Search Results (2,306)

Background: Ambient yoghurt, also known as room-temperature yoghurt, has gained increasing attention due to its convenience in distribution and consumption without needing cold storage. To ensure extended shelf life, ambient yoghurt normally undergoes an additional heat treatment during manufacturing, the post-fermentation sterilisation process (typically at 65–85 °C), which may induce the formation of fine particle aggregates and result in undesirable textural attributes, particularly graininess. Assessing textural attributes of such products remains a challenge. Methods: By mimicking the oral behaviour of ambient yoghurt, this study uses rheological as well as tribological techniques for objective assessment of the textural sensations of slipperiness and graininess. Various experimental conditions, including the amount of saliva incorporation, sliding speed, and ball-contact and plate-contact lubrication, were examined, and results were analysed against perceived texture by panellists. Main findings: The results indicate that viscosity changes are closely associated with perceived slipperiness under the tested conditions. The friction coefficient obtained from a plate-contact tribometer shows a positive correlation with the sensation of graininess (Pearson’s r was 0.74, p < 0.05, N = 8). It was also observed that a 20% saliva incorporation showed the closest agreement with sensory perception, although this observation should be interpreted cautiously due to the limited sample size. Implications: Results obtained from this work indicate the feasibility of using rheology and tribology techniques for texture prediction in ambient yoghurt. The findings are exploratory in nature, and further studies with larger sample sets are required to validate the proposed approach. The methodology presented here may serve as a reference framework for investigating texture perception in other dairy systems. Full article

This study addresses a key limitation in meso-scale discrete element modeling (DEM) of ultra-high performance concrete (UHPC). Most existing DEM frameworks rely on extensive macroscopic calibration and do not provide a clear, transferable pathway to derive contact law parameters from measurable micro-scale properties, limiting reproducibility and physical interpretability. To bridge this gap, we develop and validate a micro-indentation-informed, poromechanics-consistent calibration framework that links UHPC phase-level micromechanical measurements to a flat-joint DEM contact model for predicting uniaxial compression, direct tension, and flexural response. Elastic moduli and Poisson’s ratios of the constituent phases are obtained from micro-indentation and homogenization relations, while cohesion (c) and friction angle (α) are inferred through a statistical treatment of the indentation modulus and hardness distributions. The tensile strength limit (σₜ) is identified by matching the simulated flexural stress–strain peak and post-peak trends using a parametric set of (c, α, σₜ) combinations. The resulting DEM model reproduces the measured UHPC responses with strong agreement, capturing (i) compressive stress–strain response, (ii) flexural stress–strain response, and (iii) tensile stress–strain response, while also recovering the experimentally observed failure modes and damage localization patterns. These results demonstrate that physically grounded micro-scale measurements can be systematically upscaled to meso-scale DEM parameters, providing a more efficient and interpretable route for simulating UHPC and other porous cementitious composites from indentation-based inputs. Full article

Background: Implant material may influence interfragmentary mechanics in medial malleolar (MM) fracture fixation. This study aimed to compare stainless steel, titanium, magnesium, and PLGA screws under identical conditions using finite element analysis (FEA). Methods: A CT-based ankle model with a unilateral oblique MM fracture (θ = 60° to the medial tibial plafond) was fixed with two parallel M4 × 35 mm screws placed perpendicular to the fracture plane (inter-axial distance 13 mm). Contacts were defined as nonlinear frictional, and each screw was assigned a pretension force of 2.5 N. Static single-leg stance was simulated with physiologic tibia/fibula load sharing. Four scenarios differed only by screw material. Primary outputs were interfragmentary micromotion (maximum sliding and gap). Secondary measures included fracture interface contact/frictional stresses, screw/bone von Mises stress, global construct displacement, and average tibiotalar cartilage contact pressure. Results: Interfragmentary micromotion increased as screw stiffness decreased. Maximum sliding was 32.2–33.8 µm with stainless steel/titanium, 40.4 µm with magnesium, and 65.0 µm with PLGA; corresponding gaps were 31.2–32.0 µm with stainless steel and titanium, 31.2 µm with magnesium, and 54.1 µm with PLGA, respectively. Interface stresses followed the same pattern: contact pressure (3.18–3.24 MPa for stainless steel/titanium/magnesium vs. 4.29 MPa for PLGA); frictional stress (1.46–1.49 MPa vs. 1.98 MPa). Peak screw von Mises stress was highest in stainless steel (104.1 MPa), then titanium (73.4 MPa), magnesium (47.4 MPa), and PLGA (17.9 MPa). Global axial displacement (0.26–0.27 mm) and average tibiotalar cartilage contact pressure (0.73–0.75 MPa) were essentially unchanged across materials. All conditions remained below commonly cited thresholds for primary bone healing (gap < 100 µm); however, PLGA exhibited a reduced safety margin. Conclusions: Under identical geometry and loading conditions, titanium and stainless steel yielded the most favorable interfragmentary mechanics for oblique MM fixation; magnesium showed intermediate performane, and PLGA produced substantially greater micromotion and interface stresses. These findings support the use of metallic screws when maximal initial stability is required and suggest that magnesium may be a selective alternative when reducing secondary implant removal is prioritized. Full article

Modern power transmission systems are required to meet increasingly stringent demands, including a wide range of transmission ratios, compact dimensions, high precision, energy efficiency, reliability, and thermal stability under dynamic operating conditions. Among the solutions that satisfy these requirements, cycloidal reducers are particularly prominent, with their application continuously expanding in industrial robotics, computer numerical control (CNC) machines, and military and transportation systems, as well as in the satellite industry. However, as with all mechanical power transmissions, friction in the contact zones of load-carrying elements in cycloidal reducers leads to power losses and an increase in operating temperature, which in turn results in a range of adverse effects. These undesirable phenomena strongly depend on lubrication conditions, namely on the type and properties of the applied lubricant. Although manufacturers’ catalogs provide general recommendations for lubricant selection, they do not address the fundamental tribological mechanisms in the most heavily loaded contact pairs. At the same time, the available scientific literature reveals a significant lack of systematic and experimentally validated studies examining the influence of lubricant type on the energetic and thermal performance of cycloidal reducers. To address this identified research gap, this study presents an analytical and experimental investigation of the effects of different lubricant types—primarily greases and mineral oils—on the thermal stability and efficiency of cycloidal reducers. The results demonstrate that grease lubrication provides lower total power losses and a more stable thermal operating regime compared to oil lubrication, while oil film thickness analyses indicate that the most unfavorable lubrication conditions occur in the contact between the eccentric bearing rollers and the outer raceway. These findings provide valuable guidelines for engineers involved in cycloidal reducer design and lubricant selection under specific operating conditions, as well as deeper insight into the lubricant behavior mechanisms within critical contact zones. Full article

Chromium-doped diamond-like carbon (DLC-Cr) nanocomposite films were successfully deposited using a high-power impulse magnetron sputtering (HiPIMS) system. The Cr content in the films was controlled by adjusting the Cr target powers. The influence of Cr content on the microstructure, mechanical properties, tribological performance, and wettability of the films was systematically investigated. The results show that the Cr content and deposition rate of the films increased with increases in the target power. The surface topography of the films evolved from smooth to rough as the Cr target increased from 10 W to 70 W. At low Cr doping rates, the film mainly exhibited an amorphous structure, whereas the nanocomposite structure was formed at proper Cr doping rates. Raman and XPS analyses revealed that Cr incorporation altered the I_D/I_G ratio and promoted the formation of Cr-C bonds, leading to a more graphitic and nanocomposite-like structure. The nanoindentation results show that an optimal Cr content enhances both hardness and elastic modulus, while higher Cr concentrations lead to a decline in mechanical strength due to more graphitization and decreasing stress. Tribological tests exhibited a significant reduction in the friction coefficient (0.21) and wear rate (0.63 × 10⁻¹⁴ m³/N·m) at a moderate Cr level. Additionally, the surface wettability evolved toward enhanced hydrophilicity with increasing Cr power, as evidenced by reduced water contact angles and increased surface energy. These findings demonstrate that controlled Cr incorporation effectively tailors the structure, stress state, and surface chemistry of DLC films, offering a tunable pathway to achieving optimal mechanical performance and tribological stability for advanced engineering applications. Full article

Rubber materials undergo continuous wear in high-pressure seal applications. To address the risk of adhesive wear and consequent leakage of rubber seals operating under reciprocating sliding in high-pressure hydrogen storage and refueling systems, this study employed high-pressure hydrogen tribology testing. Ball-on-disk reciprocating tests were conducted using a 316L stainless-steel ball against silica-filled nitrile butadiene rubber (NBR), and the friction response and wear-morphology evolution were compared under ambient air, 1 MPa hydrogen (H₂), 50 MPa H₂, 50 MPa nitrogen (N₂), and grease-coated conditions. Under dry sliding, the coefficient of friction (COF) of NBR in air and hydrogen ranged from 1.34 to 1.44, whereas it decreased markedly to 0.942 in 50 MPa N₂. The wear volume under the four dry conditions was concentrated in the range of ~0.292–0.320 mm³. After grease coating, the steady-state COF in air and at 50 MPa H₂ dropped to 0.099 and 0.105, respectively, and the wear features changed from ridge-like wear patterns/tear pits to regular, smooth indentations with slight running marks. The results demonstrate that a lubricating film can effectively separate direct metal–rubber contact and suppress stick–slip, enabling a low-friction, low-wear, and highly stable interface in high-pressure hydrogen, and providing a practical engineering route for reliable operation of rubber seals in hydrogen service. Full article

The rocket sled slider is a key connection component between the rocket sled and the track for support, guidance and load-bearing, ensuring the system’s safe and reliable operation. Wear of sliders under high—velocity and heavy—load conditions is crucial for equipment reliability. This study establishes a wear prediction model for sled rails using ANSYS, incorporating a dimensionless acceleration factor into the simulation. By analyzing dynamic characteristics of contact friction stress, wear volume, depth, and stress over time, the tribological characteristics of 30CrMnSiNi2A steel sliders were studied. The simulation results showed that during dry—friction sliding, slider wear is highly related to speed and load, increasing significantly as they increase. The slider’s contact surface has non-uniform stress distribution with stress concentration and gradient changes. Quantitative analysis has revealed that friction stress is positively correlated with load, and its sensitivity to speed changes is high at low speeds and relatively low at high speeds. Full article

Accurate prediction of the rocking and sliding response of free-standing rigid blocks under seismic excitation remains challenging, particularly in regimes where rocking and sliding are strongly coupled and motion mode transitions occur. This study presents a modified semi-analytical framework and an optimized Finite Element Method (FEM) approach to investigate the nonlinear dynamics of rigid rectangular blocks subjected to initial angular displacements, assuming Coulomb friction and near-inelastic impacts. The proposed semi-analytical formulation explicitly captures the coupling between rocking and sliding motions, enabling systematic identification of rest, rocking, sliding, rocking–sliding, and free-flight response modes. Benchmark comparisons with Veeraraghavan’s classical model show overall agreement in limiting cases but reveal notable differences in intermediate regimes, where motion mode transitions are highly sensitive to friction coefficient and slenderness ratio. These discrepancies arise from the ability of the present formulation to resolve transitional rocking–sliding behavior that is not fully represented in uncoupled or limiting-case assumptions. Complementary FEM simulations employing both rigid and deformable body representations further elucidate the role of contact modeling and energy dissipation. While rigid-body FEM models offer computational efficiency, they exhibit localized penetration and residual bouncing due to contact enforcement limitations. In contrast, deformable FEM models more closely approximate near-inelastic collision behavior and dissipate impact energy more effectively, albeit at higher computational cost. The combined semi-analytical and FEM results provide a robust framework for interpreting motion mode transitions, quantifying contact and penetration effects, and defining the applicability limits of simplified rigid-body models. These findings offer practical guidance for selecting appropriate modeling strategies for seismic response assessment of free-standing rigid blocks. Full article

Aiming at analyzing the load characteristics and friction torque of triple-row hub bearings for new energy vehicles, this work established a comprehensive theoretical and experimental methodology for predicting the internal load distribution and friction torque. Firstly, considering the preload effect via an initial negative clearance, deformation coordination and force balance equations for the triple-row bearing under axial load were formulated, to analyze the external loads under various driving conditions. Based on contact deformation theory, a quasi-static model was developed to combine radial, axial, and moment loads. The Newton–Raphson iterative algorithm was employed to solve the ball load distribution equations, and the correctness was verified by using the finite element method. Furthermore, accounting for the elastic hysteresis, differential sliding, and spin sliding, the theoretical models for friction torque components were established, to investigate the influence of structural parameters and the total friction torque under different driving conditions. Finally, to confirm the effectiveness and the precision of the model, a finite element simulation and experimental measurements of friction torque were conducted, respectively, which showed good agreement with theoretical calculations. The main innovations include proposing a mechanical modeling method for triple-row hub bearings that accounts for preload effects, and establishing an integrated friction torque analysis model applicable to multiple driving conditions. This work provides theoretical support and a methodological foundation for the design of next-generation hub bearings for new energy vehicles. Full article

This study addresses the issues with traditional rolling protection bearings in vertical magnetic levitation flywheel energy storage systems (FESSs), which are prone to impact, wear, and temperature rise under abnormal conditions, such as drops. It designed a permanent magnet axial protection bearing based on a Halbach array, utilizing N42SH permanent magnet material. The five-layer Halbach array achieved a maximum axial magnetic force of 86 KN and a maximum air gap magnetic flux density of 2.2 T, meeting the application requirements. Simulation results, combined with rotor drop dynamics and thermal analysis, show that under an 8000 rpm drop condition, the permanent magnet bearing reduces radial and axial contact forces by approximately 60% and 54%, respectively, and wear by around 70%. Additionally, the maximum system temperature decreases from 109 °C to 74 °C, with a 32% reduction in temperature rise. Friction experimental analysis indicates that low frequency, low load, and moderate temperatures improve friction stability and reduce wear. Overall, the permanent magnet axial protective bearing effectively mitigates drop impact, reduces friction heat and wear, and enhances the safety and reliability of the flywheel energy storage system under abnormal working conditions, providing valuable theoretical support and a design reference for engineering applications. Full article

Fiber laser surface texturing was applied to AA1050 aluminum to improve friction and wear performance of PTFE coatings. A Taguchi L16 design varied texture geometry (square, diamond, hexagon, circle), scanned area ratio (20% to 80%), and laser power (40 to 100 W) prior to primer plus PTFE topcoat deposition (25 to 35 µm). Dry reciprocating sliding against a 6 mm 100Cr6 ball was conducted at 20 N, 1 Hz, and 50 m, and wear track geometry was measured by non-contact profilometry. The non-textured reference exhibited an average COF of 0.143, whereas the lowest mean COF was achieved with diamond 60% and 40 W (0.095) and the highest with hexagon 60% and 100 W (0.156); hexagon 20% and 60 W matched the reference. ANOVA indicated scanned area ratio as the dominant contributor to COF (39.72%), followed by geometry (35.07%) and power (25.21%). Profilometry confirmed reduced coating penetration for optimized textures: the reference wear track was approximately 1240 µm wide and 82 µm deep, compared with 930 µm and 34 µm for square 80% and 40 W, 997 µm and 39 µm for diamond 60% and 40 W, and 965 µm and 36 µm for hexagon 40% and 40 W. Full article

Vulcanized NR-SBR is widely used in vehicle components; however, its irreversible crosslinking limits recyclability and contributes to the large number of tires discarded annually worldwide, and in this context, this work presents an experimental comparative assessment of the tribological behavior of conventional tire rubber and silicone VMQ, motivated by a wheel concept based on a detachable tread aimed at improving durability and sustainability rather than proposing an immediate material substitution. Wear and friction behavior were investigated under abrasive and self-friction conditions using pin-on-disk testing with an abrasive counterpart representative of asphalt, supported by optical and scanning electron microscopy. The results show that NR-SBR undergoes severe abrasive and erosive wear, characterized by deep and irregular wear tracks, pronounced fluctuations in the dynamic friction coefficient, and strong sensitivity to load and sliding speed, particularly during the initial stages of track formation. In contrast, VMQ exhibits mild abrasive wear dominated by viscoelastic deformation, leading to shallow and stable wear tracks, lower friction coefficients, and significantly reduced material loss once the contact track is fully developed. These differences are attributed to the distinct mechanical responses of the elastomers, as the higher hardness and limited strain capacity of rubber promote micro-tearing and unstable material removal, while the high elasticity of silicone enables stress redistribution and stable contact conditions under abrasive loading. UV aging increases stiffness of rubber, resulting in reduced wear and friction, while silicone remains largely unaffected after 750 h due to the stability of its Si–O–Si backbone. Self-friction tests further indicate that smooth silicone sliding against rubber yields the lowest friction values, highlighting a favorable material pairing for detachable tread concepts. Factorial design analysis confirms material type as the dominant factor influencing both wear and friction. Overall, for the specific materials and operating conditions investigated, VMQ demonstrates higher durability, greater tribological stability, and improved aging resistance compared to NR-SBR, providing experimental evidence that supports its potential for long-life, more sustainable detachable tread applications. Full article

This study conducts systematic experimental and numerical investigations to address the parameter calibration issue in the discrete element model of seashells, aiming to establish a high-fidelity numerical model that accurately characterizes their macroscopic mechanical behavior, thereby providing a basis for optimizing parameters of seashell crushing equipment. Firstly, intrinsic parameters of seashells were determined through physical experiments: density of 2.2 kg/m³, Poisson’s ratio of 0.26, shear modulus of 1.57 × 10⁸ Pa, and elastic modulus of 6.5 × 10¹⁰ Pa. Subsequently, contact parameters between seashells and between seashells and 304 stainless steel, including static friction coefficient, rolling friction coefficient, and coefficient of restitution, were obtained via the inclined plane method and impact tests. The reliability of these contact parameters was validated by the angle of repose test, with a relative error of 5.1% between simulation and measured results. Based on this, using ultimate load as the response indicator, the PlackettBurman experimental design was employed to identify normal stiffness per unit area and tangential stiffness per unit area as the primary influencing parameters. The Bonding model parameters were then precisely calibrated through the steepest ascent test and design, resulting in an optimal parameter set. The error between simulation results and physical experiments was only 3.8%, demonstrating the high reliability and accuracy of the established model and parameter calibration methodology. Full article

The accurate calculation of gear time-varying mesh stiffness is of significant importance for the dynamic modeling of gear systems. Currently, research on calculation methods for helical gear mesh stiffness is relatively limited, with the primary approaches being finite element methods and analytical methods. This paper proposes an optimized helical gear meshing stiffness model. Building upon the slice potential method, this approach comprehensively accounts for the effects of tooth-surface friction and local contact deformation. Results indicate that tooth surface friction causes abrupt changes in meshing stiffness values, while local contact deformation leads to an overall decrease in meshing stiffness values. To validate the application value of the optimized calculation method, the contact line method was replaced with the optimized slice potential energy method for simulating the external sound field of locomotive traction transmission systems. Comparisons with actual measurement data revealed that the sound pressure level data from this study’s meshing stiffness model align more closely with experimental results than those from the contact line method model, with the maximum error decreasing from 5% to 2.2%, effectively enhancing the accuracy of the rapid modeling method. Full article

For long horizontal-section drilling in reservoirs and complex formations, efficient and robust trajectory planning with real-time closed-loop control must be achieved under curvature and mechanical constraints. This study systematically investigates the application of the Dubins curve, a shortest-path model satisfying a minimum curvature constraint, in closed-loop wellbore trajectory control. Six canonical configurations (LSL, RSR, LSR, RSL, LRL, and RLR) are analyzed, and a standardized procedure for path solution and coordinate reconstruction is established. Parametric analyses reveal the effects of curvature limit, target direction, and target distance on trajectory feasibility and path length. Case studies show that unoptimized Dubins trajectories can achieve a high reservoir-contact ratio (99.69%) but exhibit curvature discontinuities at segment junctions, which induce torque and friction peaks. By introducing a multi-objective optimization strategy combining minimum turning-radius expansion and adaptive target adjustment, these curvature discontinuities are effectively mitigated: the maximum curvature was reduced to 11.15°/30 m, the average curvature to 2.57°/30 m, the average friction to 1118.7 N, and the cumulative torque to 31,468 Nm, while maintaining nearly unchanged reservoir contact. The proposed method effectively improves trajectory smoothness and mechanical drillability while preserving real-time computational efficiency, offering a practical approach for closed-loop trajectory optimization in complex geological settings. Full article