Increase In Friction Coefficient Research Articles

Optimization analysis of carrier-track collision in braiding process

Abstract The relationship between the speed of the driver plate and the collision of the spindle and the track is studied in this work. It is theoretically analyzed that the spindle will collide with the track in different degrees in the process of motion, and the impact is more intense due to the vibration of the mechanism. First, the dynamic equation of the spindle-track model is established. Then, fireworks algorithm is used to optimize the speed of the driver plate, to reduce the collision and impact times of the spindle on the track, so as to reduce the severe collision times between the spindle and the track, resulting in the wear of mechanical parts and affecting the braiding effect. Finally, it is concluded that the number of collisions increases sharply with the increase in recovery coefficient when the random disturbance is not considered; second, the number of collisions decreases with the appropriate increase in friction coefficient when the random disturbance is not considered; and third, the number of collisions increases sharply with the increase in random disturbance.

Changing the Oral Tribology of Emulsions Through Crystallization of the Dispersed Triglyceride Phase.

Suspoemulsions are used for food, cosmetic and pharmaceutical products, including food such as dairy products and non-dairy alternatives. Product properties, such as flow behavior or sensory perception of non-dairy products differ from those of dairy products and are therefore perceived by consumers as products of inferior quality. One reason for this may be the crystallization behavior of the added triglycerides leading to differences in solid fat content in comparison to cow milk. This is discussed with the solidity of the dispersed phase as a parameter of suspoemulsions. The solidity was varied by using low and high melting triglycerides and measuring at different temperatures. The dispersed phase fraction is φ = 30%. The droplet size distribution showed a x50,3 of 1.2 and 3.66 μm, mimicking the droplet sizes of milk and dairy cream. Rheological frequency sweeps were carried out within a temperature range from 5°C to 50°C. The differences in solidity of the dispersed phase caused no changes in viscosity at each temperature. In contrast, oral tribology distinguished different solidities of the dispersed phase with changes in the friction coefficient. The friction coefficient was determined for increasing rotational speeds (0.01-100 mm/s), to compare the so called Stribeck curves with each other. In general, with increasing solidity of the dispersed phase, the friction coefficient increases. Comparing the Stribeck curves of pure butter fat suspoemulsion with those of plant-based fat suspoemulsions, different plant-based fats can be mixed, to mimic the friction profile of milk products in plant-based alternatives.

An innovative approach combination of powder metallurgy and accumulative press bonding to fabricate Al/ graphite nanocomposites and investigate the tribological and wear properties

In this study, Al/Gr Nanocomposites (NC) were fabricated using an innovative approach that is a combination of powder metallurgy (PM) and accumulative press bonding (APB). By this combination method, many of defects are removed from the composite matrix which improves the mechanical properties. The APB process is a unique technique that made it possible to create NCs with distinct properties. In simpler terms, this process involves compressing a series of overlapping bulky samples that achieves a specific reduction ratio, such as 50 %. It is worth noting that extensive research has been done to understand the properties of Al/Gr-NCs comprehensively. By increasing the Gr value up to 10 %, hardness and friction coefficient dropped and wear rate increased by 23 %, 214 % and 37 %, respectively. Focusing on the analysis of microstructural, and tribological properties (TP), with special emphasis on the effect of Gr content as an additive component. In addition, the use of a scanning electron microscope (SEM) has facilitated the study of the surface and microstructure of tribo–NC. The result of this study revealed desirable behaviors. It was observed that with the increase of Gr content, the hardness and friction coefficient (FC) of the NC samples decreased, while the density and WR rate of the samples increased. These results indicate the importance of Gr addition in adjusting the MP and TP of NCs. Finally, the combination of PM and the APB process offers a promising way to fabricate nanoparticle (NP)-reinforced materials with desirable MP.

Enhanced braking performance of copper metal matrix composites incorporating fine mosaic pitch coke when mated with 30CrMnVA and C/C-SiC

By substituting 10 wt% of conventional graphite particles, pitch coke particles with fine mosaics demonstrate superior performance in enhancing the braking properties of copper metal matrix composites (CMMCs) operating at various conditions. When mated with C/C-SiC, the coefficient of friction increases by 18.6 % at low speeds and 38.8 % at high braking speeds, along with a significant enhancement in wear resistance across various counterparts. This improvement is attributed to the incorporation of pitch coke with fine mosaics and superior mechanical properties, which not only imparts high thermal capacity and mechanical strength to the CMMCs but also fosters a synergistic interaction between pitch coke and the iron oxide layer, stabilizing the friction layer.

Effect of B/N dual doping on mechanical and tribological properties of Mo-S-B-N sputtered films

Doping with non-metal element is effective to improve the porous morphology and enhance the mechanical and tribological properties of transition metal dichalcogenides (TMDs) based film. However, the mechanical properties of TMDs based film with single additive should be enhanced further for better wear resistance. In this work, B/N dual-doping was used to further enhance the deformation resistance and toughness of MoS2 based films deposited by magnetron sputtering, while the effect of B/N dopants on the structure, mechanical and tribological properties has been investigated. Mo-S-B-N film with B content of 20.91 at. % and N content of 18.13 at. % consists of MoS2 and amorphous nitride/boride, in which B/N dual doping film forms a higher ordered MoS2 lamellar structure compared to B doping film. With a hardness of 11.6 ± 0.9 GPa and improved toughness, the film achieves a low wear rate and average friction coefficient is achieved. Comparing B/N dual doping film to B doping film, the stable formation of tribolayer with more strengthened deformation resistance results in the steady friction and the improved wear resistance, while the limited TMDs reorientation leads to the slight increase of friction coefficient.

Comparative analysis on high temperature tribological behaviour of additive manufactured and cast AlSi10Mg alloy

Abstract In recent years, additive manufacturing (AM) of AlSi10Mg, a material widely used in the aerospace and automotive sectors, has gained considerable interest for its ability to produce intricate shapes with improved mechanical properties. This proposed study aims to experimentally assess the high-temperature tribological performance of as-printed AlSi10Mg and compare it with traditionally cast AlSi10Mg to determine its suitability for high-temperature tribological applications. Samples of AlSi10Mg were manufactured via powder bed fusion, followed by tribological testing at elevated temperatures (30 °C, 100 °C, 200 °C, and 300 °C). The performance of both printed and cast AlSi10Mg pins was compared against an EN31 disc. The microstructure, worn surface, and wear debris of both printed and cast AlSi10Mg were examined using XRD and SEM with EDX analyses. As the load and temperature increase, both printed and cast AlSi10Mg materials demonstrate an increase in wear rate and friction coefficient. The wear rate of printed AlSi10Mg decreased by 60% compared to cast AlSi10Mg at higher temperatures. There is a consistent trend in the coefficient of friction between printed and cast AlSi10Mg samples at low temperatures and loads. Abrasive wear predominantly occurs in both printed and cast AlSi10Mg samples at 30 °C within a load range of 10 to 20 N, while adhesive wear predominates in the same samples at temperatures ranging from 100 °C to 300 °C with an applied load of 30 N. At low temperatures, smaller wear debris is observed, whereas at high temperatures and under a load of 30 N, larger wear debris is observed for both cast and printed AlSi10Mg samples.

Analysis of bolt bonding surfaces by the finite element method based on the equivalent Iwan model

This study establishes a finite element model based on the Iwan model to accurately characterize the force–displacement relationship and energy dissipation in bolted joints under small-amplitude tangential displacement. The force–displacement behavior of the Iwan model is transformed into a stress–strain relationship using a hybrid hardened intrinsic model. A subroutine developed with UMAT and UHARD is used to simulate the elastic–plastic behavior of the Iwan model during surface contact in the finite element model. Three-dimensional modeling and joint simulation are conducted using ABAQUS software. Experimental data verify the model's validity, and the effects of multiple factors on the bolted bonding surface are analyzed. The influence of friction coefficient, cyclic displacement amplitude, and preload on the force–displacement relationship of the bolted bonding surface is explored. Polynomial interpolation of the loading and unloading curves is applied to investigate the energy dissipation phenomenon. Results show that the finite element method can effectively reflect the hysteresis and energy dissipation behavior of the bonding surface. Increased friction coefficient and preload improve residual stiffness and energy dissipation capacity, while larger cyclic displacement amplitudes increase energy dissipation but have a minimal effect on residual stiffness.

On Lubrication Regime Changes during Forward Extrusion, Forging, and Drawing

The tribological phenomena concerning the lubrication regime change (LRC) during bulk metal forming are comprehensively studied. A multi-step cold forward extrusion process shows the evolution of LRC and reveals the shortcomings of the traditional Coulomb friction law. The previous works of the specific author’s research group on friction are reviewed, focusing on the LRC during bulk metal forming. Various LRC phenomena from various examples are revealed. It has been found that the drawing and forward extrusion processes are vulnerable to LRC because of significant sliding motion at the material–die interface, and that when the strain hardening of the material is slight, the influence of friction increases, and as a result, the influence of LRC increases excessively. The new findings also include the impact of LRC on the macroscopic phenomena of the process and the reason for the sharp increase in friction coefficient via LRC, which is validated by the work of Wilson. This paper aims to make engineers and researchers think much of the tribology with lubricant in bulk metal forming with a focus on the dependence of tribological phenomena on the state of the lubricants and the irrationality of traditional friction law, especially in the forging of materials with a low strain hardening capability.

Axial behaviour of steel pipelines buried in sand: effects of surface roughness and hardness

Surface roughness and coating hardness of underground pipelines are expected to play decisive roles in their axial pullout behaviour, which is an important aspect of pipeline design. Existing guidelines and previous studies underestimated or ignored these effects, resulting in potentially unsafe design. To address this problem, in the current study, nine large-scale physical modelling tests were conducted on pipes in dry and dense sand. Five steel pipes with varying normalised roughness (0·04–1·01) and coating hardness (32·6–59·0 HRA) were used and instrumented with a novel type of film-like piezoresistive sensors for measuring soil–pipe contact pressure. The measured pullout resistance of rough pipes is 2·70–2·85 times that of smooth pipes, significantly greater than the value specified in current design guidelines (i.e. 1·17 times). This substantial increase stems from an increase in interface friction coefficient (accounting for 72–79%) and a contact pressure increase induced by constrained dilation and soil arching (contributing the remaining 21–28%). Regarding coating hardness, a critical hardness was observed (around 35 HRA). Owing to equivalent roughness from particle embedding, pipes with hardness below this value exhibited similar behaviour to rough pipes. Finally, a new and simple method was proposed for calculating the pullout resistance with consideration of the effects of roughness and dilatancy.

High-temperature tribological evaluation of cobalt-based laser cladded disc for automotive brake systems

This study investigates the high-temperature wear behavior of laser-cladded (LC) cobalt-based Stellite 6 alloy coatings and compares the wear resistance of the cladding layer to the grey cast iron (GCI) substrate material at three different elevated temperatures: 150 °C, 250 °C, and 350 °C. Wear mechanisms at elevated temperatures were analyzed using SEM-EDS and Raman Spectroscopy to understand the material removal processes and degradation for the discs and counterpart composite friction material pins, respectively.The results indicated a significant improvement in wear resistance for cobalt-based alloy cladding at high temperatures. Wear rates were reduced by 5.0 %, 43.0 %, and 16.0 % at 150 °C, 250 °C, and 350 °C, respectively. The LC - brake pin tribo-pair exhibited a continuous increase in friction coefficients (CoF) with an increase in testing temperatures. The wear mechanism for laser-cladded discs exhibited a combination of abrasive and adhesive wear, with abrasive wear prevailing at 150 °C and increased adhesive wear at 250 °C and 350 °C. However, at 350 °C, decomposition of phenolic resin and the adhesive wear mechanism, led to brake pin failure. For GCI discs oxidative wear was identified as the predominant wear mechanism. The improved knowledge of wear mechanisms on LC Stellite 6 against composite brake pins, is set to enhance surface modification of GCI for brake disc applications.

Design and performance analysis of carbon brush collector ring end-face contact for hydro generator

Abstract In hydro generators, the conventional radial contact method often results in unstable contact between carbon brush collector rings due to collector ring deflection. This paper presents a novel end-face contact method designed to enhance stability. The trajectory equations of the brush/ring contact are established when the collector ring swings and the “loss of contact” gaps of the two contact methods are compared. Further comparative analysis is conducted on the current-carrying friction wear of carbon brushes and collector rings in two contact modes. The results show that compared with the radial contact method, the brush/ring in the end-face contact method has a smaller gap and shorter time, the carbon brushes are less susceptible to spark erosion, the increase in friction coefficient and wear rate is small, and the contact resistance is lower and more stable. Scanning electron microscope analysis also shows that the spark erosion on the surface of the carbon brushes in the end contact mode is significantly weaker than that in the radial contact mode.

Flow and sensitivity analysis of MHD radiative hybrid nanofluid flow across a permeable wedge with slip condition: Response surface methodology

AbstractThis current paper has been written to investigate the effect of a hybrid Tiwari and Das nanofluid model along with optimizing the flow using sensitivity analysis. Heat transfer rates and skin friction assessments were examined with the supplementation of external effects like heat source, thermal radiation, buoyancy forces, velocity slip as well as magnetic effect with spherical‐shaped nanoparticles. The mathematical modeling was formulated using a system of nonlinear PDE. Similarity transformations were implemented in the governing equations for obtaining the final set of nondimensional equations which were then solved using bvp4c code in MATLAB. The results obtained were in close agreement with published results. Some of the significant results obtained included an increase in Nusselt number by 2.26% for an increase in velocity ratio parameter () from to 0.3 along with an increase in skin friction coefficient by 0.77% with magnetic () parameter to . The heat transfer profile was augmented by 0.79% with increasing radiation parameter to while an increase of 18.84% was observed for skin friction profile values recorded for the hybrid model as compared to the base fluid model. Nusselt number reduced by 0.51% for a transition to nanofluid model from regular fluid and by 1.76% for the hybrid model compared to the nanofluid model The unblocked face‐centered central composite design (CCD) was used for analyzing the sensitivity analysis of independent, continuous input parameters on the response parameters, skin friction coefficient, and Nusselt number. The high values for , and , for Nusselt number and skin friction coefficient values, respectively, validate the ANOVA results obtained using response surface methodology (RSM). Only shows positive sensitivity for both the Nusselt number and skin friction responses. The present hybrid nanofluid model finds extensive applications in bio‐toxicity studies, manufacturing of water heaters, and forging of hot exhaust valve heads.

Wheel-rail wear characteristics of a modern tram passing curves with small radius

The wheel-rail wear was predicted for modern trams with independently rotating wheelset running on a groove-shaped rail. The tram vehicle-track coupled dynamics model, considering the wheel-rail multi-point contact, was developed using software UM to evaluate the dynamic responses of the vehicle and track. Hertz contact theory, the FastSim algorithm, and Archard material wear model were used to solve the normal contact stress, tangential contact stress, and wheel-ail wear, respectively. The wheel and rail profiles were updated when the wear depth reached to 0.1 mm. In calculation, the wheel and rail wear was calculated and analyzed separately. The results of groove rail and independently rotating wheelset wear predicted by this model coincided with relevant literature, which proved the effectiveness of this model. The wheel and rail wear characteristics of modern trams passing through curved tracks with small radii and the influence of wheel-rail friction coefficient on wheel and rail wear were calculated and analyzed using this model. The results show that the wheel and rail wear on the circular curve and the rear transition curve is more intense. The wheel wear is the most intense on circular curve while the rail wear is on the rear transition curve. The wear of inner and outer rails and wheels of wheelset one increases with the increase of wheel-rail friction coefficient while the wear of inner and outer wheels of wheelset three have no obvious change. The wear of the inner and outer rails is the most intense at the gauge corner position while is the lightest at the guard rail. The wear of wheelset one is more intense than that of wheelset three and the inner wheel wear is more intense than that of the outer wheel. The present analysis contributes to improve the life of tram wheel and rail and reduce the frequency of wheel-rail maintenance during operation.

Comparison of high-temperature friction and wear behaviours of Ti6Al4V produced by additive manufacturing and casting

Additive manufacturing (AM) methods, especially selective laser melting (SLM), have recently attracted attention because they enable the quick and easy production of complex parts that cannot be produced with traditional manufacturing methods. However, residual stresses in the fabricated components impact their mechanical characteristics and may necessitate additional heat treatments. In this study, SLM-produced Ti6Al4V parts were subjected to a stress relief treatment under argon gas at 790°C for 2 h. The microstructure, microhardness and high-temperature tribological properties were examined comparatively with the traditional casting method. Dry sliding tribological experiments were carried out at different temperatures up to 600°C to compare high-temperature performance. It has been determined that the microstructure of samples produced by casting and SLM comprised β and α phases. The casting sample had 66.02% α grains, whereas the SLM sample had 59.02% α grains. The average microhardness in the SLM sample was marginally higher than that in the casting due to the formation of martensitic α. The results showed that wear rates increased with temperature for each sample. SLM samples exhibited slightly higher wear rates at each test temperature compared to the casting sample, which is attributed to the oxidative wear mechanism. The higher percentage of oxygen in the triboxide layers in the casting sample increased the wear resistance. When examining friction coefficients, an increase in average friction coefficients was observed at a test temperature of 300°C, while a decrease was observed at a test temperature of 600°C.

Mechanism of three-body abrasive grain grinding on GaN textured surfaces under uniform acceleration and variable depth

In this study, molecular dynamics (MD) was used to simulate the three-body grinding process on the textured surfaces of gallium nitride (GaN) and to investigate the effect of the processing parameters during the grinding process on the quality of the process and the removal mechanism of the material. The results show that the friction coefficient, normal force, tangential force, grinding temperature and potential energy increase with the increase of the accelerated interval segment, while the stress, subsurface damage depth and dislocation length decrease. Overall, higher speed value classes in the GaN grinding process are favorable for improving the surface finish quality. In addition, under the conditions of variable depth machining, with the increase of rising speed, the coefficient of friction, the tangential force, the normal force, the potential energy increase, the grinding temperature increases, the stress decreases, and the subsurface damage of the workpiece and the nucleation of dislocations are also significantly reduced, and the surface finish quality and the surface integrity of the workpiece are improved. The textured surfaces is an innovation in GaN processing.

FLOW AND HEAT TRANSFER IN A RIBBED CONVERGING-DIVERGING U-DUCT UNDER ROTATING AND NON-ROTATING CONDITIONS

Abstract A numerical study based on steady RANS with the SST turbulence model was performed to investigate the flow and heat transfer in a ribbed U-duct with a rectangular cross section that converges linearly in the radially outward direction and diverges linearly in the radially inward direction under rotating and non-rotating conditions. Parameters examined include rotation number (Roi = 0, 0.0219, 0.0336, 0.0731), Reynolds number (Rei = 46,000, 100,000, and 154,000), and the duct's taper angle (α = 0° and 1.41°) under conditions relevant to gas turbines used for electric power generation. Results obtained show that increasing the taper angle from 0° to 1.41°, which appears negligibly small, significantly increases both the friction coefficient and the Nusselt number whether there is rotation or not. With rotation at Roi = 0.0336 and Rei = 100,000, the maximum increase in the average friction coefficient and Nusselt number was found to be 41.7% and 36.6% respectively. Without rotation at Rei = 46,000, those are 11.5% and 14.7% respectively.

Investigation of supercritical pressure hydrocarbon fuel heat transfer performance in rotating wing shape channels with different wing structural parameters

This paper details and develops novel wing shape hydrocarbon fuel cooling channel for enhancing the heat transfer capability of hypersonic vehicle electricity supply blades under rotating conditions. The effect of parameters such as wing base position and height on the thermal performance in the rotating situation is studied. The calculation results show that the wing base height H = 0.6D-0.8D wing shape channels have generally higher thermal performance and generally lower friction coefficient. Thermal performance of the channel with wing base parameters L = 10 D, H = 0.6 D is maximally increased by 350.2 % and friction coefficient is maximally reduced by 98.5 % compared with the straight channel at inlet temperature of 590 K and rotational speed of 35,000 rpm. As the wing base position L increases, both the thermal performance and the friction coefficient increase and then decrease under the influence of the pressure difference. Under the condition of high rotational speed, the wing base height H = 0.8 D and H = 0.6 D wing shape channels will obtain the maximum value of thermal performance in the range of L = 2 D-4 D and L = 6 D-10 D of the wing base position, respectively.

Effects of fatigue load characteristics on bending tribo-corrosion-fatigue damage of steel wire ropes in seawater and pure water

Tribo-corrosion-fatigue coupling damage greatly affects the service safety of wire rope. A self-made test rig was employed to investigate the influences of fatigue load characteristics (amplitude, stress ratio, maximum) on bending tribo-corrosion-fatigue damage of wire ropes. The tribological properties and electrochemical corrosion of the wire ropes, and the coupling damage and mechanisms were discussed in detail. Results indicate a lower friction coefficient between wire ropes in artificial seawater. The main wear mechanisms in seawater are adhesive wear, fatigue wear, oxidation wear and corrosion wear as compared to abrasive wear, adhesive wear, oxidation wear and fatigue wear in pure water. Lower stress ratios amplify corrosion and adhesive wear. Fatigue fractures are mainly ductile, with stress ratio being a significant factor. Tribo-corrosion-fatigue coupling exacerbates damage in contact ropes compared to fatigue ropes. Seawater increases fatigue rope damage but reduces contact rope damage. Higher fatigue load amplitude and maximum value, and lower stress ratios, increase friction coefficient, deformation, volume loss, wire breakage, and decrease corrosion resistance. These findings provide essential data for assessing wire rope service life under seawater corrosion conditions and ensuring offshore drilling safety.

Mechanisms Underlying Rail Corrugation on Tracks Equipped with Cologne-Egg Fasteners

Rail corrugation is the most common type of abnormal damage in subway track systems, and there is currently no unified theory that fully explains this specific wear phenomenon. In this research, a coupled rigid–flexible dynamics model and a multi-rigid body dynamics model was established, accounting for the effects of fastener systems, to study severe rail corrugation on tracks equipped with Cologne-egg fastener (CE fastener). The low vertical support stiffness of CE fasteners, combined with heavy train loads, leads to the “soft mud effect.” This effect causes the creep force between the wheel and rail to become saturated more easily, which is the root cause of frequent rail corrugation on both tangent tracks and curved tracks with large radii. Additionally, drawing on the theory of friction-driven self-excitation vibration, a finite element model of a wheelset–rails system with CE fasteners was established to study the unstable vibration caused by wheel–rail sliding. An increased friction coefficient increases the tendency toward unstable vibration in a wheelset–CE fastener–rail system. Three types of composite under-rail vibration absorbers were designed to suppress rail corrugation, with the continuous-type absorber demonstrating the best suppressive effect.

Simplified formulas for calculating bearing capacities of standing seam metal roof systems under uniformly distributed downward and upward loads

Finite Element (FE) models of standing seam metal roof systems (SSMRSs) are established and verified by experimental results. A comprehensive parametric study on the bearing capacities of SSMRSs under uniformly distributed loads through FE simulations encompassing 281 SSMRSs is conducted. Simplified formulas for calculating the bearing capacities of SSMRSs under uniformly distributed loads are proposed as functions of fundamental parameters, including roof panel thickness, roof panel width, purlin spacing, material strength, friction coefficient, and support head width. These simplified formulas avoid the necessity for calculating the effective section during the verification of bending failure and avoid the necessity for wind uplift experiments during the verification of connection failure of the SSMRSs in conventional building codes and guidelines. The results show that for per 0.1 mm increase in roof panel thickness, the ultimate bearing capacities under downward and upward loads increase by about 14.03 % and 19.88 %; for per 100 mm increase in roof panel width, they decrease by about 27.14 % and 36.45 %; for per 200 mm increase in purlin spacing, they decrease by about 12.82 % and 5.01 %; for per 20 MPa increase in material strength, they increase by about 11.40 % and 2.24 %; for per 0.1 increase in friction coefficient, they increase by about 3.16 % and 9.01 %. Future studies can focus on the ultimate bearing capacities of SSMRSs under non-uniform loads with temporal and spatial fluctuation.