Friction Force Research Articles

Sedimentation and photophoretic levitation of aerosol clusters in the free molecular regime

Sedimentation of fractal aerosol clusters in rarefied gas medium in the dark and under external illumination similar to sunlight is studied in a numerical experiment taking into account orientation effects, depending on fractal dimension varying within a broad range. The calculation of forces and their moments, including friction forces and photophoretic forces, was carried out on the basis of approximation of free molecular gas kinetic regime and previously developed Monte-Carlo algorithms. Calculation involved 10000 clusters, each of them containing 160 primary spherical particles and efficiently absorbing sunlight and IR radiation, similarly to the particles of soot aggregates.The velocity of multi-particle cluster settling in the absence of illumination, when particle temperatures are equal to the temperature of the gaseous environment, is a distinct function of fractal dimension and is rather close to the velocity of settling of single spherical particles. The settling velocity approximation depending on fractal dimension has been obtained.Illumination brings dramatic changes into sedimentation pattern. The range of cluster sedimentation rate variations broadens substantially, which is a manifestation of gravito-photophoretic effect, so that some clusters even start to levitate. The proportion of levitating clusters is essentially dependent on fractal dimension. For soot-like clusters under irradiation similar to sunlight and pressure equal to atmospheric at the altitude of 30 km, the proportion of levitating aggregates is approximately 7%, which is in good agreement with the experimental data. In the dark and under irradiation, the aggregates rotate, and their trajectories are shaped as spirals.In the context of photophoretic phenomena, a result of principle has been obtained: under irradiation with sunlight, gravito-photophoretic levitation of aerosol soot-like aggregates composed of identical primary particles is possible at a pressure corresponding to the stratospheric altitudes. This result points to the possibility of substantial influence of gravito-photophoretic effect on transport and localization of soot aerosol in the Earth’s stratosphere and mesosphere.

A novel cohesive interlayer model considering friction

To understand the influence of friction on the shear-slip behavior of heterogeneous brittle composites, a novel cohesive interlayer model that can effectively capture the friction effect was proposed based on the classical Park-Paulino-Roesler model. Meanwhile, the unified potential energy function governing the interface tangential and normal behaviors was introduced to realize the mechanical interaction between Mode I fracture and Mode II fracture, and a smooth friction growth function was added in the elastic deformation stage for calculating the accurate contact pressure and friction force. Furthermore, the capability of the proposed model in addressing unloading and reloading was improved, and the fracture energy can vary accordingly during cyclic loading. To verify the effectiveness of the proposed model, it was examined by modelling the shear behavior of a masonry wallette. The results show that the relative error of the proposed model is 14.92% which is much lower than those of the other three pre-existing models when calculating the displacement corresponding to peak shear stress. Meanwhile, in terms of peak shear stress and initial displacement at residual stage, the relative errors of the proposed model are only 1.82% and 5.04%, respectively, indicating the high accuracy. Besides, the tangent stiffness determined by the second-order integration of the potential energy function is also continuous and smooth, which ensures the effective convergence of the proposed cohesive model.

Модель расчёта момента силы трения при вращательном движении тела

The article discusses one of the types of mechanical movement – rotational movement. To automate the calculation of the frictional moment, an algorithm was proposed and a program was written in Python. The algorithm consists of a block for inputting initial data, blocks for calculating intermediate values and the desired value, and outputting the calculation results. Keywords: FRICTION FORCE, MECHANICAL MOTION, BODY, PYTHON LANGUAGE, ROTATION AXIS, ALGORITHM, LOAD

Low friction characteristics and tribochemistry analysis of novel AlTiN/a-C based nanocomposite coatings

Friction reduction of AlTiN-based hard coatings is gaining much attention among researchers worldwide to broaden their tribological applications. Metal/non-metal inclusions, as well as the design of a novel coating architecture, are primarily focused on reducing friction while retaining wear resistance. This study investigates the tribological characteristics of magnetron sputtered AlTiN coatings by incorporating amorphous carbon (a–C) at different concentrations (5–25 at.%), as well as the compositionally graded AlTiN/a-C coatings (CGC). The XPS and Raman spectroscopy results confirm the presence of a-C features, while XRD reveals the formation of ceramic carbide phases in AlTiN coatings with higher carbon content and CGC coatings. The CGC AlTiN/a-C have shown a maximum hardness of 34.3 GPa and an elastic modulus of 321 GPa due to their refined grain structure. The CGC had the lowest friction (0.18 at 300 K and 0.37 at 673 K), as well as improved wear resistance (2.74 × 10−7 mm3/Nm (300 K) and 4.93 × 10−7 mm3/Nm (673 K)). The tribolayers are found to be mainly composed of sp2/sp3 bonded a-C features (including C=C/C─C, C─N, and C─O), which reduces the friction force significantly. The CGC AlTiN/a-C coating has exhibited improved wear resistance behavior due to their finely grained structure and improved mechanical properties.

УТОЧНЕНА МОДЕЛЬ ДВОКАНАЛЬНОГО ЕЛЕКТРОПРИВОДА ПОДАЧІ З ПІДСУМОВУВАННЯМ РУХІВ НА ХОДОВІЙ ГАЙЦІ ДЛЯ ВИСОКОТОЧНИХ МЕТАЛОРІЗАЛЬНИХ ВЕРСТАТІВ

The iterative two-channel feed electric drive (ED) with the summation of movements on the rotating sliding nut (RSN) is designed to increase the speed and accuracy of traditional single-channel ED feed mechanisms (FM) of metal-cutting machines with an inertial working tool (WT). A refined generalized mathematical model of movement of the two-channel ED with RSN was obtained, which was built for WT FM of the high-precision coordinate metal-cutting ma-chine of the 24К60АФ4 model. The model takes into account the main static moments of resistance during metalwork-ing, as well as the nonlinear nature of the sliding friction forces in the machine WT FM. Convenient recurrence rela-tions are obtained for the calculation and modeling of sections of the linearized friction characteristic. The structural-algorithmic diagram of the compensated iterative two-channel feed ED with subordinate configuration of control chan-nels is proposed, which makes it possible to compensate in steady-state conditions the negative impact on the accuracy of WT feed of the main static moments of resistance and nonlinearities of sliding friction forces in the drive load. Ref. 9, fig. 3, table.

Onset, rate, and depth of wetting front progression in membrane distillation

In this study, electrochemical impedance spectroscopy (EIS) is used to characterize the onset, rate, and depth of wetting front progression in real time through commercial polytetrafluoroethylene (PTFE) membrane distillation (MD) membranes. Results showed that higher salinities, elevated transmembrane hydraulic pressures, and larger membrane pore sizes are associated with earlier onset, higher rates, and/or greater depths of wetting front progression – but, notably, in the absence of pore breakthrough. It was also shown that wetting is not an on/off switch; instead, membrane wetting resistance acts as a frictional force that can slow down or stop wetting front progression at different depths in the membrane. PTFE MD membranes were observed to often operate in a deeply wetted, but stable, transition state with normalized impedance values of ∼0.6 to ∼0.1, indicating mid-depth wetting, where the wetting front progresses into the bulk of the membrane and holds its position, or deep wetting, where the wetting front holds its position near the distillate-side surface of the membrane without pore breakthrough. Normalized impedance values as low as 0.04 held constant throughout a 14-day experiment in which pore breakthrough did not occur. These new impedance results strongly support the hypothesis that during MD, for saline feed solutions and under elevated transmembrane pressures – and especially for larger membrane pore sizes – the distillate-side surface can act as a final barrier to pore breakthrough.

Study on the Effect of Starved Lubrication on the Dynamic Characteristics of Locally Failed Roller Bearings

When the lubricant is not enough to maintain the ideal lubrication state of the bearing, the deep groove ball bearing will enter the starved lubrication state, which leads to the change of the vibration response of the deep groove ball bearing with localized defects. Previous bearing dynamics models mainly consider the lubrication state as an ideal lubrication condition, which may not reveal the effect of starved lubrication on the vibration characteristics of defective bearings. In this paper, the internal interaction of the system under starved condition is taken into account, and a dynamic model of defective deep groove ball bearings with insufficient lubricant is established to investigate the effects of different starved lubrication degrees on the contact force, friction force, cage speed, and system vibration characteristics. The results show that the lubricant insufficiency significantly changes the contact force inside the bearing, and the increase in friction caused by the increase in the degree of starved lubrication leads to the suppression of the degree of bearing slipping. The root mean square (RMS) value of the time-domain signal and the outer ring fault frequency both increase with the increase of the starved degree. The results of the study are helpful for fault diagnosis and condition monitoring of related equipment.

Heterogeneous solvent dissipation coupled with particle rearrangement in shear-thinning non-Brownian suspensions.

Dense non-Brownian suspensions exhibit significant shear thinning, although a comprehensive understanding of the full scope of this phenomenon remains elusive. This study numerically reveals intimate heterogenous coupled dynamics between many-body particle motions and solvent hydrodynamics in shear-thinning non-Brownian suspensions. In our simulation systems, we do not account for frictional contact forces, reflecting experimental conditions under low shear rates where shear thinning occurs, while hydrodynamic interactions are directly incorporated using the Smoothed Profile Method. We demonstrate the spatially correlated viscous dissipation and particle motions; they share the same characteristic length, which decreases with increasing shear rate. We further show that, at lower shear rates, significant particle density changes are induced against the incompressibility of the solvent, suggesting the cooperative creation and annihilation of gaps and flow channels. We discuss that hydrodynamic interactions may substantially restrict particle rearrangements even in highly dense suspensions, influencing the quantitative aspects of macroscopic rheology.

Construction of a Science Teacher's Topic-Specific Pedagogical Content Knowledge in the Gifted Class

This study examines a science teacher's pedagogical content knowledge during instruction on the topics work and energy, simple machines, and friction force in a gifted class. The research adopts a single case study approach, employing qualitative methods. The participant is a middle school science teacher, and data collection tools include interviews, observations, card-sorting activities, and lesson plans. The main findings of the study are: (1) gifted students required additional science practice beyond the scope of the traditional curriculum, (2) the participating teacher encountered challenges when designing and implementing enrichment activities, (3) the characteristics of gifted students positively influenced the development of the teacher's pedagogical content knowledge, and (4) the presence of gifted students prompted a shift in the teacher's science teaching orientation from traditional methods to reform-based practices. Teachers need to have additional knowledge bases or Pedagogical Content Knowledge components. Notably, the research underscores the relevance of the knowledge of enrichment curriculum and knowledge of characteristics of gifted students in the training of science teachers, along with the crucial role of STO in the education of gifted students, especially in the context of teaching physics. These findings offer significant implications for the curriculum designed for gifted students, particularly concerning the teaching and learning of physics topics.

Large Scale Simulation of 3D Fault Rupture Subjected to Far‐Field Loading With PDS‐FEM: Application to the 2018 Palu Earthquake

AbstractSimulating dynamic rupture of fault systems can be computationally demanding, as it requires reproducing complex fault geometry and accurately capturing waves propagating away from the rupture front. It is in particular challenging to predict an initial stress state consistent with fault geometries, heterogeneous distribution of surrounding materials, and far‐field tectonic loading. While standard techniques such as contact analysis and Lagrangian multipliers can be used to model the fault, it can lead to significant computational overhead in FEM. We extended Particle Discretization Scheme‐FEM, which provides numerically efficient crack treatment, without requiring contact analysis, to simulate dynamic fault rupture as a frictional crack propagating along a pre‐existing shear crack surface. Initial stress, which is consistent with initial frictional forces, material distribution and fault geometry, is derived using Coulomb friction and far‐field boundary conditions. The study first demonstrates the ability of the numerical method to reproduce a 2D ideal supershear scenario, and the underlying Burridge‐Andrew rupture mechanism. The methodology is then applied to the large scale simulation of the 2018 Palu earthquake on the Palu‐Koro fault. The simulation successfully reproduces the early and sustained supershear rupture which was observed for the Palu earthquake. Also, it indicates that the presence of an off‐fault damage zone can contribute to the low rupture velocity measured during the earthquake. Unlike sub‐Rayleigh earthquakes, the shockwave propagation was observed to lead to significant amplitudes of the ground motion even far from the fault.

Tunable High-Static-Low-Dynamic Stiffness Isolator under Harmonic and Seismic Loads

High-Static-Low-Dynamic Stiffness (HSLDS) mechanisms exploit nonlinear kinematics to improve the effectiveness of isolators, preserving controlled static deflections while maintaining low natural frequencies. Although extensively studied under harmonic base excitation, there are still few applications considering real seismic signals and little experimental evidence of real-world performance. This study experimentally demonstrates the beneficial effects of HSLDS isolators over linear ones in reducing the vibrations transmitted to the suspended mass under near-fault earthquakes. A tripod mechanism isolator is presented, and a lumped parameter model is formulated considering a piecewise nonlinear–linear stiffness, with dissipation taken into account through viscous and dry friction forces. Experimental shake table tests are conducted considering harmonic base motion to evaluate the isolator transmissibility in the vertical direction. Excellent agreement is observed when comparing the model to the experimental measurements. Finally, the behavior of the isolator is investigated under earthquake inputs, and results are presented using vertical acceleration time histories and spectra, demonstrating the vibration reduction provided by the nonlinear isolator.

Experimental Analysis of Wear Rate and Frictional Coefficient of Various Steel Material

This research study focuses on experimentally investigating the wear rate and frictional coefficient of different steel materials using a pin-on-disk testing machine. The tribological properties of steel materials play a crucial role in determining their performance and reliability in various applications. The objective of this study is to assess and compare the wear characteristics and frictional behavior of multiple steel materials under controlled testing conditions. The experimental setup involved employing a pin-on-disk testing machine, where a steel pin was brought into contact with a rotating steel disk. To ensure consistency, the pin and disk specimens were fabricated from various steel materials with uniform dimensions and surface finish. Several test parameters, such as load, sliding speed, and duration, were carefully selected to mimic real-world operating conditions. Throughout the experimental runs, the frictional forces and wear rates were continuously monitored and recorded. The wear rate was quantified by measuring the weight loss of the pin and disk specimens after each test run. Additionally, the frictional coefficient was calculated by dividing the frictional force by the applied load. By comparing these parameters among the tested steel materials, the researchers aimed to identify variations in their tribological performance. The results obtained from the experimental investigation indicated significant disparities in the wear rate and coefficient of friction among the tested steel materials. Certain steel materials exhibited lower wear rates and frictional coefficients, suggesting improved tribological properties compared to others. The observed differences in wear patterns and frictional behavior were thoroughly analyzed to gain insights into the underlying mechanisms responsible for the performance variations.

Energy required to cut the soil with No.4 circumferential knives of the large rotor of the straight-through rotary ripper

Introduction. To solve the problem of the fast and high-quality road construction, when economic facilities and settlements are located at a considerable distance from each other, cannot be solved without the use of a complex of continuous units. The continuous ditch forming unit and the tunneling unit contain straight-through rotary rippers. Insufficient theoretical studies in this area do not enable to calculate the interaction of the elements of a direct-flow rotary ripper with the soil. Therefore, there is a need for theoretical studies to determine the energy parameters of the large rotor, in particular, that which is necessary for cutting the soil with the No.4 circumferential knives of the large rotor.The research method. The methods for calculating the required energy inputs: to separate the reservoir from the soil mass; separation of the reservoir into fragments; creating a gap in the soil mass; deformation of a part of the soil mass; overcoming the friction of the ground on the edge of the blade; overcoming the soil pressure on the front surface; movement of the soil by the front surface; overcoming the friction of the ground on the front surface have been developed.Results. On the basis of the developed methods, the parameter calculations were made. From the plane models and the spatial model of the forces of interaction with the soil of the circumferential knives No.4 of the large rotor, resultant forces, their components, normal forces were revealed. The force of friction of the soil on the edge of the blade and the front surface of No4 circumferential knives was calculated. The volumetric energy required for cutting with No.4 circumferential knives when mining one cubic meter of soil with a straight-through rotary ripper is calculated.Conclusion. The energy required to drive the circumferential knife includes separating the seam from the soil mass; separation of the reservoir into fragments; creating a gap in the soil mass; deformation of a part of the soil mass; overcoming the friction of the ground on the edge of the blade; overcoming the soil pressure on the front surface; movement of the soil by the front surface; overcoming the friction of the ground on the front surface. As a result of the calculations, the total energy required for cutting with No.4 circumferential knives, when mining one cubic meter of soil with a straight-through rotary ripper, was 9110 joules.

Enhancing Tribological Characteristics of Titanium Grade-5 Alloy through HVOF Thermal-Sprayed WC-Co Nano Coatings by TOPSIS and Golden Jack Optimization Algorithm.

Thermal spray coatings have emerged as a pivotal technology in materials engineering, primarily for augmenting the characteristics related to wear and tribology of metallic substrates. This study aimes to delve into applying High-Velocity Oxygen Fuel (HVOF) thermalsprayed WC-Co nanocoatings on Titanium Grade-5 alloy (Ti64). The coating process, utilizing nano-sized WC-Co powder, undergoes systematic optimization of HVOF parameters, encompassing the flow rate of carrier gas, powder feed rate, and nozzle distance. Experimental assessments via Pin-on-Disc (PoD) tests encompass Loss of Wear (WL), Friction Coefficient (CoF), and Frictional Force (FF). Later, an exhaustive optimization of responses is conductede using the Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS) method and the golden jack optimization algorithm (GJOA). Outcomes show a substantial increase in WL, CoF, and FF with a rise in the carrier gas and powder feed rate. However, with increasing spraying distance of powder, the WL, CoF, and FF tend to lower due to higher bonding, which leads to increased wear resistance. The ideal parametric settings achieved from TOPSIS and GJOA are 245 mm of spray distance, 30 gpm rate of powder feed, and 11 lpm of carrier gas flow rate. The powder feed rate contributes 88.99% to the control action, as seen from ANOVA. The confirmation experiment presents that the WL, CoF, and FF output responses are 42.33, 27.97, and 9.38% less than the mean of experimental data. These results highlight the HVOF process in spraying WC-Co nanocoatings to fortify the durability and performance of Ti64 alloy that can be patented for diverse engineering applications.

Spines and Inclines: Bioinspired Spines on an Insect-Scale Robot Facilitate Locomotion on Rough and Inclined Terrain.

To navigate complex terrains, insects use diverse tarsal structures (adhesive pads, claws, spines) to reliably attach to and locomote across substrates. This includes surfaces of variable roughness and inclination, which often require reliable transitions from ambulatory to scansorial locomotion. Using bioinspired physical models as a means for comparative research, our study specifically focused on the diversity of tarsal spines, which facilitate locomotion via frictional engagement and shear force generation. For spine designs, we took inspiration from ground beetles (Family Carabidae), which is a largely terrestrial group known for their quick locomotion. Evaluating four different species, we found that the hind legs host linear rows of rigid spines along the entire tarsus. By taking morphometric measurements of the spines, we highlighted parameters of interest (e.g., spine angle and aspect ratio) in order to test their relationship to shear forces sustained during terrain interactions. We systematically evaluated these parameters using spines cut from stainless steel shim attached to a small acrylic sled loaded with various weights. The sled was placed on 3D-printed models of rough terrain, randomly generated using fractal Brownian motion, while a motorized pulley system applied force to the spines. A force sensor measured the reaction force on the terrain, recording shear force before failure occurred. Initial shear tests highlighted the importance of spine angle, with bioinspired anisotropic designs producing higher shear forces. Using this data, we placed the best (50○ angle) and worst (90○ angle) performing spines on the legs of our insect-scale ambulatory robot physical model. We then tested the robot on various surfaces at 0, 10 and 20○ inclines, seeing similar success with the more bioinspired spines.

Predicting Low Sliding Friction in Al-Steel Reciprocating Sliding Experiment after a Controlled Grinding of the Steel Counterface

The aim of this study was to identify the areal surface parameters that correlated with lowering of sliding friction. Different ground surfaces were created on stainless steel and the lubricated sliding friction generated at the contact interface with a flat-faced aluminum pin was studied. The frictional force encountered is an order of magnitude lower for a P1200-finished surface than the other ground surfaces. Using 3D surface profilometry, a unique surface parameter ratio “Spk/Sk” was found to predict the frictional performance of these surfaces. When this surface parameter ratio was less than 1, average sliding friction was close to 0.1. When this ratio was greater than 1, the coefficient was an order of magnitude lower. Using energy dispersive spectrometry, such surfaces after wear showed the presence of a uniform dispersed layer of iron oxide on the surface of the pin. This was absent on the surfaces having high friction, indicating the role of the steel counter surface in building this beneficial transfer layer. Scanning electron microscopy provided topography images to visualize the surface wear. The motivation for the authors was to use a commercially scaled process like precision grinding for the surface modifications on stainless steel.

Quasi-static cyclic tests of FRP-confined steel-reinforced HPFRCC circular columns

This study presents a novel composite component comprising of steel-reinforced high-performance fiber reinforced cementitious composites (HPFRCC) circular columns confined by fiber-reinforced polymer (FRP), with the goal of improving the mechanical behavior of conventional reinforced concrete (RC) columns. Quasi-static cyclic loading tests were conducted to investigate various aspects of the column specimens, including failure phenomena, load-displacement response, sectional compression-bending performance, plastic hinge length, and lateral strain distributions in the FRP jacket, etc. A self-designed frictional force measurement device was employed to accurately measure the actual force borne by the specimen. The experiment results revealed that FRP confinement effectively improved the load-bearing capacity and deformation capacity of the specimens and delayed the deterioration of the sectional compression-bending performance. The superior tensile ductility of HPFRCC led to increased yielding displacement and peak load compared to FRP-confined concrete specimen, although this enhancement was limited. Furthermore, the peak load of the FRP-confined HPFRCC specimen increased with axial load, while the sectional compression-bending performance after the peak load remained relatively stable until approaching the collapse prevention (CP) limit state.

An analytical solution for shear bearing capacity of circumferential joints of precast concrete segmental tunnel linings considering dowel action

AbstractThe capacity of the circumferential joint of the precast concrete segmental tunnel lining (PCTL) structure in terms of shear performance principally includes the dowel action by connector/bolt as well as friction force, and it is a vital parameter to assess the mechanical response of the circumferential joint. Further, as there was no analytical model available for precise estimation of a circumferential joint in terms of the shear‐bearing capacity considering the dowel action of the bolt in the presence of axial/normal force, therefore in this investigation, an analytical model has been proposed to estimate the shear‐bearing capacity of the circumferential joint. Furthermore, the analytical model's precision and accuracy were validated via large‐scale experimental investigation on a circumferential joint of PCTL. Upon comparing analytical model outcomes with experimental results, absolute error varied between +5% and −9%, with an average value of the coefficient of friction at the yield point of the bolt. Moreover, the formation of hinges on the side of the bolt within the segment was considered a failure of the circumferential joint. Additionally, the parametric investigation revealed that with just a 1% change in axial force, the diameter, pre‐tightening, and yield strength of the bolt and concrete strength improved by 2.85%, 1%, 0.27%, 0.26% and 0.17% shear‐bearing capacity of the circumferential joint respectively. Axial force variation greatly influences the shear‐bearing capacity of circumferential joint followed by diameter, pre‐tightening, yield strength of the bolt, and concrete strength. Conclusively, with analysis of axial force distribution around the ring for the tunnel, the proposed model has been applied to a full ring to estimate shear bearing capacity.

Clinical efficiency of new generation elastomeric ligatures over conventional: An in-vivo study

Friction being an imperative element in clinical orthodontics affects all stages of treatment and high frictional forces can affect the treatment duration and outcome in a deleterious manner. This study was done to appraise frictional resistance of non-conventional elastomeric modules in comparison with conventional elastomeric modules, during the retraction of teeth. The study sample size includes 30 patients (11 males and 19 females) undergoing orthodontic treatment. They were grouped into 3, namely, Group A- Slide nonconventional elastomeric ligatures Group B- super slick nonconventional elastomeric ligatures, and Group C- the conventional ligature. The study models were obtained to assess canine retraction rate, anchor loss, canine rotation, and molar rotations at different time intervals and subjected to statistical analysis. : The canine retraction rate(maxilla) for Group A, B and C was 1.674+/-0.092, 1.187+/-0.156, and 1.147+/-0.113,(mandible)1.765+0.099, 1.300+0.099 and 1.270+0.111 respectively. Mean anchorage loss(maxilla) group A- 1.054mm, group B- 1.080mm, group C -1.715mm (mandible) 1.024mm, 0.952mm and 1.664mm respectively. Canine rotation(maxilla) of Group A, B and C is 8.550+/-1.506, 5.300+/-1.386, 6.100+/-1.315and(mandible) 8.930/-+1.474, 5.830+/-1.096, 6.880+/-1.813 respectively. Mean molar rotation (maxilla) 2.580+0.735, 2.210+0.549 and 2.210+0.700 (mandible)2.900+0.541, 2.650+0.639 and 2.780+0.604 in group A, B and C respectively. Mean anchor loss was lesser in non-conventional modules, canine retraction rate was higher with Slide ligature, canine rotations were least in superslick more in Slide ligature, and rotation of molar was apparent for all the groups.

High Temperature Induced Low Friction and Wear in a-C:Si via Formation of a "H Passivation Layer/a-SiO2/H Passivation Layer" Structure in a Humid Environment.

Doping Si into amorphous carbon can decrease humidity sensitivity, improve thermal stability, and retain excellent friction performance. Experimental studies have shown that Si-doped amorphous carbon formed Si-OH structures and frictional oxides in high-temperature and humid environments. However, the formation process of Si-OH and frictional oxides, as well as their structure, formation conditions, and antifriction properties, remains unclear. In this paper, reactive force field molecular dynamics (ReaxFF MD) was used to investigate the frictional performance of a-C and a-C:Si (7.2 atom %) at temperatures of 300, 700, and 1500 K in H2O environments. The results showed that with increasing temperature, the friction force of a-C increases from 8.2 nN at 300 K to 15.51 nN at 1500 K, while that of a-C:Si decreases from 10.3 nN at 300 K to 5.6 nN at 1500 K. In H2O environments, a-C:Si formed a "H passivation layer/a-SiO2/H passivation layer" structure, which inhibited the formation of interfacial bonds between the upper and lower substrates and reduced the wear of the substrate while ensuring the antifriction and antiwear properties of a-SiO2. This paper reveals the mechanism behind the low friction characteristics of a-C:Si in high-temperature and humid environments, providing theoretical guidance for the application of a-C:Si under such conditions.