Three-point Bending Research Articles

Effects of Semaglutide and Tirzepatide on Bone Metabolism in Type 2 Diabetic Mice

Background/Objectives: Type 2 diabetes and weight loss are associated with detrimental skeletal health. Incretin-based therapies (GLP-1 receptor agonists, and dual GIP/GLP-1 receptor agonists) are used clinically to treat diabetes and obesity. The potential effects of semaglutide and tirzepatide on bone metabolism in type 2 diabetic mice remain uncertain. Methods: Combined streptozotocin and high fat feeding were employed in female C57BL/6J mice to promote hyperglycemia. Mice were administered for 4 weeks with a saline vehicle (sc., once-daily), semaglutide (40 μg/kg/d, sc., every three days), or tirzepatide (10 nmol/kg, sc., once-daily). Bone strength was assessed by three-point bending. Femur microarchitecture was determined by micro-CT, and bone formation and resorption parameters were measured by histomorphometric analysis. Serum was collected to measure bone resorption (C-telopeptide fragments of type I collagen, CTX) and formation (procollagen type 1 N-terminal propeptide, P1NP) biomarkers, respectively. The expression of bone metabolism-related genes was evaluated in the bone using RT-PCR. Results: Glucose levels significantly reduced after 4 weeks of semaglutide and tirzepatide treatment (both p < 0.05) compared with vehicle treatment. Tirzepatide led to more weight loss than semaglutide. Compared to saline-treated diabetic mice, the mean femur length was shorter in the tirzepatide group. After treatment with tirzepatide or semaglutide, cortical bone and trabecular bone parameters did not change significantly compared to saline-treated diabetic mice, except that cortical thickness was lower in the semaglutide group compared to the saline group (p = 0.032). Though CTX and P1NP levels decreased, however, the change in CTX and P1NP levels did not differ among the four groups during the 4 weeks of treatment (all p > 0.05). Semaglutide affected RANKL and OPG mRNA expression and increased the ratio of OPG/RANKL. No significant difference was found in the quantity of Col1a1, RANKL, OPG, and RUNX2 between tirzepatide- and saline-treated diabetic mice. Conclusions: The 4-week treatment with semaglutide and tirzepatide had a neutral effect on bone mass compared with the controls, and most of the bone microarchitecture parameters were also comparable between groups in diabetic mice. A better understanding of incretin-based therapies on bone metabolism in patients with diabetes requires further evaluation in large clinical trials.

Response of perforated pipes buried in sand under lateral soil-pipe movements

The use of perforated pipes can be seen increasingly in many applications to facilitate drainage/infiltration of liquid through opening channels in the pipe wall. Design of perforated pipes lacks consideration for lateral soil-pipe interaction induced by differential ground movement, which can generate large pipe stresses and strains. In this study, in-air three-point bending tests were conducted on perforated pipes, which were subsequently evaluated through lateral dragging tests. The mechanical responses of perforated pipes with different hole diameters (d), spacings between holes (s), and layers of holes (l) were interpreted. It is found that the load-displacement curves for all tests generally did not show significant difference. The pipe wall thickness had a significant impact on midspan deflection, reflecting by the smallest midspan deflection due to a higher flexural rigidity. All tested perforated pipes were safe, since the maximum pipe strains were well below the linear elastic limit of 3% for polyvinyl chloride (PVC) material. Finally, the efficacy of two prediction methods was assessed. The approach of Cholewa et al. (2009) provided relatively close estimations, while the solution of Ye et al. (2023a) was suitable for use at relatively small pipe end displacements before the mobilization of peak soil resistance.

Biomechanical Analysis of Camellia oleifera Branches for Optimized Vibratory Harvesting

To investigate the biomechanical properties of Camellia oleifera branches under two loading speeds within a specific diameter range, three-point bending tests were conducted using a universal material–testing machine. The tests were performed at loading speeds of 10 mm/min and 20 mm/min on branches with diameters ranging from 5 mm to 40 mm. This study aims to provide insights into the design of a manipulator gripper used in a vibrating harvester for Camellia oleifera fruit. Four main varieties of Camellia oleifera were tested to determine their elastic modulus. The nonlinear least squares method, based on the hyperbolic tangent function, was employed to fit the bending load–deflection curves of the branches. This process constructed multi-parameter transcendental equations involving elastic modulus, diameter, and loading speed. Results indicated that the branches of four Camellia oleifera varieties exhibited significant differences in their biomechanical properties, with their modulus of elasticity ranging from 459.01 MPa to 983.33 MPa. This suggests variability in the bending performance among different varieties. For instance, Huaxin branches demonstrated the highest rigidity, while Huashuo branches were softer in general. For the proposed empirical fitting equations, when the fitting parameter k is 168 ± 20 and the parameter c is 3.102 ± 0.421, the bending load–deflection relationship of the branches can be predicted more accurately. This study provides a theoretical basis for enhancing the efficiency of mechanized vibratory picking of Camellia oleifera and optimising the design of the gripper.

Investigation of temperature effect on thermo-mechanical property of carbon fiber/PEEK composites

Abstract Considering the temperature sensitivity and two-phase incompatibility of the fiber matrix interface, carbon fiber-reinforced thermoplastic composites suffer from weak interfacial bonding strength. To investigate the delamination damage and shear failure mechanism of T700/PEEK composites at varying temperatures, interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) were performed by employing micro debonding experiments and three-point bending. The results indicated that at temperatures below the glass transition, the IFSS of T700/PEEK composites was positively correlated with temperature, and the average strength recorded was 52 ± 6 MPa. When the glass transition temperature was exceeded, the bonding state between polyether ether ketone material and fiber surface became tighter, resulting in a slight increase in IFSS, reaching 60 ± 4 MPa. Further, the ILSS of T700/PEEK composites was tested, and the results indicated a negative correlation between ILSS and temperature, with a maximum ILSS of 40 ± 2 MPa observed at 23°C, and a minimum of 11 ± 1 MPa recorded at 230°C. The decline in bending strength observed with increasing temperature was attributed to the separation of the fiber and matrix interface at high temperatures, which reduced the mechanical properties of T700/PEEK composites. By conducting temperature related mechanical performance tests on T700/PEEK composite materials, the obtained test results will help researchers expand the application scenarios of this material, deepen the relationship between the temperature and its performance, and thus more quickly explore the mechanism of temperature action.

Ablation and mechanical properties of carbon/high silica/phenolic composites: Using experimental analysis and five machine learning models for correlating and generalizing to diverse compositional ratios

This paper investigates the thermal and mechanical properties of carbon/high silica/phenolic composites with varying reinforcement ratios. Five hybrid samples were fabricated: 100% carbon, 75% carbon/25% silica, 50% carbon/50% silica, 25% carbon/75% silica, and 100% silica. A three-point bending test evaluated their strength, while an ablation test at 3000°C for 1 minute measured backside temperature, linear ablation rate, and mass ablation rate. Results indicated that the 100% carbon sample had the highest bending strength, while the 50% carbon/50% silica sample achieved the lowest linear and mass ablation rates, demonstrating an effective balance between fire retardancy and insulation, resulting in minimal backside temperature during ablation. Additionally, five machine learning models (Linear Regression, Decision Trees, Random Forests, Gradient Boosting Machines, and Neural Networks) were utilized to predict mass ablation rate, linear ablation rate, and strength. Decision Trees and Gradient Boosting Machines exhibited the highest prediction accuracy, while Linear Regression struggled with non-linear data, resulting in lower accuracy for ablation rate predictions. Notably, these models were also able to generalize to other percentages, showcasing their robustness and versatility in optimizing material compositions beyond the tested scenarios. This study highlights the potential of machine learning in predicting the properties of advanced composites, contributing to the development of high-temperature resistant materials.

Design and characterization of natural fiber reinforced cotton-epoxy composites

This research paper focuses on the design and fabrication of natural cotton epoxy composites. By combining natural cotton fibers with epoxy resin, the study aims to develop composite materials with desirable mechanical properties. To evaluate their performance, the composites were subjected to three-point bending tests, which revealed an average flexural strength of 50 MPa and a flexural modulus of 3.8 GPa, highlighting the material’s capacity to bear bending loads. The bending tests provided insights into the composite’s response to flexural loads, including its strength, stiffness, and failure mechanisms. Post-test analysis using an optical microscope revealed that the primary failure modes included delamination and fiber breakage. Delamination, characterized by the separation of layers within the composite, and fiber breakage, caused by the fibers’ inability to withstand stress exceeding their tensile strength of approximately 300 MPa, led to crack propagation through the material. These findings indicate that the composite's failure was primarily driven by these mechanisms. This study provides valuable insights into improving the composite's design and enhancing its mechanical properties, contributing to the broader understanding of natural fiber-reinforced composites and their behavior under mechanical stress.

Calibration and experiments of discrete element flexible model parameters for kiwifruit stalk

A method combining experimental and simulation optimization was used to calibrate parameters to enhance the accuracy of discrete element model parameters during kiwifruit stem separation. First, physical experiments were conducted to determine the intrinsic and contact parameters of kiwifruit stalk. Second, the mechanical parameters of the kiwifruit stalks were determined using three-point bending and shear tests. On this basis, simulation tests were conducted on kiwifruit stalks by combining the Hertz-Mindlin model with a bonding model, and the optimal combination of bonding parameters was confirmed using the bending strength and maximum shear force. Finally, a discrete element model of the kiwifruit was built with the determined bonding parameters and simulated, and the reliability of the model was verified through mechanical tests. The results showed that the density was 867.5 kg/m3, Poisson's ratio was 0.26, the modulus of elasticity was 3.25 × 108 Pa, the recovery coefficient between the fruit stalks and steel parts was 0.365, and the average values of the static and dynamic friction coefficients between the kiwifruit stalks and steel parts were 0.268 and 0.152, respectively. The kiwifruit stem bonding parameters were normal stiffness per unit area kn=7.201×1011 N/m3, shear stiffness per unit area kt=2.379×1011 N/m3, critical normal stress σmax=5.937×108 Pa, critical shear stress tmax = 2.354×109 Pa, and bonded disc radius Rj=0.164 mm. Compared with the results of the mechanical tests, the relative errors of the bending strength and maximum shear of the discrete element model were 2.13% and 2.84%, respectively. The results showed that the discrete element model improves the simulation of the bending and shearing processes of kiwifruit stalks and is capable of characterizing the physical properties of kiwifruit stalks. The results of this study provide a theoretical foundation for the optimal design of end effectors.

Mechanical Properties and Fire Resistance of 3D-Printed Cementitious Composites with Plastic Waste

The study focuses on the development of cementitious composites using 3D printing and plastic waste as a sustainable aggregate substitute. This study involves experimenting with various percentages of plastic waste as a partial substitute for ground granulated blast furnace slag (GGBFS) in a control mix. The study examines the anisotropy of the 3D printing process, comparing it with properties of mold-cast samples. In addition, it assesses the fire resistance and mechanical properties of samples at elevated temperatures (100 °C, 300 °C, and 600 °C). Key mechanical properties, including 28-day compressive stress and flexural strength, are determined through experimental testing using a standard compression test and three-point bending test. The study also considers the modulus of elasticity (MOE) in compressive tests to evaluate a sample’s ability to deform elastically and the flexural toughness index to assess energy absorption and crack resistance of flexural samples. Following the experimental testing, the study’s key findings suggest that significant mass loss occurred at 300 °C and above, with plastic samples demonstrating increased mass loss at 600 °C. At 600 °C, plastic degradation led to the formation of voids and cracks within samples due to heightened internal pressure. Anisotropy was evident in 3D-printed samples, with loads parallel to the layer direction resulting in greater compressive strength and MOE. Furthermore, layer direction parallel to the longitudinal axis of flexural samples yielded higher flexural strength and flexural toughness. Mold-cast samples displayed superior compressive strength and stiffer behavior, with higher MOE compared to 3D-printed samples. However, 3D-printed plastic samples exhibited superior flexural strength compared to mold-cast samples, attributed to the alignment of plastic within the samples. The study also observed a reduction in compressive strength with the addition of plastic, explained by the poor bonding of plastic with cement due to its hydrophobic nature. Despite this, flexural strength generally improved with plastic addition, except at 600 °C, where plastic samples showed significant degradation in both compressive and flexural strength due to plastic degradation within the samples.

Improvement of the nylon (N)-glass fiber (G) reinforced polyester composite properties by varying oxide ceramic particles and stacking sequences of N and G

Abstract This study investigated the mechanical and physical properties of hybrid composites made with nylon fiber mesh (N), woven glass fiber (G), and unsaturated polyester (UPE) resin filled with different oxide ceramic particles (CPs) (ZnO, Al2O3, ZrO2, and TiO2). The influence of the stacking order of N and G (GGNNGG, GNGGNG, NGGGGN, and NNGGGG) on the mechanical properties of the composites was also studied. The goals of this study are to determine the best CP and stacking sequence for enhancing composite properties (flexural and impact properties) and reducing water absorption. The composites were manufactured in two steps using hand lay-up and press molding techniques. The first step involved fabricating N/G/UPE-2%CPs composites with a ratio of 8:14:78 (vol%) and a GNGGNG stacking sequence, referred to as type 1. In the second step, a composite with optimum properties obtained from type 1 was used as a reference and compared to composites with three different stacking sequences of GGNNGG, NGGGGN, and NNGGGG, known as type 2. The three-point bending, Charpy impact, and water absorption tests were conducted. The results revealed that the mechanical properties of N/G/UPE-2Al2O3 and N/G/UPE-2ZnO composites are nearly identical and higher than the others. However, N/G/UPE-2Al2O3′s water absorption is lower than that of N/G/UPE-2ZnO. These results suggest that the N/G/UPE-2Al2O3 composite, with a GGNNGG stacking pattern and a flexural strength of 125.12 MPa, an impact strength of 84.2 kJ m−2, and a low water absorption of 0.56%, could potentially serve as biomaterials.

Comprehensive analysis of mode-I cracking in ice: Exploring full-range rate dependency

Ice, as a crystalline material, demonstrates a unique response in its mode-I fracture toughness to variations in loading rates, characterized by an initial decrease and subsequent increase in toughness. This phenomenon has been explored in limited studies. In this work, an extensive numerical analysis of mode-I ice cracking is conducted by using the distinct lattice spring model (DLSM). Norton-Bailey Drucker-Prager DLSM (NB-DP-DLSM) is initially employed to investigate the classical explanations of creep and stress relaxation for the anomaly observed in ice’s fracture toughness at lower loading rates, but this approach does not successfully replicate the experimentally observed strain rate dependency. Then, two rate-dependent constitutive models are introduced to further examine the mode-I fracture mechanics of ice. Our numerical simulations of three-point bending tests show that the relationship between fracture toughness and strain rate at lower levels is more accurately captured by rate-dependent models. For higher strain rates, our numerical modeling of notched semi-circular bending tests indicates that a rate-independent constitutive model can replicate the loading rate dependency of ice’s mode-I fracture toughness. In conclusion, these observations suggest that a reverse-stage-like dynamic constitutive model for DLSM can potentially capture the full range of loading rate dependencies observed in ice.

Study on flexural resilience of composite foam sandwich structures under hygrothermal environment

Under hygrothermal environments, the structural stability and strength of all-fiber composite aircraft are significantly affected during long-term flight use. The wing skin, as a critical structural component, plays a vital role in bearing and transmitting aerodynamic loads. Therefore, it is crucial to investigate the structural compressive stability and strength of the wing skin throughout the aircraft's entire life cycle under these conditions. This study employs a real wing carbon fiber foam sandwich structure to investigate the compressive stability and strength of the wing skin structure of a new energy aircraft under actual flight conditions, specifically during the entire process of the room temperature dry state (RTD) and elevated temperature wet state (ETW). Initially, three-point bending tests were conducted on carbon fiber reinforced polymer (CFRP) laminates, foam cores, and CFRP reinforced foam sandwich structures. The CFRP laminates fully rebounded after bending damage in both the RTD and ETW environments. While CFRP reinforced foam sandwich structures also rebounded fully in the RTD environment, their rebound performance diminished in hygrothermal conditions due to the thermoplastic mobility of the foam cores, resulting in only weak rebound capabilities. In hygrothermal environments, the thermoplastic mobility of the foam core leads to diminished resilience after bending damage, resulting in only weak rebound capabilities. Subsequently, compressive instability tests were conducted on the wing skin foam sandwich structure. The results indicated that the basic test study effectively predicted the structural test outcomes. Structural components in the RTD environment exhibited overall flexural instability under compressive load, with damage morphology resembling a circular curve; the damaged specimens fully rebounded after unloading. Conversely, specimens in the ETW environment displayed localized instability, characterized by a wrinkled damage profile, resulting in only weak rebound capabilities after unloading.

Comparative analysis of flexural strength prediction in SFRC using frequentist, Bayesian, and Machine Learning approaches

Steel fiber reinforcement significantly enhances the flexural strength of concrete, which is vital for structural integrity. Annex L of the new Eurocode 2 classifies steel fiber-reinforced concrete by its flexural performance, aiding engineers in designing resilient structures. This study investigates the flexural behavior of steel fiber-reinforced concrete (SFRC) using three data-driven methodologies: Frequentist Inference (FI), Bayesian Inference (BI), and Machine Learning (ML). A comprehensive database was constructed from three-point bending tests on SFRC specimens, encompassing various compressive strengths, fiber quantities, and geometric parameters, to identify key factors influencing material properties.The findings indicate that all three methodologies yield comparable predictive capabilities for flexural responses in SFRC. Notably, FI models emphasize the importance of compressive strength and fiber volume fraction, along with fiber properties such as non-dimensional length and tensile strength. BI models enhance predictive stability by integrating prior knowledge and quantifying uncertainty, demonstrating their advantage, particularly in data-scarce situations. Additionally, ML analysis reveals that linear regression (LR) models can achieve accuracy similar to or greater than that of more complex models. This research provides novel insights into the application of BI and ML in concrete technology, emphasizing their potential to enhance predictive modeling. Additionally, it offers practical guidelines for optimizing SFRC design through a case study that compares residual flexural strengths obtained via Bayesian analysis, classifying the material in accordance with Annex L of the new Eurocode 2.

AI-driven data fusion modeling for enhanced prediction of mixed-mode I/III fracture toughness

This research evaluates the use of artificial intelligence to enhance the accuracy of predictions for mixed-mode I/III fracture toughness in polymethyl methacrylate . Traditionally, assessing fracture toughness relies heavily on destructive testing methods, specifically using edge-notch disc bend specimens subjected to three-point bending tests. These established methods are not only expensive and time-consuming but also frequently limited by the availability of data. To address these challenges, this study introduces a data fusion source modeling approach. This approach integrates primary fracture toughness test data with secondary predictive data derived from the maximum tangential stress criterion and the local strain energy density criterion. By employing adaptive boosting and general regression neural network algorithms, the models developed in this research demonstrate a marked improvement in predictive performance compared to traditional primary source models. Additionally, a feature importance analysis using Shapley Additive exPlanations values reveals that the mode mixity parameter, specimen thickness, and radius are critical factors influencing fracture toughness. The study highlights that while mode mixity emerges as the most significant factor, a reduction in specimen thickness generally leads to decreased fracture toughness, whereas an increase in radius has a more complex, often negative, effect. The results of this study indicate that AI-powered models using data fusion can overcome limitations related to data scarcity, enabling more accurate predictions in fracture mechanics. Furthermore, this approach provides a pathway for utilizing AI in other engineering domains where data sets are limited.

The influence of SC-CO2 on the shales’ fracture behavior described by using ultra-fast time resolution method and the damage fracture constitutive model: A case study of the Cretaceous Qingshankou formation in Gulong Depression, Songliao Basin, NE China

Supercritical CO2 (SC-CO2), as an innovative non-aqueous fracturing fluid, has gained extensive application in arid regions. However, its influence on the fracture propagation behavior of shale in very short timescales remains poorly understood. Therefore, a series of three-point bending tests were conducted on shale samples with 0°-90° bedding inclinations. To describe the influence of water-heat-SC-CO2 treatment, a damage fracture constitutive model based on a normal distribution was developed. The theoretical fitting curves of this constitutive model agree well with the experimental results. The whole crack propagation processes were captured using the ultra-fast time resolution method, achieving a time resolution of fast to 15 ps. Identical three-point bending tests were repeated after subjecting the shale samples to water-heat-SC-CO2 treatment for 48 h. The experimental results reveal that after the water-heat-SC-CO2 treatment, there were significant changes in the key mechanical parameters of shale samples. Moreover, the influence of water-heat-SC-CO2 was observed to increase progressively with the bedding inclinations. And by combining the image captured by the ultra-fast time resolution method with this constitutive model, the fracture behavior change of the shale sample after water-heat-SC-CO2 treatment predominantly is affected by the weak planes of shale, with negligible influence on the matrix.

Flexural tensile behaviour of alkali-activated slag-based concrete and Portland cement-based concrete incorporating single and multiple hooked-end steel fibres

In this study, three-point bending tests on notched beams according to EN 14651 have been performed to evaluate the flexural post-cracking behaviour of alkali-activated slag-based concrete (AASC) and Portland cement-based concrete (PCC) incorporating single (3D) and multiple (4D, 5D) hooked-end steel fibres in different volume fractions up to 0.75%. According to the experimental results, the post-cracking residual flexural strength increases with the increase in the fibre volume fraction for each fibre and concrete matrix type. AASC mixes incorporating 3D and 4D fibres show higher values of residual flexural strength for the same crack opening than PCC mixes with the same fibre type and dosage. Only for the mixes incorporating 5D fibres, steel fibre-reinforced PCC (SFRPCC) mixes outperform steel fibre-reinforced AASC (SFRAASC) mixes in terms of post-cracking behaviour. According to EN 14651, the values of the residual strengths and , corresponding to a crack mouth opening displacement (CMOD) of 0.5 mm and 2.5 mm, respectively, and their corresponding characteristic values and , respectively, can be derived from the experimental load-CMOD curves. Following the fib Model Code 2020, each mix can then be classified according to the values of and the ratio. As a result, empirical models have been developed for SFRPCC to predict the values of and and the applicability of such models to SFRAASC is evaluated in this study. Once the values of and are known, tensile constitutive models can be derived according to the fib Model Code 2020 and used as input parameters for finite element modelling. In this study, the accuracy of the code-based constitutive model to predict the flexural behaviour of SFRAASC and SFRPCC is evaluated using the concrete damage plasticity (CDP) model available in ABAQUS. The numerical model based on the tensile stress-strain curve in the fib Model Code 2020 can qualitatively capture the post-cracking behaviour of SFRAASC and SFRPCC incorporating 3D, 4D and 5D at 0.25% fibre volume fraction, despite overestimating their tensile strength. For higher fibre volume fractions, the CDP model, in conjunction with the mode I parameters derived from the fib Model Code 2020, is unable to adequately describe the post-hardening behaviour exhibited by the composites.

Improved fracture toughness evaluation for fiber-reinforced asphalt concrete through double-parameter theory

Fracture toughness serves as a key parameter in the design and durability assessment of asphalt concrete. Quantifying the fracture toughness for fiber-reinforced asphalt concrete (FRAC), remains challenging due to the incorporation of fibers. This study proposes an improved method for evaluating the fracture toughness of FRAC, based on the double-parameter theory derived from the theoretical concepts of stress intensity factor K and energy release rate (double-K and double-G fracture models). Using Digital Image Correlation (DIC) technology, crack propagation during three-point bending beam tests on FRAC beams was measured, refining the calculation of critical crack length ac in the double-K fracture parameters. Additionally, a method is introduced to calculate the improved solution of double-G fracture parameters by monitoring crack propagation in real-time to determine the effective crack length a, and simultaneously computing the energy absorbed per unit crack extension, thereby constructing the J-R curve during stable crack growth phases. The fracture toughness of FRAC is evaluated by the improved method obtained double-G fracture parameters were used in Virtual Crack Closure Technique (VCCT) simulations to achieve virtual modeling of FRAC. The results demonstrate that the improved method provides accurate fracture performance indicators for FRAC. Moreover, the study establishes modified calculation formulas for (GICu) and (KICu) at unstable fracture toughness for FRAC at different temperatures, considering various fiber types and contents, thereby enhancing computational efficiency for practical applications. This research contributes to more accurate and effective methods for testing and evaluating the fracture performance of FRAC

Effects of 5 Nanosilica Concentrations and Humid Environments at 6 Different pH Levels on Fracture Toughness and Moisture Absorption of Dental Polymethyl Methacrylate Resin‎ Reinforced With Silica Nanoparticles: An Explorative Experimental Scanning Electron Microscopy Study.

No study has assessed the effects of nanosilica within polymethyl methacrylate (PMMA) resin and environmental pH on resin's fracture resistance and moisture absorption. A total of 90 specimens were divided into 30 subgroups of three, as per the ASTM D5045 standard: five groups of nanosilica percentages (0%/2%/5%/7%/10%), each ‎divided into six subgroups of pH levels (pH = 5/6/7/8/9, + "dry" control). The specimens were prepared by mixing silica nanoparticles with PMMA powder in a vacuum mixer. Then, the specimens were mixed with a diluent liquid (TEGDMA) according to the manufacturer's instructions. For each of the five weight percentages, 36 samples were produced. The 18 specimens in each group were randomly divided into six subgroups of pH levels. The specimens were kept in containers of liquid at different pH levels at room temperature for 1 week. Their before- and after-storage weights were recorded to calculate moisture absorption. The fracture resistance test was performed (ASTM D5045 standard) using the three-point bending method. Scanning electron microscopy was performed. Data were analyzed. Both nanosilica extents and pH levels significantly affected the fracture toughness with a significant interaction (p < ‎‎0.00001). All post hoc comparisons of different pH levels (except pH= 5 vs. 6) were significant (p < ‎‎0.0001). All post hoc comparisons of different nanosilica concentrations were significant (p < ‎‎0.0001). Both nanosilica extents and pH levels significantly influenced the fracture toughness with a significant interaction (p < ‎‎0.00001). All post hoc comparisons of different pH levels and also between different nanosilica concentrations were significant (p < ‎‎0.0001). The correlation between moisture absorption and fracture toughness was significant (R = -0.382, p = 0.0009). Fracture toughness decreases when placed in humid and acidic environments. Also, the samples that were placed in a humid environment suffered a brittle fracture. Increasing silica nanoparticles improved fracture toughness (becoming optimal at 5 wt% nanosilica). The objective of this study was to investigate the fracture toughness of dental samples made of PMMA reinforced with various percentages of nanosilica at various pH levels. For this purpose, dental resins with various amounts of nanosilica were placed in moist media at different pH values ranging from 5 to 9 (mimicking the normal pH range of the human mouth).

A green inorganic binder for material extrusion of ultra-low shrinkage and relatively high strength metakaolin ceramics at low sintering temperature

Ultra-low shrinkage and relatively high strength metakaolin ceramics printed by material extrusion were innovatively fabricated using inorganic aluminum dihydrogen phosphate (Al(H2PO4)3) as a binder and low sintering temperature. The optical microscopy, scanning electron microscopy (SEM), electronic vernier caliper, three-point bending test, Archimedes method and X-ray diffraction (XRD) were used to measure and evaluate the surface morphology, microstructure, dimensional shrinkage, flexural strength, porosity and phase composition of the printed ceramics sintered at different temperatures. The results showed that when the mass ratio of metakaolin, Al(H2PO4)3 and deionized water was 17:6:2, the rheological characteristic of the purely green inorganic ceramic slurry was very suitable for material extrusion additive manufacturing, and the corresponding printed ceramic green bodies possessed high-quality formability. The ceramic samples sintered at 750 °C possessed the best whiteness, the lowest shrinkage (<2%), relatively high flexural strength (9.02 MPa). As the sintering temperature increased, Al(H2PO4)3 transformed to aluminum metaphosphate Al(PO3)3, and then decomposed into aluminum phosphate (AlPO4) and phosphorus pentoxide gas (P2O5), which caused pores and reduced strength, and alumina oxide (Al2O3) and silicon oxide (SiO2) in metakaolin gradually transformed to mullite and cristobalite with more stable structure and higher strength.

Design Method of Gyroid Lattice Structure Based on the Load Paths Direction and Capacity

The Design of lattice structures with triply periodic minimal surface (TPMS) can improve the specific stiffness, strength, heat dissipation, and energy absorption functions of their physical structures. The load-transferred law in the structure can serve as a crucial basis for the design, including the distribution and anisotropy of the unit cells. In this paper, a design method based on load paths is proposed and a series of Gyroid lattice structures with variable density cells, variable direction cells, and combination of variable density and direction cells, are designed with better mechanical properties. The load paths within a given structure are extracted to explicitly provide the load-transferred law. The capacity of the load paths is then proposed to guide the distribution of the cells, and a mapping relationship with the parameters controlling the porosity is established. The lattice structures with variable density cells are designed. Afterwards, the pointing stress vectors of the load paths is defined as the main load-transferred direction in the local region to guide the direction of the cells. Based on the anisotropic behavior of the Gyroid cells, the direction setting principles are formulated, and the lattice structures with variable direction cells are designed. Furthermore, a model generation method is proposed, and the Gyroid lattice structures that combine variable density and direction cells are implemented. Two models are applied to validate the proposed method, including a two-dimensional three-point bending beam and a three-dimensional supporting beam. The obtained results show that for the same porosity, both the variable density and variable direction designs of Gyroid cells allow to improve the mechanical properties. The variable density design outperforms the variable direction design. In addition, the Gyroid lattice structures combining variable density and direction cells have significantly higher performance, which indicates that the proposed design method can more effectively increase the load-bearing performance.

Preparation of enhanced erosive wear resistance SiC-fiber-reinforced SiC ceramic matrix composites integrated with a knit fabric via high temperature crystallization of amorphous Si–C–O–Al fibers

We report the enhanced erosive wear resistance of SiC/SiC CMCs that were integrated with a knit fabric via high-temperature crystallization of relatively inexpensive first-generation (amorphous) fibers of Si–C–O–Al (AM; short for Tyranno™ AM) for use as sliding components. A pyrocarbon (PyC) interface was formed via dip coating in liquid phenolic resin, and matrix densification was achieved by hot pressing at 1900 °C for 1 h at 30 MPa. The PyC-coated AM fibers exhibited low tensile strength values at temperatures below 1600 °C, which increased significantly at 1900 °C (2.68 ± 0.74 GPa). The hot-pressed AM-SiC/SiC CMCs exhibited typical quasi-ductile fracture in a three-point bending test. The erosive wear of the CMCs was investigated using a slurry erosion test, and the associated mechanism was clarified by laser-microscopy-based 3D profiling and scanning-electron-microscopy-based microstructural examination. The matrix of the hot-pressed AM-SiC/SiC CMCs was dense (1.99% porosity), rigidly structured, and hard (27.1 ± 2.91 GPa), enabling the CMCs to outperform conventional SiC/SiC CMCs in terms of slurry erosion resistance.