Friction Coefficient Behavior Research Articles

Impact of slip velocity-dependent friction coefficient on surface traction, wear, RCF and curve squeal noise prediction in wheel-rail contact

Wheel-rail contact friction coefficient is often assumed to be constant through the entire contact patch for the calculation of surface traction. In reality, however, the friction value in a certain point decreases when transitioning from adhesion to slip regimes. Including this friction coefficient behaviour in the estimations of surface traction on the contact patch can potentially provide more accurate calculations of wear and rolling contact fatigue (RCF). In the present work, a slip velocity-dependent friction coefficient is implemented in the tangential contact solver using the concept of ‘Friction Memory’. The effect of this implementation on traction estimations and on the prediction of wear and RCF is analysed by comparing the results with a case with constant friction coefficient in the contact patch. Furthermore, the slip velocity-dependent friction coefficient provides a creep curve with a maximum creep forces value, and a decreasing creep force for higher creepages. This is commonly known as one of the possible mechanisms of curve squeal noise generation. The results provide insights into the likelihood of curve squeal generation, and an on-set curve squeal noise detection technique is proposed that also accounts for the influence of profile changes due to wear.

JOULE HEATING EFFECT ON TERNARY NANOFLUID FLOW AND HEAT TRANSFER OVER A PERMEABLE CYLINDER

This study presents a comprehensive numerical investigation into the Joule heating effect on ternary nanofluid flow and heat transfer over a permeable cylinder. The nanofluid consists of copper, alumina, and titania nanoparticles suspended in a water base fluid. Key physical parameters, including magnetic field strength and suction, are incorporated into the model to assess their effects on the flow and thermal performance. The governing partial differential equations are transformed into ordinary differential equations via similarity transformation and solved using the bvp4c solver. The results are validated against previously published studies, showing excellent agreement. The analysis reveals that Joule heating significantly impacts the temperature distribution within the boundary layer, increasing its thickness. However, its influence on the skin friction coefficient and overall flow behavior remains minimal. These findings provide valuable insights into optimizing heat transfer and fluid flow in systems that utilize ternary nanofluids, with potential applications in advanced cooling technologies and industrial heat management systems.

Enhancing tribological performance of AISI 52100: the role of laser surface texturing in dry and lubricated conditions

Abstract Laser surface texturing (LST) is a valuable technique in surface engineering that offers significant improvements in the tribological behavior of metals and alloys. This study investigates the synergistic effect of incorporating hexagonal boron nitride (h-BN) as a solid lubricant with laser surface texturing on the tribological performance of AISI 52100. Dimple textures with varying pitch distances (100, 150, and 200 μm) were created on the surfaces of the mentioned materials using LST. The friction coefficient and wear behavior of both non-textured surface (NTS) and textured surfaces (TS) were analyzed under dry sliding (DS) and lubricating sliding (LS) conditions. Wear tests were conducted using a universal tribometer under a load of 10 N, a sliding frequency of 10 Hz, and a sliding time of 1250 s. The results demonstrate that the presence of dimple textures significantly influences the tribological behavior of the materials. In DS, the wear coefficient exhibits a significant reduction compared to NTS, with decreases of 88.1% for TSP-100, 28.5% for TSP-150, and 76.1% for TSP-200. In LS, the TSP-L-100 (h-BN NPS) surface demonstrates the lowest average wear coefficient among all textured surfaces. Specifically, the TSP-L-100 surface shows a remarkable 97.61% reduction in average wear coefficient compared to NTS. This study demonstrates the potential of LST combined with h-BN as a solid lubricant in improving the tribological properties of metals, offering valuable insights for surface engineering applications in various industries.

Thermophoresis & Soret-DuFour on MHD Mixed Convection of a Nano Fluid with a Porous Medium over a Stretching Sheet with a Non-Uniform Heat Source/Sink

This work aimed to examine the effects of thermal diffusion (Soret) and diffusion-thermo (DuFour) on MHD mixed convective flow of a viscous nanofluid across a stretching sheet under a magnetic field embedded in a porous medium in the presence of non-uniform heat source/sink and chemical reaction. The governing equations are transformed into a set of ordinary differential equations using the similarity transformation approach. They are subsequently resolved computationally by use of the efficient Keller box method. The effects of different physical factors on concentration, temperature, and velocity profiles are graphically shown. Increasing Du values decreases temperature, although concentration profiles indicate the reverse. As temperature rises, the chemical reaction parameter Kr values increase, while the concentration profile decreases. The temperature was found to rise when the space-dependent (A1) and temperature-dependent (B1) parameters for heat source/sink increased. Additionally, a tabular presentation of the skin friction coefficient, Nusselt number, and Sherwood number behaviour is provided. Mixed convection heat and mass transfer flows are very important in manufacturing for designing reliable equipment, nuclear power plants, gas turbines, and various propulsion devices for aircraft, rockets, satellites, and spacecraft. The effects of non-uniform heat sources/sinks, thermophoresis, and chemical reactions on mixed convection flow play an important role in space technology and high-temperature processes.

Tribological behavior evaluation of poly-ether-ether-ketone (PEEK) in dry journal bearing on shaft wear test

This paper investigated the tribological behavior of pure PEEK playing as a dry journal bearing, sliding against stainless steel, under real-life operating conditions in a wear test lasting 2 h. Four conditions were carried out with different magnitudes of normal load and sliding speed, while keeping a constant PV parameter. Sample topography assessments were performed with scanning electron microscopy and white light interferometry techniques. In addition, PEEK samples were also evaluated by Fourier Transformed Infrared Spectroscopy and thermal analyses by Differential Scanning Calorimetry. The coefficient of friction (COF) changed throughout the wear test and exhibited a running-in period followed by a transition, with an increase of COF, and then a tendency to reach a steady-state. Moreover, the COF behavior obtained suggests that there was an influence of the wear test parameters, mainly right after the running-in period — and the COF averages for the steady-state period were statistically equal. Stainless steel samples showed mild wear, while PEEK samples had a drastic alteration of their topography imposed by the wear test — including an increase in its degree of crystallinity. Nonetheless, the PEEK journal bearing samples did not fail from wear and their mass losses were small. Polymeric wear particles were generated and were found weakly adhered to both the body and the counter body. PEEK exhibited a lumpy transfer process — nonetheless, SEM images evaluation was useful to verify that these particles were eventually merged during sliding, and kneaded in the convex-concave contact, which provided them a film-like appearance. Furthermore, adhesive and abrasive wear mechanisms were identified, which were shown to be related to the journal bearing on shaft wear test arrangement.

Effect of radiation sensitizer on the friction, mechanical and thermal degradation properties of electron beam cured FKM-PTFE composite

Friction coefficient behaviour of electron beam cured vinylidene fluoride-hexafluoropropylene copolymer fluorocarbon rubber (FKM) with 30% loading of polytetrafluoroethylene micro-powder (PTFEMP) irradiated at 250 kGy dose were studied by using a pin-on-disk tribometer for a total testing distance of 360 m in dry conditions at a sliding speed and applied normal load (FN) of 0.05 m/s and 1 N respectively. The same tests were done on the 70/30 blend added with radiation sensitizers n,n-1,3 phenylene bismaleimide (HVA2), trimethylol propane triacrylate (TMPTA) and tripropylene glycol diacrylate (TPGDA). The average friction coefficient (μ) value of all the composites with sensitizer decreased with the TMPTA system recording the lowest μ value which reduced by almost half compared to the pure composite due to better crosslinking density of the vulcanizate. Analysis of the friction coefficient curve behaviour showed an initial low value but displaying an increasing trend versus distance in the TMPTA and TPGDA composites while HVA2 composite recorded an initial high value but showed a reducing trend versus distance. HVA2 composite also recorded the best tensile strength results due to its influence in promoting better synergistic effect and miscibility of PTFEMP filler in FKM matrix.

Binder assisted graphene derivatives as lubricants in copper: Improved tribological performance for industrial application

Originally derived from graphite, high-quality single-layer graphene is an excellent anti-wear and -friction additive in metal matrix. Here, the tribological performance of 3 different commercialized graphene derivatives (e.g., graphene oxide [GO], reduced graphene oxide [RGO], and graphene nanoplatelet [GNP]) as additives in a Cu matrix, were investigated from an industrial perspective. To increase the interaction of graphene derivatives with Cu particles, and addressing the aggregation problem of the graphene derivatives, different binders (polyvinyl alcohol [PVA] and cellulose nanocrystals [CNC]) were introduced into the system. Benefiting from such a strategy, a uniform distribution of the graphene derivatives in Cu matrix was achieved with graphene loading up to 5 wt%. After high-temperature sintering, the graphene is preserved and well distributed in the Cu matrix. It was found that the GNP-containing sample shows the most stable friction coefficient behavior. However, GO and RGO also improve the tribological performance of Cu under different circumstances.

Recycling Automotive Plastic Waste: Residual Polyvinyl Butyral (rPVB) as Solid Lubricant in Polyoxymethylene (POM) Blends

Polyoxymethylene (POM) is an engineering thermoplastic commonly used in tribological applications due to its low friction and auto-lubrication properties. To improve its performance further and broaden its applications to higher sliding speeds and loads, it is commonly reinforced with different particles, fibers, or solid lubricants. In this study, the effect of adding residual polyvinyl butyral (rPVB) from automotive windshields production lines on the tribological performance of POM during pin-on-disk wear tests at different loads (12, 15, and 18 N) and sliding speeds (0.25, 0.50, and 0.75 m/s) is investigated. It was found that rPVB acts as a solid lubricant, reducing the coefficient of friction (CoF) up to 50%. It is suggested that the formation of a protective layer of adhered material on the wear track is the mechanism behind CoF reduction. Melt flow index, Shore D hardness and elastic properties decrease linearly with rPVB content. However, the reduction in tensile strength, and thus shear strength of the blends, seems to be more significant on their CoF behavior than the reduction in hardness. No trend was found for wear resistance. Under certain sliding conditions rPVB decreased volume loss, but in other cases it increased it. It is suggested that, for the conditions analyzed in this study, adding 10 wt% of rPVB to a POM matrix results in the best balance of tribological performance, with an overall CoF reduction of 36%, and an average volume loss increase of only 1%.

Wear performance of short fiber added polyamide composites produced by additive manufacturing: Combined impacts of secondary heat treatment, reinforcement type, and test force

AbstractIn recent years, the number of studies focusing on the additive manufacturing has increased seriously to elucidate the critical points such as physical, chemical, and mechanical properties. Contrary to common trends and for the first time in the literature, this experimental endeavor aims to comprehend the combined impact of reinforcement type and heat treatment on the wear features of additively manufactured polyamide 6 (PA6) composites. As reinforcement materials, glass, and carbon fibers were utilized and all samples were created through the fused filament fabrication. Half of the samples were subjected to annealing treatment after the main production, and characterization works were performed using a fused emission scanning electron microscope, differential scanning calorimetry, and dynamic mechanic analysis. From the outcomes, it is seen that heat treatment has a positive effect on the hardness, and wear resistance of the composites. Besides, glass fiber‐reinforced samples display lower friction coefficient and lower volume loss results than other samples. For all samples, secondary annealing causes a positive impact on wear endurance in most cases. On the other side, the wear mechanism of the tested samples changes with the test force level and reinforcement type. At lower test forces, abrasive wear‐induced debris parts are detected on the deformed surfaces of PA6 and carbon‐added samples, but this case is opposite for the highest force of 40 N.Highlights Additive manufacturing was underlined as a promising way to create polymer composites with high dimensional accuracy. The combined effect of secondary annealing and reinforcement type on the wear resistance of 3D‐printed PA6 composites was examined for the first time in the literature. Carbon and glass fibers were compared to explore their effect on friction coefficient and wear behavior of polymer composite samples produced via FFF technology. Hardness and surface roughness measurements were used to comprehend the dry sliding wear results. Depending on the increasing test force levels and reinforcement type, deformation, and abrasion mechanisms were analyzed.

Enhancing friction and vibration reduction properties of a polymer using h-BN particles

The unstable contact state of the water-lubricated bearings can induce severe friction and vibration behavior in extreme conditions, posing a threat to the reliability and stability of ship propulsion systems. Enhancing the self-lubrication and reducing the frictional excitation forces are crucial for eliminating or suppressing the friction-induced vibration behavior during the frictional processes. This study developed a new composite material by incorporating hexagonal boron nitride (h-BN) particles into a thermoplastic polyurethane (TPU) matrix. Frictional vibration experiments were conducted to investigate the influence of h-BN particles on frictional vibration behavior. Comprehensive evaluations were performed on the coefficient of friction (COF), wear mass loss, vibration behavior, morphology, and element distribution to elucidate the influences of h-BN particles. The findings demonstrated that adding h-BN imparted excellent self-lubricating properties to TPU and significantly reduced the deformation on the worn surface. It effectively reduced COF behavior as well as its fluctuation amplitude, thereby enhancing the wear resistance and attenuating the vibration behaviors of the friction system. TPU modified by 6 wt.% h-BN exhibited the lowest COF with minimal fluctuation amplitude and the best vibration reduction properties, particularly at higher frequencies. The knowledge obtained herein will aid in a better understanding of the influences of h-BN on friction and vibration reduction, facilitating the design of water-lubricated TPU matrix composite bearings with promising self-lubrication and frictional vibration reduction performances.

Scientific exploring of Marangoni convection in stagnation point flow of blood-based carbon nanotubes nanofluid over an unsteady stretching surface

This study examines Marangoni convection in blood-based carbon nanotubes nanofluid's stagnation point flow over a time-dependent stretching surface. This study is inspired by the emerging importance of nanofluids in a variety of scientific and technical fields due to their unique and varied uses and effective thermal activities. Some examples of potential applications of these fluids include cancer treatment, magnetic refrigeration, drug delivery, and magnetic resonance imaging. Two types of nanoparticles are considered name is single wall carbon nanotube and multi wall carbon nanotube blood is takin as base fluid. Nonlinear partial differential equations are used to simulate the specified flow issue using momentum and energy conservation principles. Using a similarity transformation, the resultant is transformed into nonlinear with reduced dimensions. The relations for velocity profile and temperature distribution are calculated from the developed nonlinear ordinary differential equation by using an approximate analytical technique called the homotopy asymptotic method. Subsequently, these equations are implemented and executed within Mathematica software. The investigation focuses on significant outcomes such as momentum filed, energy filed, Skin friction coefficients, and Nusselt number. Graphs are used to interpret the effects of several factors, including the Marangoni parameter, nanoparticle volume friction, stretching parameter, slip parameter, and Prandtl number. The behavior of Nusselt's number and skin friction coefficient was also checked with the help of graphs and tables. The convergence of the solutions is checked with the help of auxiliary functions as well.

Investigation of Microstructure and Wear Behaviors of AZ91 Alloy Under Different Heat Treatments

This article aims to experimentally investigate the effect of heat treatment applied to AZ91 magnesium alloys on wear behavior under different applied load conditions. Apart from as-cast AZ91 alloy, AZ91 alloy samples were subjected to both solid-solution treatment (400°C for 16 hours) and three different aging processes (216°C for 4, 8 and, 12 hours) under three different applied loads (10 N, 25 N and, 50 N). Microstructural, characteristic, hardness, friction coefficient, and wear rate behavior under various applied loads were investigated against each other.
 
 The results showed that the wear rate increased in all samples with the applied load, while the friction coefficient decreased. While the highest wear rate was observed only in the solid-solution treated sample, it was observed that the wear rate changed inversely with the aging time. Furthermore, the micro-hardness increased in direct proportion with the aging time. While it was observed that the sample, which was aged for 12 hours, wore 13.6% less under 10 N load than the sample that was only treated with solid-solution, the results showed that the same sample wore about 25% less under 50 N load. The increase in β-precipitates in the structure with the aging period increased the micro-hardness, while the increase in hardness decreased the wear.

Effect of friction and tensile behaviour of the constituent yarns of three-layer fabrics, and cloth fit on the spike penetration

The aim of using protective clothing against penetration of sharp objects such as spikes is to absorb and dissipate the kinematic energy of the object to prevent body injury. In this study, the role of friction coefficient and tensile behaviour of the constituent yarns of three-layer woven fabrics prepared with various weft-wadded yarns including wool, jute, nylon and polypropylene on its resistance against penetration of three spikes with various geometrical characteristics were examined, in both states of cloth fit including tight and loose conditions. The obtained outcomes reveal that increment of the tensile modulus of the weft-wadded yarns leads to the reduction of the penetration depth. Moreover, utilizing yarns with higher friction coefficient such as wool decrease the penetration depth due to the yarn’s resistance against movement during penetration. For all prepared samples, the geometry of the spikes especially tip angle is a parameter that can affect the penetration process and fabric damage. In addition, the results of penetration test of samples demonstrate that the penetration energy of tight state is higher than loose state and in turn the severity of fabric damage in the tight samples is more than loose samples.

Research on the relationship between the tightening torque and the preload of composite bolted structures

Bolted joints are widely used in assembly of composite structures that transmit large loads. The relationship between torque ( T) and preload ( F) is needed to be obtained when using the torque method to tighten bolts. In this paper, the T- F relationship in the process of bolt tightening composite laminates was analyzed through bolt tightening experiments. The variation behavior of friction coefficient in this process was also studied. On this basis, a progressive damage finite element model was established using the improved LaRC05 criterion to analyze the stress and damage of the composite laminate during tightening. The various stages in the bolt tightening were divided and the mechanical properties of each stage were analyzed. The results of the study showed that the thread friction coefficient μth and the bearing friction coefficient μb change with the preload during the tightening process. Its behavior can be described using an exponential function. Serious stress concentration and assembly damage can be formed in the direct extrusion area of the outer edge of the locknut when the composite laminate is bolted. The bolt tightening process of composite laminates can be divided into five stages. Research conclusions are valuable for understanding composite structures and formulating the bolt tightening process.

Adhesion behaviour of borided AISI 4140 steel

ABSTRACT In this study, the adhesion behaviour of the borided AISI 4140 steel was estimated. A di-iron boride layer (Fe2B = ∼22 µm) was obtained on the surface of the AISI 4140 steel preheated at 773 K for 30 min to prevent thermal shock; afterwards, the samples were exposed to 1173 K for 30 min. The scratch tests were developed over the surface of the Fe2B/substrate system using a Rockwell-C diamond indenter with a normal force increasing from 0.5–80 N. The friction coefficient behaviour and the residual depth values were measured considering the scratch length that was monitored during the test, according to the ASTM C1624 standard procedure. Critical loads were determined through the combination of the normal force and visual inspection over the worn surface with cracks (cohesive failure) or detachment (adhesive failure) and are explained according to the mechanical properties of the Fe2B/substrate system.

Influence of rotation speed on abrasive wear behavior of the UHMWPE in lubrication environment

AbstractTo better understand the damage failure mechanism of ultra‐high molecular weight polyethylene (UHMWPE) in engineering application environments, a study was conducted to explore the effect of rotation speed on its abrasive wear performance in lubricant media containing abrasive particles, especially in comparison to the water. The wear mechanism was analyzed by friction coefficient and wear behavior. The results show that UHMWPE has excellent tribological properties in the water and is seriously worn in the abrasive environment. Under the condition of abrasive wear, there exists a critical rotation speed (360 r/min) leading to a shift in the wear mechanism of UHMWPE and obtaining the lowest wear rate of about 8.49 × 10−6 mm3/N•m. At below critical rotation speed, three‐body abrasive wear and adhesive wear mainly occur in UHMWPE; And at above critical rotation speed, the wear mechanism is mainly the plowing effect of particles on the material, and the furrow width can reach 40 μm. It is believed that this study can help to improve the understanding of the wear mechanism of UHMWPE, which can support the enhancement modification of the material and the application in complex environment.

Evaluation of the Friction Coefficient for TRIP1000 Steel under Different Conditions of Lubrication, Contact Pressure, Sliding Speed and Working Temperature

The use of ultra-high-strength steels (UHSS) has been growing in recent years, mainly in the automotive industry. Since these steels have high strength and hardness, more applied stresses are required to deform them, probably also impacting friction behaviour. In this article, a variation in the process parameters commonly observed in sheet-metal forming, such as contact pressure, sliding speed, lubrication and working temperature was performed. The material used was TRIP1000. These process parameters were varied, aiming to investigate the friction-coefficient behaviour; however, it was observed that there were no significant variations, indicating that the steel hardness may have contributed to this. Another finding is that, even if the lubricant did not change the average value of the friction coefficient, it contributed to a more stable process, favouring the absence of premature wear of the tools.

Effect of Williamson parameter on Cu-water Williamson nanofluid over a vertical plate

The objective of this study is to analyze the augmentation of thermal conductivity and mass transfer rate over a semi-infinite vertical plate on account of nanoparticles suspended in Williamson fluid. Tiwari and Das model for nanofluids involving infinite shear rate viscosity is used in the current review to explain the heat transfer performance of nanofluids. The finite difference method of an implicit type is used to solve the governing dimensionless equations numerically. Graphical illustrations demonstrate the effects of the Williamson parameter on momentum, energy, and concentration, the behavior of skin friction coefficient and heat, and mass transfer rate. According to the present study, higher values of the Williamson parameter increases the skin friction, heat and mass transfer rate.The visualization of velocity, temperature, and concentration in the contour plots are also depicted. It is observed that Weissenberg number increases the velocity temperature and concentration of fluid flow near the plate significantly.

Untersuchung des anwendungsnahen, dynamischen Reibverhaltens nasslaufender Lamellenkupplungen am Beispiel zweier Tribosystemvarianten

In order to be able to design the tribological system in a targeted way for use as a mechatronic actuator, e.g. for influencing vibration-dynamic properties, knowledge of the friction behavior occurring in the application is necessary. The method described in this paper supports the characterization of the dynamic, application-related friction behavior of a wet-running multi-plate clutch. This enables more accurate and in particular, application-related predictions of behavior in wet-running friction contact, such as the transmissible torque in dynamic operation with adjusted tribological systems. It supports the early stage design of functional extensions in the wet-running clutch system. In this paper, the method is used with two tribological system variants that vary in their friction lining. Differences in their dynamic friction coefficient behavior were identified.

Experimental study on nonlinear friction behavior of granular flow lubrication

Solid granules have good lubrication performance and load-bearing capacity, which has been concerned by researchers. However, the correlation mechanism between lubrication performance and granular medium dynamics is hardly focused on. In this study, the characteristics of two parallel friction pairs lubricated by the granular medium are experimentally investigated to study the nonlinear friction behavior during this process. The experimental results showed that the fluctuation behavior of friction force and friction coefficient with time shows a more flat nonlinear trend with the increase of the shear velocity and the pressure load. The discrete element simulation results corresponding to the experiment revealed that the change of nonlinear behavior of measured friction and friction coefficient is closely related to the evolution of force chains and dynamic characteristics of this granular flow lubrication system. The shear dilatancy amplitude of this granular flow lubrication system decreases obviously with the increase of the shear velocity and the pressure load. The flow states of granular medium is the main reason influencing the nonlinearity of shear gap. This study reveals the key factors affecting the friction nonlinearity and provides an evidence for the formation of granular shear dilatancy between two friction pairs lubricated by granular medium.