Search Results (304)

The increasing depth of coal mine construction has led to complex geological conditions involving high ground stress and elevated groundwater levels, presenting new challenges for water-sealing technologies in rock microfissure grouting. This study investigates ultrafine cement grouting in microfissures through systematic analysis of slurry properties and grouting simulations. Through systematic analysis of ultrafine cement grout performance across water–cement (W/C) ratios, this study establishes optimal injectable mix proportions. Through dedicated molds, sandstone-like microfissures with 0.2 mm apertures and controlled roughness (JRC = 0–2, 4–6, 10–12) were fabricated, and instrumented with fiber Bragg grating (FBG) sensors for real-time strain monitoring. Triaxial stress-permeation experiments under 6 and 7 MPa confining pressures quantify the coupled effects of fissure roughness, grouting pressure, and confining stress on volumetric flow rate and fissure deformation. Key findings include: (1) Slurry viscosity decreased monotonically with higher W/C ratios, while bleeding rate exhibited a proportional increase. At a W/C ratio = 1.6, the 2 h bleeding rate reached 7.8%, categorizing the slurry as unstable. (2) Experimental results demonstrate that increased surface roughness significantly enhances particle deposition–aggregation phenomena at grouting inlets, thereby reducing the success rate of grouting simulations. (3) The volumetric flow rate of ultrafine cement grout decreases with elevated roughness but increases proportionally with applied grouting pressure. (4) Under identical grouting pressure conditions, the relative variation in strain values among measurement points becomes more pronounced with increasing roughness of the specimen’s microfissures. This research resolves critical challenges in material selection, injectability, and seepage–deformation mechanisms for microfissure grouting, establishing that the W/C ratio governs grout performance while surface roughness dictates grouting efficacy. These findings provide theoretical guidance for water-blocking grouting engineering in microfissures. Full article

Gas leak detection in oil and gas processing facilities is a critical component of the safety production monitoring system. Non-contact detection technology based on infrared imaging has emerged as a vital real-time monitoring method due to its rapid response and extensive coverage. However, existing pixel-level segmentation networks face challenges such as insufficient segmentation accuracy, rough gas edges, and jagged boundaries. To address these issues, this study proposes a novel pixel-level segmentation network training framework based on anchor box annotation and enhances the segmentation performance of the YOLOv8-seg network for gas detection applications. First, a dynamic threshold is introduced using the Visual Background Extractor (ViBe) method, which, in combination with the YOLOv8-det network, generates binary masks to serve as training masks. Next, a segmentation head architecture is designed, incorporating dynamic kernels and multi-branch collaboration. This architecture utilizes feature concatenation under deformable convolution and attention mechanisms to replace parts of the original segmentation head, thereby enhancing the extraction of detailed gas features and reducing dependency on anchor boxes during segmentation. Finally, a joint Dice-BCE (Binary Cross-Entropy) loss, weighted by ViBe-CRF (Conditional Random Fields) confidence, is employed to replace the original Seg_loss. This effectively reduces roughness and jaggedness at gas edges, significantly improving segmentation accuracy. Experimental results indicate that the improved network achieves a 9.9% increase in F1 score and a 7.6% improvement in the mIoU (mean Intersection over Union) metric. This advancement provides a new, real-time, and efficient detection algorithm for infrared imaging of gas leaks in oil and gas processing facilities. Furthermore, it introduces a low-cost weakly supervised learning approach for training pixel-level segmentation networks. Full article

The abandoned goaf resulting from coal resource integration in China poses a significant threat to coal mine safety. The transient electromagnetic method (TEM) has emerged as a crucial technology for detecting goafs in coal mines due to its adaptable equipment and efficient implementation. In recent years, small-loop TEM has demonstrated high resolution and adaptability in challenging terrains with vegetation, such as coal mine ponding areas, karst regions, and reservoir seepage scenarios. By considering the sedimentary characteristics of coal seams and addressing the resistivity changes encountered in single-point inversion, a joint optimization inversion process incorporating lateral weighting factors and vertical roughness constraints has been developed to enhance the connectivity between adjacent survey points and improve the continuity of inversion outcomes. Through an OCCAM inversion approach, the regularization factor is dynamically determined by evaluating the norms of the data objective function and model objective function in each iteration, thereby reducing the reliance of inversion results on the initial model. Using the Xiaolong Coal Mine as a geological context, the impact of lateral and vertical weighting factors on the inversion outcomes of high- and low-resistivity structural models is examined through a control variable method. The analysis reveals that optimal inversion results are achieved with a combination of a lateral weighting factor of 0.5 and a vertical weighting factor of 0.1, ensuring both result continuity and accurate depiction of vertical and lateral electrical interfaces. The practical application of this approach validates its effectiveness, offering theoretical support and technical assurance for old goaf detection in coal mines, thereby holding significant engineering value. Full article

Microelectromechanical system (MEMS) devices are specialized electronic devices that integrate the benefits of both mechanical and electrical structures. However, the contact behavior between the interfaces of these structures can significantly impact the performance of MEMS devices, particularly when the surface roughness approaches the characteristic size of the devices. In such cases, the contact between the interfaces is not a perfect face-to-face interaction but occurs through point-to-point contact. As a result, the contact area changes with varying contact pressures and surface roughness, influencing the thermal and electrical performance. By integrating the CMY model with finite element simulations, we systematically explored the thermal conductance regulation mechanism of MEMS contact switches. We analyzed the effects of the contact pressure, micro-hardness, surface roughness, and other parameters on thermal conductance, providing essential theoretical support for enhancing reliability and optimizing thermal management in MEMS contact switches. We examined the thermal contact, gap, and joint conductance of an MEMS switch under different contact pressures, micro-hardness values, and surface roughness levels using the CMY model. Our findings show that both the thermal contact and gap conductance increase with higher contact pressure. For a fixed contact pressure, the thermal contact conductance decreases with rising micro-hardness and root mean square (RMS) surface roughness but increases with a higher mean asperity slope. Notably, the thermal gap conductance is considerably lower than the thermal contact conductance. Full article

The surface quality of biomedical implants, such as shoulder joint caps, plays a critical role in their performance, longevity, and biocompatibility. Most biomedical shoulder joints fail to reach their optimal functionality when finished through conventional techniques like grinding and lapping due to their inability to achieve nanometer-grade smoothness, which results in greater wear and friction along with potential failure. The advanced magnetorheological finishing (MRF) approach provides enhanced surface quality through specific dimensional control material removal. This research evaluates how MRF treatment affects the surface roughness performance and microhardness properties and wear resistance behavior of cobalt–chromium alloy shoulder joint caps which have biocompatible qualities. The study implements a magnetorheological finishing system built with an electromagnetic tool to achieve the surface roughness improvements from 0.35 µm to 0.03 µm. The microhardness measurements show that MRF applications lead to a rise from HV 510 to HV 560 which boosts the wear protection of samples. After MRF finishing, the coefficient of friction demonstrates a decrease from 0.12 to 0.06 which proves improved tribological properties of these implants. The results show that MRF technology delivers superior benefits for biomedical use as it extends implant life span and decreases medical complications leading to better patient health outcomes. The purposeful evaluation of finishing techniques and their effects on implant functionality demonstrates MRF is an advanced technology for upcoming orthopedic implants while yielding high precision and enhanced durability and functional output. Full article

With the ongoing development of lightweight automobiles, research on new aluminum alloys and welding technology has gained significant attention. Friction stir welding (FSW) is a solid-state joining technique for welding aluminum alloys without melting. In this study, novel squeeze-cast Al-Si-Mg-Fe-Zn alloys with different Zn contents (0, 3.4, 6.5, and 8.3 wt%) were friction stir welded (FSWed) at a translational speed of 200 mm/min and a rotational speed of 800 rpm. These parameters were chosen based on the observations of visually sound welds, defect-free and fine-grained microstructures, homogeneous secondary phase distribution, and low roughness. Zn can affect the microstructure of Al-Si-Mg-Fe-Zn alloys, including the grain size and the content of secondary phases, leading to different mechanical and corrosion behavior. Adding different Zn contents with Mg forms the various amount of MgZn₂, which has a significant strengthening effect on the alloys. Softening observed in the weld zones of the alloys with 0, 3.4, and 6.5 wt% Zn is primarily attributed to the reduction in Kernel Average Misorientation (KAM) and a decrease in the Si phase and MgZn₂. Consequently, the mechanical strengths of the FSWed joints are lower as compared to the base material. Conversely, the FSWed alloy with 8.3 wt% Zn exhibited enhanced mechanical properties, with hardness of 116.3 HV_0.2, yield strength (YS) of 184.4 MPa, ultimate tensile strength (UTS) of 226.9 MP, percent elongation (EL%) of 1.78%, and a strength coefficient exceeding 100%, indicating that the joint retains the strength of the as-cast one, due to refined grains and more uniformly dispersed secondary phases. The highest corrosion resistance of the FSWed alloy with 6.5%Zn is due to the smallest grain size and KAM, without MgZn₂ and the highest percentage of {111} texture (24.8%). Full article

The shear strength of rock discontinuities is a critical parameter in rock engineering projects for assessing the safety conditions of rock slopes or concrete dam foundations. It is primarily controlled by the frictional contribution of rock texture (basic friction angle), the roughness of discontinuities, and the applied normal stress. While proper testing is essential for accurately quantifying shear strength, engineering geologists and engineers often rely on published historical databases during early design stages or when test results show significant variability. This paper serves two main objectives. First, it intends to provide a comprehensive overview of the basic friction angle concept from early years until its emergence in the Barton criterion, along with insights into distinctions and misunderstandings between basic and residual friction angles. The other, given the influence of the basic friction angle for the entire rock joint shear strength, the manuscript offers an extended database of basic friction angle values. Full article

In the domain of agricultural machinery, the utilization of carbon fiber-reinforced plastics (CFRP) for structural components, such as the chassis, facilitates substantial weight reduction. To integrate additional components, stainless-steel connection points can be bonded to the CFRP chassis using adhesives. This study investigates surface preparation methods to enhance adhesive bonding strength at the coupon level. Three adhesives (DP490, MA8110, SG300) were tested on untreated, sandblasted, and sandpaper-grinded steel surfaces. Contrary to predictions, the highest strength (28.7 MPa) for DP490 was achieved after simple acetone cleaning, despite lower surface roughness (Ra = 1.60 µm), while sandblasting (Ra = 3.71 µm, 22 MPa) and grinding (Ra = 2.78 µm, 25.95 MPa) performed worse due to incomplete adhesive penetration. Subsequent tests on DP490 with laser structuring (Ra = 88.8 µm) and sandblasting with coating (Ra = 1.94 µm) provided strengths of 27.5 MPa and 29.3 MPa, respectively. The findings indicate that, under the examined conditions, surface cleanliness plays a more critical role in adhesive bonding strength than surface roughness. Practically, acetone cleaning is a cost-effective and time-efficient alternative to treatments like sandblasting or laser structuring. This makes it attractive for industrial use in agricultural machinery. While this study focuses on coupon-level surfaces, the findings provide a basis for scaling to component-level applications in future research. Full article

Understanding nonlinear fluid flow in fractured rocks is critical for various geoengineering and geosciences. This study investigates the evolution of seepage behavior under varying fracture surface roughness, confining pressures, and shear displacements. A total of four sandstone fracture specimens were prepared using controlled splitting techniques, with surface morphology quantified by Joint Roughness Coefficient (JRC) values ranging from 2.8 to 17.7. Triaxial seepage tests were conducted under four confining pressures (3–9 MPa) and four shear displacements (0–1.5 mm). Experimental results reveal that permeability remains stable under low hydraulic gradients but transitions to nonlinear regimes as the flow rate increases, accompanied by significant energy loss and deviation from the cubic law. The onset of nonlinearity occurs earlier with higher roughness, stress, and displacement. A critical hydraulic gradient Jc was introduced to define the threshold at which inertial effects dominate. Forchheimer’s equation was employed to model nonlinear flow, and empirical regression models were developed to predict coefficients A, B, and Jc using hydraulic aperture and JRC as input variables. These models demonstrated high accuracy (R² > 0.92). This work provides theoretical insights and predictive approaches for assessing nonlinear fluid transport in rock fracture. Future research will address mechanical–hydraulic coupling and incorporate additional factors such as scale effects and flow anisotropy. Full article

The torsional stiffness of rehabilitation robot joints is a critical performance determinant, significantly affecting motion accuracy, stability, and user comfort. This paper introduces an innovative traction drive mechanism that transmits torque through friction forces, overcoming mechanical impact issues of traditional gear transmissions, though accurately modeling surface roughness effects remains challenging. Based on fractal theory, this study presents a comprehensive torsional stiffness analysis for advanced traction drive joints. Surface topography is characterized using the Weierstrass–Mandelbrot function, and a contact mechanics model accounting for elastic–plastic deformation of micro-asperities is developed to derive the tangential stiffness of individual contact pairs. Static force analysis determines load distribution, and overall joint torsional stiffness is calculated through the integration of individual contact contributions. Parametric analyses reveal that contact stiffness increases with normal load, contact length, and radius, while decreasing with the tangential load and roughness parameter. Stiffness exhibits a non-monotonic relationship with fractal dimension, reaching a maximum at intermediate values. Overall system stiffness demonstrates similar parameter dependencies, with a slight decrease under increasing output load when sufficient preload is applied. This fractal-based model enables more accurate stiffness prediction and offers valuable theoretical guidance for design optimization and performance improvement in rehabilitation robot joints. Full article

Colloidal silica can seep through calcareous sand in the subgrade, forming colloidal-silica-cemented sand with self-sensing ability—that is, it is sensitive to stress changes caused by vehicle loading. Its self-sensing sensitivity is higher than that of traditional Portland-cement-based self-sensing materials. The self-sensing mechanism is attributed to the ionic conductive network formed by seawater. However, a change in tidal water level causes an unsaturated state, and foundation deformation leads to cracking of the roadbed. The effect of unsaturation and cracking on self-sensing remains unclear, and they have not been studied in the previous literature. The aim of this paper is to study the self-sensing ability of subgrades formed via colloidal-silica-cemented sand under unsaturated and cracked states, as well as to explore the underlying mechanisms. Specimens with different degrees of saturation and different levels of joint roughness in precracks were prepared; then, the self-sensing ability was tested using the four-electrode method for each specimen under cyclic stress loading. NMR (nuclear magnetic resonance) and an unsaturated triaxial apparatus were also used to investigate the underlying mechanisms. This paper discovers that (1) either unsaturation or crack alone can increase self-sensing, but their self-sensing sensitivities are on the same order; (2) under the coupled effect of unsaturation and cracking, the self-sensing sensitivity increases by one order of magnitude, which is higher than when only unsaturation or cracking exists; and (3) the joint roughness of precracks does not affect self-sensing in the saturated state, but it affects self-sensing dramatically in the unsaturated state. The NMR test demonstrated the conductive ionic water within nanopores, which forms the conductive network for self-sensing. Unsaturation causes suction-induced shrinkage based on the unsaturated triaxial apparatus, while unsaturation increases self-sensing sensitivity, indicating that shrinkage is accompanied by self-sensing improvement. This paper provides the effects of unsaturation and cracking on the self-sensing capabilities of colloidal-silica-cemented sand, and the findings can contribute to the knowledge of subgrades formed via colloidal-silica-cemented sand for stress-sensing under traffic loading. Full article

The paper presents the effect of the symmetric and asymmetric semi-metallic gasket core shape on the tightness level in bolted flange joints. Experimental tests, as well as numerical calculations based on the finite element method, revealed that the asymmetric gasket core provides a higher strain on the sealing graphite layer and leads to a more uniform distribution of strain on the particular ridges of the core. Furthermore, the leakage rate of the asymmetric gasket was reduced by approximately 60% compared to the symmetric gasket. It was also observed that the uniformity of pressure and strain distribution in a gasket with an asymmetric core occurs over about 80% of the gasket width. The leakage reduction effect in a flange joint sealed with a gasket with an asymmetric core was theoretically explained. As shown, the main leakage flows through the porous structure of the graphite layer, while the leakage path at the interface between the metal rough profile and the graphite layer is several orders of magnitude smaller. Full article

Filled joints are widely found in natural rock masses and are one of the main factors causing rock mass engineering instability. The use of bolts can effectively control the shear slip of filled joints, research on bolts filled joints in the filling degree, and other key parameters of the influence of the law, to ensure the stability of the engineering rock body is of great significance. This paper presents shear experiments on bolted filled joints of Basalt Fiber-Reinforced Polymer (BFRP) materials with different joint roughness and filling degrees, while acoustic emission technology monitors the shear failure process of the specimens. The results show that the peak shear strength decreases with the increase in filling degree, and the peak shear strength decreases by 23.9% when the filling degree changes from 0 to 2.0 at 4 MPa and J2 conditions, while the normal stress, the Joint Roughness Coefficient (JRC) and the peak shear strength both show a positive correlation. The normal deformation of bolted filled joints exhibits three distinct evolutionary patterns depending on the filling degree, while both JRC and normal stress significantly influence the magnitude of shear dilatancy-shrinkage deformation. The shear resistance of BFRP bolts is mainly reflected in the post-peak plastic stage, and some of the fibers break during its shear deformation to form controlled yielding, with vertical and horizontal deformation controlled within 15.5~22.3 mm and 4.7~6.9 mm, respectively. The Acoustic Emission (AE) results show that the AE events are mainly in the post-peak plasticity stage, and the proportion is about the sum of the proportion of the other two phases, and this proportion increases with the increase in the filling degree. Full article

Surface roughness plays a vital role in determining surface integrity and function. Surface irregularities or reduced quality near the surface can contribute to material failure. Surface roughness is considered a crucial factor in estimating the fatigue life of structures welded by FSW. This study attempts to provide a deeper understanding of the nature of the surface formation and roughness of aluminum joints during FSW processes. In order to form more efficient joints, the frictional temperature generated was monitored until reaching 450 °C, where the transverse movement of the tool and the joint welding began. Hardness and tensile tests showed that the formed joints were good, which paved the way for more reliable surface roughness measurements. The surface roughness of the weld joint was measured along the weld line at three symmetrical levels using welding parameters that included a rotational speed of 1250 rpm, a welding speed of 71 mm/min, and a tilt angle of 1.5°. The average hardness in the stir zone was measured at 64 HV, compared to 50 HV in the base material, indicating a strengthening effect induced by the welding process. In terms of tensile strength, the FSW joint exhibited a maximum force of 2.759 kN. Average roughness (Rz), arithmetic center roughness (Ra), and maximum peak-to-valley height (Rt) were measured. The results showed that along the weld line and at all levels, the roughness coefficients (Rz, Ra, and Rt) gradually increased from the beginning of the weld line to its end. The roughness Rz varies from start to finish, ranging between 9.84 μm and 16.87 μm on the RS and 8.77 μm and 13.98 μm on the AS, leveling off slightly toward the end as the heat input stabilizes. The obtained surface roughness and mechanical properties can give an in-depth understanding of the joint surface forming and increase the ability to overcome cracks and defects. Consequently, this approach, using adaptive thresholding image processing coupled with grayscale histogram analysis, yielded significant understanding of the FSW joint’s surface texture. Full article

The shear mechanical properties of rock discontinuities with different joint wall compressive strengths are a practical basis for the stability analysis of layered rock mass. Shear tests on discontinuities possessing different joint wall strengths were carried out. The shear strength and failure characteristics were analyzed, and the influences of discontinuity morphology on its shear properties were investigated. Meanwhile, numerical tests were performed to study the shear mechanical behavior and dilation evolution of discontinuities possessing different joint wall compressive strengths. Results show that the shear process of discontinuities possessing different joint wall strengths can be divided into four stages: meshing and compacting, climbing wear of soft rock and crack formation of hard rock, shear of part of soft rock and crack expansion of hard rock, complete shearing of the rock discontinuity. Shear failure of discontinuities was mainly concentrated on the morphological structure facing the shear direction. The dilatancy evolution process of discontinuities was mainly affected by the roughness and normal stress. The magnitude of dilation, peak shear strength and residual shear strength of discontinuities possessing different joint wall strengths were between the discontinuities possessing identical joint wall strengths composed of soft and hard rock, under the same loading condition. Full article