Search Results (1,296)

Wearable assistive exoskeletons require lightweight, compact, and backdrivable transmission systems with low output impedance to ensure safe and comfortable human–robot interaction. These efficient, modular actuators benefit from reduction mechanisms that minimize axial bulk while providing high motion regularity. While existing transmissions perform well on some of these metrics, their practical implementation is often constrained by geometric complexity, low backdrivability, limited reduction ratios, or standard component sizes. This paper presents a novel combination of a Rolling Element Eccentric (REE) stage and a planetary gearbox, specifically designed for wearable exoskeleton actuation. The proposed architecture integrates a bearing-based REE drive concentrically within the sun gear of a planetary transmission, reducing mechanical complexity and friction and improving regularity. Moreover, the design exploits additively manufactured bearings, enabling substantial weight reduction, reduced encumbrance, and increased design freedom without reliance on standard bearing dimensions. A prototype reducer has been designed and fabricated using additive manufacturing techniques. It was experimentally evaluated and compared with state-of-the-art transmission designs. These investigations demonstrated low friction, minimal backlash, good torsional stiffness, and sufficient backdrivability, despite the high reduction ratio, while maintaining a compact, flat form factor. The experimental results indicate that the proposed rolling element eccentric planetary transmission is a viable and effective solution for lightweight, efficient, axially compact (independently of the implemented reduction ratio), and backdrivable actuators in assistive wearable robotics. Full article

Salt dust storms are a distinct and highly hazardous type of dust storm in arid and semi-arid regions. Salt crusts commonly develop on the surfaces of desiccated lake beds, and variations in their structure and properties directly influence dust release. To investigate how wetting–drying alternation affects the erodibility of sodium sulfate salt crusts with varying salt contents, four crust types with 0%, 1%, 3%, and 5% sodium sulfate were prepared under controlled laboratory conditions. A combination of wind-tunnel tests, direct shear tests, and surface morphology observations was employed to evaluate changes in mechanical properties and wind-erosion responses before and after wetting–drying treatment. The results showed that wetting–drying alternation induced pronounced cracking, salt crystallization, and the formation of a loose surface layer in salt-bearing crusts, with structural damage severity increasing with salt content. In contrast, the physical crust without added salt exhibited minimal surface deterioration. Direct shear tests revealed that after wetting–drying, the internal friction angle of salt-bearing crusts first decreased and then increased with salt content, while cohesion declined markedly; the 5% salt crust showed a 32.4% reduction in cohesion, indicating substantial structural degradation. Wind-tunnel tests further demonstrated that wind-erosion intensity increased significantly after wetting–drying treatment across all salt contents, with the largest relative increase observed in the 1% salt crust. Wind-erosion intensity also scaled approximately as a power function of salt content. These findings demonstrate that wetting–drying alternation is a critical trigger for the degradation of sodium sulfate salt crusts and for enhancing their erodibility. Post wetting–drying, salt crusts may evolve into highly erodible surfaces, becoming major potential sources of salt dust storms. This study provides a theoretical foundation for understanding salt dust release from desiccated lake beds and for improving early warning of ecological hazards in arid regions. Full article

The contradiction between high compliance and low load-bearing capacity of flexible manipulators limits their engineering applications. Meanwhile, the theoretical modeling of the deformation and variable stiffness characteristics of flexible joints still faces considerable challenges. This paper proposes a positive-pressure double-airbag gap-constrained particle-jamming variable stiffness method and develops a novel actively variable stiffness pneumatic flexible bending joint with an integrated configuration of actuator, variable stiffness device (VSD), and primary structure. Based on classical elasticity theory and Coulomb–Amontons’ law of friction, theoretical models for the bending angle and tangential stiffness are established and verified through prototype experiments. With VSD activation, the joint reaches a bending angle of 56.35° at 0.4 MPa. At 40° forward bending, VSD activation increases the tangential stiffness from 0.167 N/mm to 0.832 N/mm, with the stiffness ratio between 40° and 0° increasing from 1.56 without VSD to 4.80 with VSD activation. Model predictions agree well with experimental data, yielding mean relative errors of 6.77% for the bending-angle model with VSD and 6.76% for the forward tangential-stiffness model with VSD activation. A coupling effect between bending deformation and stiffness is observed. The results demonstrate that the proposed joint achieves substantial stiffness regulation, providing a basis for its application in flexible robotic systems. Full article

Ultra-high molecular weight polyethylene (UHMWPE) is the preferred bearing material for total knee arthroplasty, yet its limited service life (15–20 years) remains a clinical challenge. This study investigates graphene oxide (GO) nanoplatelets as reinforcing fillers to enhance the mechanical and tribological performance of UHMWPE for longer-lasting implants. GO/UHMWPE composites with 0–1 wt% GO were fabricated via solution blending and hot compression molding. Direct SEM imaging combined with oxygen elemental mapping confirmed uniform GO dispersion up to 0.5 wt%, whereas higher loadings induced agglomeration. Dynamic mechanical analysis showed that the storage modulus at 37 °C increased with GO content, peaking at 0.5 wt% (improved by ~28% over neat UHMWPE), then decreased due to aggregation. Tribological tests under dry reciprocating sliding revealed that GO progressively reduced the wear rate (up to ~45% at 1.0 wt%), but also raised the steady-state friction coefficient from 0.13 to 0.19, attributed to molecular chain anchoring. The optimal balance of enhanced stiffness and wear resistance, with only a marginal friction increase, was achieved at 0.5 wt% GO. The reinforcement mechanism involves efficient stress transfer to rigid GO sheets and reduced surface peeling. This work provides a robust processing route and direct dispersion evidence, offering practical guidance for designing high-performance UHMWPE composites for orthopedic applications. Full article

Developing Cu-based composites with excellent electrical and mechanical properties under multiphysics-coupled service conditions remains challenging. Novel Cu-Nb-Gr composites were fabricated by high-energy ball milling and High-pressure Multi-field Assisted Rapid Sintering. Experiments combined with computational fluid dynamics (CFD) and finite element method (FEM) simulations were used to investigate how Gr regulates material performance. The incorporation of 3 vol.% Gr promoted the formation of a semi-continuous Gr-rich structure coupled with an Nb-rich load-bearing structure. Under arc erosion, the semi-continuous Gr-rich structure provided efficient heat-conduction pathways, reducing the peak temperature and metal-vapor recoil force, while the Nb-rich load-bearing structure suppressed liquid–metal spattering and stabilized the molten pool. Simultaneously, Gr dynamically spread to form a continuous solid-lubricating film during sliding friction, significantly reducing the coefficient of friction and interfacial shear stress. Furthermore, under compressive loading, the semi-continuous Gr-rich structure coupled with the Nb-rich load-bearing structure alleviated interfacial elastic–modulus mismatch and extreme stress concentration, limiting macroscopic plastic deformation of the matrix. Consequently, Cu-Nb-3Gr achieved a favorable balance of arc-erosion resistance, wear resistance, and compressive performance, providing a new strategy for improving conventional Cu-based composites. Full article

The bent sub is a main deflection component in the near-bit assembly of small-diameter push-the-bit guided coring tools, and its parameters affect build-up capability and local structural response. Existing studies mainly focus on conventional rotary steerable drilling systems, whereas slim-hole constraints, including narrow annular clearance and cross-sectional weakening induced by internal coring channels, remain insufficiently considered. To address this problem, a static bending model of the near-bit section was established based on Euler–Bernoulli beam theory. Channel-induced cross-sectional weakening was represented using the actual concentric annular geometry of the primary load-bearing outer tube, and the bent-sub initial curvature, dual push-the-bit loads, axial weight on bit, and borehole-wall contact and friction effects were incorporated. The build-up rate (BUR), maximum equivalent stress, and maximum curvature served as response indicators. A control-variable approach was used to analyze the bent-sub length L_b, bend angle γ, and distance from the bit D_b. The results showed that D_b had the strongest effect on BUR, and all parameters exhibited a trade-off between steering performance and structural safety. Increasing L_b from 0.30 m to 0.80 m reduced BUR from 12.65°/30 m to 9.79°/30 m, whereas increasing γ from 0.5° to 2.5° increased BUR from 4.12°/30 m to 10.70°/30 m. Considering structural constraints and normalized BUR retention, the recommended engineering ranges are L_b = 0.65–0.80 m, γ = 1.3°–1.9°, and D_b = 0.50–0.70 m. Full article

To improve the bending resistance and support the domestic development of deepwater subsea wellhead equipment, a three-dimensional finite element model (FEM) of the SXW-15 subsea wellhead system was established in ANSYS Workbench considering contact nonlinearity and rigid-locking mechanisms. Based on representative deepwater drilling and completion conditions, the effects of the friction coefficient, locking preload, blowout preventer (BOP)/lower marine riser package (LMRP) top load, casing hanger internal pressure, and tubing load on the ultimate bending capacity of the system were systematically investigated. The results show that the bending capacity increases with increasing friction coefficient and locking preload, whereas it decreases with increasing top load and tubing weight. The internal pressure of the casing hanger exhibits a pronounced nonlinear influence on the bending resistance, and the maximum bending capacity occurs at an internal pressure of approximately 4000 psi. Based on the mechanical analysis, several innovative designs were proposed, including a layered load-bearing structure, a gravity-set metal sealing assembly, a self-supporting rigid-locking mechanism, and an integrated multifunctional tool system, aiming to improve load-transfer efficiency, connection stiffness, and high-pressure sealing stability. Land-based testing and offshore field applications were subsequently conducted to verify the engineering applicability of the system. The subsea wellhead system with innovative designs maintained satisfactory structural integrity and sealing reliability under conditions of 15,000 psi internal pressure and 12.7 million lb axial load. Good agreement was obtained between finite element predictions and field test results. The present study provides theoretical support and guidance for the structural designs and engineering applications of deepwater subsea wellhead systems. Full article

As piston rods for excavator boom hydraulic cylinders shift from integral forging to welded assemblies of separately manufactured rod bodies and rod heads, joint reliability becomes critical to load-bearing performance. In this study, 60 mm diameter quenched-and-tempered/as-rolled 1045 steel joints were fabricated by continuous-drive friction welding under three coupled secondary-friction pressure–time conditions. Joints made with two quenched-and-tempered base metals were compared under the same high-pressure/short-time condition. Optical microscopy, electron backscatter diffraction, microhardness testing, tensile testing, and scanning electron microscopy were used to characterize microstructure and failure behavior. Fine, multi-oriented reconstructed microstructures formed in all weld zones, while a hardness valley developed in the heat-affected zone on the quenched-and-tempered side. As the machine-displayed secondary-friction pressure increased from 1.43 to 2.14 MPa, the actual secondary-friction time decreased from 57.3 to 37.5 s. Under the corresponding high-pressure/short-time condition, heat-affected-zone softening was slightly mitigated and tensile strength increased from 743.37 to 755.78 MPa. Different elongations were observed between the two joint types. All specimens fractured in the softened heat-affected zone on the quenched-and-tempered side and exhibited dimple-dominated fracture surfaces. Under the present tensile-testing conditions, the weld zone was not the fracture-controlling region. Full article

While the beneficial effect of residual compressive stress (RCS) on rolling bearing fatigue life is empirically well-established, the underlying mechanisms, particularly its influence on the subsurface stress field responsible for fatigue initiation, remain inadequately explored. This study employs a sophisticated finite element (FE) model of a ball–raceway contact, which incorporates a depth-dependent gradient of RCS, to elucidate the underlying mechanisms. The results demonstrate that RCS not only reduces the contact stress at the interface but also fundamentally alters the subsurface stress field by shifting the location of the maximum shear stress to a greater depth and reducing its inclination angle. These changes collectively delay crack initiation and propagation, explaining the observed enhancement in fatigue life. Furthermore, the study demonstrates that the beneficial effect of RCS is depth-dependent and persists significantly even under high-friction conditions. Full article

Existing methods for calculating the bearing capacity of cast-in-place piles in coral reef formations usually treat coral reef strata as ordinary sandy soil or conventional rock–soil media, without explicitly considering grout penetration and cementation in highly porous coral reef rock. This may lead to an incomplete evaluation of pile end bearing capacity and shaft resistance. To address this limitation, this study proposes a semi-empirical calculation framework that incorporates the contribution of the grout-induced cementation-enhanced zone. In the proposed model, the pile end bearing capacity is divided into three components: the intact coral reef rock contribution, the grout–coral reef rock cemented interface contribution, and the vertical effective stress term. The shaft resistance is divided into interface friction resistance and additional cementation-induced friction resistance. Key parameters were determined through an integrated procedure combining established laboratory and field techniques, including saturated weighing, mercury intrusion porosimetry, CT scanning, field coring, tracer observation, CT-based back-analysis, unconfined compression tests, and interface shear tests. For the investigated engineering case, the comprehensive porosity was 35%, the effective grout penetration radius was 0.118 m, the shear strength of intact coral reef rock was 2.5 MPa, and the shear strength of the cemented interface was 3.0 MPa. The calculated pile end bearing capacity was 1.76 MN, close to the field static load test value of 1.72 MN, with a relative difference of about 3%. The calculated total shaft resistance was 2.59 MN, compared with the measured value of 2.63 MN, with a relative difference of about 1.5%. The results suggest that considering the cementation-enhanced zone can better reflect the bearing response of cast-in-place piles in the investigated coral reef project. However, because the assessment is based on a single project and several parameters were obtained from local tests or back-analysis, the proposed method should be regarded as a site-specific semi-empirical framework. Further independent field tests are needed to examine its transferability and statistical reliability. Full article

The Triboelectric Nanogenerator (TENG), as an emerging self-powered sensor, is widely used in the field of rotating machinery bearing fault diagnosis. Due to its working principle based on frictional electrification and electrostatic induction effects, the surface morphology and charge transfer efficiency of the friction layer have a significant impact on the output performance of TENGs. Under long-term mechanical motion, the friction layer may experience wear, and continuous wear can lead to surface morphology damage and even damage to the friction layer structure, gradually destroying the TENG’s signal acquisition and output capabilities, causing signal degradation and bearing fault feature deviation, which results in a decrease in bearing fault diagnosis accuracy. Traditional solutions focus on material properties and structure. This article derives the mechanism of the influence of friction layer thickness on the output signal through the TENG output voltage formula and simulates different degrees of wear with friction layers of different thicknesses to conduct deep learning-based bearing fault diagnosis experiments. The experimental results show that although the CNN model can recognize TENG signals well for bearing fault classification, the bearing fault features of the worn signals shift, and the accuracy of CNN diagnosis decreases. The introduction of a one-dimensional self-attention-enhanced convolutional neural network model and an incremental learning method improved the accuracy of bearing fault diagnosis after wear and tear. This study provides theoretical support and practical solutions for long-term, stable bearing fault diagnosis in TENG under wear conditions. Full article

Wear occurs in sliding bearings as they often operate under mixed friction conditions in heavy-duty applications. Over the years, this has led to the development of wear simulations to predict wear evolution in sliding bearings. As part of wear evolution, bearing surface topography changes, and the bearing clearance varies due to temperature rise. For realistic wear predictions, both the surface topography changes and thermal effects must be considered. However, existing wear simulations do not accurately account for thermal effects during mixed friction. Effects such as local and transient temperature rise and thermal expansion alter bearing contact conditions (clearance) and thus influence wear evolution. Since these effects are not accurately modelled, realistic wear prediction in sliding bearings remains challenging with current approaches. Therefore, this paper introduces the extension of wear simulations by local and transient modelling of bearing temperature and clearance changes. The novelty lies in enabling the simultaneous consideration of transient thermal changes and surface topography changes during wear evolution. This enables a more realistic prediction of wear development in sliding bearings which can be applied to evaluate wear safety in bearing designs. The thermal wear simulation is validated using experimental measurement of friction torque, bearing temperature, and wear volume obtained from a radial sliding bearing test bench. Full article

This study investigates the tribological performance of chromium nitride (CrN)-coated polyether ether ketone (PEEK) polymers. CrN coating was deposited by physical vapor deposition (PVD) onto two commercially available substrates: neat PEEK and a modified PEEK. The suitability of the coated substrates for tribological applications was evaluated using ball-on-disc tests against stainless-steel (SS) counterparts. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) confirmed the high thermal stability of the PEEK substrates, ensuring compatibility with low-temperature coating deposition. Microstructural analysis revealed dense and continuous CrN coatings with an average thickness of ~1.5 µm on both substrates. Tribological results of selected PEEK-based polymers showed that under the applied load of 2 N, uncoated PEEK substrates exhibited lower coefficients of friction (COFs) and smoother wear tracks compared with coated samples. In contrast, under the applied load of 4 N, CrN-coated PEEK substrates demonstrated reduced friction and improved stability relative to uncoated PEEK. This behavior is attributed to load-induced tribo-oxidation and the formation of a chromium-oxide-rich tribolayer that stabilized the sliding interface and suppressed adhesive wear. Overall, the results demonstrate that CrN coatings significantly enhance the load-bearing capacity and tribological performance of selected PEEK substrates under applied load of 4 N, highlighting their potential for advanced lightweight engineering applications requiring improved wear resistance. Full article

Conventional bond-slip models generally represent ribbed GFRP bars as equivalent smooth cylinders, limiting their ability to describe local rib-bearing, interface degradation, and non-uniform stress transfer. This study establishes a three-dimensional finite-element model for helically ribbed GFRP bars embedded in concrete, explicitly incorporating the helical rib geometry, cohesive-frictional interface interaction, and concrete damaged plasticity. Validation against independent pull-out tests yields minor peak bond-stress errors of −0.55% and −2.49% across different bar diameters, with numerical reliability confirmed through mesh and energy checks. The results indicate that bond resistance evolves from cohesive transfer to rib-bearing action, followed by localized concrete damage, frictional sliding, and residual interlocking. Stress transfer is highly non-uniform along the bonded length, and post-peak interface degradation causes the active transfer zone to migrate dynamically away from the loaded end. Parametric analyses reveal conditional main-effect trends within the investigated ranges, demonstrating that rib height has the strongest influence on residual resistance and energy dissipation, whereas the benefit of increasing concrete strength gradually diminishes. Increasing the bonded length or bar diameter raises the total pull-out force but reduces the nominal bond efficiency due to shear lag. Finally, a simplified four-stage bond-slip relationship is proposed, wherein each stage physically aligns with distinct interface degradation phases, to facilitate computationally efficient structural-scale simulations. Full article

The digital transformation of manufacturing associated with Industry 4.0 and the human-centric paradigm of Industry 5.0 requires advanced predictive tools that can improve the performance, reliability, and sustainability of tribological systems. In this context, accurate prediction of friction behavior in rolling contacts is crucial for intelligent monitoring and optimization of bearing components. This study presents a machine learning-based methodology for predicting the coefficient of friction in rolling contact of 100Cr6 steel bearing discs as a function of surface roughness and rolling distance parameters. Experimental studies were conducted using discs with different surface topography under controlled rolling contact conditions. Surface roughness characteristics and rolling distance data were correlated with experimentally measured friction coefficients to create a comprehensive dataset for artificial intelligence (AI) modeling. Several dozen machine learning (ML) algorithms, including random forest, support vector regression, and artificial neural networks, were developed and comparatively evaluated to capture nonlinear relationships between operational and surface parameters. The predictive ability of the models was assessed using statistical metrics such as the coefficient of determination (R²), mean absolute error (MAE), and root mean square error (RMSE). The obtained results demonstrate that ML methods provide high prediction accuracy and effectively identify the combined effects of surface roughness and rolling distance on rolling contact friction. Feature importance analysis revealed that roughness parameters dominate friction behavior during the run-in phase, while rolling distance becomes increasingly important under stabilized operating conditions. The proposed approach supports the development of intelligent tribological systems, predictive maintenance strategies, and data-driven decision-making frameworks aligned with Industry 4.0 and Industry 5.0 concepts. The presented methodology can contribute to the implementation of intelligent manufacturing solutions, the sustainable operation of bearing systems, and AI-assisted monitoring of machine components in modern industrial environments. Full article