Higher Load Carrying Capacity Research Articles

Effect of Cavity Shapes on the Lubrication Performance of High Precision Static and Dynamic Thrust Bearing under Eccentric Load

Abstract The oil cavity shapes, which represent the spatial structures for storing lubricant in static and dynamic thrust bearings, and offset distances, defined as the horizontal distances between the load center and the bearing rotational axis under eccentric loads, directly impact the flow mode of lubricant, pressure, and temperature distribution during bearing operation, so these are the key factors that influence the lubrication performance and the accuracy of bearings. The equations for flow and load capacity of the sector, runway, and double rectangular cavities are derived, and mathematical models are established for different cavities at various tilt positions. Then pressure and temperature fields at different offset distances are analyzed. As the offset distances increase, there is a corresponding increase in the maximum pressures within the sector, runway, and double rectangular cavities by 90.5 kPa, 93.3 kPa, and 30.9 kPa, but average pressures show only minor fluctuations. Concurrently, the maximum temperatures within these cavity shapes are observed to increase by 0.5 K, 0.6 K, and 0.8 K, respectively. The results show that appropriate offset distance can improve the lubrication performance. The runway cavity has the highest load-carrying capacity among the three cavity shapes, while the sector cavity experiences the slightest temperature increase. As the temperature increase in all three cavity shapes is small, the runway cavity exhibits superior performance. The error between simulation and experimental results is less than 10%, which verifies the correctness of the simulation method.

A novel 3D-printed unit cell with the compression-torsion coupling effect and negative Poisson’s ratio

Metamaterials have received extensive research interests since they can be artificially designed to achieve unprecedent material properties beyond what we can obtain from the nature. As such, it is widely acknowledged that metamaterials have great potential application perspectives in many areas, e.g., mechanical engineering, civil engineering, aerospace, biomedical engineering, etc. Recently, mechanical metamaterials that are designed based on multi-functional properties or behaviours have received much attention due to the increasing demands of new materials with superior properties. Inspired by the grasshopper’s leg, this paper proposes a novel unit cell where 3D ‘zig-zag’ rods are introduced to connect the circular planar elements. The mechanical behaviours of this novel unit cell under axial compression are studied both experimentally and numerically. In particular, the effect of different geometric parameters of the 3D ‘zig-zag’ rod on both compression-torsion coupling (CTC) and negative Poisson’s ratio (NPR) are studied for this novel unit cell. Compared with previous designs, the novel unit cell proposed in this work can improve the design flexibility, achieve large NPR, strong CTC, and high load-carrying capacity, simultaneously. Finally, this work can provide some references for designing novel metamaterials with multiple deformation mechanisms.

Experimental study on seismic performance of squat precast concrete sandwich shear walls under low axial load ratio

To improve the thermal performance and seismic resistance of structures, precast concrete sandwich shear wall (PCSSW) emerges as a promising option due to its low thermal conductivity and favorable structural performance. This study aims to examine the effectiveness of a new type of vertical connection between the PCSSW and foundation under reversed cyclic loading. The proposed vertical connection is achieved by embedding steel bars in the precast wall and foundation, respectively, followed by casting fresh concrete in place. Considering pre-embedded steel bar arrangements (single-row or double-row) and cast-in-place (CIP) concrete strength as variables, three precast specimens were designed. Seismic performance was investigated through low reversed cyclic loading tests, with a comparison made against two CIP control specimens. The results showed that the behavior of all the tested walls was governed by shear, with the ultimate bearing capacity of the PCSSW determined by the horizontal shear capacity at the weak position. Under low axial compression ratios, the specimens with double-row steel bar arrangement had higher load-carrying capacity and ductility than single-row steel bar arrangement and could be equivalent to the CIP shear walls. Results from this study were compared with the predicted values from different codes to provide some reference value for the engineering design of the proposed structure.

Seismic performance and skeleton curve model of prefabricated coral aggregate concrete-filled aluminum tube joint

Corrosion-resistant and high load-carrying capacity coral aggregate concrete-filled aluminum tube (CCFAT) structures show promising applications in island construction. However, research on CCFAT joints related to structural safety remains scarce. To advance the engineering application of this structure, a novel prefabricated CCFAT beam-column semi-rigid joint with bolt connections is designed in this study. The seismic performance of the joint is investigated through a pseudo-static method, analyzing the effects of each parameter on failure mode, hysteresis curve, deformation characteristics, and energy dissipation performance, considering the earthquake-prone nature of islands. The primary objective of this study is to explore the influence of different parameters on the seismic performance of the CCFAT joint and establish the moment-rotation relationship of this joint. It is observed that the ultimate moment relationship between the beam and connector significantly impacts the failure mode of the joint, thus affecting its seismic performance. Hence, prioritizing the ultimate moment relationship between the beam and connector in the design phase is crucial to avoid undesirable joint failures. The skeleton curve of CCFAT joints differs significantly from that of steel and reinforced concrete structures, rendering existing joint theories inapplicable to CCFAT joints. Considering joint material, structure, and failure mode, this paper proposes a theoretical calculation method for the initial stiffness and ultimate moment of the CCFAT joints. This method is based on the component method and mechanical model, establishing an exponential three-parameter skeleton curve model for the joint. This model enables an accurate prediction of the moment-rotation relationship of the CCFAT joint, aiding in its seismic performance evaluation.

Time-dependent performance of large piled raft in clayey soil

In this study, three-dimensional numerical analysis has been performed to comprehend the time-dependent behavior of large piled rafts founded in saturated clayey soil, explicitly for the time of superstructure construction and post-construction up to the end of soil consolidation. The performance under different construction times for the corresponding unpiled raft and the piled raft with uniform pile length configuration of varying pile number, spacing, and length have been examined and then compared with that of non-uniform length configuration for the same total pile length. The dissipation of excess pore water pressure, average settlement, and differential settlement are presented and discussed in detail. A quicker dissipation rate of excess pore pressure is noted with either fewer piles, wider pile spacing, or shorter-length piles. An increase in construction time results in a lesser total average settlement at the end of consolidation. The piled raft with uniform pile length configuration shows a higher differential settlement than the unpiled raft. However, by adopting a suitable non-uniform length configuration, negligible differential settlement, higher load-carrying capacity, and a significant reduction in pile material volume can be achieved. Predictive expressions have been proposed to estimate the average and differential settlements of piled raft with uniform length configuration.

Determining the Gear Design Parameters Which Have Strong Correlation with Gear Volume and Contact Ratio for Helical Gear Design Optimization

The market has a significant demand for low-cost, compact size, extended fatigue life and high load-carrying capacity helical gears. One way to manufacture such gears is by minimizing gear volume and maximizing contact ratio. Most researchers focus on gear design optimization, but minimal study has been conducted to identify design variables that significantly impact gear volume and contact ratio. Hence, it is crucial to determine gear design parameters that strongly correlate with gear volume and contact ratio beforehand. A single-stage helical gear train of local electric multiple units (EMU) is used as the gear model, and the calculations are done based on ISO 6336. Seven parameters have been chosen as independent variables; module, number of teeth of pinion, gear ratio, helix angle, tooth thickness factor, normal pressure angle and addendum factor. Graphs of total gear volume and contact ratio against independent variables are plotted to examine their relationship. The results indicate that normal module, number of teeth of the pinion, and gear ratio strongly correlate with the total gear volume. Meanwhile, the number of teeth of pinion, helix angle, tooth thickness factor, normal pressure angle and addendum factor strongly correlate with contact ratio. Therefore, these design parameters must be considered to improve the accuracy of the gear design optimization model, which aims to optimize gear volume and contact ratio.

Two-way flexural behavior of biaxial voided slab using cuboidal shape of void formers

A biaxial voided slab is an innovative type of slab system developed recently, that has proven its excellence in terms of its structural, environmental, and economic benefits. In the present research, an experimental study was carried out to investigate the two-way flexural behavior of biaxial voided slab using the cuboidal shape of void formers. Two-way flexure test was performed over two voided slab specimens (VS-100 and VS-140) and one solid slab specimen using a new technique of sixteen-point loading. An innovative type of positioning reinforcement was used to fix the voids at their desired locations in voided slab. The ultimate load carrying capacity, deflection, flexural stiffness, and crack pattern were examined through experimental and theoretical investigations and compared the results with solid slab. Nonlinear finite element analysis was performed to validate the experimental results using ABAQUS software. Parametric study was undertaken to investigate the flexural performance of voided slab thoroughly; varying the factors like type of loading, positioning reinforcement, and grade of concrete. These investigations revealed that the voided slab with a cuboidal shape of void former exhibits classical flexural behavior which was same as that of a solid slab. Also, it was observed that yield line theory and the finite element model predicts the similar load-carrying capacity precisely enough with the experimental investigations. Parametric study reveled that prediction of ultimate load capacity of voided slab depends on type of loading, and with uniformly distributed loading predicting relatively higher load carrying capacity. Incorporating the proposed positioning reinforcement helps to improve the overall two-way flexural behavior of voided slab.

Optimization of surface texture distribution on the thrust bearing using the mass-conserving cavitation boundary condition: Theory and experiments

This study developed a numerical optimization model for the texture distribution in thrust bearings, employing the flat-headed chevron and circular dimple, and utilizing a mass-conserving cavitation boundary. A hybrid of the genetic algorithm and sequential quadratic programming algorithm is utilized. The results indicate the highest load-carrying capacity can be obtained by optimizing the texture distribution based on the flat-headed chevron. The primary mechanism is that the optimal distribution can efficiently harness the collective effect of texture, thereby effectively building up pressure. The optimal distributions of the flat-headed chevron and circular dimples exhibit asymmetric chevron and herringbone shapes, respectively. Furthermore, verification experiments show that the optimal distribution can shift the transition point to a lower rotation speed and higher normal load.

Behavior of high strength reinforcing steel rebars after high temperature exposure: Tensile properties and bond behavior using pull-out and end beam tests

High strength reinforcing steel (HSRS) is increasingly being adopted in the construction industry in North America due to its high load-carrying capacity, yet their behavior relative to normal grade rebars under external hazard events such as fire exposure still need further research. In current work, the first goal is to investigate the residual tensile properties of different types of HSRS and normal rebars including ASTM A706, A615, A1035CS, and A1035CM with grades of 420, 550, and 690 before and after high temperatures (350 °C and 700 °C), that simulates residual capacity after different levels of fire exposure. The second goal is to explore the residual bond strength of these rebars using both pull-out and end-beam tests after heat exposure, facilitating a comparison among test methods and evaluating their reliability under fire hazard conditions. The tensile test results indicated insignificant changes in the mechanical properties of all rebars after 350 ℃ heat exposure. However, there was a significant reduction of more than 30% in both yield and ultimate strength after 700 ℃ heat exposure for high grades like grade 690 of ASTM A1035. Among all rebar types and grades, only grade 420 of ASTM A706 retained most of its ductility and strength, making it the most reliable rebar among those tested against fire hazards. In the bond tests, splitting failure was observed at both ambient and after 500 °C heat exposure. Heat exposure resulted in a 73% reduction in bond strength across all rebars for the pull-out tests, with no significant variations between rebar types. On the other hand, end-beam tests indicated a 12.6% average reduction in bond strength with a 9% improvement in bond behavior for ASTM A706 grade 420. However, for ASTM A1035 CS grade 690 and ASTM A706 grade 550 there were slight reductions in bond behavior, with decreases of 9% and 14%, respectively. Compared to the end-beam test, the pull-out test results in a significant reduction in bond strength due to its high dependency on excessive compressive strength reduction resulting in brittle splitting failure. Based on comparison with empirical models, it is recommended not to use models derived from pull-out tests to estimate bond strength, as they tend to overestimate it. Instead, empirical models based on end-beam tests are recommended, since they show consistency with test results. It should be noted that although the bond strength based on splitting failure is primarily dependent on concrete properties, changes were observed in the bond behavior among different rebars, which can be attributed to changes in friction at the interface due to morphological changes in the rebar surface after heat exposure, as well as potential variations in thermal expansion properties, which need further research.

Sealing performance and optimization design of squamous textured mechanical seal

The work focuses on the optimization of surface texturing and their geometrical characteristics to improve the sealing performance of mechanical seal. The hydrodynamic model is developed to predict the sealing performance of four textures, including dimple, triangle, chevron and squamous textures. Result indicates that the squamous texture exhibits better sealing performance with high ratio of load-carrying capacity to leakage and ratio of oil film stiffness to leakage at various angular speeds and pressures. Furthermore, the functions of squamous texture characteristics with the load-carrying capacity and leakage ratio are revealed by the response surface methodology. And the squamous texture is optimized with high load-carrying capacity and low leakage ratio through the multi-objective optimization algorithm NSGA-II to achieve the Pareto-optimal set.

Sky-Worker: a heterogeneous dual-arm robot with dynamic authority assignment for live-line working

Purpose The current difficulties of distribution network working robots are mainly in the performance and operation mode. On the one hand, high-altitude power operation tasks require high load-carrying capacity and dexterity of the robot; on the other hand, the fully autonomous mode is uncontrollable and the teleoperation mode has a high failure rate. Therefore, this study aims to design a distribution network operation robot named Sky-Worker to solve the above two problems. Design/methodology/approach The heterogeneous arms of Sky-Worker are driven by hydraulics and electric motors to solve the contradiction between high load-carrying capacity and high flexibility. A human–robot collaborative shared control architecture is built to realize real-time human intervention during autonomous operation, and control weights are dynamically assigned based on energy optimization. Findings Simulations and tests show that Sky-Worker has good dexterity while having a high load capacity. Based on Sky-Worker, multiuser tests and practical application experiments show that the designed shared-control mode effectively improves the success rate and efficiency of operations compared with other current operation modes. Practical implications The designed heterogeneous dual-arm distribution robot aims to better serve distribution line operation tasks. Originality/value For the first time, the integration of hydraulic and motor drives into a distribution network operation robot has achieved better overall performance. A human–robot cooperative shared control framework is proposed for remote live-line working robots, which provides better operation results than other current operation modes.

Collaborative Design of Static and Vibration Properties of a Novel Re-Entrant Honeycomb Metamaterial

A novel re-entrant honeycomb metamaterial based on 3D-printing technology is proposed by introducing chiral structures into diamond honeycomb metamaterial (DHM), named chiral-diamond-combined honeycomb metamaterial (CDCHM), and has been further optimized using the assembly idea. Compared with the traditional DHM, the CDCHM has better performance in static and vibration isolation. The static and vibration properties of the DHM and CDCHM are investigated by experiments and simulations. The results show that the CDCHM has a higher load-carrying capacity than that of the DHM. In addition, the vibration isolation optimal design schemes of the DHM and CDCHM are examined by experiments and simulations. It is found that the vibration suppression of the CDCHM is also improved greatly. In particular, the optimization approach with metal pins and particle damping achieves a wider bandgap in the low-frequency region, which can strengthen the suppression of low-frequency vibrations. And the introduction of particle damping can not only design the frequency of the bandgap via the alteration of the dosage, but also enhance the damping of the main structure. This work presents a new design idea for metamaterials, which provides a reference for the collaborative design of the static and vibration properties of composite metamaterials.

A hybrid beam system of aramid-fibre-reinforced concrete and high-strength concrete

ABSTRACT This paper investigates the flexural behaviour of hybrid reinforced concrete (RC) beams having aramid fibre reinforced concrete (AFRC) in the tension zone and high-strength concrete (HSC) in the compression zone. In two series of experimental investigations, the depth of AFRC layer and the concrete strength in the compression zone were varied. The hybrid beams were tested in series 1 to explore the effects of the depth of AFRC layer on load-carrying capacity and flexural toughness. The effects of compressive strength of the concrete in the top half of the hybrid beams on load-deflection behaviour, failure mode and cracking pattern were studied in series 2. The experimental results reveal that the use of AFRC only in the bottom half of the beam enhanced load-carrying capacity and flexural toughness by 62.44% and 87.66%, respectively, compared to the control specimen with no AFRC. The hybrid beam with AFRC-HSC exhibited 5% higher load-carrying capacities, 45% higher ductility and better cracking behaviour than the conventional RC beam. These enhanced structural performances are beneficial for specific purposes such as structures in marine environment where rebar corrosion is the main concern, or structures under extreme loadings where high ductility is required.

Cyclic loading response of precast concrete beam-column connections with partially bonded draped prestressing tendon

An emulative precast concrete beam-column connection consists of prefabricated columns, T-shaped composite beams with partially bonded post-tensioned (PT) tendon, and cast-in-place (CIP) core region is proposed in this study. Experimental study was carried out to examine the hysteretic behavior of four full-scale beam-column connections under a high axial compression ratio (μ = 0.4). The specimens included a precast interior connection (PC1), a precast exterior connection (PC2), and two corresponding conventional CIP control specimens (RC1 and RC2). Performance assessment of the suggested connection was conducted by evaluating various factors, including failure mode, hysteresis curve, deformation, stiffness, and energy dissipation capacity. Test results revealed that all specimens fulfilled the design objective of strong column-weak beam with flexural failure showed at beams ends. In comparison to RC1, PC1 exhibited a 6.4 % increase in peak load-carrying capacity in the positive loading process and a 7.1 % decrease in the negative loading process. On the other hand, PC2 demonstrated approximately 11.9 % higher load-carrying capacity in the positive loading and a 2.0 % lower capacity in the negative loading when compared to RC2. The ductility coefficients of PC1 and PC2 was 3.39 and 2.64, respectively, which were slightly higher than that of RC1 and RC2 (3.01 and 2.43). All specimens exhibited good deformation restoring capacity and plump hysteretic loops, demonstrating satisfactory energy dissipation capacity. Overall, the proposed connection with partially bonded PT tendon showed comparable seismic performance with their CIP counterparts, indicated its promising potential for use in practical engineering applications.

A critical review of the effect of nano-lubricant on the performance of hydrodynamic journal bearing

The applications of nano-lubricants in journal bearing are found to be capable of improving load-carrying capacity and reducing friction. Many numerical and experimental investigations have been performed to find the effect of nano-lubricants on the performance of the journal bearing. In this paper, a state-of-the-art review is done of the articles of numerical and experimental assessments of the effect of nano-lubricants on the performance of journal bearings. Here research articles are classified on the basis of nanoparticles used as nano-additive, which are further classified in the category of numerical and experimental study. It is seen that the application of nano TiO2, CuO and Al2O3 based nano-lubricants gives much higher load-carrying capacity than the base lubricants. This article concludes by discussing the effect of different nanoparticle-based nano-lubricants on the performance characteristics of the journal bearing and mathematical models used for numerical investigations.

Particle swarm optimized fuzzy proportional-integral-derivative controller-based transverse leaf spring active suspension for vibration control

The transverse leaf spring (TLS) suspensions are a promising option for van vehicles due to their high load-carrying capacity and excellent handling stability. However, its ride comfort remains a major challenge. This paper investigates and compares the effects of semi-active and active control strategies to enhance the ride comfort of TLS suspensions. Firstly, a four-degree-of-freedom (4-DOF) half-car model and a multi-body dynamics (MBD) model of the TLS suspensions are established. The MBD model has higher accuracy and can describe the medium and high frequency characteristics of the TLS suspensions, such as the suspension offset frequency and the frequency response function of the body vertical acceleration (BVA). Therefore, based on the MBD half-car model with TLS suspensions, this paper proposes an optimal fuzzy PID active control strategy considering the left and right suspension coupling. The optimization objectives are the BVA, the left and right suspensions dynamic deflection, and the left and right wheels dynamic displacement. The integral absolute error is used as the evaluation criterion. The left and right fuzzy PID controllers’ parameters are obtained through particle swarm optimization. Simulation results demonstrate that the particle swarm optimization fuzzy PID active control strategy effectively controls the low-frequency vibration of the TLS suspensions and suppresses the medium- and high-frequency vibration characteristics compared with the traditional skyhook semi-active control strategy. This technology provides a reference for improving the ride comfort of the TLS suspensions.

Corrosion-resistant L12-strengthened high-entropy alloy with high strength and large ductility

Corrosion-resistant alloys with high strength and large ductility are desirable for applications in harsh environments where high structural load-carrying capacity is required. In this work, we designed an L12-strengthened high-entropy alloy (HEA) of composition (NiCo)77Cr13Al5Nb5 (at.%) that combines excellent mechanical properties and good corrosion resistance. The formation of a thin passive film of non-stoichiometric compounds with an amorphous structure, characterized by an enrichment of Cr2O3 and Nb2O5, contributes to the superior localized corrosion resistance. The precipitation strengthening brought about by coherent L12 particles and the multi-stage plastic deformation dominated by stacking faults (SFs) provides ultrahigh strength and appreciable ductility, respectively.

Robust Design of Herringbone Grooved Journal Bearings Using Multi-Objective Optimization With Artificial Neural Networks

Abstract Herringbone grooved journal bearings (HGJBs) are widely used in micro-turbocompressor applications due to their high load-carrying capacity, low friction, and oil-free solution. However, the performance of these bearings is sensitive to manufacturing deviations, which can lead to significant variations in their performance and stability. In this study, design guidelines for robust design against manufacturing deviations of HGJB supported micro-turbocompressors are proposed. These guidelines are based on surrogate model-assisted multi-objective optimization using ensembles of artificial neural networks trained on a large dataset of rotor and bearing designs as well as operating conditions. The developed framework is then applied to a series of case studies representative of heat-pump and fuel-cell micro-turbomachines. To highlight the importance of rotor geometry and bearing aspect ratio in the robustness of HGJBs, two types of optimizations are performed: one focusing on optimizing the bearing geometry, and the other focusing on both the bearing and rotor geometries. The analysis of the Pareto fronts and Pareto optima of each type of optimization and case study allows for the derivation of design guidelines for the robust design of HGJB supported rotors. Results suggest that by following these guidelines, it is possible to significantly improve the robustness of herringbone grooved journal bearings against manufacturing deviations, resulting in stable operation. The best design achieved ±8 μm tolerance on the bearing clearance, and designs optimized for both rotor and bearing geometry outperformed those optimized for bearing geometry alone. This work successfully identifies guidelines for the robust design of herringbone grooved journal bearings in micro-turbocompressor applications, demonstrating the strength of surrogate model-assisted multi-objective optimization. It provides a valuable tool for engineers seeking to optimize the performance and reliability of these bearings.

Tensile, bending, and impact properties of laminated carbon/aramid/glass hybrid fiber composites

Abstract In this study, hybrid (carbon, glass, and aramid) fabric epoxy composite laminates were fabricated with different layering sequences by hand lay-up. The effects of layering arrangements of laminated composite fibers on the mechanical properties of hybrid composites were investigated. Tensile, bending, and impact tests were performed to obtain the mechanical behaviors of hybrid composites. It was found that the layering sequences significantly affect the tensile, bending strength, and impact energy. As a result of the tensile tests, the highest tensile strength was obtained in the 3C + 3G combination. The highest load-carrying capacity in three-point bending tests was obtained in the 2G + 2A + 2C combination. The combination with the highest impact energy was 2C + 2G + 2A, and the lowest was 3C + 3G. It has been observed that hybrid composites containing aramid fiber absorb higher impact energy than others. The results showed that the layering sequences are essential in hybrid composites with the same fiber and layer number.

Role of Additives in Compacted Concrete Pavements

Roller compacted concrete (RCC) is an emerging pavement technology especially for secondary roads and is additionally valued for its lower installation costs, faster opening to traffic, high load-carrying capacity, and durability. One major drawback to use of RCC in secondary roads is the balance of smoothness and target surface durability over time. To achieve more consistent RCC mixes, the compaction (flow) performance and rheology of about 40 freshly prepared zero-slump graded aggregate concrete pastes were explored with selected types and levels of additives and water saturation levels. Viscosity modifiers were found to be critical to achieve the highest yield strength formulations. The high yield strength RCC formulations identified from this study followed the key guidance, namely graded aggregate, viscosity, and lubricity, of the Superpave program for fresh asphalt concrete.