinding and sintering schedules for an optimized microstructure and functionality.
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•Manufacturability of a β-Tricalcium Phosphate-filled resin using LCD stereolithography is systematically analyzed.•Maximum/minimum producible geometries are tested and illustrated.•TGA analysis and SEM imaging guided the processing and characterization.•Guidelines for a better manufacturability are given.
Optimizing the process of vat photopolymerization for ceramics necessitates the thorough understanding of the complex interactions between light and ceramic particles. However, it is not yet fully ...described how the size distribution of ceramic particles affects the curing behavior of ceramic-filled resins. Thus, this contribution provides insight into the influence of the particle size distribution (PSD) on the rheological behavior and the polymerization kinetics of photo-curable ceramic-filled resins. Four grades of alpha-aluminum oxide with different PSDs in an acrylate-based photo-curable resin were investigated. The PSD was measured using a laser diffraction particle size analyzer based on the Mie theory. The quantum of attenuated light was measured with an Ultraviolet/Visible (UV/Vis) spectrophotometer equipped with a modified integrating sphere accessory. UV/Vis measurements revealed that samples with a smaller mean particle size result in larger attenuation in the UV region of the spectrum (i.e., ∼190 nm–420 nm). Moreover, photo-rheology measurements revealed that larger particles generally result in faster polymerization rates without a noticeable change in the degree of conversion. In addition, rheological and sedimentation tests revealed that ceramic-filled resins with a larger mean particle size exhibit lower viscosity and lower sedimentation stability. The findings of this work contribute to the optimization of the process of ceramic powder selection. This results in an increase in the sedimentation stability of ceramic-filled resins, and a customization of their curing behavior.
•X-ray CT reveals voids-distribution in the joint of a brazed sample.•High resolution is possible for materials with similar absorption coefficients.•Image reconstruction techniques offer accurate ...quantitative analysis of voids.•Factors for a successful scan and dataset postprocessing are presented.
Brazing is a relatively fast process that offers sufficient strength in the joint of dissimilar materials. Cemented carbides are often brazed onto steel components in order to improve the wear resistance of engineering tools. In the case of brazing such materials in an ambient atmosphere, a flux is necessary to improve the wetting of the liquid filler alloy on the surfaces. In some cases, the flux cannot be sufficiently removed from the small joint, thus forming voids during solidification. This phenomenon can greatly affect the integrity of the joint. Such voids are not adequately detectable by visual inspection or common nondestructive testing methods, such as ultrasonic scanning, acoustic emission testing, or thermography. In this study, X-ray microscopy is shown to provide adequate visualization and a quantitative analysis of the dispersion of voids within brazed components of cold work steel, 115CrV3, and cemented carbide, K10 (ISO 513). One of the challenging tasks when analyzing the aforementioned brazed materials is achieving a sufficiently high resolution within the joint gap, since the sample materials have similar X-ray absorption coefficients. Such high resolution was successfully achieved in this study by means of multiple scanning and image reconstruction techniques, such as beam filtering, dataset levelling, and noise removal. The voids on the 115CrV3-side are found to expand radially towards the edges of the specimen up to a maximum volume of 1.18E + 07 µm3. The same radial pattern was detected on the side of the K10, where the voids contracted in volume towards the center of the specimen. However, the K10-side was found to exhibit relatively larger voids with a maximum volume of 7.70E + 07 µm3, that is approximately seven times larger than that detected on the 115CrV3-side.
Advances in technology have provided fresh generations of stiff polypropylene block copolymers for gravity sewerage applications. The aim of this study is to further enhance the stiffness of these ...materials through the incorporation of inorganic fillers. In this study, three talc filled PP and one glass fiber filled PP composites were characterized in order to be used as a middle layer in a three‐layer sewage pipe. The obtained results showed an increase of approximately more than 100% and 250% in tensile and flexural moduli by the use of 30%–50 wt% talc‐filled PP and 30 wt.% glass fiber‐filled PP, respectively. This high increase in the rigidity of the material would allow manufacturing pipes with improving ring stiffness. Composites filled with 30 wt% talc or glass fiber showed good filler‐matrix interaction and good filler distribution and dispersion. However, reduced filler‐matrix interaction was observed in the case of the composite filled with 50 wt% talc. In addition, the use of Differential Scanning Calorimetry analysis revealed that the addition of fillers enhanced the crystallization temperature of the polypropylene matrix. Furthermore, Thermogravimetric Analysis showed that the high modulus PP grade retained its thermal stability in the various composites.
Improvement of the ring stiffness of a plain pipe by the development of a multilayer composite pipe.
Background: High levels of non-HDL cholesterol (non-HDL-C), triglycerides (TG), lipoprotein (a) (Lp(a)), and Proprotein convertase subtilisin/kexin type 9 (PCSK9) as well as low levels of HDL-C are ...strongly associated with cardiovascular disease (CVD). Our study aims to estimate the prevalence of dyslipidemia and high Lp(a) in the Lebanese population and to study the relationship of these variables with gender, age, body mass index (BMI), and PCSK9. Methods: This cross-sectional study was carried out on a sample of healthy volunteers aged 18 to 65. Blood samples were drawn from volunteers for total cholesterol (TC), HDL-C, TG, PCSK9, and Lp(a) measurements. Non-HDL-C was calculated by subtracting HDL-C from TC. Results: In total, 303 volunteer subjects with an average age of 38.9 years were included in the study. Respectively, 44%, 29.8%, and 44% of men had high non-HDL-C and TG with low HDL-C versus 23.5%, 8%, and 37% in women. Non-HDL-C and TG were significantly higher in men than in women, while the reverse was observed for HDL-C (p < 0.0001 for the three comparisons). Non-HDL-C and TG were significantly correlated with age and BMI (p< 0.0001 for all correlations), while HDL-C was inversely correlated with BMI (p < 0.0001) but not with age. Abnormal Lp(a) levels (≥75 nmol/L) were found in 19.1% of the population, predominantly in women (24.1% versus 13.4% in men, p = 0.004). The median PCSK9 and its interquartile was 300 (254−382) ng/L with no gender difference (p = 0.18). None of the following factors: gender, age, BMI, non-HDL-C, HDL-C, or TG, were independently associated with Lp(a), while PCSK9 was significantly correlated with age, non-HDL-C, and TG in both men and women and inversely correlated with HDL-C in men. Dyslipidemia is very common in the Lebanese population and is associated with age, high BMI, and male sex. Lp(a) is higher in women without any correlation with the lipid profile, whereas PCSK9 is associated with non-HDL-C and TG. Further studies are needed to evaluate the potential role of Lp(a) and PCSK9 in predicting CVD in healthy populations.
