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Coefficient of friction, μ, versus film parameter, λ, in the lubricated sliding of metals. BL ¼boundary lubrication, ML ¼mixed lubrication, (E)HL ¼ elastohydrodynamic lubrication. Blue and red dots indicate test conditions. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Coating is one of the innovative approaches used to improve the wear resistance and load-carrying capacity of surfaces in rolling-sliding contact, such as gears and rolling element bearings. In this study, the tribological performance of standard gear material (EN 16MnCr5) and two kinds of powder metallurgy (PM) gear material (Distaloy AQ + 0.2% C...
Contexts in source publication
Context 1
... of the test lubricant are presented in Table 4. By varying the sliding velocity, we can obtain different minimum film thicknesses. The general relationship between the friction coefficient and the film parameter (λ, i.e., the ratio of the film thickness and the RMS value of the roughness amplitude) is represented by the Stribeck curve (Fig. 3). The film parameter is calculated ...
Context 3
... lambda value (λ) shown in Fig. 3 measures the severity of the asperity contact during lubricated sliding. Between these regimes, when 1oλo3, is a mixed lubrication regime under which the load is carried partly by the asperities and partly by the lubricating oil. In the test run at the high sliding speed of 4 m/s, the λ value was approximately 2.2, indicating a mixed ...
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Citations
... A pin-on-disc tester was instrumented to operate as a two-electrode cell for performing highly controllable and isolated unelectrified and electrified lubricated sliding tests, as depicted in Fig. 2. Similar pin-ondisc testers have been demonstrated as a suitable method for assessing the sliding contact behaviors of gears under lubricated condition by some other research groups [25,26]. The test conditions are shown in Table 1. ...
Electrification of drivelines of electric vehicles (EVs) can give rise to damaging shaft voltages/currents that can potentially impair the tribological performance of sliding and rolling elements in these driveline systems. In fact, previous research has shown that the existence of shaft voltages/currents in electric machines is indeed highly detrimental for the service life of tribological components of EVs. Such currents/voltages originate from magnetic flux asymmetry, inverter-induced voltage and triboelectrification and may also interfere with the normal sliding condition of other electrically conductive tribological components connected to the electric motors in addition to those that are comprised in the driveline, e.g., gears. In the past, the influence of shaft voltages/currents in gear systems has been explored scarcely. Accordingly, this work aims to investigate specifically the lubricated sliding friction and wear behavior of gear materials under the influence of DC electrification. For this, tests were conducted on a gear material in a two-electrode-cell-based pin-on-disc tribometer representing the sliding contact of a gear interface. The tests were run under different currents (0, 1.5 and 3 A) and using different lubricants (pure mineral base oil, gear oil and transformer oil). The differences in sliding contact temperature, coefficient of friction (CoF), wear volumes and underlying mechanisms, as well as the chemical changes occurred in the lubricating oils by electrification are analyzed and discussed. Overall, the results confirmed that electrification can indeed have a strong influence on friction and wear of gear materials besides increasing contact temperature and thus accelerating the oxidation at the sliding interfaces for all the lubricants. The increase in wear is most likely due to three-body abrasion caused by increased oxidation and/or oxide-based debris formation under electrification. CoF was found to decrease by electrification, which was ascribed to the formation of a larger wear scar (that reduced contact pressure) and continuous replenishment of an oxide layer affording lower friction to sliding surfaces.
... where "V" denotes the volume loss (mm 3 ), "N" represents the applied load in Newtons, and "S" shows the wear distance in meters. The volume loss was determined by Eq. (2) [34][35][36] in which "R" and "d" are the radius of the wear track (mm) and the width of the wear track (mm), while "r" denotes the radius of the pin. ...
Because the important properties of the NiTi alloy, such as the shape memory effect, pseudoelasticity, and wear resistance, originate from a thermoelastic reversible martensitic transformation, these properties can be controlled using internal and external stresses. In this research, to improve the wear resistance and to minimize the mismatch stress in the matrix, YSZ microparticles with a thermal expansion coefficient close to that of an NiTi alloy were used as the reinforcement. In samples consolidated using spark plasma sintering, the role of YSZ reinforcement on microstructure and wear behavior was investigated and compared with NiTi-ZrO2 samples. The microstructural studies showed that using YSZ instead of monoclinic zirconia as the reinforcement can produce a lower mismatch stress and, therefore, a higher fraction of austenitic phase remains in the matrix. The austenite phase possesses strain recovery, which is beneficial for tribological applications. Therefore, NiTi-YSZ samples with a higher percentage of austenite and better mechanical properties demonstrated superior wear resistance. For example, the addition of 5 wt% YSZ to NiTi reduced the wear rate from 5.74 × 10−3 to 1.03 × 10−3 mm3/N.m. Investigation of wear mechanisms showed that abrasive, delamination and adhesive mechanisms mainly govern the wear process.
... Thus, this work aims to contribute with an experimental approach for exploring the tribological behavior of gear materials subjected to controlled electrified sliding wear by the implementation of a pin-on-disc tribometer. This tribotester has been broadly demonstrated to be suitable for evaluating the general tribological performance of gear materials simulating the sliding part of a gear contact by reproducing sliding point contacts [24,30,31]. The pin-on-disc testing of point contacts is strongly suggested in the ASTM G99 standard procedure [32]. ...
In contrast to conventional powertrains from internal combustion engine vehicles (ICEV), the tribological performance of powertrains of electric vehicles (EVs) must be further evaluated by considering new critical operating conditions such as electrical environments. The operation of any type of electric motor produces shaft voltages and currents due to various hardware configurations and factors. Furthermore, the common application of inverters intensifies this problem. It has been reported that the induced shaft voltages and currents can cause premature failure problems in tribological components such as bearings and gears due to accelerated wear and/or fatigue. It is ascribed to effects of electric discharge machining (EDM), also named, sparking wear caused by shaft currents and poor or increasingly diminishing dielectric strength of lubricants. A great effort has been done to study this problem in bearings, but it has not
yet been the case for gears. Considering that EVs powertrains can be configurated with an electric motor coupled to a single-speed or multi-speed transmission, it is expected that shaft currents can also affect gears to some extent. The pin-on-disc test has been widely used to study sliding wear of gear materials under comparable or realistic operating conditions. This accelerated test is effective for screening materials, lubricants and operating conditions allowing evaluations of their friction and wear properties. However, it has not been implemented for studying gear materials under electrified environments. Thus, this paper aims to explore the friction coefficient and wear of gear materials under non-electrified and electrified sliding in a pin-on-disc tester applying typical of EVs powertrain shaft currents during sliding. The tests were carried out at two
different DC currents under comparable gear dry and lubricated sliding contact conditions. Friction coefficient, wear volumes and morphologies were evaluated and reported in this work.
... The samples were weighed using a RADWAG WAS 160/C/2O scale, with a measurement accuracy of 0.1 mg. Of course, the sample had to be carefully cleaned before weighing; this is usually conducted using products such as acetone or washing benzene, and failure to take this step can lead to the results being seriously flawed [29][30][31][32]. Harsh operating conditions, resulting from frequent and significant changes of temperature, as well as the corrosive environment in which the brake system works (water and salt, especially during winter) may, in time, result in a permanent change of the friction material's structure, leading to changes in the tribological properties of the brake pads and discs. ...
... The samples were weighed using a RADWAG WAS 160/C/2O scale, with a measurement accuracy of 0.1 mg. Of course, the sample had to be carefully cleaned before weighing; this is usually conducted using products such as acetone or washing benzene, and failure to take this step can lead to the results being seriously flawed [29][30][31][32]. ...
The braking system is one of the most important components in any motor vehicle. Its proper function in emergency situations may save road users’ lives. Today, as vehicles have more and more power at their disposal, leading to increased acceleration and maximum speed, the issue of effective braking is particularly important. It must also be noted that brakes are used in harsh conditions (water and salt, especially during winter), and must provide appropriate durability (on average, circa 30,000 km). For these reasons, many institutions conduct research aimed, among other things, at minimizing fading. However, this study looked into a different matter, focusing on how the operating conditions mentioned above, including the lifespan of brakes, impact the tribological properties of the friction pair. To achieve this, samples from brake pads were obtained (both brand new and used). Next, using a pin-on-disc tribological test, it was shown that the pads have lower coefficients of friction and abrasive wear rates. The results indicated that both parameters change in a manner that is dependent on how long the brake system has been in use.
... Pores strongly influence mechanical and tribological properties of sintered samples [23,26,28,41,48]. Therefore, precise control and characterization of pores are required in PM. ...
This work critically scrutinizes and compares the tribological performance of randomly distributed surface pores in sintered materials and precisely tailored laser textures produced by different laser surface texturing techniques. The pore distributions and dimensions were modified by changing the sintering parameters, while the topological features of the laser textures were varied by changing the laser sources and structuring parameters. Ball-on-disc tribological experiments were carried out under lubricated combined sliding-rolling conditions. Film thickness was measured in-situ through a specific interferometry technique developed for the study of rough surfaces. Furthermore, a machine learning approach based on the radial basis function method was proposed to predict the frictional behavior of contact interfaces with surface irregularities. The main results show that both sintered and laser textured materials can reduce friction compared to the untextured material under certain operating conditions. Moreover, the machine learning model was shown to predict results with satisfactory accuracy. It was also found that the performance of sintered materials could lead to similar improvements as achieved by textured surfaces, even if surface pores are randomly distributed and not precisely controlled.
... The tests of physical properties were performed with the use of a T-11 pin-on-disc tribotester (Fig. 3). This method can be used both in dry friction tests and in the presence of various lubricants [23][24] [26][27]. The stand makes it possible to determine the average friction coefficient between a friction pair and to assess the wear rate of friction surfaces. ...
Copper is one of the main components of friction materials used in vehicles’brake systems. It is mainly used due to two features: good thermal conductivity and lubricity. Unfortunately, it is harmful no only to humansbut also more to aquatic life. For this reason, there is anattempt to minimize its use. This paper presents the results of testing four groups of samples with different Cu contents(5, 10, 15,and 20%). Laboratory tests were performed using calorimetry, hot wire method,and pin-on-disc method. This allowed to determine selected physico-chemical material properties of samples, which were then used for simulation studies. They were intended to check how the heating process of friction materials with a chemical composition such as made samples will proceedin real conditions, in real brake pads.
... In all the wear experiment, the normal load was 20 N, sliding speed was 0.07 m/s, and sliding distance was 100 m. The calculation of wear rate was performed according to the procedure described in Ref. [28]. The coefficient of friction (COF) was automatically recorded during experiments. ...
In this study, NiTi-x wt% monoclinic ZrO2 (x = 0, 5, and 10) samples were fabricated with spark plasma sintering method and the role of zirconia microparticles addition on the microstructure, martensitic transformation, and wear behavior of NiTi–ZrO2 samples was investigated. Microstructural observations using scanning electron microscopy equipped with energy dispersive spectroscopy confirmed the formation of Ti–rich regions in NiTi/zirconia interfaces. The evolution of mismatch stress in the composite samples can increase the dislocation density, especially at the interfacial regions. This facilitates the diffusion of titanium from the matrix which leads to the formation of NiTi2 phase in the composite samples. According to differential scanning calorimetry analysis, the martensitic transformation temperatures of zirconia reinforced samples increases that shows the higher stability of the martensite phase at room temperature. Rietveld refinement analysis also approved this finding. According to wear test results, the wear rate of NiTi sample is 5.74 × 10−3 mm3/N m. However, after the addition of 5 wt% ZrO2, the wear rate decreases to 1.49 × 10−3 mm3/N m which confirms the positive effect of zirconia reinforcements on the wear performance of NiTi-based samples. This improvement can be attributed to a better combination of hardness and pseudoelasticity in this sample.
... Of course, the sample has to be carefully cleaned before weighing using products like acetone or washing benzene. Otherwise the results may be seriously flawed ( Li et al., 2016;ASTM G99-17, 2017;Ramesh et al., 2015;Nair et al., 2009). ...
Disc brakes in passenger cars are extremely important due to safety concerns. Their operational quality largely rests on the conditions of contact between the working elements, which mainly consists offlat and dry sliding. The tribological phenomena thatoccur during braking are, unfortunately, extremely complex and difficult to recreate in laboratory settings. Many scientific institutes conduct research to improve our understanding of these phenomena. The results they present make it possible to continuously simplify the procedures for selecting friction materials and reducing the costs of identifying the properties of new products. This article analyses the methods commonly used by researchers. It also presents different set-ups of research stations, as well as the advantages and drawbacks of each method.
... However, unlike the microtextures fabricated by LST methods that can be precisely designed and tightly controlled, in powder metallurgy (PM) it is difficult to manage the pore size, distribution, and morphology by controlling the sintering parameters and powder particle properties. Furthermore, pore morphology is also influenced by total porosity (Martin et al. (17); Li, et al. (18)). The tribological behavior of sintered materials depends both on total porosity and on pore characteristics, as reported in Martin,et al. (17). ...
The effect of surface topography on lubricated systems plays a crucial role in terms of friction performance, because surface micro-irregularities can improve the load-carrying capacity of mechanical parts in lubricated conformal and nonconformal contacts. Sintered materials, which can be applied to manufacturing several mechanical components such as gears, axial thrust bearings, and disc brake pads, are interesting candidates, because they present pores that could be somewhat compared to microcavities produced by surface texturing techniques. This work aims at studying the influence of surface pores originated from the sintering process on the frictional performance of lubricated contacts under different lubrication regimes and slide-to-roll ratios (SRR). The research contributes to understanding how random micro-irregularities could change lubrication conditions and promote effects similar to those of more expensive and precise surface features produced by texturing techniques. The experimental results showed that a decrease in porosity led to a reduction in the coefficient of friction. Furthermore, less porous samples promoted friction reduction compared to nonporous materials due to the probable additional load support caused by small-scale surface pores. Therefore, in addition to the traditional appeal of the use of sintered materials to reduce production costs, the present contribution reveals that this type of material could also be used to reduce friction in contacting mechanical components operating under certain tribological conditions.
... However, unlike the microtextures fabricated by LST methods that can be precisely designed and tightly controlled, in powder metallurgy (PM) it is difficult to manage the pore size, distribution, and morphology by controlling the sintering parameters and powder particle properties. Furthermore, pore morphology is also influenced by total porosity (Martin et al. (17); Li, et al. (18)). The tribological behavior of sintered materials depends both on total porosity and on pore characteristics, as reported in Martin,et al. (17). ...
This work aims to study the tribological effect of surface pores varying sliding/rolling conditions. A UMT-2 BRUKER tribometer was used with a device that permits discrete variation of SRR (Slide to Roll Ratio) through different geometrical configurations. Two SRRs and pure sliding were evaluated. Sintered parameters were changed to produce three different porosities and pore morphologies. Furthermore, a non-porous sample was used as reference material. Principal results showed that the decrease of porosity leads to friction coefficient reduction. Less porous samples promoted less friction than non-porous material. Therefore, sintered materials could increase mechanical system performance in sliding/rolling conditions and the use of sintering in large scale manufacturing processes would reduce production costs and bring benefits to the economy.
