Search Results (3,704)

In order to protect the high-sensitivity optical lens of the “magnetic field and velocity field imager” in extreme deep space environments, this paper proposes a new type of dual redundant planetary differential lens cover drive mechanism. In view of the critical vulnerability that traditional single-motor direct drive is prone to sudden mechanical jamming and catastrophic single-point failure (SPF) in severe tasks such as Jupiter exploration, this study constructs a “dual input single output (DISO)” rigid decoupling architecture from the perspective of physical topology. Through theoretical analysis and kinematic modeling, the adaptive decoupling mechanism of the two-degree-of-freedom (2-DOF) system under unilateral mechanical stalling is revealed. Dynamic analysis shows that in the nominal dual-motor synergy mode, the system shows a significant “kinematic load-sharing effect”, thus greatly reducing the sliding friction and gear wear rate. In addition, under the severe dynamic fault injection scenario (maximum gravity deviation and sudden jam superposition of a single motor), the cold standby motor is activated and the dynamic takeover is quickly performed. The high-fidelity transient simulation based on ADAMS verifies that although the fault will produce transient global torque spikes and pulsed internal gear contact forces at the moment, all extreme dynamic loads remain well within the structural safety margin. The output successfully achieved a smooth transition, which is characterized by a non-zero-crossing velocity recovery. This research provides an innovative theoretical basis and a practical engineering paradigm for the design of high-reliability fault-tolerant mechanisms in deep space exploration. Full article

This study examines the effect of tool rotational speed on the microstructure and dry sliding wear behavior of brass–tungsten (brass/W) surface composites fabricated through friction stir processing. Microstructural analysis confirmed a uniform distribution of tungsten particles within the stir zone, with no observable clustering. Improved properties were achieved at a lower traverse speed of 40 mm/min combined with a higher rotational speed of 1168 rpm, which promoted finer grain formation (~4 µm) and better particle dispersion. An increase in rotational speed led to a corresponding rise in hardness, from 142 HV at 832 rpm to 165 HV at 1168 rpm. In terms of wear behavior, the sample processed at lower rotational speed exhibited abrasive and micro-cutting wear, whereas the sample processed at higher rotational speed predominantly showed adhesive wear. Full article

Background: We aimed to study the association between accelerometer-measured physical activity and metabolic markers of diabetes in a nationwide representative sample of U.S. adults. Methods: This cross-sectional analysis included 1259 adults aged ≥18 years from the 2003–2004 National Health and Nutrition Examination Survey (NHANES), the only cycle incorporating objective accelerometry. Physical activity was assessed using hip-worn accelerometers, with moderate-to-vigorous physical activity (MVPA) and sedentary time derived from validated count thresholds. Metabolic outcomes included fasting glucose, fasting insulin, glycated hemoglobin (HbA1c), and insulin resistance estimated by the Homeostatic Model Assessment (HOMA-IR). Survey-weighted linear regression models accounting for the complex sampling design were applied, with sequential adjustment for demographic, socioeconomic, anthropometric, and behavioral covariates. Sensitivity analyses tested alternative MVPA thresholds and wear-time criteria. Results: In unadjusted models, higher MVPA was inversely linked with fasting glucose and insulin concentrations; but, these associations were attenuated after full multivariable adjustment. In contrast, MVPA established a constant inverse association with insulin resistance. Higher MVPA was connected with lower HOMA-IR values, and this relationship remained statistically significant in fully adjusted models and across all sensitivity analyses (all p < 0.001). Associations between sedentary time and metabolic markers were non-sustainable after multivariable adjustment. No significant effect modification by sex was detected. Conclusions: Objectively measured moderate-to-vigorous physical activity is independently linked with lower insulin resistance in U.S. adults. These results emphasize the value of accelerometer-based assessments for identifying early metabolic risk and reinforce physical activity promotion as a key strategy for improving insulin sensitivity. Full article

Planetary gear systems offer compact design and high-power density, but they are strongly influenced by transmission error (TE), which originates from geometric deviations and elastic deflections. This study presents a dynamic model that integrates elastic compliance, mesh stiffness, damping, and error excitation to evaluate coupled gear responses. Numerical results show that planet–ring contacts undergo larger forces and deflections than sun–planet meshes. Time–frequency analysis with continuous wavelet transform (CWT) reveals nonstationary vibration patterns, while gear tooth flank inspection confirms torque bias and micro-pitting. The findings connect modeling predictions with observed wear, offering insights for planetary gear diagnostics and design. Full article

Industrial synthetic and natural fibers play an indispensable role in modern manufacturing, aerospace, automotive, and textile engineering. However, the enhanced mechanical performance of advanced industrial fibers has introduced significant challenges in cutting processes, since brittle, high-tensile, and viscoelastic fibers exhibit totally different fracture behaviors from conventional solid materials. At present, the complex motion coupling mechanisms between fibers and cutting tools under free-form conditions are insufficient; there is no unified framework for understanding the mechanisms of fiber cutting; it is difficult to effectively link the microscopic fracture physics of different fiber types with their macroscopic cutting properties. Furthermore, research into the dynamic interaction between the cutting tool and the fiber, cross-scale cutting characteristics, and tool wear mechanisms has not been sufficiently systematic, and non-contact cutting methods have not yet been the subject of systematic study. Through a systematic review, this review identified three primary categories of difficult-to-cut industrial fibers and summarized the distinctions in their fundamental material properties. The static, kinematic, and dynamic characteristics of fiber cutting under both free and fixed forms were discussed. The fracture mechanisms of fibers under diverse loading scenarios were also systematically revealed. Furthermore, this review summarizes the effects of cutting tool wear characteristics, geometric parameters, and material types on cutting performance. Finally, non-contact methods for cutting fiber were listed. Based on the above analysis, three critical directions for future research were proposed to bridge the existing knowledge gaps in the literature. This review of the interdisciplinary interactions among mechanics, materials science, and textile engineering provides a theoretical foundation and research directions for achieving high efficiency and a long tool life during cutting industrial fibers. Full article

Fretting wear significantly limits the service life of metal O-rings operating under harsh conditions. To address this limitation, this study investigates the wear behavior of metal O-rings under equivalent accelerated reciprocating motion and establishes an accelerated life prediction model based on similarity theory. Fretting wear experiments were conducted using Inconel 718 alloy and 304 stainless steel to replicate service conditions in a controlled laboratory environment. Wear morphology was characterized using laser scanning confocal microscopy, revealing a progressive transition from mild abrasive and adhesive wear to severe abrasive wear accompanied by material spalling. Based on the experimental results, regression analysis was performed to estimate the acceleration model coefficients, leading to the formulation of an equivalent acceleration equation capable of predicting seal wear life under practical service conditions. The resulting equivalent acceleration model can establish a quantitative connection between the acceleration test and the operating conditions. This model can shorten the testing time and can be used to predict parameters related to the surface morphology of static seals, providing a theoretical and experimental basis for reliable life assessment. This provides a practical basis for improving the reliability and safe operation of metal O-ring seals in critical applications, including nuclear energy and chemical processing systems. Full article

To address the increasing demands for lightweight, high-temperature resistant braking materials under extreme service conditions, a novel C_f/SiC-B₁₂(C,Si,B)₃ composite was developed in this work. The composite was fabricated via a hybrid slurry infiltration-reactive melt infiltration (SI-RMI) process. The tribological performance under coupled temperature–velocity conditions was systematically evaluated using a ball-on-disk tester over temperatures from 25 to 600 °C (at 900 r/min) and sliding speeds from 300 to 900 r/min (at 600 °C). The results indicate that temperature dominates the friction and wear behavior. At room temperature, the composite exhibits a friction coefficient of 0.52 and a wear rate of 4.019 × 10⁻⁴ mm³/(N·m). With increasing temperature, friction coefficients decreased to 0.43 at 400 °C and 0.41 at 600 °C, while wear rates increased sharply to 12.025 × 10⁻⁴ mm³/(N·m) at 400 °C before declining to 5.228 × 10⁻⁴ mm³/(N·m) at 600 °C. Under the fixed temperature of 600 °C, raising rotational speed from 300 to 900 r/min increased the wear rate only marginally (4.953 to 5.228 × 10⁻⁴ mm³/(N·m)). Surface analysis indicates that a continuous Si-B-O oxide layer (mainly SiO₂ and B₂O₃) forms at 600 °C, which may provide solid lubrication and oxidation resistance. The present work offers a preliminary exploration of the tribological evolution and self-lubrication mechanisms of C_f/SiC-B₁₂(C,Si,B)₃ composites, providing potential insights for the design of advanced ceramic-matrix braking materials. Full article

We report on tool wear and surface roughness for hybrid additive manufacturing of Inconel 718 components. The hybrid additive manufacturing comprises laser powder bed fusion (PBF-LB/M) and an in situ high-speed milling process, i.e., milling is performed within the powderbed, which deteriorates the surface quality by additionally occurring wear mechanisms. Therefore, in this comparative study milling path suction is used to improve tool wear characteristics and thus enhance surface quality. As a result, we quantify the improvement of the maximum tool life according to the flank wear, which is granted by the milling path suction. Additionally, the dominant wear mechanisms are investigated, revealing adherence and abrasion as the main contributing factors to wear. Furthermore, surface analysis shows an improvement of surface quality by the use of the milling path suction. Specifically, a reduction in surface roughness of hybrid manufactured Inconel 718 components down to a minimum of $Ra$ = 0.55 μm is highlighted. Full article

Conventional gel electrodes are the gold standard for surface electromyography (sEMG), yet their bulkiness, stiffness, and limited gel lifetime prevents seamless day-long integration with wearable robots. We integrated ultrathin skin-conformal temporary tattoo electrodes with a powered unilateral hip exoskeleton and compared signal quality during treadmill walking against gel. In this pilot study, five healthy participants completed three consecutive walking blocks at fixed speed: (1) using gel electrodes; (2) using tattoo electrodes to compare signal quality; and (3) using the same tattoo electrodes (not repositioned) after eight hours of wear to simulate a full day of typical device use and to evaluate potential degradation in signal quality over time. Electrodes were positioned on muscles not covered by the exoskeleton interface (tibialis anterior and gastrocnemius medialis), as well as on muscles located beneath the exoskeleton cuff, which were potentially subject to motion artifacts due to the application of external forces by the exoskeleton (rectus femoris and biceps femoris, BF). Across all muscles, for both gel and tattoo electrodes, the root mean square error (RMSE) between normalized sEMG envelopes and biological activation profile was 0.069 ± 0.048, and Pearson’s correlation coefficient (ρ) was 0.844 ± 0.091. Re-testing the same tattoo electrode pair after eight hours confirmed day-long stability without the need for recalibration. Statistical analysis revealed no significant differences in signal quality, also when applying assistive forces, between the two electrode types and across all muscles (RMSE, all p ≥ 0.3125; ρ, all p ≥ 0.1250), as well as no degradation after eight hours (RMSE and ρ: all p ≥ 0.0626, uncorrected). Finally, in a proof-of-concept session, BF activity measured with tattoo electrodes was found reliable to drive hip-extension assistance in real time. Collectively, these results show that tattoo electrodes deliver signal quality comparable to gel electrodes while offering a low-profile skin-conformal interface and day-long usability, making them a promising option for enhancing EMG-based control in wearable robots. Full article

The clinical effectiveness of clear orthodontic aligners mainly depends on the thermomechanical stability of the polymers in this challenging hydrothermal environment. In this study, we compare the water-induced viscoelastic changes and glass transition temperature (Tg) stability of four polymers with different microarchitectures. Specifically, we examined directly printed photopolymer networks (Tera Harz TC-85 and LuxCreo 4D Aligner), a monolithic thermoplastic (Duran+), and a multilayer thermoplastic (ClearCorrect). Samples were immersed in physiological saline (0.9 wt.% NaCl) at 37 °C for 7 days, and Dynamic Mechanical Analysis (DMA) was performed in three conditions: dry, after immersion, and after a 2 h desorption step, mimicking a typical clinical 22:2 wear cycle. All polymers showed a decrease in Tg after immersion, with TC-85 exhibiting the greatest reduction relative to the dry baseline. Tg recovery after a 2 h ambient desorption step was incomplete and was significantly associated with the amount of water retained after 2 h drying (expressed as % of initial uptake; R² = 0.419), whereas total water absorption after 7 days was not associated with short-term thermal recovery. Full article

Background: Corneal sensitivity is a key indicator of ocular surface health. This prospective, cross-sectional study evaluated agreement between corneal sensitivity thresholds obtained from equivalent stimulus settings on a contemporary, enhanced dual-temperature non-contact corneal aesthesiometer (NCCA) and a previously validated (standard) device. Methods: Central corneal sensitivity thresholds were measured in the right eyes of healthy participants using both devices. Participants with previous ocular surgery, laser treatment, trauma, contact lens wear, diabetes, or peripheral neuropathy were excluded. Sensitivity thresholds were determined using a forced-response, double-staircase protocol. Inter-device agreement was assessed using Bland–Altman analysis, and consistency was assessed using intraclass correlation coefficients. Results: Median corneal sensitivity thresholds in 51 healthy participants (32 female, 19 male; mean age: 33 ± 14 years) did not differ between enhanced (0.23 [0.18 to 0.38]) and standard (0.25 [0.15 to 0.35]) NCCA instruments (p = 0.73). Bland–Altman analysis demonstrated moderate inter-device agreement, with a mean difference of −0.01 mbar (95% limits of agreement: −0.41 to 0.39 mbar). Linear regression analysis identified greater measurement discrepancies at higher thresholds (p < 0.05), indicating greater variability in individuals with reduced corneal sensitivity. Conclusions: The enhanced NCCA yields reliable corneal sensitivity measures for a room-temperature stimulus and acceptable agreement with the existing (standard) model. Full article

TC4DT (ELI) is a damage-tolerant titanium alloy characterized by high fracture toughness and slow crack propagation rates, and is, therefore, considered one of the standard materials for model fasteners in modern equipment. However, its high yield strength leads to excessive tool wear and forming defects. This paper presents a complete FE simulation framework to investigate the thread-rolling process of TC4DT(ELI) bolts M16 × 1.5. Using the actual geometries of the workpiece and rollers, an elasto-plastic three-dimensional finite element model was built in ABAQUS/Explicit to perform verification simulations, with the theoretical blank diameter and forming force as the reference benchmarks. The simulation results agreed well with the actual industrial data. This study carried out single-factor analyses of the effect of three important process parameters—the roll speed, friction coefficient, and initial temperature—on the resulting stress–strain distribution, forming force, and thread formation depth. A modal analysis was performed in ANSYS Workbench to check the structural integrity and avoid resonance while operating. According to the results, the optimized parameters decreased the maximum forming force by 14.8% and improved thread filling. Compared with experimental data, the simulation error in the blank diameter was controlled within 1.2%. The present work, a reliable numerical underpinning for replacing expensive and time-consuming trial-and-error processes, forms a basis for high-performance titanium alloy fasteners and assists in the wider application of such fasteners in modern equipment and any advanced manufacturing industries. Full article

Although bio-hydrogenated diesel (BHD) offers drop-in compatibility and high oxidative stability, its poor lubricity remains a critical barrier to long-term engine deployment. Previous studies have primarily relied on short-term tribological assessments, leaving insufficient empirical data on sustained wear behavior under realistic conditions. This study addresses that gap through a 200 h durability evaluation of BHD–biodiesel blends in a single-cylinder diesel engine under constant load conditions per Thai Industrial Standard TIS 2618-2557. Five fuels, namely diesel, pure BHD, BHD90, BHD70, and pure biodiesel, were tested to identify the critical biodiesel threshold for optimal tribological and oxidative performance. BHD90 (90% BHD + 10% biodiesel) emerged as the optimal formulation, delivering the lowest torque reduction (11.2%) and minimal iron wear particles (101 ppm), while preserving oxidation stability. Biodiesel concentrations exceeding 10% induced accelerated lubricant oxidation through hygroscopic effects, negating the lubricity benefits. Fourier-transform infrared spectroscopy (FTIR) analysis of piston carbon deposits further revealed that higher biodiesel blends produced more oxygenated compounds, whereas pure BHD and diesel generated predominantly aliphatic hydrocarbons. These findings establish a mechanistic relationship between fuel composition, oxidation, and wear under endurance conditions, providing a practical guideline for renewable diesel formulation that balances lubrication performance, oxidation control, and long-term engine durability. Full article

Pin–bushing bearings in heavy-duty construction machinery operating in severe industrial environments are susceptible to accelerated wear, grease degradation, and lubrication failure, yet application-specific guidance for lubricant selection and re-greasing intervals under such conditions remains limited. This study evaluates the combined effects of bushing material (hardened steel, cast bronze, and Cu–Sn alloy), grease type (three commercially used greases with viscosities of 120, 460, and 150 mm²/s at 40 °C), and lubrication interval (8, 12, and 24 h) on grease-condition indicators in a field-operating wheel loader used in slag handling, where surrounding slag temperatures may reach 700–800 °C. A Taguchi L9 orthogonal array was used to define nine experimental configurations, each applied for approximately one week under real operating conditions. Grease samples were characterised using the SKF grease analysis kit based on NLGI consistency grade, base oil release rate, and contamination particle count. All greases showed an increase in NLGI grade from 2 to 3–4 during service, indicating thickening and a possible risk of lubrication channel blockage. Oil release rates decreased by up to 60% in some configurations, indicating reduced base oil mobility during service. When the three grease-condition indicators were evaluated together by Grey Relational Analysis, the combination of steel bushing, type B grease (ISO VG 460, lithium complex with MoS₂), and a 12 h lubrication interval showed the most balanced overall response. These findings provide field-based guidance for grease selection and maintenance scheduling in pin–bushing systems operating under demanding service conditions. Full article