86,828 results on '"Friction"'
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2. Quantum rates in dissipative systems with spatially varying friction.
- Author
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Bridge, Oliver, Lazzaroni, Paolo, Martinazzo, Rocco, Rossi, Mariana, Althorpe, Stuart C., and Litman, Yair
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CLASSICAL mechanics , *MOLECULAR dynamics , *LOW temperatures , *HIGH temperatures , *FRICTION - Abstract
We investigate whether making the friction spatially dependent on the reaction coordinate introduces quantum effects into the thermal reaction rates for dissipative reactions. Quantum rates are calculated using the numerically exact multi-configuration time-dependent Hartree method, as well as the approximate ring-polymer molecular dynamics (RPMD), ring-polymer instanton methods, and classical molecular dynamics. By conducting simulations across a wide range of temperatures and friction strengths, we can identify the various regimes that govern the reactive dynamics. At high temperatures, in addition to the spatial-diffusion and energy-diffusion regimes predicted by Kramer's rate theory, a (coherent) tunneling-dominated regime is identified at low friction. At low temperatures, incoherent tunneling dominates most of Kramer's curve, except at very low friction, when coherent tunneling becomes dominant. Unlike in classical mechanics, the bath's influence changes the equilibrium time-independent properties of the system, leading to a complex interplay between spatially dependent friction and nuclear quantum effects even at high temperatures. More specifically, a realistic friction profile can lead to an increase (or decrease) of the quantum (classical) rates with friction within the spatial-diffusion regime, showing that classical and quantum rates display qualitatively different behaviors. Except at very low frictions, we find that RPMD captures most of the quantum effects in the thermal reaction rates. [ABSTRACT FROM AUTHOR]
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- 2024
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3. Observation of the early stages of environmental contamination in graphene by friction force.
- Author
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Almeida, Clara M., Ptak, Felipe, and Prioli, Rodrigo
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GRAPHENE , *FRICTION , *POLLUTANTS , *SURFACE area - Abstract
Exposure to ambient air contaminates the surface of graphene sheets. Contamination may arise from different sources, and its nature alters the frictional behavior of the material. These changes in friction enable the observation of the early stages of contaminants' adsorption in graphene. Using a friction force microscope, we show that molecular adsorption initiates at the edges and mechanical defects in the monolayer. Once the monolayer is covered, the contaminants spread over the additional graphene layers. With this method, we estimate the contamination kinetics. In monolayer graphene, the surface area covered with adsorbed molecules increases with time of air exposure at a rate of 10−14 m2/s, while in bilayer graphene, it is one order of magnitude smaller. Finally, as the contaminants cover the additional graphene layers, friction no longer has a difference concerning the number of graphene layers. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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4. Hydrodynamic slip characteristics of shear-driven water flow in nanoscale carbon slits.
- Author
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Shuvo, Abdul Aziz, Paniagua-Guerra, Luis E., Yang, Xiang, and Ramos-Alvarado, Bladimir
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RHEOLOGY , *MOLECULAR dynamics , *INTERFACIAL friction , *ELECTRONIC structure , *VISCOSITY , *FRICTION - Abstract
This paper reports on the effects of shear rate and interface modeling parameters on the hydrodynamic slip length (LS) for water–graphite interfaces calculated using non-equilibrium molecular dynamics. Five distinct non-bonded solid–liquid interaction parameters were considered to assess their impact on LS. The interfacial force field derivations included sophisticated electronic structure calculation-informed and empirically determined parameters. All interface models exhibited a similar and bimodal LS response when varying the applied shear rate. LS in the low shear rate regime (LSR) is in good agreement with previous calculations obtained through equilibrium molecular dynamics. As the shear rate increases, LS sharply increases and asymptotes to a constant value in the high shear regime (HSR). It is noteworthy that LS in both the LSR and HSR can be characterized by the density depletion length, whereas solid–liquid adhesion metrics failed to do so. For all interface models, LHSR calculations were, on average, ∼28% greater than LLSR, and this slip jump was confirmed using the SPC/E and TIP4P/2005 water models. To address the LS transition from the LSR to the HSR, the viscosity of water and the interfacial friction coefficient were investigated. It was observed that in the LSR, the viscosity and friction coefficient decreased at a similar rate, while in the LSR-to-HSR transition, the friction coefficient decreased at a faster rate than the shear viscosity until they reached a new equilibrium, hence explaining the LS-bimodal behavior. This study provides valuable insights into the interplay between interface modeling parameters, shear rate, and rheological properties in understanding hydrodynamic slip behavior. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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5. Transferable local density-dependent friction in tert-butanol/water mixtures.
- Author
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Mathes, Moritz, Klippenstein, Viktor, and van der Vegt, Nico F. A.
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FRICTION , *LANGEVIN equations , *MOLECULAR dynamics , *PARTICLE dynamics , *PSEUDOPOTENTIAL method - Abstract
Coarse-grained (CG) models informed from molecular dynamics simulations provide a way to represent the structure of an underlying all-atom (AA) model by deriving an effective interaction potential. However, this leads to a speed-up in dynamics due to the lost friction, which is especially pronounced in CG implicit solvent models. Applying a thermostat based on the Langevin equation (LE) provides a way to represent the long-time dynamics of CG particles by reintroducing friction to the system. To improve the representability of CG models of heterogeneous molecular mixtures and their transferability over the mixture compositions, we parameterize an LE thermostat in which the friction coefficient depends on the local particle density (LD). The thermostat friction was iteratively optimized with a Markovian variant of the recently introduced Iterative Optimization of Memory Kernels (IOMK) method. We simulated tert-butanol/water mixtures over a range of compositions, which show a distinct clustering behavior. Our model with LD-dependent friction reproduces the AA diffusion coefficients well over the full range of mixtures and is, therefore, transferable with respect to dynamics. [ABSTRACT FROM AUTHOR]
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- 2024
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6. Exploration of Stokes hydrodynamic law at molecular length scales.
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Acharya, Subhajit and Bagchi, Biman
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MOLECULAR force constants , *FRICTION , *COMPUTER simulation , *MEASUREMENT of viscosity , *SOLVENTS - Abstract
The celebrated generalized Stokes law predicts that the velocity of a particle pulled through a liquid by an external force, Fex, is directly proportional to the force and inversely proportional to the friction ζ acted by the medium on the particle. We investigate the range of validity of the generalized Stokes law at molecular length scales by employing computer simulations to calculate friction by pulling a tagged particle with a constant force. We thus calculate friction for two model interaction potentials, Lennard-Jones and soft sphere, for several particle sizes, ranging from radius (a) smaller than the solvent particles to three times larger. We next obtain friction from diffusion (D) by using Einstein's relation between diffusion and friction ζ in an unperturbed liquid. We find a quantitative agreement between the two at a small-to-intermediate pulling force regime for all the sizes studied. The law does break down at a large pulling force beyond a threshold value. Importantly, the range of validity of Stokes' scheme to obtain friction increases substantially if we turn off the attractive part of the interaction potential. Additionally, we calculate the viscosity (η) of the unperturbed liquid and find a good agreement with the Stokes–Einstein relation ζ = Cηa for the viscosity dependence with a value of C close to 5 π, which is intermediate between the slip and stick boundary condition. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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7. A review on application areas and surface geometry in superhydrophobic materials
- Author
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Akinci, Serhat, Karaomerlioglu, Filiz, and Kaygusuz, Emre
- Published
- 2024
8. Two-state model of energy dissipation at metal surfaces.
- Author
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Tully, John C.
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ENERGY dissipation , *CHEMICAL kinetics , *CONDUCTION electrons , *METALLIC surfaces , *MOLECULAR dynamics , *FRICTION - Abstract
The rates and pathways of chemical reactions at metal surfaces can be strongly influenced by energy dissipation due to the nonadiabatic excitation of metallic conduction electrons. The introduction of frictional forces to account for this dissipation has been quite successful in situations for which the nonadiabatic coupling is weak. However, in cases where nonadiabatic coupling is strong, such as when electron transfer occurs, the friction model is likely to break down. Ryabinkin and Izmaylov have proposed 2-state and 3-state alternatives to the friction model for introducing electronic dissipation in molecular dynamics simulations. Here, we examine their 2-state model using some simple examples of atom–surface scattering. We find that, with the addition of decoherence, the 2-state model can produce quite promising results. [ABSTRACT FROM AUTHOR]
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- 2024
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9. Electronic friction near metal surface: Incorporating nuclear quantum effect with ring polymer molecular dynamics.
- Author
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Bi, Rui-Hao and Dou, Wenjie
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METALLIC surfaces , *QUANTUM rings , *QUANTUM theory , *GROUND state energy , *FRICTION , *MOLECULAR dynamics - Abstract
The molecular dynamics with electronic friction (MDEF) approach can accurately describe nonadiabatic effects at metal surfaces in the weakly nonadiabatic limit. That being said, the MDEF approach treats nuclear motion classically such that the nuclear quantum effects are completely missing in the approach. To address this limitation, we combine Electronic Friction with Ring Polymer Molecular Dynamics (EF-RPMD). In particular, we apply the averaged electronic friction from the metal surface to the centroid mode of the ring polymer. We benchmark our approach against quantum dynamics to show that EF-RPMD can accurately capture zero-point energy as well as transition dynamics. In addition, we show that EF-RPMD can correctly predict the electronic transfer rate near metal surfaces in the tunneling limit as well as the barrier crossing limit. We expect that our approach will be very useful to study nonadiabatic dynamics near metal surfaces when nuclear quantum effects become essential. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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10. Plasma density distribution and its perturbation by probes in axially symmetrical plasma.
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Godyak, Valery and Sternberg, Natalia
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PLASMA density , *CYLINDRICAL plasmas , *PLASMA oscillations , *FRICTION , *PLASMA gases , *MICROWAVE plasmas - Abstract
An analysis of plasma density distributions at arbitrary ion–atom collisionality for one-dimensional axially symmetrical cylindrical and annular plasmas is presented. Perturbations of plasma densities caused by a cylindrical probe are studied for arbitrary ion–atom collisionality. Analytical expressions for the plasma characteristics near the probe for low collisionality have been obtained. The plasma was modeled by the hydrodynamic neutral plasma equations, taking into account ionization, ion inertia, and a non-linear ion frictional force, which dominates the plasma transport at low gas pressures. Significant plasma density depletion around the probe has been observed for a wide range of ion–atom collisionality. The presented results predict underestimation of plasma density obtained from the classical Langmuir probe procedure and should provide a better understanding of electrostatic, magnetic, and microwave probes inserted into plasmas at low gas pressure. [ABSTRACT FROM AUTHOR]
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- 2024
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11. Verification of modulation mechanism of the interfacial dipole effect by changing the stacking sequence of monatomic layers in perovskite oxides.
- Author
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Tamura, Atsushi and Kita, Koji
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EPITAXIAL layers , *FRICTION , *LATERAL loads , *IMAGE analysis , *SURFACE forces - Abstract
The magnitude of the dipole effect detected by the cutoff energy measurement was modulated for SrTiO3 (STO)/LaAlO3 (LAO)/SrRuO3 (SRO)/STO (001) subs. epitaxial stacks by ultrathin SrAlOx (SAO) insertion prior to LAO deposition. The difference in frictional forces on the LAO surfaces between the stacks with and without SAO insertion was clearly detected by lateral force microscopy (LFM), which indicated the change in dominating surface atomic layers. From the statistical analysis of LFM images, the SAO insertion was found to improve the lateral uniformity of the stacking sequence of charged monatomic layers in epitaxial LAO along the c-axis [(LaO)+ and (AlO2)−], taking account of the inevitable correlation between the surface-terminating atoms with the stacking sequence of the charged monatomic layers in epitaxial LAO. These results are consistently explainable with the proposed model that the interface dipole effect along the c-axis of the perovskite epitaxial stack is determined by the stacking sequence of charged monatomic layers of LAO. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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12. Influence of friction on the packing efficiency and short-to-intermediate range structure of hard-sphere systems.
- Author
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Tang, Jiajun, Wen, Xiaohui, Zhang, Zhen, Wang, Deyin, Huang, Xinbiao, and Wang, Yujie
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RADIAL distribution function , *FRICTION , *SPHERE packings , *SPHERES , *STATISTICAL correlation , *FACTOR structure - Abstract
Using particle-resolved computer simulations, we investigate the effect of friction on the packing structure of hard-sphere mixtures with two kinds of particles under external compression. We first show that increasing friction between the particles results in a more disordered and less efficient packing of the local structure on the nearest neighbor scale. It is also found that standard two-point correlation functions, i.e., radial distribution function and static structure factor, show basically no detectable changes beyond short-range distances upon varying inter-particle friction. Further analysis of the structure using a four-point correlation method reveals that these systems have on the intermediate-range scale a three-dimensional structure with an icosahedral/dodecahedral symmetry that exhibits a pronounced dependence on friction: small friction gives rise to an orientational order that extends to larger distances. Our results also demonstrate that composition plays a role in that the degree of structural order and the structural correlation length are mainly affected by the friction coefficients associated with the more abundant species. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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13. Inferring free-energy barriers and kinetic rates from molecular dynamics via underdamped Langevin models.
- Author
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Girardier, David Daniel, Vroylandt, Hadrien, Bonella, Sara, and Pietrucci, Fabio
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LANGEVIN equations , *CONDENSED matter , *MOLECULAR dynamics , *CHEMICAL reactions , *PHASE transitions , *FRICTION - Abstract
Rare events include many of the most interesting transformation processes in condensed matter, from phase transitions to biomolecular conformational changes to chemical reactions. Access to the corresponding mechanisms, free-energy landscapes and kinetic rates can in principle be obtained by different techniques after projecting the high-dimensional atomic dynamics on one (or a few) collective variable. Even though it is well-known that the projected dynamics approximately follows – in a statistical sense – the generalized, underdamped or overdamped Langevin equations (depending on the time resolution), to date it is nontrivial to parameterize such equations starting from a limited, practically accessible amount of non-ergodic trajectories. In this work we focus on Markovian, underdamped Langevin equations, that arise naturally when considering, e.g., numerous water-solution processes at sub-picosecond resolution. After contrasting the advantages and pitfalls of different numerical approaches, we present an efficient parametrization strategy based on a limited set of molecular dynamics data, including equilibrium trajectories confined to minima and few hundreds transition path sampling-like trajectories. Employing velocity autocorrelation or memory kernel information for learning the friction and likelihood maximization for learning the free-energy landscape, we demonstrate the possibility to reconstruct accurate barriers and rates both for a benchmark system and for the interaction of carbon nanoparticles in water. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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14. Dynamics of Tribofilm Formation in Boundary Lubrication Investigated Using In Situ Measurements of the Friction Force and Contact Voltage.
- Author
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Tsai, Anna and Komvopoulos, Kyriakos
- Subjects
additives ,blend formulations ,boundary lubrication ,contact voltage ,dispersants ,friction ,tribofilms ,zinc dialkyl dithiophosphate - Abstract
The complex dynamics of tribofilm formation on boundary-lubricated steel surfaces were investigated in real time by combining in situ measurements of the temporal variation of the coefficient of friction and contact voltage. Sliding experiments were performed with various blends consisting of base oil, zinc dialkyl dithiophosphate (ZDDP) additive, and two different dispersants at an elevated oil temperature for a wide range of normal load and fixed sliding speed. The evolution of the transient and steady-state coefficient of friction, contact voltage, and critical sliding distance (time) for stable tribofilm formation were used to evaluate the tribological performance of the tribofilms. The blend composition affected the load dependence of the critical sliding distance for stable tribofilm formation. Tribofilm friction was influenced by competing effects between the additive and the dispersants. Among various formulations examined, the tribofilm with the best friction characteristics was found to be the blend consisting of base oil, a small amount of ZDDP, and a bis-succinimide dispersant treated with ethylene carbonate. The results of this study demonstrate the effectiveness of the present experimental approach to track the formation and removal of protective tribofilms under boundary lubrication conditions in real time.
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- 2024
15. 表面激光熔覆改性技术减摩抗阻特性的研究.
- Author
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张亚超, 王海军, and 陈文刚
- Abstract
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- Published
- 2024
16. Improvement of microhardness property by novel hash pattern welding of EN10083 steel compared to present technique of friction welding.
- Author
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Vishal, A., Pradeep, A., and Thiruchelvam, V.
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FRICTION welding , *STEEL welding , *FRICTION , *VICKERS hardness , *NUMERICAL control of machine tools - Abstract
In order to improve microhardness qualities, the article compares the traditional friction welding approach with the innovative hash pattern friction welding of EN 10083 steel. In total, two groups commercial and hash pattern friction welding were used in the study. There are sixteen pieces of work in each category. The dimension of the material is 30 mm in diameter and 60 mm in length. It is then welded by a CNC machine with care, and the micro-Vickers hardness tester is used to specify the microhardness of it. This process has a G power of 80%, and the sample size is calculated using α = 0.05 per set and the total sample size calculated is 32. Time, temperature, frictional force, and spindle speed are taken into consideration for results that have Z-pattern friction welding or commercial friction welding with increased microhardness. Between two groups, there were statistically significant differences since the significant value of p=0.000 (2-tailed), which is less than (P<0.05). The hash pattern friction welding has a 5.6% higher microhardness than standard friction welding (571>539) HV. Because of the increased frictional temperature caused by the pattern in the workpiece, the metallurgical bonding was strong enough to have greater Microhardness. The results of this experiment indicate that, although commercial friction welding has a Vickers hardness of 539 HV at 1400 rpm, 5.5ton, 4mm depth of penetration, and 25 seconds, hash pattern friction welding's hardness of 571 HV. [ABSTRACT FROM AUTHOR]
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- 2024
- Full Text
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17. Turbulent thermal-hydraulic performance of nanofluid in circular and non-circular ducts with insert: Numerical approach.
- Author
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Ngieng, A. T. T., Wong, S. F., and Tan, H. L.
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REYNOLDS number , *HEAT transfer , *TUBES , *ALUMINUM oxide , *FRICTION , *NANOFLUIDS - Abstract
This study investigates numerically the thermal-hydraulic performance of 0.02-1% water-based Al2O3 nanofluid in circular and square ducts with and without twisted tape insert. Two twist ratios of 5 and 0.579 are examined. The Reynolds number considered is from 20000 to 100000. The two-phase approach is employed to simulate the flow of nanofluid. The thermal performance of nanofluid in the circular pipe with insert is better than the case of the square duct with insert, but the friction factor of the circular tube is also relatively larger. Furthermore, a lower twist ratio yields a higher heat transfer rate. The results also reveal that the incorporation of nanoparticles and twisted tape insert contributes to heat transfer augmentation but at the expense of a higher friction factor. Nevertheless, from the thermal-hydraulic perspective, their application in circular and square tubes is considered practicable as the values of performance evaluation criteria obtained are more than one. The maximum thermal performance factor of 2.546 is achieved by 1% Al2O3 nanofluid in the circular duct with insert (twist ratio: 0.579) at the Reynolds number of 20000. Therefore, the use of the circular tube with insert is more favourable compared to that of the square tube. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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18. The influence of side frictions on urban arterial traffic characteristics in Al-Diwaniyah city.
- Author
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AL-Khuzai, Jullnar and Al-Jameel, Hamid
- Subjects
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CITY traffic , *CAMCORDERS , *ECONOMIC activity , *SPEED limits , *FRICTION - Abstract
The urban road network is the center of all economic activity in urban settlements worldwide, ensuring the people's survival. The growth population growthsulted in an increase in the number of vehicles on the road. The static and dynamic characteristics of these vehicles are vastly different. Side friction's role in limiting speed and capacity while increasing traffic congestion in city streets has long been known and remedied. On the other hand, the impact of side friction is mainly dependent on several factors, including the presence of pedestrians and on-street parking. This study investigates the influence of side friction on four arterial streets in Al-Diwaniyah, Iraq: Al-Jameaah, Al-Arouba, Al-Wakfa, and Al-Askary. Then, using a video camera positioned on both divided and undivided metropolitan roadways, field data was collected. The end product proved that side friction has a significant impact on vehicle speed on urban roads and that it could cause accidents. The results indicate that the side friction effect was medium to high in the selected streets, which reduces the speed to 20% in the case of medium SF and 38% in the case of high SF. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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19. Thermo-hydraulic performance of turbulent flow through ribbed air channel (experimental study).
- Author
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Salih, Mohammed. J., Jehhef, Kadhum Audaa, and Yasin, Nabil J.
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TURBULENT flow , *HEAT flux , *TURBULENCE , *HEAT transfer , *FRICTION - Abstract
An experimental investigation of thermo-hydraulic performance for a square cross-section air channel with dimensions of (15cm×15cm) and a length of (1.3 m) is considered in the present work. The experimental rig is fabricated from steel (ASM4120) with rectangular periodic eight ribs with dimensions of (3.75 cm ×7.5cm) along the lower wall of the air channel and its exhibition to constant heat flux (1500 and 3000) W/m2. The range of the Reynold numbers is varied by (6000,8000,1000 and 12000). All results are compared with the smooth channel model, the results showed that the best heat transfers are noted in the case of (Re = 8000 and q" = 3000 W/m2) where the Nusselt is enhanced by 7 % when using the ribbed lower surface of the air channel. Also, the maximum value of the friction factor occurs in the case of a ribbed duct at the condition of (Re = 6000 and 3000 W/m2) where the friction factor is increased by 19 %. Finally, the thermo-hydraulic performance factor was about 1.11 and which indicates the enhancement that occurred by adding the ribs for the smooth channel. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
20. Experimental study of viscosity and capillary flow of liquid.
- Author
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Bani, Wellstandfree K., Marngar, Laphiradashisha, Kurkalang, Phibanbet, Reassureson, R., Nonglait, L., Mukhim, Nerisa, Sangriang, Banshanskhem, and Kharbhih, Tonystone
- Subjects
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CAPILLARY tubes , *VISCOSITY , *FRICTION , *GRAVITY , *MOLECULES - Abstract
A water solution is allowed to flow under gravity through a horizontal capillary tube of uniform bore and small area of cross section. The molecules in contact with the wall of the capillary tube are at rest, and those along the axis of the tube flow with a maximum speed. This difference in the movement of molecules from one layer to the next inside the capillary tube resists the flow of water solution due to molecular friction of the liquid known as viscosity. The flow of water solution from one end to another of the horizontal capillary tube is due to a difference in pressure at the two ends. We perform an experiment to measure the coefficient of viscosity η and the resistance R of flow of water solutions for different concentrations c using Poiseuille's viscosity apparatus. [ABSTRACT FROM AUTHOR]
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- 2024
- Full Text
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21. Friction reduction in pipe flow of coarse slurry by fines addition – experimental study.
- Author
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Matoušek, Václav, Chára, Zdeněk, Konfršt, Jiří, Krupička, Jan, and Novotný, Jakub
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FRICTION , *SLURRY , *FLUID flow , *PRESSURE drop (Fluid dynamics) , *BASALT - Abstract
Very coarse basalt-water slurry forming fully stratified flow with a sliding bed and producing considerable friction loss was tested in a laboratory pipe. A considerably finer fraction of sand was added in steps to gradually increase the concentration of this fraction in the flowing slurry. The frictional pressure drop was measured together with the slurry discharge and slurry density. Furthermore, solid particles and their motion were observed at the bottom of the pipe. This observation indicated that finer particles in basalt-based bimodal slurry flows positioned themselves below the coarse particles at the pipe wall. The experimental results show that a quite small amount of fines is sufficient to produce a considerable friction reduction in settling slurry flow. Furthermore, the results indicate that there is a certain optimum quantity of fines at which the maximum reduction is reached and further addition of the fines does not bring any further improvement. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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22. Experimental evaluation of resistance of eroded bed in sediment laden open channel flow: Combined load transport case.
- Author
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Matoušek, Václav
- Subjects
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CHANNEL flow , *FRICTION , *FLUID flow , *SEDIMENT transport , *BED load - Abstract
A relation between the discharge and the flow depth in an open channel is quite sensitive to resistance (expressed by the friction coefficient) of the channel bottom. This relation is straightforward if the bottom is a fixed boundary, and the discharge is a result of one-phase (water) flow. The relation is considerably more complex if the channel bottom is an eroded mobile bed and the flow is solid-liquid flow. Sediment-transport experiments with various model lightweight sediments in a tilting flume of the Water Engineering Laboratory at Czech Technical University in Prague produced information suitable for an evaluation of the eroded bed resistance at conditions of intense bed load and intense combined load in the upper plane bed regime. An evaluation of the bed load condition has been published recently. This paper discusses a description and quantification of the bed resistance in the case of transported combined load, i.e., at the condition where a certain portion of the sediment is transported as bed load and the rest is transported as suspended load. The results show that the presence of transported sediment tends to increase the bed resistance and hence increases a flow depth for a certain discharge of water in an open channel with an eroded bed. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
23. Effect of friction dampers on seismic response control of irregular building.
- Author
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Tadas, Abhilesh and Sanghai, Sanket
- Subjects
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LITERATURE reviews , *SHEARING force , *FRICTION , *DESIGN services , *COMPUTER simulation , *SEISMIC response - Abstract
This study examines how friction dampers affect the regulation of irregular buildings' seismic response. The study's goal is to assess how well friction dampers work to minimize the dynamic response of irregular structures during seismic events. Through a literature review and numerical simulations, the behavior and performance of friction dampers in various irregular building configurations are analyzed. The evaluation includes majorly inter-story drifts, base shear forces, and floor accelerations. The findings contribute to the knowledge of seismic response control in irregular buildings and provide insights into the potential benefits and limitations of friction dampers in enhancing their seismic resilience. The research aims to improve design practices for irregular buildings in seismic-prone regions, promoting their safety and reliability. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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24. Tribotronic and electrochemical properties of platinum–nanofluid interfaces formed by aqueous suspensions of 5 and 40 nm TiO2 nanoparticles.
- Author
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Seed, C. M., Acharya, B., Nunn, N., Smirnov, A. I., and Krim, J.
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ELECTROPHORETIC deposition , *QUARTZ crystal microbalances , *DRAG force , *FRICTION , *DRAG reduction , *LUBRICANT additives , *PLATINUM electrodes - Abstract
Nanoparticles (NPs) can be highly beneficial as additives to lubricating fluids, and the tribotronic response of charged NPs tuned by external fields represents an area of great technological potential. Tribotronic response, however, is expected to be highly size dependent, which represents a significant design challenge. To explore this issue, quartz crystal microbalance and cyclic voltammetry were employed to characterize nanotribological and electrochemical behavior of platinum–nanofluid interfaces formed by aqueous suspensions of different-sized negatively charged titanium dioxide (TiO2) NPs. Suspensions of 5, 40, and 100 nm NPs were all observed to reduced interfacial frictional drag forces upon introduction into pure water in zero field conditions, with reductions for the 40 nm NPs about twice those of 5 nm particles at comparable concentrations. Suspensions of 100 nm NPs produced even greater reductions, but rapidly precipitated from the suspension when left unstirred. NPs were also driven to and from Pt electrode surfaces by applying external electric fields with varying amplitudes and modulation frequencies. For electric fields of sufficient amplitude and duration, the 40 nm TiO2 nanosuspension exhibited tribological properties consistent with a reversible electrophoretic deposition of the NPs, accompanied by changes in the electrochemical attributes and increasing interfacial drag. The 5 nm NP properties were consistent with progressive reductions in interfacial drag forces at the NP–suspension interface linked to field-induced increases in concentration. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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25. Evolution of the microstructure of amorphous polyethylene under friction-induced plastic flows: A reactive molecular investigation.
- Author
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Zheng, Ting, Gu, Jingxuan, Zhang, Yu, and Zhang, Huichen
- Subjects
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REACTIVE flow , *POLYETHYLENE , *MICROSTRUCTURE , *CAVITATION erosion , *PLASTICS , *MOLECULAR dynamics , *CAVITATION , *FRICTION - Abstract
The plastic flow of ultra-high molecular weight polyethylene (UHMWPE) at a frictional interface, which is critical to the wear behavior, was investigated by reactive molecular dynamics simulations. The UHMWPE substrate was found to experience various deformations during the friction process. First, some polyethylene (PE) chains could detach from the substrate because of their rapid movement. Second, the frequent motion of PE chains also resulted in the intermittent formation and breaking of cavities between intermolecular PE chains. These deformations were more obvious on a surface with a convex protrusion, where the plowing effect exacerbated the cavitation and elastic deformation of PE chains. Correspondingly, the plastic flow in turn reconstructed the convex protrusion by displacing the surface atoms on the Fe slab. The plastic flow of PE chains broke the C–C bonds, and the carbon moieties were then chemically bonded onto the metal surface. A rapid change of atomic charge, hence, happened when the bonds broke. Meanwhile, PE chains release short alkyl radicals gradually after bond breakage, indicating gradual wear of the substrate during friction. This work provides molecular insight into the evolution of interfacial microstructure under plastic flow on a UHMWPE substrate. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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26. Equilibrium molecular dynamics evaluation of the solid–liquid friction coefficient: Role of timescales.
- Author
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Oga, Haruki, Omori, Takeshi, Joly, Laurent, and Yamaguchi, Yasutaka
- Subjects
- *
MOLECULAR dynamics , *FRICTION , *SHEARING force , *EQUILIBRIUM , *ANALYTICAL solutions - Abstract
Solid–liquid friction plays a key role in nanofluidic systems. Following the pioneering work of Bocquet and Barrat, who proposed to extract the friction coefficient (FC) from the plateau of the Green–Kubo (GK) integral of the solid–liquid shear force autocorrelation, the so-called plateau problem has been identified when applying the method to finite-sized molecular dynamics simulations, e.g., with a liquid confined between parallel solid walls. A variety of approaches have been developed to overcome this problem. Here, we propose another method that is easy to implement, makes no assumptions about the time dependence of the friction kernel, does not require the hydrodynamic system width as an input, and is applicable to a wide range of interfaces. In this method, the FC is evaluated by fitting the GK integral for the timescale range where it slowly decays with time. The fitting function was derived based on an analytical solution of the hydrodynamics equations [Oga et al., Phys. Rev. Res. 3, L032019 (2021)], assuming that the timescales related to the friction kernel and the bulk viscous dissipation can be separated. By comparing the results with those of other GK-based methods and non-equilibrium molecular dynamics, we show that the FC is extracted with excellent accuracy by the present method, even in wettability regimes where other GK-based methods suffer from the plateau problem. Finally, the method is also applicable to grooved solid walls, where the GK integral displays complex behavior at short times. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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- View/download PDF
27. Tribological properties and synergistic effects of ionic liquids and silver complexes
- Author
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Sun, Long, Jin, Chengjie, Tang, Xiaodong, Cao, Kexin, Wang, Songquan, and Hu, Ningning
- Published
- 2024
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28. Cooperative control of variable damping error port Hamiltonian and backstepping nonsingular terminal sliding mode control for manipulators driven by PMSMs.
- Author
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Guo, Qingkun, Yu, Haisheng, Yang, Qing, Gao, Xunkai, and Meng, Xiangxiang
- Subjects
- *
SLIDING mode control , *PERMANENT magnet motors , *BACKSTEPPING control method , *GAUSSIAN function , *FRICTION , *MANIPULATORS (Machinery) - Abstract
To improve the disadvantages of signal control and energy control, a cooperative control strategy combining signal control and energy control is proposed for manipulators driven by permanent magnet synchronous motors (PMSMs) in this article. The cooperative control strategy is achieved by way of the convex combination of signal controller and energy controller, and Gaussian function is selected as cooperative function. The energy controller applies variable damping error port Hamiltonian and the signal controller uses backstepping nonsingular terminal sliding mode control. The PMSM with loss model is applied to obtain higher efficiency. To deal with modeling errors and joint friction, a nonlinear disturbance observer is used for manipulators system. Simulation and experiment results display that the designed strategy not only increases efficiency, but also enhances dynamic and steady‐state performance of manipulators. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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29. Dynamic Characteristics of a Supercritical Helicopter Tail Transmission System with Self-Excited Vibration and Rubbing Impact.
- Author
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Zhu, Haimin, Hu, Shunan, Zhang, Li, Li, Miaomiao, and Zhu, Rupeng
- Subjects
- *
DYNAMICAL systems , *BEVEL gearing , *COORDINATE transformations , *NUMERICAL analysis , *SPLINES , *SELF-induced vibration - Abstract
This study presented a novel analytical method to investigate the coupled dynamic behavior of a supercritical helicopter tail transmission system, taking into account the friction-induced self-excitation of the floating spline, the rubbing between the limiting ring device and the shaft, and the time-varying meshing excitation experienced by multiple spiral bevel gear pairs. The tail transmission shaft was first modeled using Timoshenko beam elements in local coordinates. Subsequently, the centralized parameter method was employed to build dynamic models of critical components such as the floating spline, limiting ring devices, and multiple spiral bevel gear pairs. Finally, the system's dynamic equations were derived utilizing the interface coordination principle and spatial coordinate transformation. Numerical analyses were conducted to examine the dynamic behavior of the system, including the coupled vibration properties and the impact laws of the limiting ring device and floating spline on the system's response. The findings indicated that the limiting ring device resulted in a cross-critical vibration reduction in the tail horizontal shaft, achieved through the mechanisms of dry friction and rubbing impact. However, as a consequence, the natural and rubbing frequencies of the other shafts were generated. The self-excited vibration of the system, brought about by the friction of the spline tooth surface, had a significant impact on the shaft that was directly connected. The emergence of the self-excited vibration occurred when the speed surpassed the first-order natural speed of the directly connected shaft, with the corresponding self-excited frequency being the first-order natural frequency of said shaft. With the increase in the tooth surface friction coefficient of the spline, it even caused continuous rubbing between the shaft and the limiting ring device under a supercritical condition. The proposed dynamic analysis approach holds promise in offering theoretical guidance for the reduction of vibration and noise generated in supercritical tail transmission systems. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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30. Friction and corrosion behaviors of the copper reinforced with MoS2 nano-layers coated with silver.
- Author
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Yehia, Hossam M., Ali, Ahmed I., Abd-Elmotalib, Tamer, Abd-Elhameed, Ehab, and Daoush, Walid M.
- Subjects
ALUMINUM oxide ,COPPER corrosion ,MECHANICAL wear ,MOLYBDENUM disulfide ,BALL mills - Abstract
The effect of 10 wt% alumina, 20 wt% (10Al 2 O 3 -10MoS 2), and 30 wt% (10Al 2 O 3 -10MoS 2 -10Ag) reinforcements on the tribological and corrosion properties of copper was investigated. The nanocomposites were prepared by the ball milling coating method and then fabricated by the cold and hot compaction technique. The copper's hardness increased gradually from 96 HV to 227 HV for the 30 wt% (Al 2 O 3 -MoS 2 -Ag) representing an increase of 136.48 %. Adding 30 wt% (Al 2 O 3 -MoS 2 -Ag) to the copper reduced the wear rate from 22 mg/min to 0.3 mg/min under 50 N applied load, owing to the presence of two types of self-lubricating materials, MoS 2 and Ag. This nanocomposite recorded the lowest mean coefficient of friction of 0.166 compared with 0.23 for copper. Adding the alumina increased the copper corrosion rate to 3.83 mm/year due to increased oxidation ratio that facilitates the penetration of the electrolyte. However, the Cu/(Al 2 O 3 -MoS 2 -Ag) sample recorded corrosion rates of 0.467 mm/year compared with 0.446 mm/year for copper. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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31. Numerical Analysis of 3D Unilateral Quasi-static Contact: Effect of Coating Thickness and Mechanical Properties.
- Author
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Djamai, Andel, Zaidi, Hamid, Bekhouche, Djamel, and Bouchoucha, Ali
- Abstract
In this study, a numerical model for unilateral quasi-static contact between a rigid sphere and an elastic coating has been developed. The contact problem was solved using a numerical procedure based on the FFT technique, considering various coatings with different thicknesses and mechanical properties, implemented through a Matlab code. The model calculates the contact surface deformation and pressure field through a double iteration process. The first iteration solves the contact problem for a given indenter penetration, while the second iteration refines this penetration by minimizing the difference between the fixed and calculated loads. To achieve this, influence coefficients are derived from the elasto-static equations using the Papkovich-Neuber potentials. The study discusses the influence of coating thickness and friction coefficient value on the tribological behavior of the coating. The results indicate that contact pressure increases (ranging from 1.9 to 2.5) as the coating becomes thicker or more rigid (0.02 mm to 0.2 mm). Additionally, the tribological behavior of the coated surface is affected by the coating's thickness, hardness, and friction coefficient value. Importantly, this model demonstrates versatility by being applicable to both smooth and rough surfaces. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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32. Self‐lubricating polyamide 6 and polyamide 6.6 microcapsule‐based composites.
- Author
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Grünewald, Moritz, Herbig, David, Heilig, Michael, Rudloff, Johannes, Bastian, Martin, Engelmann, Gunnar, Hirsekorn, Max, and Latnikova, Alexandra
- Subjects
CORE materials ,MECHANICAL wear ,POLYMERIZATION ,POLYAMIDES ,SERVICE life - Abstract
Polymeric applications with extended service life and low energy loss due to friction are of great interest in conveyor and power transmission technology. Self‐lubricating systems utilizing microcapsules hold significant potential for increasing energy efficiency and extending the operational life of these applications. This study focuses on synthesizing oil‐filled microcapsules through in situ polymerization of polyamide and their incorporation in polyamide 6 and polyamide 6.6. Microcapsules with a core made of thermally stable lubricant Food Lube, and particle diameter D90 of 50 μm were synthesized and isolated as a free‐flowing powder via spray‐drying procedure. The resulting powder demonstrated high thermal stability (loss of 5% at 350°C) due to the high thermal stability of both core and shell materials. A compounding process utilizing a twin‐screw extruder was developed to blend microcapsules into thermoplastic matrices. An injection molding machine forms tension rods. The composites' tribological properties are assessed through ball‐on‐disc tests conducted in both oscillation and rotation. The friction coefficient and wear rate of the composites experience a reduction of 79% and 56% for polyamide 6, as well as 77% and 75% for polyamide 6.6. Mechanical testing of the microcapsule composites reveals a decrease in mechanical properties. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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- View/download PDF
33. Performance assessment of agricultural waste based eco‐friendly brake friction composites.
- Author
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Kılıç, Halil
- Abstract
Highlights There has been growing interest in using sustainable and eco‐friendly products to produce engineering materials. For this purpose, composite material applications obtained from agricultural wastes are gaining popularity. This study examines the synergistic effect of rice husk and rice stalk wastes on the fade and recovery performance of brake friction composites. Brake friction materials were developed using rice husk and rice stalk separately and in two different weight percentages as a 5–10 ratio in the formulation. For comparison purposes, a reference brake pad using copper as a substitute and a commercially available brake pad were used. Various physical, mechanical and thermal properties were analyzed. The tribological behavior of friction composites was evaluated on the Krauss test device in line with the ECE R90 procedure. The worn surface properties were analyzed using scanning electron microscopy. Tribo test results of friction composites were taken as criteria for performance optimization. While the importance weight of the criteria was determined by AHP, the VIKOR method was used in the sorting of alternatives. The experimental results have revealed that rice husk‐added friction composites had a good coefficient of friction value with better fade and recovery performance compared to rice stalk‐added ones. Increasing the amount of rice husk and rice stalk in the formulation tended to decrease the fade performance; however, it has increased the wear rate and recovery properties. Optimization results have shown that the brake friction composite containing 5 wt % rice husk ranks first in meeting the desired tribological criteria. Cu‐free rice husk and rice stalk‐added friction composites were developed. Fibrous structure in the matrix developed the contact plateaus. Rice husk‐based tribo‐layer protected the composite from further wear damage. The addition of agro‐waste to friction composites exhibited good potential. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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34. Enhanced active disturbance rejection speed controller for permanent magnet synchronous motors using virtual friction feedback technique.
- Author
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Dong, Dingfeng, Huang, Wenxin, Zhu, Shanfeng, and Bu, Feifei
- Subjects
- *
STATE feedback (Feedback control systems) , *FRICTION , *SPEED - Abstract
Active disturbance rejection controller (ADRC) has been widely promoted in permanent magnet synchronous motor (PMSM) drives for its simple design and remarkable anti‐disturbance characteristics. To further improve the control performance, a variety of advanced ADRC schemes have been proposed in recent years. However, the majority of them focused on constructing more complicated extended state observers (ESOs) while ignoring the utilization of state feedback. Motivated by the above issue, this article proposes an enhanced virtual friction ADR speed controller (VFADRC). It is distinguished by the simpler structure compared with other ADRC schemes. Besides, the introduced zero in disturbance rejection function of VFADRC contributes to the preferable anti‐disturbance response. Moreover, the enhanced configuration of VFADRC proposed in the article further improves the speed dynamics and robustness to inertia variations. Both the theoretical analysis and experimental results validate the excellent performance of the proposed ADR controller. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
35. Friction properties and prediction of a novel copper-based powder metallurgy material modified with TiB2/B4C composite.
- Author
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Wen, Guoyuan, Li, Zhuan, Wu, Jiaqi, Gao, Zonglong, Li, Ye, and Zhou, Hao
- Subjects
- *
POWDER metallurgy , *FRICTION , *FERRIC oxide , *MACHINE learning , *METALLIC films , *FRETTING corrosion - Abstract
By incorporating the dual ceramic elements TiB 2 /B 4 C, we investigated their impact on the mechanical properties, thermal properties, and friction performance of copper-based powder metallurgy materials, and elucidated the friction wear mechanism. Additionally, machine learning algorithms were employed to predict the friction coefficient and stability coefficient. The conclusions are as follows:With the increase in the TiB 2 /B 4 C ratio, the trend of mechanical properties initially increases and then decreases, with the optimum ratio being 5:3 for TiB 2 and B 4 C, exhibiting superior mechanical properties. Moreover, B 4 C enhances the thermal conductivity of copper-based friction materials more effectively than TiB 2. In terms of overall friction performance, the ratio of TiB 2 to B 4 C at 5:3 yields better frictional properties. The primary components of the friction surface friction film are CuO, Cu 2 O, Fe 2 O 3 , and B 2 O 3 , transitioning from a ceramic film to a metallic film as the TiB 2 /B 4 C ratio increases. The friction wear mechanism shifts from abrasive wear to severe fatigue wear as the TiB 2 /B 4 C ratio increases, accompanied by oxidative wear. Furthermore, an AdaBoost algorithm model was developed to effectively predict the friction coefficient and stability coefficient, with accuracies of 0.9993 and 0.8739, respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
36. How are romantic cross‐class relationships sustained?
- Author
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Butler, Rose and Vincent, Eve
- Subjects
- *
CLASS differences , *EMOTIONS , *NEGOTIATION , *FRICTION , *RESPONDENTS , *SOCIAL classes , *SOCIAL mobility - Abstract
How are romantic relationships across class maintained under broader conditions of class inequality? This article draws on in‐depth interviews with 38 people who have partnered across class in Australia. It examines the emotional and interpersonal labour required to preserve such relationships within a highly differentiated class structure that is widely obscured in public and political life. We find, first, that for people in committed cross‐class relationships where this difference was openly acknowledged, class difference was acutely felt and described in highly emotional, imprecise terms. Second, this heightened awareness of class difference stimulated elevated levels of class friction and class dissonance within these relationships. We detail these experiences, as they were narrated to us, before examining certain interviewees' efforts to understand and resolve these complexities. We highlight the collaborative work undertaken by one couple in particular to navigate feelings of class discomfort and class dissonance. Third, by focussing on the emotional terrain of intimate cross‐class negotiations, we stress moments which have the potential to disrupt assumptions about class hierarchies and modes of moral distinction that take place within these relationships. Proceeding to tentatively valorise different forms of value‐making and recognition within cross‐class relationships, we also pay attention to the role of class in enabling this very capacity for adaptation. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
37. Theoretical prediction and test validation for frictional action of stacked steel disk springs with low initial cone angle.
- Author
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Ding, Yukun and Zheng, Shuaikang
- Subjects
- *
FINITE element method , *FRICTION , *STEEL - Abstract
To examine the frictional action of stacked disk springs with low initial cone angle, axial compression tests were conducted by varying sizes and stacked forms of springs. Each stacked form exhibited stable and predictable behavior and the increase of parallel springs improves frictional dissipation. Lubricating greases can reduce but not eliminate the frictional action. The finite element analysis (FEA) employing friction coefficients from 0.2 to 0.3 can match test results on the whole. Verifications show that some existing predictions, except for the prediction from the standard, can well reflect the frictional action between the end plates and disk springs. Besides, convenient formulas to correctly reflect the frictional action between parallel springs are still needed due to existing theoretical models with either low precision or implicit and complicate calculation of relative sliding deformations between parallel springs. Therefore, based on a method employing either the moment balance or the energy balance, theoretical models and convenient formulas to predict the frictional action for the stacked springs in parallel were proposed. Furthermore, a formula to comprehensively consider the frictional action for springs stacked in both parallel and series was given. The effectiveness of the proposed formulas was verified by comparing with both the FEA and the test results. In addition, possible contacts between springs and the control bar would induce additional frictional actions, which can be compensated in some degree by appropriately adjusting the friction coefficients. Equivalent coefficients that can be employed in the formula of the standard to improve precision were provided. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
38. Coned disk spring with friction or restraint at its edges: Explicit solution and experimental study.
- Author
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Zhang, Zhongwen, Yu, Yang, and Xu, Zhao-Dong
- Subjects
- *
STRESS concentration , *METAMATERIALS , *FRICTION , *ROTATIONAL motion , *EQUILIBRIUM - Abstract
The behavior of a coned disk spring can be significantly affected by friction or restraint, yet the existing theoretical solutions cannot fully capture these influences. The limitation is particularly problematic for analyzing the behavior of coned disk springs with bi-stability. This paper proposes an explicit solution that can predict the behavior of the coned disk spring under these boundary conditions. The solution considers detailed influences of friction and restraint at the edges of the coned disk spring on its moment equilibrium and location of the neutral fiber. The theoretical results are validated using existing literature, FE analysis, and a series of tests. The theoretical solution confirms that the friction force at the edge of the coned spring significantly affects the axial response of the spring but not its bending moment or distribution of tangential stress. The bending moment and overall behavior of the coned disk spring are, on the other hand, very sensitive to restraints in radial directions. The proposed explicit solution shows good accuracy for coned disk springs with restrained radial stretching and rotation. The solution is particularly useful for coned disk springs in multistable structures and metamaterials. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
39. Transitional Frictions: Intimate Ties, Grassroots Bureaucracy, and Family Reunion in Post-Mao China, 1975–1985.
- Author
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Huang, Yanjie
- Subjects
- *
FAMILY reunions , *FAMILY-work relationship , *FRICTION , *EMOTIONS , *FAMILIES - Abstract
During the Cultural Revolution, millions of youths, workers, intellectuals, and cadres were separated from their families and mobilized to work in distant places according to the needs of the state. For these families, the transition to the post-Mao era was experienced not as an epochal change but as a family reunion often delayed by specific institutional constraints. The constant friction between families' strategies to reunite and the bureaucratic logic specific to local contexts led to a sense of victimhood and a turn to domestic life and hope in children as the new sacred in life. By examining the processes of family reunion told in three sets of family letters, this article explores "transitional frictions," defined as the conflicts and tensions arising from different speeds of institutional change during a rapid transition, as a ubiquitous phenomenon in the post-Mao transition. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
40. Joint vehicle state and parameters estimation via twin-in-the-loop observers.
- Author
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Dettù, Federico, Formentin, Simone, and Matteo Savaresi, Sergio
- Subjects
- *
PARAMETER estimation , *AUTOMOBILE driving simulators , *AUTOMOBILE industry , *SIGNAL processing , *FRICTION - Abstract
Vehicular control systems are required to be both extremely reliable and robust to different environmental conditions, e.g. load or tyre–road friction. In this paper, we extend a new paradigm for state estimation, called Twin-in-the-Loop filtering (TiL-F), to the estimation of the unknown parameters describing the vehicle operating conditions. In such an approach, a digital-twin of the vehicle (usually already available to the car manufacturer) is employed on-board as a plant replica within a closed-loop scheme, and the observer gains are tuned purely from experimental data. The proposed approach is validated against experimental data, showing to significantly outperform the state-of-the-art solutions. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
41. Tire mechanical model for cornering simulation with friction coefficient calculated from viscoelasticity of rubber by multiscale friction theory.
- Author
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Nakanishi, Ryota, Matsubara, Masami, Ishibashi, Takashi, Kawasaki, Satoshi, Suzuki, Haruyuki, Kawabata, Hiroshi, Kawamura, Shozo, and Tajiri, Daiki
- Subjects
- *
MECHANICAL models , *PIEZOELECTRIC detectors , *LATERAL loads , *STRESS concentration , *FRICTION - Abstract
A friction coefficient of tire model for cornering simulation is generally set inductively to be consistent with experimental results. However, the inductively set friction coefficients have no clear relationship with the viscoelasticity of the rubber, so they cannot be used in the design of rubber formulations to obtain the desired friction coefficient. In this study, we propose a new tire mechanical model for cornering simulation that includes a friction coefficient deductively derived from the viscoelasticity of rubber based on the Persson's multiscale friction theory. In this model, the contact pressure, sliding velocity, and lateral stress distributions are calculated based on an elliptical contact patch. Because the proposed model analytically connects the lateral force with the viscoelasticity of rubber, it is applicable to rubber design for achieving the targeted cornering properties. The validity of the model was experimentally verified using an internal drum machine with quartz piezoelectric sensors on an aluminium road segment. With appropriate parameter settings, the friction coefficient distribution in the length direction calculated by the proposed model agreed well with the experimental results compared to the elliptical contact patch tire model. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
42. Relationship between Foreign Object Debris, Roughness, and Friction.
- Author
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Parsons, Timothy A. and Murrell, Scott D.
- Subjects
- *
FOREIGN bodies , *MATHEMATICAL simplification , *FRICTION , *SPACE debris , *MATHEMATICAL forms , *PAVEMENTS , *LATENT variables - Abstract
The Federal Aviation Administration (FAA) is developing new design procedures to extend airport pavement life beyond 20 years based on the concept of serviceability: the measure of how well a pavement fulfills user expectations. A key element is a new distress megaindex called serviceability level (SL) whose components represent independent aspects of airport pavement serviceability: low foreign object damage (FOD) potential, low skid potential, and smoothness. This research validates the assumption of independence previously used to develop a probability-based form for SL. Independence greatly simplifies the mathematics of the new form, in particular, the ability to decompose a pavement condition model into multiple relatively simple submodels. Friction is shown to not correlate to the other two components. FOD and roughness are conditionally independent with a latent variable of crack and spall density. Conditional independence means the proposed SL formulation is generally valid but requires that FOD and roughness measurements or predictions be made at the same time using the same assumptions. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
43. Novel approach for characterizing clinical load application of superelastic orthodontic wires.
- Author
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Mayer, Judith Tamara, Lapatki, Bernd Georg, and Schmidt, Falko
- Subjects
- *
SHAPE memory alloys , *MATERIALS testing , *FRICTION materials , *ORTHODONTIC appliances , *TOOTH mobility - Abstract
Current standardized in vitro bending experiments for orthodontic archwires cannot capture friction conditions and load sequencing during multi-bracket treatment. This means that clinically relevant forces exerted by superelastic wires cannot be predicted. To address these limitations, this study explored a novel test protocol that estimates clinical load range. The correction of a labially displaced maxillary incisor was simulated using an in vitro model with three lingual brackets. Deflection force levels derived from four different protocols were designed to explore the impact of friction and wire load history. These force levels were compared in nickel-titanium (NiTi) archwires with three commonly used diameters. The unloading path varied between protocols, with single or multiple sequences and different load orders and initial conditions. Deflection forces from the new protocol, employing multiple continuous load/unload cycles (CC incr), consistently exceeded those from the conventional protocol using a single continuous unloading path (CU decr). Mean differences in plateau force ranged from 0.54 N (Ø 0.014" wire) to 1.19 N (Ø 0.016" wire). The CC inr protocol also provided average force range estimates of 0.47 N (Ø 0.012" wire), 0.89 N (Ø 0.014" wire), and 1.15 N (Ø 0.016" wire). Clinical orientation towards CU decr carries a high risk of excessive therapeutic forces because clinical loading situations caused by friction and load history are underestimated. Physiological tooth mobility using NiTi wires contributes decisively to the therapeutic load situation. Therefore, only short unloading sequences starting from the maximum deflection in the load history, as in CC incr , are clinically meaningful. • Friction and load history affect deflection forces of orthodontic NiTi wires. • Conventional in vitro 3-bracket bending tests underestimate clinical force levels. • Physiological tooth movement must be considered to derive clinically relevant loads. • Reactive forces from wire deflection may vary because of physiological conditions. • Sequential short unloading sequences allow characterization of clinical load range. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
44. Fragility-Based Optimal Design of Friction Pendulum Bearings in Seismically Isolated Liquid-Storage Tanks.
- Author
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Bagheri, Saman, Hayati Raad, Hossein, and Farajpour, Ismail
- Subjects
- *
STEEL tanks , *PENDULUMS , *SLIDING friction , *FRICTION , *STORAGE tanks , *EARTHQUAKE resistant design - Abstract
A fragility-based probabilistic framework is proposed for the optimal design of friction pendulum (FP) bearings in seismically isolated liquid-storage tanks. The isolation period and sliding friction coefficient of the FP system, which significantly influence the seismic performance of isolated liquid-storage tanks, were analyzed as the two design parameters of the isolation system. The seismic fragility functions of the isolated tanks, generated using incremental dynamic analysis (IDA), were evaluated and used to determine the optimal ranges for these design parameters. This procedure, which yields the minimum seismic failure probability of the considered structures, was examined in the design of seismic isolation systems for two on-grade cylindrical steel storage tanks with broad and slender configurations. Moreover, the effects of including or excluding the failure mode corresponding to the excessive displacement of the isolation system from the considered failure limit states were analyzed and discussed. Finally, the present study provides recommendations for the optimal selection of design parameters for FP isolators in liquid-storage tanks. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
45. Study on the Friction Behavior and Abnormal Conditions of Non-contact Mechanical Seal Based on Acoustic Emission.
- Author
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Chen, Jinxin, Lu, Junjie, Hou, Yaochun, Ding, Xuexing, and Zhang, Wei
- Abstract
The main cause of failure in sealing friction pairs, friction wear, has presented analytical challenges due to rapidly changing and complex friction frequency characteristics. This has led to a focus on surface morphology treatment rather than direct measurement techniques in research. In this context, the present study adopted Acoustic Emission (AE) technology for direct monitoring of friction pairs, aiming to identify friction response signals during their transient contact and abrasion stages. Employing time–frequency analysis, the research delineated the state evolution of AE characteristics during the entire operational cycle of the friction pair, from start to stop. It has established the time–frequency information of AE signals in relation to the surface state of the sealing friction pair and deciphered the correlation between the friction AE signals and the surface state alterations of the friction pair. The study showed that the frequency of friction-induced signals in seals is 270 ± 40 kHz. The transition speeds for the friction pair's state, moving from boundary lubrication to mixed lubrication and then to fluid dynamic lubrication, were identified as 200 rpm and 1000 rpm, respectively. Additionally, an escalation in signal activity was observed in dry friction scenarios and when surface defects were present in the friction pair, markedly exceeding the activity in conditions of no wear. This relationship between the friction signals and the operational state of the seal facilitates precise assessments of wear and operational integrity, underpinning the theoretical aspects of periodic wear in seal tribology. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
46. Ionic Liquids as Extreme Pressure Additives for Bearing Steel Applications.
- Author
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Donato, Mariana T., Nautiyal, Pranjal, Deuermeier, Jonas, Branco, Luís C., Saramago, Benilde, Colaço, Rogério, and Carpick, Robert W.
- Abstract
The protection of steel surfaces from wear under extreme pressure conditions is of major importance in several industries as it provides better performance and longer life of machinery. The motivation for this work was to study the lubrication of steel by ionic liquids (ILs), which have recently emerged as greener alternatives to commercial lubricants and additives. Three ILs based on sulfur-containing anions, used as 2-wt% additives in polyethylene glycol base oil (MW 200; PEG 200), were tested in the lubrication of ASTM 52100 bearing steel contacts in extreme pressure conditions (under mixed lubrication with a Hertzian pressure of 1.12 GPa) using a mini traction machine (MTM). Due to the poor resistance to corrosion of bearing steel, a semi-ester of succinic acid derivative corrosion inhibitor (Lanxess RC 4801) was added to the mixtures at a 1 wt% concentration. The ILs 1-hexyl-methylimidazolium trifluoromethanesulfonate ([C6mim][TfO]) and 1-hexyl-4-picolinium trifluoromethanesulfonate ([C6-4-pic][TfO]) revealed promising results in terms of surface protection of bearing steel. In contrast, 4-picolinium hydrogen sulfate ([4-picH][HSO4]) as 2-wt% additive to PEG 200 + 1% RC 4801 did not show any improvement in wear performance compared to neat PEG 200 + 1% RC 4801. PEG 200 + 2% [C6mim][TfO] + 1%RC 4801 allowed for a decrease in wear up to ~ 76% and PEG 200 + 2% [C6-4-pic][TfO] + 1%RC 4801 up to ~ 46% when compared with neat PEG 200 + 1% RC 4801. Optical microscopy images suggest the formation of an adsorbed layer, which was further supported by chemical analysis via x-ray photoelectron spectroscopy (XPS) data for [C6mim][TfO]. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
47. Improved wear and friction properties by self-formed SiC layers in Mg/SiC composites.
- Author
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Kamei, Shuhei, Hirayama, Tomoko, Somekawa, Hidetoshi, and Matsuoka, Takashi
- Subjects
- *
MECHANICAL wear , *POWDER metallurgy , *WEAR resistance , *EXTRUSION process , *FRICTION - Abstract
The tribological properties are evaluated using several types of Mg/SiC composites, which SiC powders with particle sizes of 20∼30 nm, 130 nm and 2∼3 μm are dispersed in up to 25 % by volume fraction. Sound and bulky Mg/SiC composites are successfully fabricated by powder-metallurgy combining extrusion process. The initial SiC particle size and their dispersed volume fraction affect the wear and friction properties. The specific wear rate increases with increasing contents of SiC particles, regardless of the initial SiC particle size. However, when the SiC particle size is larger than a certain size and its content is greater than 10 %, the friction coefficient suddenly decreases. In the surface observations after friction tested specimens, the element mapping image shows the Mg ratio relative to Si ratio (=SiC) increases with reducing friction coefficient. This indicates that good wear resistance is due to the presence of self-formed SiC layers during the friction process. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
48. Atomistic insights into friction and wear characteristics of M50 bearing steel: a molecular dynamics simulation study.
- Author
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Han, Yikun, Yang, Lei, Wei, Xunkai, Wang, Hao, and Fu, Guoru
- Subjects
- *
BEARING steel , *FRICTION , *MOLECULAR dynamics , *SHEAR strain , *MATERIAL plasticity - Abstract
M50 bearing steel is a typical alloy material widely used in aeroengines due to its high hardness and fatigue life at high temperatures. To reveal the frictional mechanisms and wear behaviours of contact and sliding, a molecular dynamics simulation model consisting of an indenter and substrate is constructed. The results indicate that, during the indentation process, the normal load exhibits a linear relationship with the indentation depth at shallow depths. With further penetration, the substrate generates severe deformations and subsurface damages. Throughout the scratching process, the average friction force exhibits a linear increase with the growing scratching depth, while the coefficient of friction decreases. Surface morphologies and shear strain distributions are analyzed to elucidate plastic deformation and atomic displacement. Moreover, the wear atom shows a linear proportionality to both scratching distance and depth. These findings enhance understanding of frictional properties and atomic wear behaviour of M50 bearing steel during contact and sliding, potentially informing bearing failure prediction and material optimization. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
49. Study on high-temperature erosive wear behaviour, surface roughness and scratch resistance of NiCrAlY-based composite coating.
- Author
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Lakshmi, K P Jhansi, Raghavendra, C R, Sogalad, Irappa, and Basavarajappa, S
- Subjects
- *
SURFACE roughness , *SURFACE coatings , *COMPOSITE coating , *PLASMA spraying , *WEAR resistance , *BORON carbides , *MICROSCOPY , *SLIDING wear , *FRICTION - Abstract
This study concentrates on NiCrAlY-based coating with nano-boron carbide and cenosphere particles. The composition of NiCrAlY, B4C and cenosphere are maintained the same for all the samples. The plasma spray technique is used for coating. The erosive wear is carried out for different impingement angles of 30°, 60°, 75° and 90° at 900°C. The morphology of coating before and after erosive wears is studied using scanning electron microscopic analysis. Further, the study is carried out on surface roughness, scratch resistance and coefficient of friction of the eroded surface of the samples. The significant erosive wear resistance is reported for an impact angle of 60° followed by 30°. The surface roughness results reveal the formation of deep craters and the ploughing effect of material on the coatings. The scratch test and COF show the presence of coating and the brittle nature of the failure of the coating. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
50. Investigation of Reciprocating Wear Characteristics of Nano-B4C Reinforced AZ91D Magnesium Metal Matrix Nanocomposites Prepared Through Ultrasonically Assisted Stir Casting Technique.
- Author
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Mitra, Anirban, Bera, Tapas, Dey, Vidyut, and Rai, Ram Naresh
- Abstract
The present study aims to develop a new class of AZ91D magnesium metal matrix nanocomposites reinforced with varying wt.% (0–2%) of B
4 C nanoparticles through ultrasonic vibration-assisted stir casting technique and to evaluate the influence of B4 C particles on the microstructure, micro-hardness and wear behaviour of AZ91D nanocomposites. Microstructural characterisation was performed using field emission scanning electron microscope (FESEM) and showed that the B4 C nanoparticles were dispersed uniformly, refinement of grains and well-bonded between the AZ91D matrix and reinforcement particles. XRD patterns of as-cast MMNCs confirmed the presence of α-Mg, β-Mg17 Al12 , B4 C and MgO phases. Micro-hardness value enhanced by 53.73% with incorporation of 2 wt.% B4 C. The reciprocating wear tests of nanocomposites were examined using ball-on-disc tribotester under applied load of 2 N and observed that wear rate and friction behaviour of AZ91D-2.0B4 C nanocomposites decreased by 48.67 and 28.32%, respectively. FESEM micrographs of worn surfaces indicate that abrasion, oxidation, adhesion and delamination were the main wear mechanisms. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
- View/download PDF
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