Change In Friction Coefficient Research Articles

RESISTANCE OF HEAT-RESISTANT YTTRIUM-CONTAINING SEALING COATINGS TO MECHANICAL FRACTURE WHEN FORMING CUTTING PATHS

According to the results of tribotechnical tests of coatings made of KNA-82 alloy ligatures with the addition of yttrium of 0.1%, 0.3%, 0.5%, data were obtained that allowed us to establish the nature of changes in the dynamic coefficient of friction over the test period and numerous values of the energy intensity of material wear. The evaluation of coatings formed by the gas-flame and ion-plasma method was based on the following premise. The maximum resistance to mechanical fracture is determined by the manifestation of a constant minimum value of the dynamic coefficient of friction. This serves as an indicator of reduced friction force before reaching the fatigue limit. Another key factor is the number of separated particles produced per unit of integral work during the friction process. These evaluation parameters are lined up in a row by the number of points from 1 to 4. The maximum score corresponds to the maximum resistance, i.e., a lower value of the energy intensity of material wear and the minimum value of the stable friction coefficient. It has been determined that the same coincidence of these parameters according to the scores is almost at all stages of testing (I-III) was the coating formed by the gas-flame method with a yttrium concentration of 0.3%-0.5%. The exception was the coating formed by the ion-plasma method with a yttrium concentration of 0.1% at the fourth stage of testing.

Friction Coefficient Evolution of Si3N4 Binary Coating with a Stoichiometric Ratio of 57/43

Friction coefficient depends on various factors or surface characteristics during tribological testing, and this friction coefficient can be modified by altering the properties of one of the two contacting surfaces. It is crucial to monitor the friction coefficient continuously, not only at the conclusion of the test. This research examined the evolution of friction coefficient of silicon nitride (Si3N4) coating and H13 steel over different sliding distances (250, 500, 750, 1000 m). The study assessed surface wear and oxidation through three-dimensional profilometry and SEM/EDX. The findings indicated a reduction in friction coefficient by 22%, a decrease in wear rate by 88%, and a reduction in wear volume by 87% when comparing the silicon nitride coated steel to the uncoated steel. Furthermore, the changes in friction coefficient provided insights into the timing of the complete fracture of the hard coating.Graphical abstract

Static and dynamic influence of forces on a being threshed corncob

BACKGROUND: With the use of high-speed shooting, it was found that the corncob, getting into the gap of the threshing unit, generally, takes a position parallel to the drum axis. Let us accept that the plane of operation of the working body of the threshing drum – the beater – coincides with the generatrix of a cob. The cob changes the motion mode because of the impact of the threshing machine beater on the cob. The impact can take place in the moment when the cob even does not hit the deck cleats, so the cob gets a flying kick. AIM: Deriving the static and dynamic influence of forces on the being threshed corncob. Defining the necessary force of corn seeds breaking-off from the cob in dependence on the friction coefficient. METHODS: The value of mechanical impact of working bodies of the orienting-metering loading device and the threshing-separating device on a corn seed is limited not only by strength properties of the protecting corn cover, but by the link strength between a seed and a cob in the nose, middle and root areas. Knowledge of this mechanical-technological property helps to increase the level of variability of force impact in corncobs from the side of working bodies of the used machinery. It helps to transport the corncobs without husk, to orient them in space, to supply in small increments for the proper processing and, in addition, to thresh without causing any macro- and microdamages to the seeds. RESULTS: The seed moisture change and, consequently, the seed-to-seed friction coefficient change also influences on the ratio between the applied force P and the reacting force N. With the same load P applied to the dry and the moisty cobs, the pressure N on the dry seed is higher than on the moisty one, and seed threshing from the dry cobs is conducted with lower external forces P at free direct impact. CONCLUSION: The process of the flying kick threshing becomes more difficult with the increase of corncobs moisture due to increase of seed-to-seed friction. The flying kick threshing of corncobs stops at the seed moisture which corresponds to the friction coefficient f = 0.22. The obtained theoretical principles are confirmed experimentally.

Enhancing Tribological Performance of Micro-Arc Oxidation Coatings on 6061 Aluminum Alloy with h-BN Incorporation

Micro-arc oxidation (MAO) coatings of aluminum alloy have great potential applications due to their high hardness and wear resistance. However, the micro-pores and defects formed in the discharge channels during the MAO process limit its application in the corrosion field. This study delves into the impact of h-BN nanoparticles into MAO coatings on their structure, corrosion resistance, phase composition, and tribological properties. The results show that the incorporation of h-BN particles reduces the porosity and surface roughness of the coating while enhancing its hardness and wear resistance. The best corrosion resistance is obtained at a concentration of 2 g/L h-BN. An analysis of worn surface morphology, corrosion resistance, and friction coefficient change was conducted to evaluate the performance of this coating. This method provides a new approach to enhance the surface hardness and wear resistance of aluminum alloys, which is significant for expanding the application of aluminum alloys in corrosion environments.

Pedestrian-ground contact injury protection method under the constraint of the vehicle-front end shape and its robust analysis

This research paper introduces a novel approach for protecting pedestrians from ground contact injuries through incorporating vehicle front-end shape constraints in the braking control method. The feasibility of the proposed method is evaluated through simulations, and its resilience to different disturbances is studied. Results indicate that the proposed method effectively manages vehicle movement by monitoring the first head-vehicle contact time (t1 ) between the pedestrian’s head and the vehicle. The simulations show that the proposed method reduces ground-related Weighted Injury Cost (WIC) by up to 84%, and the proportion of ‘safe’ mechanisms increases to 74%. The robustness of the braking control method is also evidenced by its high performance during disturbances such as changes in friction coefficient, lag time, and t1 . Furthermore, the anti-disturbance abilities of each vehicle shape are comparable except for t1 disturbance. There are no significant variations in the braking control protection effect between different friction coefficients and each t1 , but noticeable differences exist between lag times. Further analysis reveals that parameter disturbances affect the deceleration of the vehicle and the impact speed of the pedestrian and vehicle, leading to changes in the Vz (Vertical head-to-ground impact velocity), thorax acceleration, pelvic lateral impact force, and knee lateral bending angle, which subsequently increases the risk of pedestrian ground contact injuries. The proposed method offers an efficient solution for protecting pedestrians from ground contact injuries by controlling vehicle braking, highlighting its practical utility.

A new analytical model for bond strength between corroded steel strand and concrete

Degradation of bond strength due to corrosion of steel strands is of great importance for serviceability of prestressed concrete structures. An analytical model is proposed to demonstrate the effect of corrosion of steel strand on reduction of bond strength. Corrosion expansion force generated by steel strand corrosion before and after corrosion cracking is firstly estimated. Then, the reduced gripping effect of the concrete, change of friction coefficient between the corroded strand and reduction force on the bearing face are considered in calculating the pre-rib extrusion force. Finally, the enhancement of bond strength due to transverse confinement of stirrups is considered and the ultimate bond strength of corroded steel strand is calculated. Comparison of results between the prediction and experimental result shows the proposed model can be used to reasonably evaluate the bond strength. The prediction result of the bond strength model is affected by the degree of strand corrosion, but almost not by the drawing method.

Investigation of friction and vibration performance of lithium complex grease containing candle soot on aviation electrical machine

The prolonged operation of the motor in the all-electric aircraft can cause the fragmentation and shortening of grease thickener fibers, ultimately resulting in the lubricating grease becoming ineffective. In order to avoid grease failure causing motor winding burnout, this paper uses a four-ball friction testing machine to test the tribological properties of six composite greases containing candle soot with different concentrations, and analyzes the changes in friction coefficient and wear diameter. In addition, by building a test platform for motor vibration and noise, this paper studies the influence of lithium complex grease on vibration and noise characteristics of aviation electrical machine at different propeller speeds. The results show that the addition of 0.04 wt% candle soot lithium grease has the best tribological properties and vibration inhibition properties, because the candle soot in the oil film changes the sliding friction into rolling friction in the contact area of some friction pair. The temperature rise test of aviation electrical machine shows that the lithium complex grease plays an active role in the heat dissipation performance of the high-speed rotating motor.

Relationship of evolution of slip-surface structure in Indian sandstone to changes in friction coefficient for a wide range of slip rates

Although many experimental studies have investigated the frictional properties of sandstone, few of them have considered the evolution of slip-surface structures with changes of friction coefficient over a wide range of slip rates. Here we report the results of rock-on-rock rotary shear experiments on specimens of Indian sandstone at slip rates from 2 × 10−4 to 1 m s−1. The resultant slip behaviors and microscale surface structures indicate two types of dependency on slip rate. At high slip rates (≥5 × 10−1 m s−1), the friction between the sandstone blocks fluctuated markedly and the surfaces of the blocks were intensively worn. At low slip rates (≤1 × 10−1 m s−1), the friction decreased gradually with increasing slip distance and the slip surfaces became reflective. The high slip-rate experiments produced abundant rock fragments (∼10–100 μm diameter), whereas the slip surfaces after low slip-rate experiments were highly polished fault mirrors accompanied by abundant rounded ultrafine grains (∼100 nm diameter). Such slip-rate-dependent evolution of slip-surface structures in Indian sandstone may arise from the relatively low cohesiveness of that rock. This insight may further our understanding of faulting and sliding mechanisms in sandstone near the ground surface.

Understanding DLC system failure influenced by progressed wear

Diamond-like carbon (DLC) coatings are among the toughest and most effective measures for preventing wear on critical surfaces. Due to its high wear resistance, the deterioration of the protective coating only occurs upon failure. Understanding the events leading to failure and identifying a mild-abrasive wear process is crucial for sustainable application. We implemented a ‘Wöhler-like’ test matrix on a tribometer with oscillating tribocontact, employing radioactive isotopes for continuous wear measurements. This method allows to analyse the relationship between load and cycling or test time. When combined with friction coefficient changes, it enables the distinction between mild and severe wear, ultimately pinpointing the point of DLC deterioration. This approach was employed to compare different diesel lubricants, and its effectiveness was demonstrated. The relationship between loading condition and remaining DLC thickness illustrates that mild-abrasive wear is the critical factor for DLC lifetime, ultimately leading to coating system failure.

EXPERIMENTAL, TRIBOLOGICAL STUDIES ON SINTERED Al–xV2O5–2B4C COMPOSITES USING BIO-OILS

This reports the tribological behavior of sintered aluminum composite with bio-oil as lubricant. The composite is fabricated by powder metallurgy route, and the aluminum is reinforced with the particles V2O5 and B4C. The bio-lubricant oil is Pongamia, Jatropha, and blended Pongamia with Jatropha of equal volume. The wear test was carried out at the sliding speed of 3[Formula: see text]m/s and load ranging up to 180 N, and the wear behavior of Al–xV2O5–2B4C composite. Then the composite’s friction coefficient and weight loss were tested on a pin-on-disc tribometer. Further, pinworn surfaces were analyzed by Scanning Electron Microscope. The mix of Pongamia with Jatropha of equal volume resulted in a good change in specific wear rate and coefficient of friction of composites.

Effect of time-varying friction coefficient on self-excited vibration of floating spline-rotor system

Different lubrication states seriously affect the stability and safety of the aviation power transmission system. This study investigates how time-varying friction coefficients impact the stability of an aviation spline-rotor system using a spline-rotor model that considers uneven stress distribution on the tooth surface. Experimental tests with a high-frequency friction and wear test machine yield time-varying friction coefficients for splines with different lubrication, surface roughness, and materials. A sharp change of friction coefficient for the sample occurs under wear debris lubrication. The average friction coefficient for the sample with roughness 1.6 is lower than those with roughness 0.8 and 3.2. Under the same lubrication conditions, the friction coefficient of Resin matrix composites is smaller than that of metallic materials. Dynamic simulation of the spline-rotor model considering time-varying friction coefficients shows rich self-excited vibration behaviors influenced by lubrication, surface roughness, and materials.

Charge pattern detection through electrostatic array sensing

As reported in previous work, electrostatic charge induced by contact potential difference (CPD) arising from oxidational wear can be detected by electrostatic button sensors. However, to detect signs of localised wear and to investigate the mechanisms involved, the charge distribution on worn regions needs to be measured. Therefore, this paper investigates the evolution of surface charge during wear processes, its interplay with friction, and the correlation between charge distribution and surface chemistry. An electrostatic bar sensor and an array sensor were initially calibrated using CPD patterns generated by dissimilar metal inserts in steel plates. After appropriate signal processing, the sensor outputs exhibited excellent agreement with the electric field strength modelled using COMSOL Multiphysics. Subsequently, the bar sensor was integrated into a reciprocating tribometer for in-situ detection of oxidational wear of steel-on-steel rubbing contacts, followed by ex-situ array sensing of worn regions. Positive picocoulomb-level surface charge during the evolution of oxidational wear were successfully detected by the bar sensor and were found to correlate to changes in friction coefficient. The array sensor effectively mapped the distribution of surface charge. EDS mapping suggested patchy formation of Fe3O4 layers over the worn areas, and these patches correlated to the surface charge map. Increased electrostatic charge levels were associated with higher concentrations of oxidational wear. Therefore, this paper evaluates the potential of electrostatic array sensors to spatially resolve surface charge patterns induced by surface chemistry transformations, which enables the monitoring of localised and smaller-scaled machinery component deterioration and provides additional information for machinery diagnosis.

TRIBOLOGICAL PROPERTIES OF A SILICONE-BASED COMPOSITEWITH INORGANIC ADDITIVES

The paper presents the results of experimental studies, including tribological tests of silicone-based compositeswith additions of hexagonal boron nitride (hBN) and titanium (Ti). The tests were conducted on a BrukerUMT2 tribotester and using a pin-on-disk setup developed by the authors, without a lubricating medium,and they employed a steel ball made of 100Cr6 steel and a sample made of the composite. During the tests,the products were not removed from the contact area. The paper analyzes the influence of additives on thetribological properties of the composite, i.e., the coefficient of friction (COF) as a function of distance and thewear of the tested samples. In the case of samples containing hBN, the COF decreases with an increase in itscontent. After reaching a volumetric percentage concentration of 20%, it begins to stabilize with the increasein mass loss. The profiles of COF changes as a function of distance for samples with different additivecontents are comparable. The self-lubricating properties of hBN have been confirmed. The addition of Tireduces the COF value, which decreases with the increase in the Ti content. Samples with a mass percentageconcentration exceeding 100% of the Ti content have a COF value equal to the initial value for silicone. Thecomposite containing hBN has a lower COF value than samples with the Ti addition, and the wear tracks ontheir surface are narrower and shallower.

A novel fiber‐reinforced polymer rope: Simulation and theoretical investigation

AbstractThe study proposed using twisted rope made of flexible fiber‐reinforced polymers (FRPs) instead of wire and synthetic ropes in high load‐bearing and corrosive environments. Finite element model verification and parameter analysis were conducted for the rope, along with deriving theoretical equations for its tensile properties. Increasing the lay length improved model accuracy, with a maximum bearing capacity within a 10% margin of error compared to experimental results. The model length had minimal impact on calculation results, while changes in radial mesh size (0.13 and 0.2 mm) and friction coefficient (0–0.2) greatly affected maximum contact stress. The tensile strength and elastic modulus of the strand remained almost constant (approximately 1142 MPa and 44 GPa) when the friction coefficient was altered. Increasing lay length (6D–20D) enhanced the tensile properties of the strand, whereas tendon diameter (1–3 mm) had negligible impact. Arranging inner and outer strands with the same lay length was better for circular ropes than those with the same lay angle. Inverse lay direction reduced rope torque and increased strand contact stress. Rectangular ropes had higher strength and modulus conversion efficiency, with lower contact stress compared to circular ones. The accuracy of rope equations improved with longer lay lengths, and adding a correction factor for lay length can modify the equation.Highlights A flexible FRP rope with high strength and twisted form was proposed. The effect of construction factors on the tensile behaviors of ropes was clarified. Equations for calculating the tensile properties of ropes were derived.

Vplyv technológie tepelného spracovania na tribologické vlastnosti vybraných oceľových materiálov

The heat treatment technology changes all sorts of materials properties. We examined the change of tribological properties of selected powder metallurgy materials and conventional steels, in this article. We used special testing equipment, for measuring the changes of friction coefficient of individual tested materials, before application of the heat treatment and after application of the heat treatment. We tested two types of powder metallurgy steels and two types of conventional steels. The changes in friction coefficient are shown in the table and charts. We used boronising, nitriding and surface hardening as procedures of heat treatment.

Fluid dynamics simulation on water lubricating performance of micro-/nano-textured surfaces considering roughness structures

With the development of surface precision machining technology and extensive studies on lubrication and friction reduction, the use of surface texture to reduce friction has attracted widespread attention, but few studies have considered the influence of surface roughness on lubrication characteristics. By employing the computational fluid dynamics (CFD) simulation method, the lubrication models with rectangular textures and the introduction of rough asperity structures at the same time are established. The effects of the corresponding structure parameters on the lubrication performance of textured and roughed surfaces are studied under water lubrication conditions. Our results suggest that the adjustment of geometric parameters on the micro-/nano-structured surfaces can influence the load-bearing capacity of the water lubrication film, thus affecting the hydrodynamic lubrication performance on the surface. In addition, the generation of vortex in the micro-textures can bring changes in vorticity, which causes energy dissipation and affects frictional forces. In the lubrication model with rectangular textures, optimal hydrodynamic lubrication performance is obtained under the appropriate depth ratio <i>H</i> = 0.6. Meanwhile, the corresponding lubrication performance can be enhanced by increasing the width ratio (<i>W</i>) of surface texture. After introducing random asperity structures on the micro-textured surface with a standard deviation <i>δ</i> = 0.5, the bearing capacity is increased by 44%, and the friction coefficient is reduced by 30.9%. Moreover, the introduction of half-sine rough asperity structures can only result in relatively minor differences in the lubrication performance, i.e. the changes of bearing capacity and friction coefficient are less than 10%. However, the introduction of compound hierarchical structure consisting of random asperity structures and half-sine rough asperity structures can result in an increase in the corresponding bearing capacity by 42% and a reduction in the friction coefficient by 31.1%, which implies a significant enhancement in the hydrodynamic lubrication performance.

Characterization of food emulsions and dispersions based on nonlinear friction dynamics

AbstractMany foods are emulsions or dispersions containing lipids. The friction properties of foods are evaluated because they affect food texture and processability. Here, we evaluated the friction characteristics of 55 liquid or semisolid foods using a sinusoidal motion friction evaluation system to classify them based on friction dynamics. The contact surface was made to resemble a biological surface using agar gel, which exhibited a fractal structure, and the movement of the contact probe mimicked living movement by sinusoidal motion. The change in average friction coefficient (Δμ), static friction coefficient (Δμs) in a round trip, delay time (Δδ), and friction profile depended on the condition and rheological properties. Principal component analysis showed that all the friction parameters of Δμ, Δμs, Δδ, and the appearance ratio of the profile were involved in the principal components, Z1 and Z2 which are composite variables obtained by the contraction of many friction parameters in a principal component analysis. In addition, the foods were classified into three groups by cluster analysis using Z1 and Z2. The condition of the foods, rheological properties, and the presence or absence of lipids was the factors that defined each group.

Effect of morphology on tribological properties of Fe3O4 as lubricant additive: Nanospheres, nanowires and nanosheets

This work investigates the morphologies of Fe3O4 nanoparticles how to affect the tribological properties when they are applied as nano-lubricating additives. Fe3O4 nanoparticles with different morphologies (nanospheres, nanowires and nanosheets) are synthesized by solvothermal method and added in liquid paraffin to test the tribological properties. Although Fe3O4 nanoparticles can achieve certain anti-friction and anti-wear effects under the same conditions, the Fe3O4 nanospheres shows the best tribological properties. In the optimal concentrations of Fe3O4 nanospheres, nanowires and nanosheets, the changes of the average friction coefficient are almost the same, the wear volume are decreased by 91.03%, 86.88% and 87.63%, respectively. Fe3O4 nanoparticles with different morphologies can form films in the gap between friction pairs when they are used as additives, which ensures that three different Fe3O4 nanoparticles can enhance the tribological properties of the liquid paraffin. Compared with Fe3O4 nanowires and nanosheets, besides the tribological films, Fe3O4 nanospheres play roles in self-healing and rolling friction effects between friction pairs, resulting in the best anti-friction and anti-wear.

An Iterative Numerical Approach to Evaluate the Variable Friction Coefficient of Steel AMS5643 Using Ring Compression Tests

The coefficient of friction is an important variable that must be defined to allow the accurate prediction of the forming geometry and stresses involved in metal forming processes. Literature reports have shown that the coefficient of friction does not remain constant with respect to variables including but not limited to contact pressure, sliding speed, surface roughness, and surface morphology. Ring compression tests provide a simple and efficient process by which to measure the variable coefficient of friction present in the bulk-metal process; however, the conventional interpolating method can result in a poor evaluation of the evolution of friction, especially if the coefficient of friction changes significantly during a test. In this article, a novel approach to evaluate the relationship between the coefficient of friction and contact pressure is outlined using friction calibration charts generated via iterative computation models and ring compression tests. This relationship can be programmed into a computational model to allow for the coefficient of friction to behave as a dynamic variable. This approach improves on the prediction of the computational model when compared to conventional interpolation methods.

Design and Optimization Analysis of Downhole Robot Support Mechanism Based on Finite Element Method

To increase the traction force of the telescopic downhole robot, the support mechanism of the downhole robot was optimized, and a slider-spring transmission mechanism was introduced to solve the problem of jamming. A mathematical model of the support mechanism was established, covering the relationship between the contact normal pressure and the hydraulic cylinder load. The finite element simulation model of the friction block of the support mechanism was established based on Ansys software. Stress analysis of the casing under different contact normal pressures was carried out, and the frictional characteristics of the support mechanism friction block were obtained. The results show that the support mechanism composed of four linkages and friction locking blocks proposed in this paper can adapt well to casing of different diameters. The slider spring, as a transmission mechanism, has the elasticity and buffering effect, which makes the support mechanism have a certain flexibility, alleviating the vibration impact during obstacle crossing and reducing the impact on logging instruments. It enables the robot to passively adjust during obstacle crossing, effectively improving the traction capability of the downhole robot. Through finite element simulation, it was found that the depth of the plow groove produced by the friction block under normal pressure is basically proportional to the normal pressure. The greater the normal pressure, the deeper the plow groove, and the plow groove friction coefficient increases continuously with the increase of normal pressure, but the change in the plow groove friction coefficient gradually decreases as the pressure increases.