Search Results (5,917)

The adhesive bonding of high-pressure die-cast (HPDC) aluminum alloy AlSi10MnMg is extensively applied in the aerospace and automotive sectors. Surface pretreatment of HPDC aluminum prior to bonding is crucial for enhancing bonding strength and durability, as it regulates surface roughness, and chemical properties. Traditional multi-step surface treatments including chromic acid anodizing for HPDC AlSi10MnMg are hazardous, complex, and often fail to balance adhesive bonding durability and corrosion protection, limiting their industrial applicability. This study examined the impact of various chemical treatments on the adhesive bonding performance of an AlSi10MnMg aluminum alloy. The treated surfaces were bonded using a structural adhesive, and bonding performance was evaluated via wedge tests under pristine conditions and after accelerated aging. A scanning electron microscope (SEM) was used to study the surface morphology, chemical composition, and corrosion characteristics of the treated surfaces. Energy dispersive spectroscopy (EDS), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization measurements were employed. Excellent adhesion characteristics, dominated by the cohesive failure of the adhesive, were observed in H₂O₂-treated samples. The H₂O₂-treated samples exhibited the shortest initial crack length, indicating a superior baseline bonding quality, and showed minimal crack propagation (only slight extension) after aging under extreme environmental conditions (70 °C and 100% relative humidity for 4 weeks). Electrochemical measurements revealed that the SG200-treated sample achieved the lowest corrosion current density (0.25 ± 0.03 μA/cm²) with an excellent corrosion resistance, while sol–gel-treated samples generally suffered from a poor adhesion, with interfacial failure. This study proposes a simplified, single-step chemical treatment using an H₂O₂ solution that effectively achieves both a strong adhesive bonding and an excellent corrosion resistance, without the drawbacks of conventional methods. It offers a viable alternative to conventional multi-step hazardous surface treatments. Full article

This study aims to evaluate the tribological performance of commercial PVD coatings in alleviating material transfer under unlubricated contact in the hot forming of aluminum alloy. The commercial PVD coatings included AlCrN, TiAlN, and Arc-DLC coatings, deposited on the forming tool surface. The warm and hot upsetting sliding test (WHUST) was used as a friction test in this study to reproduce the severe contact conditions from the hot forming process of AA6082-T6 aluminum alloy. The WHUST was performed at 300 °C, 400 °C, and 500 °C to investigate the effect of temperature on the tribological performance of each coating. The results found that the AlCrN and TiAlN coatings exhibited similar performance. They dominated the initial aluminum transfer by adhesive bonding. In contrast, the Arc-DLC coating mainly caused the initial aluminum transfer by mechanical plowing due to its lower chemical affinity to the aluminum alloy. In addition, the tribological performance of each coating highly depended on the temperature. Higher temperatures resulted in both stronger intermetallic bonding at the interface and lower yield strength of the aluminum alloy. These behaviors led to the variations in the coefficient of friction, the 3D topography and the SEM morphology along the wear track of the specimen, and the thickness of the adhered aluminum layer on the coating surface. In comparison, the Arc-DLC coating provided better tribological performance in mitigating the aluminum transfer than the others. Full article

To apply 3D printing-based continuous fiber composites in shipbuilding and marine applications, the pin-bearing fastening method with notch holes can be considered as an effective method. In this study, pin-bearing strength tests were performed on a 3D-printed composite consisting of carbon fiber and Onyx to evaluate the effect of hole notches fabricated through pre- and post-processing. The experimental results showed the difference in the mechanical fastening strength of the specimens, depending on the method used to fabricate the hole notch. As the width-to-diameter ratio (W/D) decreased, ultimate bearing strength, strain, and toughness decreased. The post-treated specimens exhibited higher initial stiffness than the pre-treated specimens, and their bearing stress was up to 23% higher at smaller hole diameters (≤6 mm). In particular, for specimens with 0° fiber orientation, the post-processed specimens showed markedly higher toughness than the pre-processed ones, with increases at 5 mm and 6 mm hole diameters, respectively, thereby demonstrating superior performance in both strength and energy absorption. The damage modes of the circular notches were also found to depend on the pre- and post-processing conditions. These results suggest that fiber orientation, W/D ratio, and processing method should be considered when designing mechanical fasteners for 3D-printed composites in marine structures. Full article

The fracture behavior of a locking pin used in the penultimate-stage blades of a 600 MW steam turbine in a thermal power plant was investigated through microstructural and microhardness characterization, fracture surface and energy-dispersive spectroscopy (EDS) analysis, as well as finite element load simulation. The microhardness values measured on the cross-section of the service pins ranged from 528 to 541 HV0.1, showing little difference from the unused pins. Scanning electron microscopy analysis revealed that approximately 70% of the fracture surfaces exhibited an intergranular “rock candy” morphology. The results indicate that pin failure was primarily caused by the combined effects of fretting wear and stress corrosion cracking (SCC). Specifically, vibration at the blade root, impeller, and pins due to start–stop cycles and load variations led to fretting wear, forming pits approximately 75 μm in size. Under the combined effects of weakly corrosive wet steam environments and shear stresses, SCC initiated at the high stress concentration points of these pits. Early crack propagation primarily followed original austenite grain boundaries, while later stages mainly extended along martensite plate boundaries. As cracks advanced, the cross-sectional area gradually decreased, causing the effective shear stress to increase until it exceeded the shear strength, ultimately leading to fracture. These findings not only provide a scientific basis for enhancing the reliability of steam turbine locking pins and extending their service life, but also contribute to a broader understanding of the failure mechanisms of key components operating under corrosive and fluctuating load environments. Full article

Ceramic membrane technology plays an important role in water and wastewater treatment. Strategic sourcing of various natural mineral resources has contributed to developing low-cost ceramic membranes. The combination with calcination of inorganic and organic wastes from domestic and agricultural activities results in fully sustainable ceramic membrane materials. In this work, ceramic membranes were developed using 96% clay, 2% almond shells and 2% lime. Sintering at 900, 950, and 1000 °C enabled the production of membranes (MK-900, MK-950, and MK-1000) in a clean, simple, and cost-effective manner. The average pore diameter and porosity decreased slightly from 44 to 42 nm and from about 30% to 26% with increasing sintering temperature, while the flexural strength increased from 25 to 40 MPa. The pure water permeability was 68 and 59 L·m⁻²·h⁻¹·bar⁻¹ for MK-900 and MK-950, respectively. Effective color (as Indigo blue) removal of 78% and 92% was observed for MK-900 and MK-950, respectively. More than 90% of the initial permeability was recovered after three cycles of dye filtration using water backwashing at each stage, indicating good fouling resistance of the prepared membranes. Full article

This study investigates the potential of waste marble slurry as a partial replacement for ordinary Portland cement, with particular emphases on the influence of the water-to-cement (w/c) ratio and the objectives of determining the effect of water content and the optimum marble slurry concentration. Cement pastes were prepared with three w/c ratios (0.3, 0.4, and 0.5) and five substitution levels of marble slurry (0%, 5%, 10%, 15%, and 20%). Workability was assessed through mini slump flow tests, while mechanical performance was evaluated via compressive and flexural mechanical tests. The initial and final setting times were also investigated. Electrical resistivity measurements, combined with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), were used to examine chemical composition and microstructure. Results showed that marble slurry behaves as an inert filler, rather than a reactive component. Its incorporation, up to 10%, significantly improves the fresh properties and mechanical performance of mixes with higher w/c ratios (0.4 and 0.5). At lower w/c ratios (0.3), strength was adversely affected due to insufficient hydration. Electrical resistivity measurements indicated that pastes with w/c = 0.5 and up to 10% slurry replacement became slightly more resistant to electrical current, whereas mixes with lower w/c ratios (0.3 and 0.4) showed only minor reductions at 5% and 10% cement substitution. SEM imaging demonstrated a denser microstructure when marble slurry was incorporated, consistent with a filler effect. Marble slurry was also found to accelerate the setting of cement pastes, an effect most evident at lower w/c ratios and higher substitution levels. Overall, the findings highlight that waste marble slurry can be effectively utilized at moderate replacement levels in cement-based materials, contributing to sustainable construction practices by reducing cement consumption and marble waste disposal. Full article

A transition metal-free synthesis of 1,2,5-trisubstituted 1H-indoles by a deprotonation–S_NAr cyclization sequence from 1-aryl-2-(2-fluoro-5-nitrophenyl)ethan-1-one (deoxy-benzoin) Schiff bases is reported. The starting deoxybenzoins were prepared by Friedel-Crafts acylation of activated aromatic compounds by 2-(2-fluoro-5-nitrophenyl)acetyl chloride with AlCl₃ or the corresponding acid with (CH₃SO₂)₂O. The Schiff bases were generated by slow distillation of toluene (18–24 h) from a heated solution of each deoxybenzoin (1 equiv) with a benzyl- or phenethylamine, a high-boiling aliphatic amine, or an aniline derivative (5 equiv). Subsequent addition of N,N-dimethylformamide, 2 equiv of anhydrous K₂CO₃, and heating at 90–95 °C for 18–24 h completed the synthesis. Benzyl-, phenethyl-, and high-boiling amines gave excellent yields while the heating requirements for the initial condensation made volatile aliphatic amines difficult to use and gave low yields. Aniline reactivities correlated with substituent-derived base strength, although modified conditions allowed some yields to be improved. Several anticipated competing processes had minimal impact on the outcome of the cyclizations. Full article

Language difficulties have been highlighted as a cornerstone of the developmental profile in Down Syndrome (DS), but very few studies have examined early language abilities in children with DS to determine the initial strengths and weaknesses that might inform early language interventions to support language development in this population. This study focused on the early perception of intonation and examined whether it differed between infants with DS and typically developing (TD) peers. Using a visual habituation paradigm from a previous study on TD infants’ ability to perceive the intonation of statements and questions, infants with DS were able to successfully discriminate statement and question intonation, similarly to TD infants. However, unlike for TD infants, an age group effect was found, with older infants with DS being unable to discriminate the intonation contrast. Our findings highlight the importance of prosody in early development also in infants with DS. Moreover, the unexpected decrease in early sensitivity to intonation in older infants with DS pinpoints a crucial developmental window—the first semester of life—for early interventions using intonation to support language learning in these infants. Full article

Cyclic Solvent Injection (CSI) is a method for enhanced heavy oil recovery, offering a reduced environmental impact. CSI processes typically involve fluid flow through both wormholes and the surrounding porous media in reservoirs. Therefore, understanding how foamy oil behavior differs between bulk phases and porous media is crucial for optimizing CSI operations. However, despite CSI’s advantages, limited research has explained why foamy oil, a key mechanism in CSI, displays weaker strength and stability in bulk phases than in porous media. To address this gap, three advanced visual micromodels were employed to monitor bubble behavior from nucleation through collapse under varying porosity with a constant pressure reduction. A sandpack depletion test in a large cylindrical model further validated the non-equilibrium bubble-reaction kinetics observed in the micromodels. Experiments showed that, under equivalent operating conditions, bubble nucleation in porous media required less energy and initiated more rapidly than in a bulk phase. Micromodels with lower porosity demonstrated up to a 2.5-fold increase in foamy oil volume expansion and higher bubble stability. Moreover, oil production in the sandpack declined sharply at pressures below 1800 kPa, indicating the onset of critical gas saturation, and yielded a maximum recovery of 37% of the original oil in place. These findings suggest that maintaining reservoir pressure above critical gas saturation pressure enhances oil recovery performance during CSI operations. Full article

This research presents a preliminary proposal for a rehabilitation exercise aimed at patients with muscle weakness in the distal upper limb. A virtual environment was developed, where the user engages in a rehabilitation activity focused on rehabilitating the pinch grip. The goal is to strengthen the patient’s grasp and reduce muscle weakness. The virtual environment was designed as a video game in order to generate greater interest and encourage patients to adhere to their rehabilitation activities. This virtual game utilizes the haptic device Novint Falcon for the interaction with the environment. This preliminary work implements an impedance control with neural compensation; the control strategy produces signals to adapt the force exerted by the patient, with the goal that the device can give a force of the same magnitude but in the opposite direction. Consequently, regardless of the patient’s initial strength, the device will always deliver an assistive force to guide the patient along a desired trajectory. Initial experimental results with the proposed virtual-haptic rehabilitation system are presented, indicating the feasibility of the approach; however, further studies are required to validate its clinical effectiveness. Full article

To investigate the mechanism by which the rheological properties of drilling fluids affect the stability of the wellbore in brittle mud shale, this study systematically examines the influence of drilling fluids with different rheological properties on the hydration dispersion and rock strength of brittle mud shale through a series of laboratory experiments, including thermal rolling tests and uniaxial compressive strength tests on core samples. The results reveal that for weakly dispersible brittle mud shale, the rheological properties of drilling fluids have a minor effect on hydration dispersion, with rolling recovery rates consistently above 90%. However, the rheological properties of drilling fluids significantly influence the strength of brittle mud shale, and this effect is coupled with multiple factors, including rock fracture intensity index, soaking time, and confining pressure. Specifically, as the viscosity of the drilling fluid increases, the reduction in rock strength decreases; for instance, at 5 MPa confining pressure with an FII of 0.46, the strength reduction after 144 h was 69.8% in distilled water (from an initial 133.2 MPa to 40.2 MPa) compared to 36.3% with 3# drilling fluid (from 133.2 MPa to 88.7 MPa, with 100 mPa·s apparent viscosity). Both increased soaking time and confining pressure exacerbate the reduction in rock strength; a 5 MPa confining pressure, for example, caused an additional 60.9% strength reduction compared to 0 MPa for highly fractured samples (FII = 0.46) in distilled water after 144 h. Rocks with higher fracture intensity indices are more significantly affected by the rheological properties of drilling fluids. Based on the experimental results, this study proposes a strength attenuation model for brittle mud shale that considers the coupled effects of fracture intensity index, soaking time, and drilling fluid rheological properties. Additionally, the mechanism by which drilling fluid rheological properties influence the strength of brittle mud shale is analyzed, providing a theoretical basis for optimizing drilling fluid rheological parameters and enhancing the stability of wellbores in brittle mud shale formations. Full article

Chloride erodes steel bars through concrete pores, seriously affecting the durability of reinforced concrete structures. Improving the binding ability to chloride is an important measure. We explored the effects of W/C, curing age, and premixed Cl⁻ concentration on the compressive strength and Cl⁻ binding capacity in cement pastes. The results indicate that a premixed 5% concentration of Cl⁻ can improve the compressive strength, whereas an excessive Cl⁻ negatively impacts the mechanical properties. The total Cl⁻ content in cement pastes is a crucial factor that influences the binding ability of Cl⁻. When the total Cl⁻ content is within 2% (i.e., the premixed Cl⁻ concentration is 5%), the cement paste has a strong binding ability of Cl⁻. W/C and curing age indirectly affect the binding ability by affecting the total Cl⁻ content. Furthermore, with the increase in content of Cl⁻, the adsorption content of Cl⁻ by C-S-H increased, while the proportion of Cl⁻ bound by Fs to the total bound Cl⁻ initially declines and then tends to stabilize. It is worth noting that a premixed concentration of 5% is a “safety limit” for cement paste, but for reinforced concrete, the presence of free Cl⁻ above normative thresholds should not be underestimated. Full article

In this study, cement, short-cut carbon fibers, and polymer water-absorbing resin were used as the main materials, with high-performance water-reducing polycarboxylic acid agent as the modified material. A new conductive cement-based grouting material was developed by incorporating functional additives. Its mix design was optimized based on initial setting time, fluidity, bleeding rate, and compressive strength. The optimal ratio of the grouting material was determined as follows: 0.4 wt% of high water-absorbent resin, 0.25 wt% of high-efficiency water reducer, 0.8 wt% of short-cut carbon fibers, and a water–cement ratio of 0.8:1. The electrical conductivity of the grouting material was studied in depth under different dosages of short-cut carbon fibers, considering factors such as curing age, temperature, and pressure conditions. The results show that with the increase in curing age, the volume resistivity of the specimen gradually increases; the resistivity of the conductive cementitious grouting material decreases with the rise in temperature, showing a negative temperature coefficient effect; additionally, the doping of an appropriate amount of short-cut carbon fibers enables the conductive cementitious grouting specimen to exhibit good pressure-sensitive properties. Field test verification indicates that the new cementitious conductive grouting material has excellent conductive properties, and the grouting quality can be effectively evaluated via high-density electrical testing. Full article

With the deepening implementation of the coordinated development strategy for energy exploitation and ecological conservation, green coal mining technology has become a critical pathway to achieve balanced resource development and environmental protection. This study investigates the stress field evolution and dynamic fracture propagation mechanisms in overlying strata during shallow coal seam mining in the Shenfu mining area. By employing a multidisciplinary approach combining triaxial compression tests (0–15 MPa confining pressure), scanning electron microscopy (SEM) microstructural characterization, elastoplastic theoretical modeling, and FLAC3D numerical simulations, the synergistic failure mechanisms of overlying strata were systematically revealed. Gradient-controlled triaxial tests demonstrated significant variations in stress-strain responses across lithological types. Notably, Class IV sandstone exhibited exceptional uniaxial compressive strength of 106.7 MPa under zero confining pressure, surpassing the average strength of Class I–III sandstones (86.2 MPa) by 23.6%, attributable to its highly compacted grain structure. A nonlinear regression-derived linear strengthening model quantified that each 1 MPa increase in confining pressure enhanced axial peak stress by 4.2%. SEM microstructural analysis established critical linkages between microcrack networks/grain-boundary slippage at the mesoscale and macroscopic brittle failure patterns. Numerical simulations demonstrated that strata failure manifests as tensile-shear composite fractures, with lateral crack propagation inducing bed separation spaces. The stress field exhibited spatiotemporal heterogeneity, with maximum principal stress concentrating near the initial mining cut during early excavation. Fractures propagated obliquely at angles of 55–65° to the horizontal plane in an ‘inverted V’ pattern from the goaf boundaries, extending vertically 12–18 m before transitioning to the bent zone, ultimately forming a characteristic three-zone structure. Experimental and simulated vertical stress distributions showed minimal deviation (≤2.8%), confirming constitutive model reliability. This research quantitatively characterizes the spatiotemporal synergy of strata failure mechanisms in ecologically vulnerable northwestern China, proposing a confining pressure-effect quantification model for support parameter optimization. The revealed fracture dynamics provide critical insights for determining ecological restoration timelines, while establishing a novel theoretical framework for optimizing green mining systems and mitigating ecological damage in the Shenfu mining area. Full article

Fractured rock masses are susceptible to stress-induced disturbances, which can lead to severe geological disasters. In recent years, the shear deformation and failure characteristics of fractured rock under cyclic shear loading have become a frontier issue in rock mechanics and engineering. A thorough understanding of the failure mechanism of fractured rock masses is of great significance for the scientific evaluation of their long-term stability in engineering applications. In this study, experiments were conducted on marble specimens with artificial fractures under constant normal stress using the RDS-200 rock mechanics shear test system. The results reveal the following three key findings: First, the residual shear displacement increases linearly with cycling numbers, and the fractures demonstrate memory functions under pre-peak tiered cyclic shear loading, with shear displacement exhibiting hysteresis effects. Second, significant differences were observed between tiered cyclic shear (TCS) and direct shear test (DST) outcomes in terms of peak shear stress and failure patterns. The peak shear strength under TCS was 17.76–24.04% lower than under DST, with the strength-weakening effect increasing with normal stress. The fracture surfaces showed more severe damage and debris accumulation under TCS compared to DST, with the contour area ratio decline rate correlating with both normal stress and initial surface conditions. Third, energy evolution analysis indicates that as cyclic shear stress increases, the elastic energy release rate exceeds the dissipation rate, and the elastic energy index progressively rises through the loading cycles. The findings of this research contribute to a better understanding of the shear instability of rock fractures under pre-peak tiered cyclic shear loading with constant normal stress. Full article