Search Results (5,467)

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

As the rotational speed increases, the centrifugal expansion of the rotor will significantly affect the performance of the porous gas bearing. However, this rotor’s centrifugal effect has not been studied thoroughly. In this paper, the rotor centrifugal expansion is simplified as a two-dimensional plane stress problem. The gas flow in the porous bushing and the gas film is governed by Darcy’s law and the modified Reynolds equation, respectively. The perturbation method and the finite difference method are adopted to calculate the bearing load and dynamic coefficients for a high-speed porous gas bearing. Comparisons between the simulated results and the available experimental and theoretical data are carried out to validate the proposed model. On this basis, the influence of rotor centrifugal expansion on the performance and the operational conditions of the high-speed porous gas bearing is studied systematically. The results indicate that rotor centrifugal expansion greatly improves the bearing load and dynamic coefficients of the high-speed porous gas bearing with a large rotor diameter and small bearing clearance, but reduces the allowable eccentricity ratio and titling angle. Full article

In modern construction, natural materials with a low carbon footprint and full recyclability are becoming increasingly important. A typical group here is products made from solid wood, including glued wood, plywood, and wood-based composites. With their many advantages, however, they all burden the environment with the costs of production processes, as well as the need to use harmful chemicals (adhesives and impregnants). Solid wood is devoid of these disadvantages; however, it is often treated as a rather archaic material. One of the arguments here is its low durability compared to, e.g., glued wood. The article discusses the durability of solid wood using the example of a group of wooden churches preserved in Poland, in Upper Silesia. Some of these buildings are over five hundred years old, making them a reliable source of information about the durability of the material from which they were built. A total of 85 churches, at least 200 years old, were analyzed, evaluating the technical state of the main load-bearing elements of their structures. In view of the number of facilities and the inability to conduct tests in most of them, the assessment was limited to a visual inspection of the technical condition, carried out by an experienced building expert. The assessment estimated the area of corrosion damage, probed its depth, and measured the depth of cracks. The relationship between their technical condition and the environmental conditions in which they were used was described and discussed. In this way, both the threats to the durability of solid wood and the ways to keep it in good condition for hundreds of years were identified, refuting the thesis that solid wood is a material with low durability. Its use in structural elements therefore supports efficient resource management and contributes to sustainable construction, especially in small and medium-sized buildings. Full article

To address the challenge of bearing load monitoring in elastically supported marine shafting systems, a multi-data fusion-based prediction model is constructed. In view of the small-sample nature of measured bearing load data, transfer learning is adopted to migrate the physical relationships embedded in finite element simulations to the measurement domain. A limited number of actual samples are used to correct the simulation data, forming a high-fidelity hybrid training set. The system—supported by air-spring isolators mounted on the raft—is divided into multiple sub-regions according to their spatial layout, establishing local mappings from air-spring pressure variations to bearing load increments to reduce model complexity. On this basis, a Stacking ensemble learning framework is further incorporated into the prediction model to integrate multi-source information such as air-spring pressure and raft strain, thereby enriching the model’s information acquisition and improving prediction accuracy. Experimental results show that the proposed transfer learning-based multi-sub-region bearing load prediction model performs significantly better than the full-parameter input model. Furthermore, the strain-enhanced Stacking-based multi-data fusion bearing load prediction model improves the characterization of shafting features and reduces the maximum prediction error. The proposed multi-data fusion modeling strategy offers a viable approach for condition monitoring and intelligent maintenance of marine shafting systems. Full article

Tissue engineering is a multidisciplinary field that aims to address tissue and organ failure by integrating scientific, engineering, and medial expertise. Gelatin is valued in this field for its biocompatibility; however, it faces thermal and mechanical weaknesses that limit its biomedical utility. This work proposes a strategy for improving gelatin properties by fabricating semi-interpenetrating polymer networks via in situ Diels–Alder crosslinking within gelatin colloidal solutions. Ten systems with variable polymer concentrations (2–4%) and crosslinking degrees (2–5%) were prepared and characterized. Rheological analysis revealed that elastic modulus, zero-shear viscosity, and complex viscosity were substantially enhanced, being especially dependent on the crosslinking degree, while critical strain values mostly depended on gelatin concentration. The incorporation of a synthetic Diels–Alder-crosslinked network also improved the thermal stability of gelatin hydrogels, particularly at physiological temperatures. Additionally, these systems exhibit favorable buoyancy, swelling and biodegradation profiles. Collectively, the resultant hydrogels are cytocompatible, solid-like, and mechanically robust, allowing for further tunability of their properties for specific biomedical uses, such as injectable matrices, load-bearing scaffolds for tissue repair, and 3D bioinks. 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

To address the dual challenges of improving precast cable trench joint performance and promoting solid waste recycling for carbon neutrality, this study developed a jute fiber-reinforced recycled aggregate concrete (JFRAC) and established a complete technical chain via experiments and numerical simulations. Compressive strength tests were conducted on JFRAC with varying jute fiber volume content and recycled coarse aggregate (RCA) replacement ratio to obtain their influence on the stress–strain relationship. A modified Concrete Damaged Plasticity (CDP) model was proposed by introducing correction coefficients for compressive strength and elastic modulus, achieving over 95% agreement with experimental data. Finite element simulations of cable trench joints showed that JFRAC outperforms C30 concrete, with the same compressive strength, in ultimate bearing capacity (↑4.17%), peak displacement (↑18.78%), and ductility (↑14.66%). JFRAC provides substantial environmental and economic advantages by reducing carbon emissions by 2.29% and saving costs of CNY 62.43 per meter of precast cable trench. Parametric studies indicated bolt grade and number are the primary performance influencers. Bolt grade’s impact diminishes as it increases from 8.8 to 10.9, while bolt number linearly enhances load-bearing capacity. This study provides a feasible path for JFRAC to replace conventional concrete in cable trenches, realizing both economic and environmental benefits. Full article

The search for innovative solutions in the field of construction materials used in aircraft manufacturing has led to the development of composite materials, particularly CFRP polymer composites. Composite airframe components, which are required to have high strength, are joined using mechanical fasteners. Considering that the composite consists of a polymer matrix, which is a material susceptible to rheological phenomena occurring rapidly at elevated temperature, there is a high probability of significant changes in the strength and performance properties. Coupled thermal and mechanical loads on composite material joints occur in everyday aircraft operation. Experimental tests were conducted using a quasi-isotropic CFRP on an epoxy resin matrix with aerospace certification. The assessment of changes in the strength parameters of the material itself showed a decrease of approx. 40% in its short-term strength at 80 °C compared to the ambient temperature and a decrease in the load-bearing capacity of single-lap bolted joints of over 25%. Even more rapid changes were observed when assessing the fatigue life of the joints assessed at ambient and elevated temperature. In addition, the actual glass transition temperature of the resin was determined using the DSC technique. Analysis of the damage mechanisms showed that at 80 °C, the main degradation mechanisms of the material are accelerated creep processes of the CFRP and softening of the matrix, increasing its susceptibility to damage in the joint area. Full article

Background/Objectives: Meniscal root tears, particularly those of the posterolateral root, are frequently associated with anterior cruciate ligament (ACL) injuries and significantly alter load distribution and knee stability. Surgical repair of the posterolateral meniscal root (PLMR) aims to restore normal biomechanics; however, postoperative rehabilitation strategies remain heterogeneous. The objective of this systematic review was to describe and analyze postoperative weight-bearing (WB) and range-of-motion (ROM) protocols following concomitant PLMR repair and anterior cruciate ligament reconstruction (ACLR), integrating both clinical and biomechanical perspectives. Methods: This systematic review followed PRISMA guidelines and analyzed biomechanical and clinical studies assessing postoperative WB and ROM management following PLMR repair combined with ACLR. Results: Eleven studies were included, describing heterogeneous postoperative rehabilitation protocols for WB and ROM following posterolateral meniscal root repair with ACLR. Biomechanical data consistently showed that root section increased tibial internal rotation and contact pressure on the lateral tibial plateau, whereas repair restored near-native load sharing. Clinically, most authors recommended non-weight-bearing or toe-touch loading for 4–6 weeks and flexion limited to 0–90° during early rehabilitation. Gradual progression to full loading and motion between 8 and 12 weeks was the most consistent strategy. Conclusions: Although the current evidence is limited and mainly based on low-level studies, available data suggest that a cautious and progressive rehabilitation protocol after PLMR repair with ACLR early controlled motion and delayed full loading may optimize repair healing while protecting graft integrity. Full article

This study investigates the tribological behavior of selective laser-sintered (SLS) sliding bearings under dry-sliding operating conditions. These polyamide-12 bearings reinforced with glass beads (PA 3200 GF) were tested against a stainless-steel sleeve in three different pressure–velocity (PV) regimes that represent real operating conditions. The coefficient of friction (COF) and contact temperatures were monitored throughout the experiment, while the specific wear rate was quantified based on mass loss measurements. The evolution of surface topography was analyzed using roughness parameters of the Abbott-Firestone family. Scanning electron microscopy (SEM) analysis was performed to identify the dominant wear mechanism. The results show a pronounced running-in phase, after which a stable thermomechanical equilibrium occurs in all regimes. Heavy-loaded regimes increase temperature but accelerate surface adaptation and lower stable coefficients of friction. Lower load regimes have the lowest thermal load but higher friction due to lower real contact. The medium PV regime has a low COF and moderate temperature rise, while peak and core roughness metrics increase more significantly. These results provide an experimentally based insight into the influence of the load regime on the tribological behavior and topography of the SLS-made polymer sliding bearings, thus contributing to a deeper understanding of their operation in real dry-sliding conditions. Full article

Grouted sleeves are commonly used to connect prefabricated structural components, but construction defects can easily occur after installation, posing potential risks to the structure. This study conducts comparative uniaxial tensile tests on 39 grouted-sleeve specimens in 13 groups—including standard specimens, defective specimens, and specimens repaired with supplementary grouting. The strain distribution patterns under different grouting lengths and loading levels are analyzed to investigate the load-transfer mechanism between reinforcement bars and grouted sleeves, as well as the influence of various supplementary grouting amounts and material strengths on the mechanical performance of defective sleeves. In the uniaxial tensile test of grouted sleeves, with grout strengths of 85 MPa and 100 MPa and HRB400-grade steel bars, when the grouted anchorage length was 4 d, insufficient anchorage length resulted in low bond strength between the grout and the steel bar, leading to bond–slip failure. When the grouted anchorage length reached 6 d, steel bar fracture occurred inside the sleeve. When the total anchorage length formed by two grouting sessions reached 8 d, specimen slippage decreased, showing a trend where the strain growth rate of the sleeve gradually decreased from the grouted end to the anchored end, while the strain growth rate of the steel bar gradually increased. The longer the total anchorage length in the sleeve after grout repair, the stronger its anti-slip capability. The bearing capacity and failure mode of the specimens depend on the strength of the steel bars connected to the grouted sleeves and the strength of the threaded connection ends at the top. Experimental results show that the anchorage length and strength of high-strength grout materials have a significant reinforcing effect on defective sleeves. The ultimate bearing capacity of specimens with anchorage length of 6 d or more is basically the same as that of steel bars. Specimens with a total anchorage length of 8 d show approximately 10%~20% less slippage than those with 6 d. The safe anchorage length for HRB400-grade steel bars in sleeve-grouted connections is 8 d, even though the bearing capacity of grouted sleeves with a 6 d anchorage length already meets the requirements. Bond strength analysis confirms that the critical anchorage length is 4.49 d. When the grouted anchorage length exceeds the critical length, the failure mode of the specimen is steel bar fracture. When the grouted anchorage length is less than the critical length, the failure mode is steel bar slippage. This conclusion aligns closely with experimental results. In engineering practice, the critical anchorage length can be used to predict the failure mode of grouted sleeve specimens. Based on experimental research and theoretical analysis, it is clear that using grout repair to reinforce defective grouted sleeve joints with a safe anchorage length of 8 d is a secure and straightforward strengthening method. Full article

Spherical caps exploit their intrinsic curvature to achieve efficient stress distribution, delivering exceptional strength-to-weight ratios. This advantage renders them indispensable for aerospace systems, pressurized containers, architectural domes, and structures operating in extreme environments, such as deep-sea or nuclear containment. Their superior load-bearing capacity enables diverse applications, including satellite casings and high-pressure vessels. Meticulous optimization of geometric parameters and material selection ensures robustness in demanding scenarios. Given their significance, this study examines the natural frequency and static response of bio-inspired helicoidally laminated carbon fiber–reinforced polymer matrix composite spherical panels surrounded by Winkler elastic foundation support. Utilizing a 3D elasticity approach and the finite element method (FEM), the governing equations of motion are derived via Hamilton’s Principle. The study compares five helicoidal stacking configurations—recursive, exponential, linear, semicircular, and Fibonacci—with traditional laminate designs, including cross-ply, quasi-isotropic, and unidirectional arrangements. Parametric analyses explore the influence of lamination patterns, number of plies, panel thickness, support rigidity, polar angles, and edge constraints on natural frequencies, static deflections, and stress distributions. The analysis reveals that the quasi-isotropic (QI) laminate configuration yields optimal vibrational performance, attaining the highest fundamental frequency. In contrast, the cross-ply (CP) laminate demonstrates marginally best static performance, exhibiting minimal deflection. The unidirectional (UD) laminate consistently shows the poorest performance across both static and dynamic metrics. These investigations reveal stress transfer mechanisms across layers and elucidate vibration and bending behaviors in laminated spherical shells. Crucially, the results underscore the ability of helicoidal arrangements in augmenting mechanical and structural performance in engineering applications. Full article

Some expressway emergency lanes adopt simplified pavement structures that fail to meet load-bearing requirements after reconstruction. To address the issue of subgrade reinforcement without excavation, a finite element method was employed to analyze the effects of enlarged-borehole grouting (EBG), considering variations in grouting depth and inter-pile subgrade modulus, on pavement load-bearing capacity. Furthermore, field experiments were conducted to evaluate grouting techniques, including enlarged-borehole micro-expansive cement casting (EB-MECC) and enlarged-borehole steel flower pipe split grouting (EB-SFPSG), and three composite grouting schemes. Results indicated that EBG effectively improved the fatigue cracking life of the semi-rigid base layer. Reinforcement effectiveness was positively correlated with grouting depth and subgrade modulus, with the latter exhibiting a more significant influence. Therefore, a 1.5 m grouting depth combined with splitting or compaction is recommended to enhance subgrade stiffness. Field experiments showed that EB-SFPSG effectively enhanced pile–subgrade interaction and mitigated stress concentration around the pile–pavement interface. Comparison of the three composite grouting schemes revealed that both the scheme employing only EB-SFPSG and the hybrid scheme using EB-SFPSG in the middle row with EB-MECC in the side rows exhibited favorable mechanical performance. The latter, however, was achieved at a lower construction cost. Another hybrid scheme that further replaced the middle row with enlarged-borehole conventional pressure grouting (EB-CPG) provided limited reinforcement and poorer uniformity. Full article

Sintered nano-silver is widely investigated as a die-attach material for next-generation power electronic modules due to its high thermal conductivity, favorable electrical performance, and stability at elevated temperatures. However, how bonding pressure and joint thickness jointly affect densification, interfacial diffusion, and mechanical reliability has not been systematically clarified, especially under the low-pressure conditions required for large-area SiC and GaN devices. In this work, nano-silver lap-shear joints with three bond-line thicknesses (50, 70, and 100 μm) were fabricated under two applied pressures (1.0 and 1.5 MPa) using a controlled sintering fixture. Shear testing and cross-sectional SEM were employed to evaluate the relationships between microstructural evolution and joint integrity. When the bonding pressure was increased from 1.0 to 1.5 MPa, more effective particle rearrangement and reduced pore connectivity were observed, together with improved metallurgical bonding at the Ag–Au interface, leading to a strength increase from 15.3 to 28.2 MPa. Although thicker joints exhibited slightly higher bulk relative density due to greater heat retention and accelerated local sintering, this densification advantage did not lead to improved mechanical performance. Instead, the lower strength of thicker joints is attributed to a narrower Ag–Au interdiffusion region, which limited the formation of continuous load-bearing paths at the interface. Fractographic analyses confirmed that failure occurred predominantly by interfacial delamination rather than cohesive fracture, indicating that the reliability of the joints under low-pressure sintering is governed by the quality of interfacial bonding rather than by overall densification. The experimental results show that, under low-pressure sintering conditions (1.0–1.5 MPa), variations in bonding pressure and bond-line thickness lead to distinct effects on joint performance, with the extent of Ag–Au interfacial interaction playing a key role in determining the mechanical robustness of the joints. Full article

In earthquake-prone regions, improving the seismic performance of bridge abutments is crucial for ensuring the overall safety and resilience of transportation infrastructure. In this study, a novel shallow foundation abutment with anchor plates and steel bundles is proposed. Quasi-static tests incorporating soil–abutment interaction were conducted on a novel shallow foundation abutment and on a conventional abutment to evaluate and compare their seismic performance. The experimental results, including failure mechanism, hysteretic behavior, backbone curve, stiffness, and damping ratio, were analyzed. The findings indicate that the inclusion of anchor plates and steel bundles effectively restricts abutment rotation and significantly enhances its ultimate bearing capacity, with an observed increase of up to 96%. The secant stiffness of the novel shallow foundation abutment is consistently greater than that of a conventional abutment, being on average 20.9% higher before a loading displacement of 20 mm. Moreover, its energy dissipation capacity surpasses that of the common abutment after a loading displacement of 8 mm. Overall, the participation of anchor plates and steel bundles substantially improves the seismic resistance of the soil–abutment interaction system. The conclusions of this study provide valuable guidance for the design, promotion, and practical application of shallow foundation abutments with anchor plates and steel bundles in seismically active areas. Full article