Surface Technology (表面技术)•2026•DOI: 10.16490/j.cnki.issn.1001-3660.2026.11.004
The operational reliability of hydroelectric generator units is critically constrained by the current-carrying tribological performance of carbon brush/collector ring systems, which are highly sensitive to ambient temperature and humidity. This study conducted controlled-atmosphere experiments on a 45 steel/carbon friction pair under temperatures of 20–40 °C and relative humidity (RH) of 40–60%. Key parameters including friction coefficient, wear rate, contact resistance, and contact temperature were measured, and surface damage mechanisms were analyzed. Results show that at 35 °C and 50% RH, the average friction coefficient reached a minimum of 0.1297, a 46.6% reduction compared to the maximum of 0.2427 at 25 °C and 55% RH. The lowest average contact resistance of 1.52 Ω was obtained at 25 °C/50% RH and 40 °C/45% RH, representing a 49.3% decrease from the maximum of 2.27 Ω at 25 °C/40% RH. Wear rate was minimized at 50% RH. Contact temperature exhibited an 'N'-shaped variation with increasing temperature at constant humidity. Elevated temperature promoted oxidation but reduced water vapor and induced desorption of water molecules, hindering water film formation. At 30 °C, friction coefficient, wear rate, and contact resistance all reached relatively low values. Increased humidity reduced surface roughness and smoothed the brush surface. Water vapor is a key factor influencing abrasive and adhesive wear, with adhesive wear minimized near 50% RH. High temperature or high humidity environments degrade current-carrying tribological performance. These findings provide optimal environmental parameters for enhancing the operational reliability of hydroelectric generator units.
Railway Engineering Science (铁道工程科学)•2026•DOI: 10.1007/s40534-025-00404-5
Interlayer degradation in heavy-haul railway (HHR) bridges under rising axle loads and transport volumes threatens structural safety. Traditional visual inspection and fixed-sensor structural health monitoring are impractical for large bridge inventories. This paper proposes a drive-by inspection methodology that combines vertical axle box acceleration (ABA) with hybrid filtering for rapid interlayer damage detection in multi-span HHR bridges. The framework introduces a Hilbert-transform-based instantaneous amplitude quartic index (IAQI) to enhance damage localization accuracy. The hybrid filtering integrates bandpass filtering targeting sleeper-passing frequency components to suppress track irregularity effects, and a statistical diagnostic tool to discriminate interlayer damage from sleeper-related driving components. Numerical analyses and a field test on an 18-span, 609.5-m simply supported HHR bridge validate the method. Results demonstrate effective detection under combined beam damage, irregularity, and noise. The field test identified five interlayer damage locations requiring on-site confirmation. The method offers a new strategy to improve inspection efficiency and ensure operational safety of HHR bridges.
Journal of Central South University•2026•DOI: 10.1007/s11771-026-6260-z
The mechanism of SiC preparation via chemical vapor deposition (CVD) of the CH3SiCl3(MTS)-H2 system remains unclear. This article integrates thermodynamic calculations, fluid dynamics simulations, and experimental validations to enable a synergistic analysis from thermodynamic equilibrium predictions to fluid dynamics-based dynamic modeling. The results systematically reveal the effects of process parameters on the SiC deposition procedure. It was found that the silicon-rich phenomenon observed at low temperatures is related to the low reactivity of CH4 and the preferential adsorption of chlorosilanes. With increasing deposition temperature, the concentration of silicon-containing molecular species such as SiCl2 rises, while unsaturated hydrocarbons like C2H2 become the dominant carbon sources at high temperature, ultimately producing nearly stoichiometric SiC coatings at 1400 ℃. Notably, thermodynamic calculation results alone exhibited deviations from experimental results, whereas coupling with fluid dynamics simulations, consistency was improved significantly. This research method not only compensates limitations inherent in thermodynamic calculations but also provides reliable theoretical basis and technical support for precise control of CVD parameters and optimization of SiC chemical composition.
Journal of Semiconductors (半导体学报 - 中国科学院半导体研究所)•2025•DOI: 10.1088/1674-4926/25020018
Silicon carbide offers distinct advantages in the field of power electronic devices. However, manufacturing processes remain a significant barrier to its widespread adoption. Polycrystalline SiC is less expensive and easier to produce than single crystal. But stabilizing and controlling its performance are critical challenges that must be addressed urgently. Due to its material properties and excellent performance in applications, 3C-SiC is gaining increasing attention in research. This article presents the electrical and material properties of a series of polycrystalline 3C-SiC samples and investigates their interrelationship. The samples were examined using TEM, which confirmed their polycrystalline structure. Combined with XRD and Raman spectroscopy, the grain orientations within the samples were analyzed, and the presence of stress was verified. EBSD was employed to statistically examine the grain structure and size across samples. For samples with similar doping levels, grain size is the most influential factor in determining electrical characteristics. Further EBSD measurements reveal the relationship between resistivity and grain size as log(ρ) = −1.93 + 8.67/d. These findings provide a foundation for the quantitative control and application of polycrystalline 3C-SiC. This work offers theoretical evidence for optimizing the performance tuning of 3C-SiC ceramics and enhancing their effectiveness in electronic applications.
Int. Journal of Mining Science and Technology (采矿与安全工程)•2025•DOI: 10.1016/j.ijmst.2025.02.009
Through a case analysis, this study examines the spatiotemporal evolution of microseismic (MS) events, energy characteristics, volumetric features, and fracture network development in surface well hydraulic fracturing. A total of 349 MS events were analyzed across different fracturing sections, revealing significant heterogeneity in fracture propagation. Energy scanning results showed that cumulative energy values ranged from 240 to 1060 J across the sections, indicating notable differences. Stimulated reservoir volume (SRV) analysis demonstrated well-developed fracture networks in certain sections, with a total SRV exceeding 1540000 m3. The hydraulic fracture network analysis revealed that during the mid-fracturing stage, the density and spatial extent of MS events significantly increased, indicating rapid fracture propagation and the formation of complex networks. In the later stage, the number of secondary fractures near fracture edges decreased, and the fracture network stabilized. By comparing the branching index, fracture length, width, height, and SRV values across different fracturing sections, Sections No. 1 and No. 8 showed the best performance, with high MS event densities, extensive fracture networks, and significant energy release. However, Sections No. 4 and No. 5 exhibited sparse MS activity and poor fracture connectivity, indicating suboptimal stimulation effectiveness.
Int. Journal of Mining Science and Technology (采矿与安全工程)•2025•DOI: 10.1016/j.ijmst.2025.02.005
Methane in-situ explosive fracturing technology produces shale debris particles within fracture channels, enabling a self-propping effect that enhances the fracture network conductivity and long-term stability. This study employs X-ray computed tomography (CT) and digital volume correlation (DVC) to investigate the microstructural evolution and hydromechanical responses of shale self-propped fracture under varying confining pressures, highlighting the critical role of shale particles in maintaining fracture conductivity. Results indicate that the fracture aperture in the self-propped sample is significantly larger than in the unpropped sample throughout the loading process, with shale particles tending to crush rather than embedded into the matrix, thus maintaining flow pathways. As confining pressure increases, contact areas between fracture surfaces and particles expand, enhancing the system’s stability and compressive resistance. Geometric analyses show flow paths becoming increasingly concentrated and branched under high stress. This resulted in a significant reduction in connectivity, restricting fracture permeability and amplifying the nonlinear gas flow behavior. This study introduces a permeability-strain recovery zone and a novel sensitivity parameter m, delineating stress sensitivity boundaries for permeability and normal strain, with m-value increasing with stress, revealing four characteristic regions. These findings offer theoretical support for optimizing fracturing techniques to enhance resource extraction efficiency.
Ship Mechanics (船舶力学)•2025•DOI: 10.3969/j.issn.1007-7294.2025.06.001
This paper investigates the target-guided coordinated control (TACC) of unmanned surface vehicles (USVs). In the scenario of tracking non-cooperative targets, the status information of the target can only be obtained by some USVs. To achieve semi-encirclement tracking of non-cooperative targets under maritime security conditions, a fixed-time tracking control method based on dynamic surface control (DSC) is proposed. Firstly, a novel TACC architecture with decoupled kinematic and kinetic control laws is designed to reduce the complexity of control system design. Secondly, the proposed DSC-based target-guided kinematic control law, including a tracking points pre-allocation strategy and sigmoid artificial potential functions (SigAPFs), can avoid collisions during the tracking process and optimize kinematic control output. Finally, a fixed-time TACC system is proposed to achieve fast convergence of kinematic and kinetic errors. The effectiveness of the proposed TACC approach in improving target tracking safety and reducing control output chattering is verified by simulation comparison results.
Chinese Journal of Mechanical Engineering•2025•DOI: 10.1186/s10033-025-01306-7
Silicon carbide (SiC) is widely used in fields such as new energy, military radar, and aerospace due to its outstanding physical and chemical properties. The surface micro-grooves of SiC can enhance the performance of micro-electro-mechanical systems, micro-sensors, and field-effect transistors. However, SiC, being a brittle and hard material, poses challenges for traditional machining methods like micro-groove machining and chemical etching, including sub-surface damage, short tool life, and low processing efficiency. This paper investigates the processing characteristics of femtosecond laser machining of SiC micro-grooves and compares them with those of single-crystal Si. The results indicate that femtosecond laser ablation of SiC primarily leads to melting and vaporization, forming modification, melted, and ablation areas in the affected area. Femtosecond laser processing of SiC micro-grooves involves three processes: heat absorption and melting, vaporization, and chipping, with vaporization as the primary material removal mechanism. The depth and width of SiC micro-grooves are positively correlated with pulse energy (Ep), pulse overlap rate (PO), and number of passes (Npass). The bottom roughness of the micro-grooves is positively correlated with Ep, negatively correlated with PO, and less affected by changes in the Npass. These findings further elucidate the material removal and micro-groove formation mechanisms of SiC under femtosecond laser irradiation, providing theoretical insights for high-quality and high-efficiency processing of SiC micro-grooves.
Chinese Journal of Mechanical Engineering•2025•DOI: 10.1186/s10033-025-01263-1
The research on rolling bearing early fault detection is mainly focused on degradation index extraction and adaptive setting of alarm threshold. The mainstream methods are to extract degradation indicators based on adaptive features and set adaptive alarm thresholds based on the Shewhart control chart. However, the adaptive feature extraction method does not consider the correlation between features, and the Shewhart control chart is not sensitive to small fluctuations caused by early faults. In this study, a rolling bearing early fault detection method based on a feature clustering fusion degradation index is proposed. The multidomain statistical features are extracted to form the initial feature set, and the improved hierarchical clustering algorithm is combined with the feature evaluation index to select features to form a preferred feature subset, to ensure the richness of index information and reduce redundancy. After the construction of the degradation index, to suppress the interference caused by nonstationary and abnormal shocks in early fault detection, the accurate evaluation method and anomaly determination strategy of control chart parameters are studied, and an improved exponential weighted move average control chart is designed to monitor the degradation index. The effectiveness and superiority of the proposed method are verified by public data sets. This research provides a rolling bearing early fault detection method, which can provide comprehensive degradation indicators, eliminate interference caused by random anomalies and running in periods, and achieve an accurate detection of early bearing failures.