Search Results (1,101)

The elastic support stiffness coefficient $k_R$ of opposing horizontal struts constitutes a critical parameter in the design of strutted retaining structures for deep excavations. The determination of the fixed-point adjustment coefficient $\lambda$ serves as a fundamental prerequisite for the quantitative assessment of this stiffness coefficient. To identify the fixed-point location and establish a computational approach for $\lambda$, the endpoint displacements of opposing horizontal struts are classified into four distinct scenarios. For each scenario, the relationship between the lateral earth pressures on both sides of the excavation is derived, the support mechanism of the internal strut is elucidated, and the corresponding fixed-point locations of the struts are determined. Utilizing the response curve between the support-point displacement of the retaining structure and the lateral earth pressure, and adhering to the principle of linearization, analytical formulas for $\lambda$ under the four scenarios are formulated. The proposed method is employed to compute and evaluate the fixed-point adjustment coefficient of the opposing horizontal struts in a case study drawn from the literature, with the results rigorously compared against the existing published data. Furthermore, the $\lambda$ values for opposing horizontal struts in a metro station excavation project are computed and contrasted with values back-calculated from monitored horizontal displacements of the retaining structure. The findings demonstrate that the proposed method for determining $\lambda$ is both computationally efficient and practically applicable. The derived $\lambda$ values can be effectively used to predict internal forces and deformations in retaining structures for asymmetrically loaded deep excavations. This research offers substantial theoretical insights and practical implications for the scientifically informed design and construction of deep excavation support systems. Full article

To address the limitations of traditional timber mortise-and-tenon joints, particularly their low pull-out resistance and rapid stiffness degradation under cyclic loading, this study proposes a novel integrated sleeve mortise-and-tenon steel–timber composite beam–column joint. Building upon prior experimental validation and numerical model verification, a comprehensive parametric study was conducted to systematically investigate the influence of key geometric parameters on the seismic performance of the joint. The investigated parameters included beam sleeve thickness (1–10 mm), sleeve length (150–350 mm), bolt diameter (4–16 mm), and the dimensions and thickness of stiffeners. The results indicate that a sleeve thickness of 2–3 mm yields the optimal overall performance: sleeves thinner than 2 mm are prone to yielding, while those thicker than 3 mm induce stress concentration in the timber beam. A sleeve length of approximately 250 mm provides the highest initial stiffness and a ductility coefficient exceeding 4.0, representing the best seismic behavior. Bolt diameters within the range of 8–10 mm produce full and stable hysteresis loops, effectively balancing load-carrying capacity and energy dissipation; smaller diameters lead to pinching failure, whereas larger diameters trigger premature plastic deformation in the timber. Furthermore, stiffeners with a width of 40 mm and a thickness of 2 mm effectively enhance joint stiffness, promote a uniform stress distribution, and mitigate local damage. The optimized joint configuration demonstrates excellent ductility, stable hysteretic behavior, and a high load capacity, providing a robust technical foundation for the design and practical application of advanced steel–timber composite connections. Full article

Glass fiber-reinforced polymer (GFRP) composites are widely used in structural applications due to their high specific strength and durability; however, their mechanical performance strongly depends on fiber architecture and environmental exposure. This study evaluates the mechanical behavior and moisture-induced degradation of GFRP laminates through tensile tests, impact tests, dynamic mechanical analysis (DMA), and thermomechanical analysis (TMA) performed on a bi-directional glass–epoxy GFRP laminate ([0°/90°]). Tensile tests revealed a maximum longitudinal strength of 369 MPa in dry specimens, while water immersion for up to 21 days led to a significant reduction in tensile strength, from 207 MPa to 63 MPa, in diagonally cut specimens. Impact tests conducted at 12 J showed larger displacements in specimens cut along directions not aligned with the fibers, indicating matrix-dominated behavior. Dynamic mechanical analysis demonstrated strong dependence of stiffness on fiber orientation, with storage modulus values decreasing by approximately 45% in 45° specimens compared with the principal directions, while the glass transition temperature remained within 59–62 °C. Thermomechanical analysis confirmed an increase in the coefficient of thermal expansion after aging, from 205.6 to 291.65 µm/(m·°C) below Tg. These results provide insights into the structure–property–environment relationships governing the durability of GFRP composites and support the optimization of their design for long-term polymer-based applications. Full article

The steel-plate–concrete composite reinforcement method is derived from the bonded steel plate and increased-section techniques. It is employed to enhance the strength of concrete structures that require a substantial increase in load-bearing capacity. To develop a flexural deformation calculation theory that accounts for slip effects in general reinforced cross-sections with bilateral symmetry, interfacial slip and deflection equations are formulated based on the relationship between interlayer slip and the rotational angle of beams in the plane, as well as the principle of force equilibrium. A numerical method, established based on this theoretical framework, is proposed to facilitate the analytical solution and is verified to be consistent with analytical results. Furthermore, the accuracy of the calculation theory is validated through bending experiments. Finally, the influence of key parameters affecting slip on the flexural stiffness of the reinforced beam is evaluated by determining the stiffness reduction coefficient according to the theory. The results indicate that the flexural stiffness of reinforced beams is governed by three non-dimensional parameters: the boundary condition parameter (μ), composite action parameter (shear connector stiffness (βl)), and relative bending stiffness parameter (G_∞/G₀). The loading mode does not affect the flexural stiffness of the reinforced beams. As βl approaches 100 and G_∞/G₀ approaches 1, η approaches 100%. In cases where high stiffness is required, reducing interfacial slip can minimize the loss of flexural stiffness in composite structures. Conservative calculations indicate that satisfying the conditions βl ≥ 8 and G_∞/G₀ ≤ 1.6 during design can ensure that the reduction in flexural stiffness of the reinforced beam remains above 90%. Full article

Aiming to predict the evolution of fracture structures under stress conditions and the Permeability process of the fracture network, a damage evolution model reflecting the coupling mechanism between topological characteristics and mechanical responses of fracture networks is established based on yield criteria and complex network theory, realizing a prediction for permeability processes. Firstly, key parameters such as degree centrality, betweenness centrality, and clustering coefficient of fracture nodes are extracted through complex network topological analysis. Combined with the finite element method to calculate the node shear stress transfer coefficient, a topology–mechanics coupling model of the fracture network is constructed. Secondly, the Coulomb–Mohr yield criterion is improved to establish a damage evolution equation considering normal stress and shear stiffness degradation. Based on the above theory, a fracture network permeability iterative algorithm was developed to simultaneously update the network topology and the stress distribution of the fracture network. The evolution process of the network was analyzed based on the adjacency matrix and the changes in the number of connected clusters. The results show that the average degree of the largest cluster directly reflects the connectivity of the fracture network; a higher average degree corresponds to greater damage to the fracture network under stress. The average clustering coefficient indicates the extent of local connectivity; a higher clustering coefficient signifies denser local connections, which enhances the fracture network connectivity. Compared with traditional static methods, the dynamic damage evolution model has a permeability prediction error within 7%, indicating the effectiveness of this method. Full article

Accurate prediction of subway-induced environmental vibrations for unopened lines remains a significant challenge due to the difficulty in determining appropriate excitation inputs. To address this issue, this study proposes an excitation modification method based on field measurements and numerical simulations. First, field measurements were conducted on a subway line in Shanghai to analyze vibration propagation characteristics and validate a two-dimensional finite element model (FEM). Subsequently, based on the validated model, frequency-band excitation modification formulas were derived. Distinct from existing empirical approaches that often rely on simple statistical scaling, the proposed method utilizes parametric numerical analyses to determine frequency-dependent correction coefficients for four key parameters: tunnel burial depth, tunnel diameter, soil properties, and train speed. The reliability of the proposed method was verified through theoretical analysis and an engineering application. The results demonstrate that the proposed method improves prediction accuracy for tunnels in similar soft soil regions, reducing the prediction error from 10.1% to 5.2% in the engineering case study. Furthermore, parametric sensitivity analysis reveals that ground vibration levels generally decrease with increases in burial depth, tunnel diameter, and soil stiffness, while exhibiting an increase with train speed. This study improves the reliability of vibration prediction in the absence of direct measurements and provides a practical tool for early-stage design and vibration mitigation for unopened lines. Full article

Vulcanized NR-SBR is widely used in vehicle components; however, its irreversible crosslinking limits recyclability and contributes to the large number of tires discarded annually worldwide, and in this context, this work presents an experimental comparative assessment of the tribological behavior of conventional tire rubber and silicone VMQ, motivated by a wheel concept based on a detachable tread aimed at improving durability and sustainability rather than proposing an immediate material substitution. Wear and friction behavior were investigated under abrasive and self-friction conditions using pin-on-disk testing with an abrasive counterpart representative of asphalt, supported by optical and scanning electron microscopy. The results show that NR-SBR undergoes severe abrasive and erosive wear, characterized by deep and irregular wear tracks, pronounced fluctuations in the dynamic friction coefficient, and strong sensitivity to load and sliding speed, particularly during the initial stages of track formation. In contrast, VMQ exhibits mild abrasive wear dominated by viscoelastic deformation, leading to shallow and stable wear tracks, lower friction coefficients, and significantly reduced material loss once the contact track is fully developed. These differences are attributed to the distinct mechanical responses of the elastomers, as the higher hardness and limited strain capacity of rubber promote micro-tearing and unstable material removal, while the high elasticity of silicone enables stress redistribution and stable contact conditions under abrasive loading. UV aging increases stiffness of rubber, resulting in reduced wear and friction, while silicone remains largely unaffected after 750 h due to the stability of its Si–O–Si backbone. Self-friction tests further indicate that smooth silicone sliding against rubber yields the lowest friction values, highlighting a favorable material pairing for detachable tread concepts. Factorial design analysis confirms material type as the dominant factor influencing both wear and friction. Overall, for the specific materials and operating conditions investigated, VMQ demonstrates higher durability, greater tribological stability, and improved aging resistance compared to NR-SBR, providing experimental evidence that supports its potential for long-life, more sustainable detachable tread applications. Full article

This study conducts systematic experimental and numerical investigations to address the parameter calibration issue in the discrete element model of seashells, aiming to establish a high-fidelity numerical model that accurately characterizes their macroscopic mechanical behavior, thereby providing a basis for optimizing parameters of seashell crushing equipment. Firstly, intrinsic parameters of seashells were determined through physical experiments: density of 2.2 kg/m³, Poisson’s ratio of 0.26, shear modulus of 1.57 × 10⁸ Pa, and elastic modulus of 6.5 × 10¹⁰ Pa. Subsequently, contact parameters between seashells and between seashells and 304 stainless steel, including static friction coefficient, rolling friction coefficient, and coefficient of restitution, were obtained via the inclined plane method and impact tests. The reliability of these contact parameters was validated by the angle of repose test, with a relative error of 5.1% between simulation and measured results. Based on this, using ultimate load as the response indicator, the PlackettBurman experimental design was employed to identify normal stiffness per unit area and tangential stiffness per unit area as the primary influencing parameters. The Bonding model parameters were then precisely calibrated through the steepest ascent test and design, resulting in an optimal parameter set. The error between simulation results and physical experiments was only 3.8%, demonstrating the high reliability and accuracy of the established model and parameter calibration methodology. Full article

The study concerns the Duffing oscillator (Duffing equation) with softening stiffness. Using numerical simulations, the upper and lower limits of the unstable region for damping equal to 0 were identified, and analytic formulas describing them were developed. The analysis shows that the developed formulas are effective for all combinations of stiffness coefficient values that were tested. The curve of the upper limit of the unstable region is a jump-down curve, and in the theory of nonlinear systems, this curve for damping equal to zero is identified as a backbone curve (the curve of natural frequency of a system). However, the classical backbone curve calculated via a formula that is commonly known and used differs visibly from that actually obtained via numerical simulations of the upper boundary of the unstable region at large amplitudes. It could therefore be concluded that the backbone curve is not equal to the upper boundary of the unstable solution region. Moreover, the paper shows that the use of the scale relative to a critical oscillation amplitude leads to the conclusion that for damping equal to 0, systems with different parameters have the same instability regions in dimensionless space. Full article

Oxidation can lead to intrinsic degradation and loss in the load-bearing capacity of ceramic matrix composites (CMCs) in high-temperature service, thereby compromising structural integrity and operational safety. To elucidate the mechanism of its oxidation effects, this study predicted the oxygen diffusion coefficient within 2.5D woven C/SiC fibre bundles based on gas diffusion and oxidation kinetics theory, and subsequently constructed a meso-scale constitutive model incorporating oxidation damage and fibre defect distribution. Furthermore, a micro-scale framework for yarns was established by integrating interfacial slip behaviour, and an RVE model for 2.5D woven C/SiC was constructed based on X-ray computed tomography reconstruction of the actual microstructure. Building upon this foundation, an oxidation constitutive model applicable to loading–unloading cycles was proposed and validated through high-temperature oxidation tests at 700 °C, 900 °C, and 1100 °C. Results demonstrate that this model effectively characterizes the strength degradation and stiffness reduction caused by oxidation, enabling prediction of CMCs’ mechanical properties under oxidizing conditions and providing a physics-based foundation for the reliable design and life assessment of C/SiC components operating in oxidizing environments. Full article

This paper presents an experimental investigation of the shear connection between outer layers of lightweight precast concrete sandwich panels (PCSP) made of high-performance concrete (HPC). The shear-transfer mechanism is based on reinforcing ribs composed of rigid polymer-based thermal insulation combined with carbon-fibre-reinforced polymer (CFRP) shear reinforcement. A total of seven full-scale sandwich panels were tested in four-point bending. This study compares three types of rigid thermal insulation used in the shear ribs—Purenit, Compacfoam CF400, and Foamglass F—and investigates the influence of the amount of CFRP shear reinforcement on the structural behavior of the panels. Additional specimens were used to evaluate the effect of reinforcing ribs and of polymer-based thermal insulation placed between the ribs. The experimental results show that panels with shear ribs made of Purenit and Compacfoam CF400 achieved significantly higher load-bearing capacities compared to Foamglass F, which proved unsuitable due to its brittle behavior. Increasing the amount of CFRP shear reinforcement increased the load-bearing capacity but had a limited effect on panel stiffness. The experimentally determined composite interaction coefficient ranged around α ≈ 0.03, indicating partial shear interaction between the outer concrete layers. A simplified strut-and-tie model was applied to predict the load-bearing capacity and showed conservative agreement with experimental results. The findings demonstrate that polymer-based materials, particularly CFRP reinforcement combined with rigid polymer insulation, enable efficient shear transfer without thermal bridging, making them suitable for lightweight and thermally efficient precast concrete sandwich panels. Full article

The traction behavior of lubricant films forms the foundation of dynamic modeling for aeroengine mainshaft ball bearings. Its accuracy directly determines the reliability of predicted dynamic responses and the available design safety margins. Existing traction models produce artificial friction in the zero slip region and exhibit strong sensitivity to ball size effects, which leads to significant deviations from experimental observations. These limitations make them unsuitable for high-fidelity analyses of aeroengine mainshaft bearings. In this study, a self-developed high-speed traction test rig was used to systematically measure the traction–slip responses of three aviation lubricants, including the newly developed 4102 (7 cSt) and the inservice 4050 (5 cSt) and 4010 (3 cSt). The tests covered a wide range of operating conditions, including maximum Hertzian pressures of 1.0 to 1.5 GPa, oil supply temperatures of 25 to 120 °C, entrainment speeds of 25 to 40 m/s, and slide–roll ratios (SRR) of 0 to 0.3. The evolution of lubricant traction characteristics was examined in detail. Based on the experimental data, a four-parameter and three-coefficient traction model was proposed. This model eliminates the non-physical traction outputs at zero slip observed in previous formulations. When embedded into the bearing dynamic simulations, the maximum deviation between the predicted friction torque and the measured values is only 3.79%. On the basis of typical operating conditions of aeroengine bearings, lubricant selection guidelines were established. Under combined high-speed, light-load, and high-temperature conditions, the high-viscosity lubricant 4102 is preferred because it suppresses cage sliding and enhances film stiffness. When the cage slip ratio is below 15% and lubrication is sufficient, the low-viscosity lubricant 4010 is recommended, followed by 4050, in order to reduce frictional heating. This study provides a theoretical basis for high-accuracy dynamic design and lubricant selection for aeroengine ball bearings. Full article

Taking advantage of the ionic size and mass disorder as component design criteria, three novel high-entropy rare-earth zirconate ceramics, including (Sm_0.2Gd_0.2Dy_0.2Er_0.2Tm_0.2)₂Zr₂O₇, (Gd_0.2Dy_0.2Ho_0.2Er_0.2Tm_0.2)₂Zr₂O₇ and (Gd_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₂Zr₂O₇, with single-phase fluorite structure were successfully synthesized. All compositions exhibited enhanced mechanical properties, with Vickers hardness and fracture toughness increasing as the grain size decreased. (Gd_0.2Dy_0.2Ho_0.2Er_0.2Yb_0.2)₂Zr₂O₇ demonstrated superior mechanical performance, achieving values of 11.41 ± 0.40 GPa and 1.78 ± 0.12 MPa·m^1/2, respectively. The thermal expansion coefficients at 1000 °C ranged from 10.80 × 10⁻⁶ K⁻¹ to 11.39 × 10⁻⁶ K⁻¹, which is proportional to the average ionic bond length. Notably, (Sm_0.2Gd_0.2Dy_0.2Er_0.2Tm_0.2)₂Zr₂O₇ exhibited low room-temperature thermal conductivity (1.58 W·m⁻¹·K⁻¹) due to pronounced size and mass disorder, without compromising structural stiffness. These findings highlight the potential of high-entropy design for advanced thermal barrier coatings. Full article

The aim of this study is to present an integrated approach to ski personalization by combining a detailed material and geometric characterization of ski structure with real-time on-slope dynamic performance data. Longitudinal and torsional stiffness were selected as the basic material parameters for a wide range of skis with different application profiles. Acceleration graphs for turns were synchronized with video footage recorded by a drone, which provided real-time monitoring of the skiers’ actual course and facilitated the precise correlation between kinematic data and on-slope performance. To estimate style similarity between different skiers, the Pearson correlation coefficient was utilized due to its robust mathematical properties. Comprehensive analyses helped to finally formulate a multistage ski personalization algorithm. Full article

This study investigates the flexural performance of geopolymer (zero-cement) concrete (ZCC) beams compared to normal concrete (NC) under monotonic and cyclic loading. Sixteen reinforced beams with compressive strengths of 20 and 30 Mpa and reinforcement configurations of 2Ø10 and 3Ø12 were tested to evaluate load–deflection behavior, ductility, energy absorption, and cracking characteristics. Under monotonic loading, ZCC beams achieved 9–17% higher ultimate strength and 5–30% greater mid-span deflection than NC beams, indicating superior ductility and energy dissipation. Under cyclic loading, ZCC beams demonstrated more stable hysteresis loops, slower stiffness degradation, and 8–32% higher cumulative energy absorption. ZCC specimens also sustained 8–12 cycles, corresponding to 70–90% of the monotonic displacement, whereas NC beams generally failed earlier at lower displacement levels. Increasing reinforcement ratio enhanced stiffness and load capacity but reduced deflection for both materials. Crack mapping showed finer and more uniformly distributed cracking in ZCC beams, confirming improved bond behavior between steel reinforcement and the geopolymer matrix. In addition, geopolymer concrete beams exhibited a significant enhancement in ductility, with the ductility coefficient increasing by nearly 50% compared to normal concrete under cyclic loading. Overall, the findings indicate that ZCC provides comparable or superior structural performance relative to NC, supporting its application as a sustainable, low-carbon material for flexure- and shear-critical members subjected to static and cyclic actions. Full article