Search Results (290)

The impact mechanism of long-term creep in gas-containing coal on coal and gas outbursts has not been fully elucidated and remains insufficiently understood for the purpose of disaster engineering control. This investigation conducted triaxial creep experiments on raw coal specimens under controlled confining pressures, axial stresses, and gas pressures. Through systematic analysis of coal’s physical responses across different loading conditions, we developed and validated a novel creep damage constitutive model for gas-saturated coal through laboratory data calibration. The key findings reveal three characteristic creep regimes: (1) a decelerating phase dominates under low stress conditions, (2) progressive transitions to combined decelerating–steady-state creep with increasing stress, and (3) triphasic decelerating–steady–accelerating behavior at critical stress levels. Comparative analysis shows that gas-free specimens exhibit lower cumulative strain than the 0.5 MPa gas-saturated counterparts, with gas presence accelerating creep progression and reducing the time to failure. Measured creep rates demonstrate stress-dependent behavior: primary creep progresses at 0.002–0.011%/min, decaying exponentially to secondary creep rates below 0.001%/min. Steady-state creep rates follow a power law relationship when subject to deviatoric stress (R² = 0.96). Through the integration of Burgers viscoelastic model with the effective stress principle for porous media, we propose an enhanced constitutive model, incorporating gas adsorption-induced dilatational stresses. This advancement provides a theoretical foundation for predicting time-dependent deformation in deep coal reservoirs and informs monitoring strategies concerning gas-bearing strata stability. This study contributes to the theoretical understanding and engineering monitoring of creep behavior in deep coal rocks. Full article

This study investigates the mechanical, morphological, and wear properties of SiO₂-filled tri-axial warp-knitted (TWK) glass fiber-reinforced vinyl ester matrix composites, with a focus on void fraction, tensile, flexural, hardness, and wear behavior. Adding SiO₂ fillers reduced void fractions, enhancing composite strength, with values ranging from 1.63% to 5.31%. Tensile tests revealed that composites with 5 wt% SiO₂ (GV1) exhibited superior tensile strength, Young’s modulus, and elongation due to enhanced fiber–matrix interaction. Conversely, composites with 10 wt% SiO₂ (GV2) showed decreased tensile performance, indicating increased brittleness. Flexural tests demonstrated that GV1 outperformed GV2, showcasing higher flexural strength, elastic modulus, and deflection, reflecting improved load-bearing capacity at optimal filler content. Shore D hardness tests confirmed that GV1 had the highest hardness among the specimens. SEM analysis revealed wear behavior under various loads and sliding distances. GV1 exhibited minimal wear loss at lower loads and distances, while higher loads caused significant matrix detachment and fiber damage. These findings highlight the importance of optimizing SiO₂ filler content to enhance epoxy composites’ mechanical and tribological performance. Full article

Bamboo scrimber is an environmentally friendly biomass building material with excellent mechanical properties. However, it is susceptible to delamination failure of the transverse fibers under compression, which limits its structural performance. To address this problem, this study utilizes steel tubes to encase bamboo scrimber, forming a novel bamboo scrimber-filled steel tubular column. This configuration enables the steel tube to provide effective lateral restraint to the bamboo material. Axial compression tests were conducted on 18 specimens, including bamboo scrimber columns and bamboo scrimber-filled steel tubular columns, to investigate the effects of steel ratio and loading mode (full-section and core loading) on the axial compression performance. The test results indicate that the external steel tubes significantly enhance the structural load-bearing capacity and deformation capacity. Primary failure modes of the composite columns include shear failure and buckling. The ultimate stress and strain of the structure are positively correlated with the steel ratio; as the steel ratio increases, the ultimate stress of the specimens can increase by up to 19.2%, while the ultimate strain can increase by up to 37.7%. The core-loading specimens exhibited superior load-bearing capacity and deformation ability compared to the full-section-loading specimens. Considering the differences in the curves for full-section and core loading, the steel tube confinement coefficient was introduced, and the predictive models for the ultimate stress and ultimate strain of the bamboo scrimber-filled steel tubular column were developed with accurate prediction. Full article

The Korla fragrant pear is a highly valued economic fruit in China’s Xinjiang region. However, biomechanical data on the fruit-bearing branches and pedicels of this species remain incomplete, which to some extent hinders the advancement of harvesting equipment and techniques. Therefore, refining these data is of great significance for the development of efficient and non-destructive harvesting strategies. This study aims to elucidate the mechanical properties of the fruiting branches and peduncles of Korla fragrant pears, thereby establishing a theoretical foundation for the future development of intelligent harvesting technology for this variety. The research utilized axial and radial compression tests, along with three-point bending test methods, to quantitatively analyze the elastic modulus and shear modulus of the branches and peduncles. The test results reveal that the elastic modulus of the fruiting branches under axial compression is 263.51 ± 76.51 MPa, while under radial compression, it measures 135.53 ± 73.73 MPa (where ± represents the standard deviation). In comparison, the elastic modulus of the peduncles is recorded at 152.96 ± 119.95 MPa. Additionally, the three-point bending test yielded a shear modulus of 75.48 ± 32.84 MPa for the branches and 30.23 ± 8.50 MPa for the peduncles. Using finite element static structural analysis, the simulation results aligned closely with the experimental data, falling within an acceptable error range, thus validating the reliability of the testing methods and outcomes. The mechanical parameters obtained in this study are critical for modeling the stress and deformation behaviors of pear-bearing structures during mechanical harvesting. These findings provide valuable theoretical support for the optimization of harvesting device design and operational strategies, with the aim of reducing fruit damage and improving harvesting efficiency in pear orchards. Full article

CFRP possesses the advantages of lightweight and high strength, but its cost is relatively high, and its ductility is insufficient; aluminum alloys have a relatively low cost and good ductility. This paper develops a CFRP-aluminum alloy laminated tube (CFRP-AL tube), which combines the advantages of CFRP and aluminum alloy. Such composite components have broad application prospects in the field of spatial structures. The CFRP-AL tubes were studied by experimental, numerical, and theoretical research on their axial compression performance in this paper. Firstly, the standard tensile test was carried out on 6061-T6 aluminum alloy. Combining the test results and references, the Johnson–Cook hardening model parameters of aluminum alloy were determined. The tensile test of CFRP was conducted to determine its material parameters. Based on composite material mechanics and fracture mechanics, a composite progressive damage model for the CFRP-AL tube was established. Secondly, axial compression tests were carried out on 27 CFRP-AL tubes and 3 aluminum alloy tubes with a small slenderness ratio. The test results show that the typical failure mode of CFRP-AL tubes with small slenderness ratios is strength failure, and the ultimate bearing capacity rises by 11~31% compared to aluminum alloy tubes. Thirdly, a user material subroutine capable of simulating CFRP failure was developed. Based on the user material subroutine, the effect of the initial imperfection, the fiber layer angle, the fiber layer thickness, the slenderness ratio, the diameter-thickness ratio and the CFRP volume ratio were discussed. And the failure mechanism and response of the CFRP-AL tubes under the axial compression were obtained. Finally, based on the strength theory, the formula predicting the bearing capacity of the strength failure was established, and the results of the formula were in a good agreement with the experimental and numerical results. Full article

This paper presents the results of an experimental study on the buckling and failure behavior of thin-walled square columns made from PLA and PETG polymers using FDM 3D printing technology. Thin-walled square columns made from thermoplastic materials, intended for use in lightweight load-bearing applications such as structural supports in transportation, construction, and mechanical assemblies, were tested under axial compression from the onset of buckling to complete failure. The novelty of this work lies in the application of an interdisciplinary experimental approach to the analysis of the behavior of thin-walled columns made of PLA and PETG materials during FDM 3D printing under compression until complete failure, as well as the use of acoustic and optical diagnostic methods for a comprehensive assessment of damage. The experimental results are as follows: Buckling load (N): PLA—1175 ± 32, PETG1—1910 ± 34, PETG2—1315 ± 27. Ultimate load (N): PLA—2770, PETG1—4077, PETG2—2847. Maximum strain: PLA—11.35%, PETG1—11.77%, PETG2—10.99%. Among the tested materials, PETG1 exhibited the highest resistance and energy absorption capacity upon failure, making it a favorable choice for manufacturing 3D-printed load-bearing columns. Full article

Traditional three-row roller YRT turntable bearings exhibit high friction torque during operation, which limits their performance in high-precision and high-response applications. To address this issue, a novel ball–roller composite turntable bearing is proposed that effectively reduces friction torque while maintaining a high load capacity. A mechanical model based on statics is established, and the Newton–Raphson method is employed to calculate the contact load. The formation mechanism of friction torque is analyzed, and a corresponding computational model is developed and validated using experimental data. The effects of axial load, eccentricity, overturning moment, rotational speed, and axial clearance on friction torque are systematically studied. Results indicate that friction torque increases with these parameters. Axial clearance has a significant influence, and an optimal clearance value between the balls and rollers is determined. Additionally, a reasonable range for the raceway curvature radius coefficient is proposed. When the numerical ratio of balls to rollers is 1, the bearing exhibits optimal friction performance. Among various roller crowning strategies, logarithmic crowning yields the best results. This study provides a theoretical basis and technical support for the optimized design of ball–roller composite turntable bearings. Full article

This study investigates how different longitudinal steel rebars influence the flexural performance and cracking mechanisms of reinforced ultra-high-performance concrete (UHPC) beams, combining axial tensile tests using acoustic emission monitoring with standard four-point bending tests. A series of experimental assessments on the flexural behavior of UHPC beams reinforced with various types of longitudinal reinforcement was conducted. The types of longitudinal reinforcement mainly encompassed HRB 400, HRB 600, and NPR steel rebars. The test results revealed that the UHPC beams reinforced with the three types of longitudinal steel rebar exhibited distinctly different failure modes. Compared to the single dominant crack failure typical of UHPC beams reinforced with HRB 400 steel rebars, the beams using HRB 600 rebars exhibited a tendency under balanced failure conditions to develop fewer main cracks (typically two or three). Conversely, the UHPC beams incorporating NPR steel rebars exhibited significantly more cracking within the pure bending zone, characterized by six to eight uniformly distributed main cracks. Meanwhile, the HRB 600 and NPR steel rebars effectively upgraded the flexural load-bearing capacity and deformation ability compared to the HRB 400 steel rebars. By integrating the findings from the direct tensile tests on reinforced UHPC, aided by acoustic emission source location, this research specifically highlights the damage mechanisms associated with each rebar type. Full article

Duplex ball bearings are common components in space satellite mechanisms, and their behaviour impacts the overall performance and reliability of these systems. During rocket launches, these bearings suffer high vibrational loads, making their dynamic response essential for their survival. To predict the dynamic behaviour under vibration, simulations and experimental tests are performed. However, published models for space applications fail to capture the variations observed in test responses. This study presents a multi-degree-of-freedom nonlinear multibody model of a hard-preloaded duplex space ball bearing, particularized for this work to the case in which the outer ring is attached to a shaker and the inner ring to a test dummy mass. The model incorporates the Hunt and Crossley contact damping formulation and employs quaternions to accurately represent rotational dynamics. The simulated model response is validated against previously published axial test data, and its response under step, sine, and random excitations is analysed both in the case of radial and axial excitation. The results reveal key insights into frequency evolution, stress distribution, gapping phenomena, and response amplification, providing a deeper understanding of the dynamic performance of space-grade ball bearings. Full article

The mechanism of low- to middle-rank coal seam gas accumulation in the Baode block on the eastern edge of the Ordos Basin is well understood. However, exploration efforts in the Shizuishan area on the western edge started later, and the current understanding of enrichment and accumulation rules is unclear. It is important to systematically study enrichment and accumulation, which guide the precise exploration and development of coal seam gas resources in the western wing of the basin. The coal seam collected from the Shizuishan area of Ningxia was taken as the target. Based on drilling, logging, seismic, and CBM (coalbed methane) test data, geological conditions were studied, and factors and reservoir formation modes of CBM enrichment were summarized. The results are as follows. The principal coal-bearing seams in the study area are coal seams No. 2 and No. 3 of the Shanxi Formation and No. 5 and No. 6 of the Taiyuan Formation, with thicknesses exceeding 10 m in the southwest and generally stable thickness across the region, providing favorable conditions for CBM enrichment. Spatial variations in burial depth show stability in the east and south, but notable fluctuations are observed near fault F1 in the west and north. These burial depth patterns are closely linked to coal rank, which increases with depth. Although the southeastern region exhibits a lower coal rank than the northwest, its variation is minimal, reflecting a more uniform thermal evolution. Lithologically, the roof of coal seam No. 6 is mainly composed of dense sandstone in the central and southern areas, indicating a strong sealing capacity conducive to gas preservation. This study employs a system that fuses multi-source geological data for analysis, integrating multi-dimensional data such as drilling, logging, seismic, and CBM testing data. It systematically reveals the gas control mechanism of “tectonic–sedimentary–fluid” trinity coupling in low-gentle slope structural belts, providing a new research paradigm for coalbed methane exploration in complex structural areas. It creatively proposes a three-type CBM accumulation model that includes the following: ① a steep flank tectonic fault escape type (tectonics-dominated); ② an axial tectonic hydrodynamic sealing type (water–tectonics composite); and ③ a gentle flank lithology–hydrodynamic sealing type (lithology–water synergy). This classification system breaks through the traditional binary framework, systematically explaining the spatiotemporal matching relationships of the accumulated elements in different structural positions and establishing quantitative criteria for target area selection. It systematically reveals the key controlling roles of low-gentle slope structural belts and slope belts in coalbed methane enrichment, innovatively proposing a new gentle slope accumulation model defined as “slope control storage, low-structure gas reservoir”. These integrated results highlight the mutual control of structural, thermal, and lithological factors on CBM enrichment and provide critical guidance for future exploration in the Ningxia Autonomous Region. Full article

Conventional bolts frequently fail under large deformations due to stress concentration in soft rock tunnels. In contrast, yielding bolts incorporate energy-absorbing mechanisms to sustain controlled plastic deformation. This study employed FLAC3D to numerically investigate the pull-out, shear, and bending behaviors of yielding bolts, evaluating their support effectiveness in soft rock tunnels. Three-dimensional finite difference models incorporating nonlinear coupling springs and the Mohr–Coulomb criterion were developed to simulate bolt–rock interactions under multifactorial loading. Validation against experimental pull-out tests and field measurements confirmed the model accuracy. Under pull-out loading, the axial forces in yielding bolts decreased more rapidly along the bolt length, reducing stress concentration at the head. The central position of the maximum load-bearing capacity in conventional bolts fractured under tension, resulting in an hourglass-shaped axial force distribution. Conversely, the yielding bolts maintained yield strength for an extended period after reaching it, exhibiting a spindle-shaped axial force distribution. Parametric analyses reveal that bolt spacing exerts a greater influence on support effectiveness than length. This study bridges critical gaps in understanding yielding bolt behavior under combined loading and provides a validated framework for optimizing energy-absorbing support systems in soft rock tunnels. Full article

In the case of strengthening building structures, the process usually involves elements that have a certain loading history and are typically subjected to loading during the strengthening process. In scientific research, on the other hand, strengthening is usually applied to elements that are not representative of real structures. This article presents a study of the effect of pre-damage on the behavior of eccentrically compressed concrete cylinders confined with PBO-FRCM (fabric-reinforced cementitious matrix with PBO fibers) composite. Concrete confinement introduces a favorable triaxial stress state, which leads to an increase in the compressive strength of concrete. FRCM systems are an alternative to FRP (fiber-reinforced polymer) composites. Replacing the polymer matrix with a mineral matrix primarily improves the fire resistance of the strengthening system. The elements were made of concrete with a compressive strength of about 40 MPa, which is typical for current reinforced concrete columns. Pre-damage was induced by loading the test elements to 80% of the average compressive strength and then fully unloading. The elements were then strengthened with three layers of PBO-FRCM composite and subjected to axial or eccentric compression with force applied at two different eccentricities. In addition to electric strain gauges, a digital image correlation system was used for measurements, to identify the initiation of PBO mesh overlap delamination. This study analyzed the elements in terms of load-bearing capacity, deformability, ductility, and failure mechanisms. In general, there was no negative effect of pre-damage on the behavior of the tested elements. Full article

This article considers the effect of constant and variable Poisson’s ratio on cracking in concrete and rock specimens under uniaxial compression using mechanical systems modeling methods. The article presents an analysis of the data confirming the increase in Poisson’s ratio under specimen loading. A system of equations for modeling the effect of Poisson’s ratio on cracking under uniaxial compression is proposed. The comparison showed that the model with a constant Poisson’s ratio predicts a thickness of the surface layer with cracks that is underestimated by approximately 10%. In practice, this means that the model with a constant Poisson’s ratio underestimates the risk of failure. A technique for analyzing random deviations of Poisson’s ratio from the variable mathematical expectation is proposed. The comparison showed that the model with a variable Poisson’s ratio leads to results that are more cautious, i.e., it does not potentially overestimate the safety factor. The model predicts an increase in uniaxial compression strength when using external reinforcement. An equation is proposed for determining the required wall thickness of a conditional reinforcement shell depending on the axial compressive stress. The study contributes to understanding the potential vulnerability of load-bearing structures and makes a certain contribution to increasing their reliability. Full article

The spindle is a critical component that significantly influences the performance of machine tools. In motorized spindles, heat generation from both the bearings and built-in motor leads to thermal deformation of structural components, which, in turn, affects machining accuracy. This study investigates the thermo-mechanical behavior of motorized spindles under various operational conditions, with the aim of accurately predicting thermally induced axial deformation and determining optimal temperature sensor placement. To achieve this, temperature rise and deformation data were simultaneously collected using appropriate data acquisition systems across varying spindle speeds. A correlation analysis confirmed a strong positive relationship exceeding 97.5% between temperature rise at all sensor locations and axial thermal deformation. Multivariate regression analysis was then applied to identify optimal combinations of sensor data for accurate deformation prediction. Additionally, a finite element (FE) thermal–mechanical model was developed to simulate spindle behavior, with the results validated against experimental measurements and regression model predictions. The four-variable regression model and FE simulation achieved Root Mean Square Errors (RMSEs) of 0.84 µm and 0.82 µm, respectively, both demonstrating close agreement with experimental data and effectively capturing the trend of thermal deformation over time under different operating conditions. Finally, an optimal sensor configuration was identified that minimizes pre-diction error while reducing the number of required sensors. Overall, the proposed methodology offers valuable insights for optimizing spindle design to enhance thermal–mechanical performance. Full article

Symmetrical bearing raceway led to the axial sliding of rolling elements, which is a crucial factor in shortening the operational lifespan. This study addresses this limitation through three-step advancements: first, a parametric equation for logarithmic spiral raceways is developed by analyzing their asymmetric geometric features; second, based on the geometrical model, we systematically investigate the parameters of the logarithmic spiral that affects the bearing performance metrics; and finally, a novel fatigue life prediction framework that integrates static mechanical analysis with raceway parameters establishes the theoretical foundation for optimizing the raceway parameters. The results of the model analysis show that the error of the maximum contact stress verified by the finite element method is less than 8.3%, which verifies the model’s accuracy. Increasing the contact angle α of the outer ring from 82 to 85 can increase fatigue life by 15.6 times while increasing the initial polar radius O of the inner ring from 7.8 mm to 8.1 mm will cause fatigue life to drop by 86.9%. The orthogonal experiment shows that the contact angle α of the outer ring has the most significant influence on the service life, and the optimal parameter combination (clearance δ of 0.02 mm, inner race and outer race strike angles α of 85°, an inner race initial polar radius $r_o$ of 7.8 mm, and an outer race initial polar radius $r_o$ of 7.9 mm) achieves a 60.7% fatigue life increase. The findings provide theoretical support and parameter guidance for the optimal bearing design with logarithmic spiral raceways. Full article