Search Results (82)

Basalt fiber-reinforced polymer (BFRP) composites are increasingly utilized in photovoltaic mounting systems due to their excellent mechanical properties and durability. Bolted connections, valued for their simplicity, ease of installation, and effective load transfer, are widely employed for joining composite components. An orthogonal experimental design was adopted to investigate the effects of key parameters—including bolt end distance, number of bolts, bolt material, bolt diameter, preload, and connection length—on the load-bearing performance of three bolted BFRP plate configurations: lap joint (DJ), single lap joint (DP), and double lap joint (SP). Test results showed that the DJ connection exhibited the highest average tensile load capacity, exceeding those of the SP and DP connections by 45.3% and 50.2%, respectively. This superiority is attributed to the DJ specimen’s longer effective shear length and greater number of load-bearing bolts. Conversely, the SP connection demonstrated the largest average peak displacement, with increases of 29.7% and 52.9% compared to the DP and DJ connections. The double-sided constraint in the SP configuration promotes more uniform preload distribution and enhances shear deformation capacity. Orthogonal sensitivity analysis further revealed that the number of bolts and preload magnitude significantly influenced the ultimate tensile load capacity across all connection types. Finally, a calculation model for the tensile load capacity of bolted BFRP connections was established, incorporating a friction decay coefficient (α) and shear strength (τ). This model yields calculated errors under 15% and is applicable to shear slip-dominated failure modes, thereby providing a parametric basis for optimizing the tensile design of bolted BFRP joints. Full article

Due to their high strength-to-weight ratio and corrosion resistance, glass fiber reinforced polymer (GFRP) composites have been used in various civil structures. However, the GFRP profiles may be perforated to allow bolting, wiring, and pipelining, causing stress concentration and safety concerns in load-carrying scenarios. A fundamental understanding of the stress concentration mechanisms and the efficacy of mitigation techniques in such anisotropic materials remains limited, particularly for the complex stress states introduced by perforations and mechanical fasteners. This study investigates the effectiveness of three techniques, adhesive filling, bolt reinforcement, and elliptical perforation design, in mitigating stress concentration and enhancing the strength of perforated GFRP plates. The effects of perforation geometry, filler modulus, bolt types, and applied preloads on the stress concentration and bearing capacity are investigated through experimental and finite element analysis. The results reveal that steel bolt reinforcement significantly improves load-bearing capacity, achieving a 13.9% increase in the pultrusion direction and restoring nearly full strength in the transverse direction (4.91 kN vs. unperforated 4.89 kN). Adhesive filling shows limited effectiveness, with minimal load improvement, while elliptical perforations exhibit the lowest performance, reducing strength by 38% compared to circular holes. Stress concentration factors (SCF) vary with hole diameter, peaking at 5.13 for 8 mm holes in the pultrusion direction, and demonstrate distinct sensitivity to filler modulus, with optimal SCF reduction observed at 30–40 GPa. The findings highlight the anisotropic nature of GFRP, emphasizing the importance of reinforcement selection based on loading direction and structural requirements. This study provides critical insights for optimizing perforated GFRP components in modular construction and other civil engineering applications. Full article

With the increased power density of internal combustion engines (ICE) and growing demands for lightweight design, the connecting rod big-end bearings are subjected to significant alternating loads. Consequently, the interference–fit interfaces become susceptible to fretting damage, which can markedly shorten engine service life and impair reliability. In the present study, the effects of the big end manufacturing process, bolt preload, and bearing bush interference fit are considered to develop a coupled lubrication–dynamic model of the connecting rod big-end bearing. This model investigates the fretting damage issue in the bearing bush of a marine diesel engine’s connecting rod big end. The results indicate that the relatively low stiffness of the big end is the primary cause of bearing bush fretting damage. Interference fit markedly affects fretting wear on the bush back, whereas the influence of bolt preload is secondary; nevertheless, a decrease in either parameter enlarges the fretting distance. Based on these findings, an optimized design scheme is proposed. Full article

In this study, a novel shape memory alloy actuated bearing active preload system (SMA-BAPS) was proposed and experimentally demonstrated. SMA actuators placed in a single or antagonistic configuration were employed to drive the screw pair and thus fulfill one-way or bidirectional preload adjustment. Moreover, the self-locking screw pair was used to maintain the bearing preload without external energy input. To determine the parameters of screw pair and SMA actuators, a detailed design process was conducted based on analytical models of the proposed system. Finally, a screw pair with a lead of 3 mm and SMA actuators with a diameter of 0.5 mm and a length of 130 mm were adopted. Prototype tests were conducted to validate and evaluate the performance of the preload adjustment with the SMA-BAPS. The resistive torque and the natural frequency of spindles were recorded to represent the preload level of the bearing. Through the performance tests, the SMA-BAPS induced a maximum 47% variation in the resistive torque and a 20% variation in the spindle’s natural frequency. The response time of the SMA-BAPS was less than 5 s when the heating current of 5 A was applied on the SMA actuator. This design highlighted the compact size, quick response, as well as the bidirectional preload adjustment, representing its potential use in aerospace mechanisms and advanced motors. 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 attenuation of bolt preload is a critical factor leading to bolt fatigue failure, whereas the study of the nonlinear attenuation behavior of preload and its mechanism during installation is an inevitable challenge in engineering practice. The attenuation of the preload of a bolt is mainly related to the stiffness of the bolt body as well as the stiffness of the connected parts. This study aimed to develop an experimental system to analyze the nonlinear attenuation behavior of preload during bolt tightening. First, a simulation system replicating the bolt installation process was constructed in a laboratory setting, incorporating blade and pitch bearing specimens identical to those used in a 10 MW wind turbine, restoring the stiffness coupling characteristics of the “composite-metal bearing” heterogeneous interface at the blade root through a 1:1 full-scale simulation system for the first time. Second, ultrasonic preload measurement equipment was employed to monitor preload variations during the bolt tightening process. Finally, the instantaneous preload decay rate of the wind turbine blade-root bolts and the over-draw coefficient were quantified. Experiments have shown that the preload decay rate of commonly used M36 leaf root bolts is 11–16%. If a more precise value is required, each bolt needs to be calibrated. These findings provide valuable insights for optimizing bolt installation procedures, enabling precise preload control to mitigate fatigue failures caused by abnormal preload attenuation. Full article

Reducing the water content in soft soil is crucial for improving its load-bearing capacity. However, traditional vacuum preloading demonstrates limited effectiveness for dredged sludge due to its high water content and low permeability, resulting in inadequate consolidation and long treatment durations. To address these limitations, this study proposes a new improvement approach that combines pressurized air injection with a polyacrylamide (PAM) addition to enhance vacuum consolidation. Experimental results demonstrated that cationic polyacrylamide (CPAM) exhibited superior performance in improving water discharge efficiency, which promoted the aggregation of fine soil particles and reduced the clogging of drainage channels through adsorption bridging. The incorporation of pressurized air injection further enhanced consolidation efficiency by increasing hydraulic gradients and inducing micro-fractures in soil, thereby improving soil permeability and vacuum pressure transmission. However, excessive CPAM addition or high-pressure air injection was found to compromise the effectiveness of the vacuum preloading treatment due to drainage channel clogging and extensive soil fracturing. The appropriate consolidation performance was achieved with a 0.075% CPAM addition and 20 kPa air pressure injection, demonstrating a 24.5% increase in water discharge mass and a 30.9% improvement in soil shear strength compared to traditional methods. Microstructural analysis revealed a more compacted soil matrix with reduced porosity and enhanced interparticle interactions. These findings provide valuable insights for improving the treatment efficiency of dredged sludge in coastal regions, particularly in the Nansha District of Guangzhou. Full article

The finite-element model was developed using ABAQUS to investigate the hysteretic properties of space joints. This study examined the effects of axial compression ratio, T-plate stiffness, column wall thickness, and bolt-preload on the joint’s hysteretic behavior. The model was verified by comparing the failure modes, hysteresis curves, and skeleton curves of the specimens with the test results of the relevant literature, ensuring the reliability of the research. The results reveal three primary failure modes: beam flange buckling, T-plate buckling, and column-wall buckling; increasing the thickness of the T-plate web or column wall significantly enhances joint stiffness and mitigates brittle failure. Specifically, the stiffness of T-plate 1 has a substantial impact on joint performance, and it is recommended that its web thickness be no less than 18 mm. In contrast, variations in the thickness of T-plate 2 have negligible effects on seismic performance. Increasing the column wall thickness improves the bearing capacity and stiffness of the joint, with a recommended minimum thickness of 12 mm, which should not be less than the flange thickness of the steel beam. While an increase in the axial compression ratio reduces the bearing capacity and stiffness, it enhances the energy dissipation capacity and ductility of the joint. Notably, variations in bolt-preload were found to have minimal influence on joint performance. These findings provide valuable insights for optimizing the design of unilateral bolted joints in steel structures to improve seismic resilience. Full article

The sheet pile wall, a widely used retaining structure in railway construction, faces limitations such as restricted height, construction difficulties, and high costs. While geosynthetic-reinforced soil technology enhances soil tensile strength, it often lacks sufficient stiffness and strength. To address these issues, this study proposes a “prestressed” geosynthetic-reinforced sheet pile retaining wall structure. The geosynthetic-reinforced soil was subjected to preloading to induce “prestress”, with enhanced soil reinforcement interaction improving load-bearing capacity, reducing horizontal displacement, and ensuring railway safety. Indoor model tests were conducted on sandy soil foundations to investigate the structure’s load settlement behavior, pile horizontal displacement, earth pressure distribution, pile bending moments, and reinforcement strain development. The results show that applying “prestress” significantly enhances soil reinforcement interaction, enabling the pile–slab wall to better retain soil and improve overall performance. The load-bearing capacity increased by 21.7% and 16.6% in two respective tests, while horizontal displacement was effectively reduced. The maximum earth pressure was observed on the right side of the pile, 20 cm above the base, and the maximum bending moment occurred in the anchored section. Prestressing also enhanced the utilization of the tensile reinforcement. The proposed structure offers a promising approach for optimizing railway retaining structures. Full article

This study evaluates the feasibility of 3D-printed polymer composite external fixator (EF) rings as a cost-effective alternative to stainless steel fixators, focusing on hybrid fixators for complex tibial fractures. Mechanical performance was assessed in three stages: (1) evaluating the initial EF–tibia configuration under axial loading and wire pre-tension conditions; (2) analyzing the stiffness evolution and weight-bearing capacity during early healing with progressive callus formation; and (3) optimizing ring designs through numerical analysis to improve structural performance under increased pre-tension. The results showed that, for the metallic EF, the axial displacement under one-leg stance reached 8.41 mm without pre-tension, reducing to 6.83 mm at 500 N pre-tension, though transverse displacement remained significant, suggesting the need for higher wire tension. Callus formation enhanced the load-bearing capacity, as expected. However, excessive displacements persisted under the one-leg stance, indicating that full weight-bearing should be delayed beyond two weeks for a fracture gap of 3 mm. A ring design assessment showed that full-ring configurations with two wires per ring improved performance. The 3D-printed full-ring design made of carbon-fiber-reinforced polylactic acid (PLA-CF) reduced stress by 85% at 500 N pre-tension compared to the initial configuration, remaining within allowable limits. While confirming feasibility, the study highlights the need for geometric refinements to accommodate higher preloads and improve transverse stiffness. Full article

The disc cutter is a key rock-breaking component of tunnel boring machines, and during operation, improper assembly preload often leads to uneven wear of the cutter. To study the effect of preload force on the friction torque of paired tapered roller bearings during rock-breaking, the transmission of preload and rock-breaking loads within the disc cutter structure is first analyzed, and a bearing load distribution model is established. Based on this model, a method for calculating the friction torque of the tapered roller bearings in the disc cutter, considering both external loads and preload force, is proposed. Next, finite element analysis is conducted to investigate the impact of preload displacement on preload force, and a relationship equation is derived using polynomial fitting. Finally, experiments on bearing preload displacement and friction torque are carried out under no-load conditions. The results show that the simulation results for the relationship between preload force and preload displacement are in good agreement with the experimental results. Additionally, the experimental results for the friction torque of the tapered roller bearings are close to the theoretical calculation results, with the overall trend matching, thus verifying the reliability of both the simulation and theoretical models. Full article

To investigate the mechanical behavior of precast columns with openings in the beam–column joint core area under axial loads, a systematic study was conducted to examine the effects of the opening parameters on the axial mechanical performance of precast columns. Two sets of six precast concrete column specimens, with opening ratios of 14% and 22%, respectively, were designed and subjected to axial compression tests. The failure patterns, opening ratios in the core area, and other relevant parameters of the specimens were thoroughly analyzed. Additionally, a finite element model incorporating material non-linearities was developed using ABAQUS (2022) software, and parametric numerical simulations were conducted to further explore the structural response. The results indicated that the variations in the opening ratio had no significant effect on the cracking load of the specimens. However, as the opening ratio increased, the peak load of the compressed columns increased by 8.6%, and the ductility factor increased by 12.9%. The study also reveals that opening ratios below 30%, the casing thickness, and the bolt preload have minimal impact on the bearing capacity of precast columns. These findings provide theoretical support for optimizing hole sizes in dry bolted connections for precast concrete structures. Full article

To address the challenge of repairing the damage to concrete box girder bridge piers on mountainous highways caused by falling rocks, this paper proposes an active underpinning technique that integrates a “井”-shaped cap system, graded preloading of the foundation, and synchronized beam body correction. The technique utilizes lateral beam preloading (to eliminate the inelastic deformation of the new pile foundation) and longitudinal beam connections (to form overall stiffness). The method involves building temporary and permanent support systems in stages. Through the two-stage temporary support system transition, the removal and in situ reconstruction of the old piers, a smooth transition from the pier–beam consolidation system to the basin-type bearing system is achieved while simultaneously performing precise correction of beam torsion. The structural safety during the construction process was verified through finite element simulations and dynamic monitoring. Monitoring results show that the beam torsion recovery effect is significant (maximum lift of 5.2 mm/settlement of 7.9 mm), and the pier strain (−54.5~−51.3 με) remains within a controllable range. Before the bridge was opened to traffic, vehicle load and impact load tests were conducted. The actual measured strength and vertical stiffness of the main beam structure meet the design requirements, with relative residual deformation less than 20%, indicating that the structure is in good, elastic working condition. The vehicle running and braking dynamic coefficients (μ = 0.058~0.171 and 0.103~0.163) are both lower than the theoretical value of 0.305. The study shows that this technique enables the rapid and safe repair of bridge piers and provides important references for similar engineering projects. Full article

To effectively adapt to seismic actions in complex earthquake environments and enhance the seismic isolation performance of building structures, this paper divides the disk spring group of traditional disk spring isolation bearings into an upper disk spring group and a lower disk spring group. By arranging different stacking layers, an improved Vertical Variable Stiffness Disk Spring Isolation (VVSDSI) bearing is proposed. The operational performance of this bearing is thoroughly investigated through a theoretical analysis, experimental testing, and numerical simulations. The research results demonstrate the following: (1) under ultimate load conditions, the working stages of the VVSDSI bearing can be divided into two phases. During the isolation phase, the vertical stiffness of the bearing is relatively low, with a value of 11.14 kN/mm, whereas in the protection phase, the vertical stiffness increases significantly to 35.34 kN/mm. (2) During the isolation phase, the preloading displacement exhibits a positive correlation with equivalent stiffness and an equivalent damping ratio, while the loading amplitude shows a negative correlation with these parameters. (3) The theoretical hysteresis model prediction value and numerical model simulation value of the VVSDSI bearing are in good agreement with the measured data, with the maximum errors of the peak load being 6.78% and 10.07%, respectively, which can accurately simulate the mechanical properties of the bearing. Therefore, this research result can provide a theoretical basis and experimental support for the design of vertical seismic isolation systems. Full article

In wind turbine systems, bolted connections in pitch bearings are subjected to working loads that reduce bolt preload. This reduction can lead to issues such as bolt loosening and eccentric loading, which in turn results in the nonuniform distribution of contact stress across joint surfaces. These issues can compromise structural integrity and reduce fatigue life. However, the study of contact stress mainly focuses on theoretical research, lacking relatively large, complex structures. Also, the stress testing methods for contact surfaces of bolted connections are limited in practical engineering. In this paper, a localized bolt connection model using the finite element method according to pitch bearings in wind turbine systems was established. The contact stress distribution patterns of bolt specimens under varying preloads were investigated. Comparative numerical simulation and experimental analysis using thin-film pressure sensors were conducted. Furthermore, the effect of bolt assembly in different tightening processes on the contours of contact stress was analyzed to identify the optimal tightening sequence. The experimental results demonstrate a positive correlation between preload and maximum contact stress, with stress distribution exhibiting symmetry around the bolt hole and decreasing radially outward. Thin-film pressure sensors can be used for contact stress detection. Furthermore, the diagonal tightening method can achieve a more uniform contact stress distribution compared to other methods, such as sequential and alternate tightening. The findings provide valuable insights for optimizing the contact stress distribution and tightening processes in bolted joint assemblies. Full article