Increase In Sliding Velocity Research Articles

Atomistic understanding of the interlayer friction of graphullerene

Graphullerene, an emerging two-dimensional carbon allotrope derived from C60, is endowed with distinctive mechanical and thermal characteristics, positioning it as a potential candidate with superior lubricating properties akin to graphene and C60. This research delves into the interlayer frictional behavior of graphullerene through molecular dynamics simulations, meticulously examining the impact of sliding velocity, normal load, flake orientation, and temperature. The findings reveal a stick-slip mode of friction with an exponential increase in friction force as sliding velocity increases. Additionally, the study captures the formation of puckering at the slider's forefront, which undergoes ballistic motion propelled by the slider's momentum. Notably, at higher velocities, a distinctive "stone skipping" effect is observed, with the graphullerene flake intermittently detaching from the substrate.

Molecular dynamics simulation on friction performance of collision sliding contacts of soft metals in vibration environment

Soft metals are often used for space mechanism lubrication because of their low shear strength. In outer space, the vibration of spatial mechanism will occur when there is a small disturbance due to the effects of microgravity environment. Studies on the friction properties of soft metals in vibration environment could contribute to the application of space lubrication materials. Taking a clearance joint as an example, the relative motion between the shaft and the bearing is simplified to a sliding contact between a cylinder and two smooth contact bodies. A molecular dynamics model of the collision sliding contact between a rigid cylindrical indenter and an elastic substrate is established. The effects of sliding velocity, collision velocity and indenter radius on the friction properties of soft metals are studied. The results show that the Ag substrate and Au substrate present strong adhesion to the Fe indenter. The indenter and the substrate are always in a state of adhesive sliding contact. The larger the initial collision velocity of the indenter, the higher the friction force. The friction force shows great values as the sliding velocity increases. As the increase of indenter radius, the contact area is enlarged, which results in a high friction force. The adhesion of the Cu substrate to the Fe indenter is weak, so the friction force shows a low value, and the friction performance of Cu is the best, while the friction performance of Au is the worst.

Internal Surface Enhancement by Magnetic Abrasive Finishing of Brass Pipe at Different Speeds and Particle Composition

Abstract: This study examined the effect of magnetic field on the interior surface finish of Brass UNS C26800 pipe. The parameters sliding velocity of electromagnets, concentration ratio (castor oil and magnetic abrasive particles), and number of cycles were modified within a predetermined range, and their effects on surface finish (%Ra) and material removal rate were determined (MRR). The remaining process parameters remained unchanged throughout the duration of the experiment. In the case of 7:3 and 8:1 concentration ratios, the percentage improvement in surface finish (%Ra) increases and subsequently drops as the sliding velocity of electromagnets increases. The only explanation is because the blunting of abrasives occurs at greater sliding speeds, which reduces the improvement of surface finish. In the event of a concentration ratio of 9:1, however, the percentage increase in surface finish increases with the increase in sliding velocity as a result of the work hardening of the surface, which enables the simple removal of surface peaks. Also, for sliding velocities of 0.62 mm/sec and 1.23 mm/sec, the percentage improvement in surface finish falls with increasing concentration ratio due to the slurrification of magnetic abrasives in the lubricant as a result of increasing oil concentration. At a sliding velocity of 2.46 mm/sec, the improvement in surface finish is proportional to the amount of oil applied due to the increased control and velocity of the surface. In addition, two cycles of electromagnets relative to the workpiece provided the finest surface finish. The MRR increases as sliding velocity increases. Consequently, MRR is minimal at the slowest sliding velocity.

The Combined Effects of Sliding Velocity and Martensite Volume Fraction on Tribological Behavior of a Dual-Phase Steel

The focus of this study was the combined effects of sliding velocity (SV) and martensite volume fraction (MVF) on the tribological behavior of dual-phase (DP) steel. Dry frictional tests were realized on a ball-on-disk tribometer by unidirectional sliding at 0.1 m/s, 0.6 m/s, and 1 m/s. Considering the increase in SV, both the friction coefficient (COF) and wear rate decrease due to the increase in oxidative wear. At 0.1 m/s, the major wear mechanism is abrasive wear, accompanied by partial material flaking and less oxidation wear; at 0.6 m/s, the wear mechanism is in the transition between abrasive wear and oxidation wear; at 1 m/s, oxidation wear becomes the dominant wear mechanism. For the same SV, specimens with lower MVF exhibited lower wear compared to specimens with higher MVF; this phenomenon is especially evident at low SV. As the SV increases, the effect of MVF on the wear decreases, and the velocity becomes the dominant factor.

Influence of Applied Load and Sliding Velocity on Tribocorrosion Behavior of 7075-T6 Aluminum Alloy

In this paper, the tribocorrosion behavior and synergistic effect of 7075-T6 aluminum alloy under different applied loads (100, 150, and 200 N) and sliding velocities (100, 150, and 200 rpm) were studied in a 3.5 wt.% NaCl solution. Tribocorrosion experiments were conducted in a tribobocorrosion system with pin-on-disc testing. The results show that the interaction between applied load and sliding velocity significantly affects the mechanical and electrochemical properties of 7075-T6 aluminum alloy. Increases in sliding velocity and applied load will accelerate the corrosion. Due to the synergistic effect of corrosion and wear, the wear rate is almost unchanged as the sliding velocity increases. When the applied load increased from 100 to 200 N, the wear rate increased from 1.97 × 10−5 to 2.08 × 10−5 mm3/N·m, and the delamination wear phenomenon was aggravated.

Mechanical behaviour of SiC particulate reinforced Cu alloy based metal matrix composite

In this study, Cu-alloy (RG10) metal matrix composite reinforced with different percentages of SiC (3%, 6%, 9%, and 12%) reinforcement were prepared using in-house developed stir casting set-up. Microstructural and wear character was performed. The microstructural study reveals that there is a uniform distribution of SiC particulates throughout the composite, and very little porosity exists. Vicker's microhardness test was conducted for the fabricated composites. It was found that the hardness increases with an increase in the percentage of SiC particulate reinforcement. The pin-on-disc testing method was used for tribological characterization. With the addition of reinforcement SiC, wear resistance of base alloys is improved enormously, and as the sliding velocity increases, the wear volume increases because of an increase in sliding distance. From density calculation, it was seen that the density of the composite decreases with an increase in addition to SiC particulate reinforcement.

Influence of Si content on the mechanical and wear behavior of Al-xSi-0.4Mg-10Fly ash metal matrix composite

The present work deals with the fabrication of composite by varying the silicon weight percentage and keeping the fly ash constant at 10 wt% to obtain hypoeutectic, eutectic and hypereutectic aluminium metal matrix composite. The microstructure, worn out surface and change in morphology of the developed composite were studied by using a scanning electron microscope. In addition to this, the hardness and tensile properties of the developed composites were discussed. It is observed from the present study that the hardness and tensile values of the composite increases with an increase in wt. % Si. The wear rate of the different composites was determined by pin-on-disk wear testing apparatus and the corresponding wear rate was calculated by varying the different wear testing parameters. It is observed from the wear results that the wear rate of the developed composites decreases as the sliding velocity increases and the wear rate increases with an increase in the applied load.

Friction and sliding wear studies on functionally graded Al LM25/WC composite

Functionally graded LM25/15 wt.% Tungsten carbide composite of dimension Øout 150 mm x Øin 110 mm x 100 mm and thickness 20 mm was studied to understand the influence of process parameters (applied load, sliding velocity, sliding distance) on the dry sliding wear rate and co-efficient of friction. A 5-level 3 parameter central composite design was developed using response surface methodology considering applied load (10-50N), sliding velocity (1-3 m/s) and sliding distance (500-2500 m) as input parameters. Dry sliding experiments were performed on pin-on-disk tribometer at ambient conditions. Significance tests, Analysis of Variance and confirmation experiments were done to check the accuracy of generated regression model. Generated surface plots revealed wear rate to be increasing as applied load and sliding distance increases and decrease as sliding velocity increases. Worn surface analysis performed revealed formation of deep grooves at high load, MML formation at high velocities and heavy delamination and particle pull-out at high sliding distances.

Sliding friction between two silicon-carbide surfaces

Sliding friction between two SiC surfaces is important due to its relevance to many practical applications. It is also important to study whether kinetic friction at the nanoscale follows Coulomb’s law. Since SiC exists both as an amorphous material and with a crystalline structure, the effect of surface roughness on the kinetic friction may also be significant. We report the results of an extensive molecular dynamics simulation of sliding friction between surfaces of the two types of SiC over a wide range of sliding velocities. The amorphous SiC was generated by the reactive force field ReaxFF, which was also used to represent the interaction potential for the simulation of sliding friction. As the sliding velocity increases, bond breaking occurs at the interface between the two surfaces, leading to their roughening and formation of excess free volume. They reduce the kinetic friction force, hence resulting in decreasing the difference between kinetic friction in the amorphous and crystalline surfaces. The average kinetic friction force depends nonlinearly on the sliding velocity V, implying that Coulomb’s law of friction is not satisfied by the surfaces that we study at the nanoscale. The average kinetic friction force Fk depends on V as Fk∝ln⁡V.

A Study on Drilling High-Strength CFRP Laminates: Frictional Heat and Cutting Temperature.

High-strength carbon fiber reinforced polymer (CFRP) composites have become popular materials to be utilized in the aerospace and automotive industries, due to their unique and superior mechanical properties. An understanding of cutting temperatures is rather important when dealing with high-strength CFRPs, since machining defects are likely to occur because of high temperatures (especially in the semi-closed drilling process). The friction behavior at the flank tool-workpiece interface when drilling CFRPs plays a vital role in the heat generation, which still remains poorly understood. The aim of this paper is to address the friction-induced heat based on two specially-designed tribometers to simulate different sliding velocities, similar to those occurring along the flank tool-work interface in drilling. The elastic recovery effect during the drilling process was considered during the tribo-drilling experiments. The drilling temperatures were calculated by the analytical model and verified by the in-situ experimental results gained using the embedded thermocouples into the drills. The results indicate that the magnitudes of the interfacial friction coefficients between the cemented carbide tool and the CFRP specimen are within the range between 0.135–0.168 under the examined conditions. Additionally, the friction caused by the plastic deformation and elastic recovery effects plays a dominant role when the sliding velocity increases. The findings in this paper point out the impact of the friction-induced heat and cutting parameters on the overall drilling temperature.

Perspectives of the Friction Mechanism of Hydrogenated Diamond-Like Carbon Film in Air by Varying Sliding Velocity

The purpose of the present work is to probe the friction mechanism of hydrogenated diamond-like carbon (H-DLC) film in air by varying sliding velocity (25–1000 mm/s). Friction tests of Al2O3 ball against H-DLC film were conducted with a rotational ball-on-disk tribometer. As the sliding velocity increases, both the friction coefficient and the surface wear of H-DLC film decrease, reach the minimum values, and then increase in the high sliding velocity region. Based on the observed results, three main friction mechanisms of H-DLC film—namely graphitization mechanism, transfer layer mechanism, and passivation mechanism—are discussed. Raman analysis indicates that the graphitization of worn surface on the H-DLC film has a negligible contribution to the variation of the friction coefficient and the surface wear. The origin of the sliding velocity dependence is due to the synergistic interaction between the graphitized transfer layer formation and the surface passivation. The present study will not only enrich the understanding of friction mechanism of H-DLC films in air, but will also help to promote their practical engineering applications.

Tribological Characteristics of LM13/Si3N4/Gr Hybrid Composite at Elevated Temperature

LM13/12wt.%Si3N43wt.%Gr hybrid composite was fabricated by liquid metallurgy route and its tribological characteristics were tested using pin-on-disc tribometer. The experiments were conducted as per L27 orthogonal array to study the influence of process parameter at normal and elevated temperature (150 °C) by varying process parameters such as load (10, 20, 30 N), sliding velocity (1, 2, 3 m/s) and sliding distance (750, 1250, 1750 m). The results revealed that the wear rate at both temperatures was proportional to load due to the stress induced which fractures Si3N4 particles and stripes aluminium matrix. As the sliding velocity increases, wear rate showed an increasing trend due to three body abrasion from eroded Si3N4 grits. The wear rate was inversely proportional to sliding distance, because of MML (Mechanically mixed layer) formed from chemical reactions between tribo-layers. When load increases COF (Coefficient of friction) decreases then increases due to lubricating and tillage effect. As velocity and distance increases, COF decreases due to thermal softening, hardening of layer and also the lubrication effect produced by chemical reactions. Analysis of variance (ANOVA) and S/N ratio at room temperature and elevated temperature for both Wear rate and COF were developed to study the most significant parameters on corresponding responses. Confirmation experiments were conducted to validate multi-linear regression model. Worn surfaces were examined using scanning electron microscope (SEM) to investigate wear characteristics. Energy dispersive X-ray spectroscopy (EDAX) and X-ray diffraction (XRD) results confirmed the formation of MML and different phases formed during wear mechanism. The developed material can be used to fabricate cylinder liners, cylinder blocks and brake rotors.

Fabrication of Cu-Sn/SiC Metal Matrix Composites and Investigation of its Mechanical and Dry Sliding Wear Properties

Requisite for advanced materials with high hardness, high tensile strength and improved wear properties has been drastically increased in recent times. The main objective of this paper is to fabricate unreinforced copper alloy and Cu-Sn/SiC composite with varying wt% of SiC (5, 10, and 15) by liquid metallurgy route and to investigate its microstructure, mechanical properties and dry sliding wear behavior. The hardness and tensile strength of alloy and composites are measured on Vickers micro hardness tester and Universal Testing Machine respectively. Tensile test specimens are further subjected to fractography analysis and the results shows ductile mode of failure for alloy and mixed ductile and brittle mode failure for composites. Based on the test results, it is observed that Cu-Sn/10 wt% of SiC have uniform distribution of particles with optimum mechanical properties. Hence only these 10 wt% SiC composite is considered for dry sliding wear analysis and experiments are conducted using Pin-on-disc tribometer. Analysis of process parameters in three levels such as applied load (15,25,35 N), sliding distance (750,1250,1750 m) and sliding velocity (1,2 and 3 m/s) is done by Taguchi’s Design of Experiments technique based on L₂₇ orthogonal array. From Signal-to-Noise ratio and Analysis of Variance approach, the rank of process parameters as well as its influence on the response is found. The results reveal that the wear rate increases as applied load and sliding distance increases and the wear rate decreases as sliding velocity increases. The load is found to have the highest influence on wear rate (38.5%) followed by sliding distance (7%) and sliding velocity (7%). Interaction between the process parameters also contributed towards wear rate. The worn surfaces were examined using Scanning Electron Microscopy and observed the formation of mechanically mixed layer at high velocity condition. Thus, the fabricated composites can be used in applications like bearings and bushes to improve the wear resistance.

Study on Abrasive Wear of Brake Pad in the Large-megawatt Wind Turbine Brake Based on Deform Software

For the friction and wear issues of brake pads in the large-megawatt wind turbine brake during braking, this paper established the micro finite element model of abrasive wear by using Deform-2D software. Based on abrasive wear theory and considered the variation of the velocity and load in the micro friction and wear process, the Archard wear calculation model is developed. The influence rules of relative sliding velocity and friction coefficient in the brake pad and disc is analysed. The simulation results showed that as the relative sliding velocity increases, the wear will be more serious, while the larger friction coefficient lowered the contact pressure which released the wear of the brake pad.

Comparison of the thermophysical properties, microstructures, and frictional behavior of lining materials used in mine hoists

Mine hoists for medium depth and deep mines in China rely on friction hoists. Proper function of the equipment involves controlled frictional contact between a rope and a lining. While there has been a lot of empirical testing of friction hoist materials, studies of the effects of their microstructure and basic properties on friction and wear have largely been neglected. Three commercial grade linings with similar compositions were investigated (trade names: K25, G30, and GM-3). Their thermo-physical properties were measured using XPS, FTIR and TGA. Their hardness and other properties were correlated with their microstructures and frictional behavior. The DTG curves of the three linings follow a similar pattern and their weight loss rate peaks occur in the second stage due to the cyclodehydration of phenolic hydroxyl and fracture of methylene. GM-3, which is highest content of inorganic filler, had the smallest weight loss. Reciprocating sliding friction and wear tests indicated that higher contents of methylene and filler improve the friction coefficient. Adhesive wear is observed when the friction material hardness is relatively low. When the sliding velocity increases, the friction coefficient of two of the linings (K25 and GM-3) increases, but that of G30 first rises then falls. The reasons for these differences in behavior are discussed.

Modelling of a rapidly evolving rockslide: the Mt. de la Saxe case study

To model the temporal evolution of complex landslides, a 1D pseudo-dynamic visco-plastic approach, based on Perzyna's theory, has been conceived. In the original version of the model the viscous nucleus has been assumed to be bi-linear: irreversible deformations develop uniquely for positive yield function values whereas, in a more general case, even for negative values. In this work the model has been enriched by considering: i) an exponential viscous nucleus, ii) a strain-rate softening to reduce friction angle as sliding velocity increases and iii) block interaction forces to cope with complex 3D geometries for the sliding mass. The application of the proposed model to the La Saxe rockslide (Italy) clearly shows how a relatively simple model can be applied to a complex landslide by considering a spatial discretization of the sliding mass.

Probing into frictional contact dynamics by ultrasound and electrical simulations

AbstractFriction arises in the interface of friction pair, and therefore, it is difficult to detect it. Ultrasonic means, as a NDT, is the correct alternative. This paper introduces a means of detecting dynamic contact and an interpretation of behaviors of dry friction. It has been determined that frictional surfaces have a specific property of dynamic response hardening (DRH). Dynamic response forces and oscillation arise during static–kinetic transition process. While the contact zone of sliding surfaces appears “hard” in motion, it appears “soft” at rest. Consequently, a separation of the surfaces occurs and the real area of contact is decreased as sliding velocity increases. This is the cause of F–v descent phenomenon. When the friction comes to a rest, the remaining process of DRH and micro-oscillation do not disappear instantaneously, instead they gradually return to their original static position. The contact area, therefore, is increased by rest period (F–T ascent characteristics). Based on analog...

STUDY OF WEAR BEHAVIOUR OF Al/ (Al2O3P and SiCP) HYBRID METAL MATRIX COMPOSITES

In this study, dry sliding wear behaviour of Aluminium Hybrid Metal Matrix Composite was investigated and a prediction model was developed using Taguchi’s method. Aluminium A356alloy reinforced with equal weight percentage of alumina and silicon carbide particles (10wt%, 20wt% and 30wt %) was produced using liquid metallurgy method. Experiments were conducted using Pin-on-disc tester. The sliding distance was kept constant and the effect of load, sliding velocity and weight percentage of reinforcement on the wear properties was evaluated. It was found that as load increases, wear rate also increases and it decreases as sliding velocity increases. By increasing weight percentage of reinforcements, the wear resistance increases and was found that 30% reinforced composite had less wear rate. The prediction model showed that the major parameter that influences the wear rate was load followed by weight percentage of reinforcement and sliding velocity. By confirmation test, the predicted wear rates were found to be close to the experimental values. Based on this approach, it was found that the improvement in the wear resistance of hybrid composites became more significant at high sliding velocity, low load and with high weight percentage of reinforcements. Keywords: Dry sliding wear, Metal Matrix Composite, Alumina, Silicon carbide, Prediction model, Taguchi’s method

CHARACTERIZATION OF FRICTION COEFFICIENT AND HEAT PARTITION COEFFICIENT BETWEEN AN AUSTENITIC STEEL AISI304L AND A TiN-COATED CARBIDE CUTTING TOOL

This work aims at characterizing the tribological behavior of an AISI304L austenitic steel and a TiN-coated carbide tool under extreme conditions corresponding to the one occurring at the cutting tool-work material in dry machining. A specially designed open tribometer has been used to characterize the friction coefficient, heat partition coefficient and adhesion in the contact versus sliding velocity and contact pressure. It has been shown that sliding velocity is the most influential parameter. An increase of sliding velocity induces a great decrease of friction coefficient, whereas contact pressure seems to play a secondary role on the friction coefficient. Adhesion is minimized when sliding speed increases. Heat partition coefficient decreases with sliding velocity, which tends to decrease the ratio of heat transmitted to cutting tools when sliding velocity increases. Finally, this work provides quantitative data of friction and heat partition coefficients versus sliding velocity and contact pressure in order to be implemented in any analytical or numerical cutting model.

Tribological Characteristics on the Helical Gear in Cold Forging Mold

The purpose of this study is to find out the tribological characteristics of the various lubricants in cold forging of helical gear, which is used in mobile auto-transmission. Five kinds of lubricant were used in this study, i.e. L1, L2, L3, L4 and L5. The pin-on-disk type of friction wear test system has been adopted here. The normal load of 20, 40, 60, 80 and 100N has been applied to the test specimen. The sliding velocities were 0.06, 0.10, 0.14, 0.18, 0.22, 0.26, 0.30 and 0.34m/s. Experimental results show that the friction coefficients of oils having higher kinematic viscosity such as L1, L2, L4 and L5 tend to increase gradually as the sliding velocity increases. The increasing rate of the friction coefficient is relatively high in lower sliding velocity range. However in case of L3 which has low kinematic viscosity the friction coefficient tends to decrease as the sliding velocity increases. The friction coefficients of Bondelube and Bondelite were 3 times higher than those of L1 and L5. The Stribeck curve indicates that L1, L2, L4 and L5 were in hydrodynamic lubrication condition and L3 was in boundary lubrication condition. SEM micrographs revealed that there were some scratch, adhesive wear, adhesion wear and scuffing on the worn surface.