Tribological Performance Parameters Research Articles

Research on Internal Flow Field Characteristics of Straight-Groove Texture Using Three-Dimensional Modeling

Surface texture modification is a reasonable strategy for improving the tribological property of friction pairs. The internal flow behavior of the surface texture significantly impacts its performance. In this study, a three-dimensional computational fluid dynamics (CFD) model is constructed to explore the internal flow behavior of the straight-groove texture in the thrust bearing. The influences of the Reynolds number, depth ratio, and area ratio of the straight-groove texture on the internal flow behavior are systematically investigated. Furthermore, the streamline and tribological performance parameters are checked to reveal the mechanism of the groove texture influencing the tribological properties. It is found that the vortex and cavitation significantly affect the tribological performance of textured surfaces under hydrodynamic lubrication. The cavitation and upstream vortex areas increase with the Reynolds number, while the downstream vortex area shows a reverse trend. The increase in depth ratio strengthens the upstream and downstream vortexes while reducing the cavitation area. Additionally, a method is proposed to determine the location of the cavitation within the groove texture. Certain operating conditions create the optimal texture depth ratio and area ratio, which could maximize the load-carrying capacity (LCC) of the oil film, and the friction coefficient is relatively small.

Effect of texture on hydrodynamic journal bearing performance under starvation lubrication

The effect of texture on tribological properties of journal bearings operating under starvation lubrication conditions is studied in this paper. The P-θ model with mass conservation boundary conditions is used to accurately predict the oil film distribution in the full oil film/starvation region of the textured bearing. The effects of various degrees of starvation lubrication on the tribological performance parameters, such as eccentricity, attitude angle, full film area, and friction coefficient, are discussed in textured bearings. The results show that the effect of texture on the bearing performance is affected by starvation lubrication conditions: (1) The effect severity varied with starvation levels; (2) The texturing still improved the operating performance of the journal bearing in the case of weak starvation; (3) Texturing increased the bearing load carrying capacity and reduced the friction coefficient, improving safety and preventing safety accidents due to oil supply problems.

A Review on Performance Characteristics of an Air Foil Thrust Bearing

The axial loads of high-speed rotating turbo machines are supported by self-acting hydrodynamic components known as air foil thrust bearings (AFTB). The load bearing capability of these bearings depends primarily on the foil structure and secondarily on the operating conditions. The present review enlightens on the tribological performance parameters of the said bearing in enhancing the load carrying capacity. Various design and fabrication methods including theoretical models are briefly summarised and comparisons of experimental results are presented in order to reveal the possible research gap that leads in optimising the gas lubricated foil thrust bearings (GFTB) for their better employment in typical applications.

Varying Cu and Zn composition in brass and its effect on the fade and recovery behavior of the phenolic‐based friction composites

AbstractBrass as a functional filler in the formulation of brake friction composites helps to improve the thermal conductivity, tribo‐load bearing ability, fade, recovery and wear resistance of the brake pads. The commercial brass alloy has 70 wt% copper and 30 wt% zinc. In this work, the tribological performance of the brass powders with 60 wt% Cu +40 wt% Zn and 80 wt% Cu +20 wt% Zn having similar morphology with the commercial brass was evaluated. The commercial and the two modified versions of brass filler were introduced in the formulation. Totally nine phenolic brake composite were formulated and fabricated by varying the brass filler types and their composition (6, 8 and 10 wt%) in the brake formulations. The tribological performance of the developed brake pads was studied using a chase‐type friction tester following IS 2742 test standard. The worn surface of the tested samples was studied using scanning electron microscopy and energy‐dispersive X‐ray spectroscopy. The tribological performance of the developed samples shows a nonlinear behavior concerning the variation in the composition. Therefore, statistical evaluation techniques such as hybrid analytical hierarchy process coupled with extension evaluation method (AHP‐EEM) and analytical hierarchy process coupled with Preference Selection Index (AHP‐PSI) were used to rank the developed samples based on the multiple tribological performance parameters. Based on the evaluation process the brake composite's composition with 8 wt% brass containing 70 wt% Cu and 30 wt% Zn has given the best overall performance.

Influence of Manufacturing Variation on the Dynamic and Tribological Performance of Tilting Pad Journal Bearings

Abstract A robust approach to investigate a tilting pad journal bearing (TPJB) as a whole tolerance stack-up assembly is presented. Normal component variation within actual design tolerances is considered. The vector loop is expanded via Taylor series for sensitive analysis. The bearing shell and tilting pad machined radiuses for each pad are found to be the more influential dimensional characteristics on the assembled clearance and preload. A leading edge relief (LER) was used to avoid unloaded pads fluttering, while maintaining a satisfactory bearing assembled clearance in the loaded pads throughout the resultant preload variation. Pivot flexibility and preload loss due to pad wear in service life were included in the preload variation assessment. Surface response multivariate multiresponse models were built for a 4-pad TPJB under load between pad (LBP) and load on pad (LOP) configurations. Desirability functions rendered the maximum and minimum rotordynamic coefficient and tribological parameter responses across speed. The LOP configuration showed more variation in the direct rotordynamic coefficients, while the LBP configuration indicated more sensitive cross-coupled coefficients with very strong sign change in some cases. Among the tribological performance parameters, the eccentricity and pad maximum pressure were more affected, followed by the minimum film thickness, and weakly by the power loss, and oil film temperature. The dispersion of the tribology parameters under normal manufacturing variation is found of importance. Four, and seven extreme geometrical state cases were identified for the LBP, and LOP bearing configurations, respectively.

Multi-metal sulfide pre-blend combination on the tribological performance of the brake friction material

Purpose The purpose of this study is the influence of various combinations of metal sulfides on the tribological performance of brake pads. Design/methodology/approach Three brake pads were prepared using the possible combination of any two of the solid lubricants from Bismuth trisulfide (Bi2S3); Tin disulfide (SnS2) and Antimony trisulfide (Sb2S3) are chosen and blended with molybdenum disulfide and graphite. The tribological performance was compared with the brake pad containing aftermarket sulfide mixture. The tribological performance parameters such as performance coefficient of friction, fade percent, recovery percent, wear thickness loss, time is taken to reach the maximum temperature and fluctuation of friction were investigated using Chase tribometer adopting IS 2742 Part-4 (1994) test procedure. Findings The friction stability of the brake pad with 4Wt% of MoS2, Bi2S3 and SnS2 was observed to be better, but it showed poor wear performance and aggressive towards the rotor, whereas the brake pad contained 4Wt% of MoS2, Bi2S3 and Sb2S3 exhibited improved wear performance. Originality/value This paper explains the influence of the combination of multiple metal sulfide in the tribological performance of the copper-free brake friction composite. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2020-0249/

Tribological performance of textured parallel sliding contact under mixed lubrication condition by considering mass conservation condition and couple-stress parameter

To enhance the tribological performance of mechanical parts, one of the reliable methods is surface topography modification, in which the surface of one/both interacting contacts were to be modified. Surface texturing is one of the surface modification techniques. In the present work, a numerical code is developed to address the effect of texture shape (elliptical and triangular), size and distribution (parallel and zigzag) on the tribological performance parameters (minimum film thickness, percentage of hydrodynamic load from the total generated pressure and frictional coefficient) under mixed lubrication regime for a known value of load support. In the present analysis, the mass conservative, i.e. Jakobson-Floberg-Ollson (JFO) cavitation condition and couple stresses of lubricant are considered. In addition, surface irregularities are considered by using the flow factors of Patir-Cheng model. The results show that texture shape has a significant effect, whereas the texture distribution has a slight effect on the tribological performance parameters. Moreover, the couple stress of lubricant has a prominent effect on the tribological performance.

Antiwear Performance Evaluation o f Halloysite Nanotube ( HNT ) Filled Polymer Nanocomposites

Polymer nanocomposites containing various types of reinforcements and fillers are oftenly used in applications such as sliding elements in the machine and automotive parts, gear assemblies etc., in which tribological performance parameters viz. friction and wear are the major issues. In this work, the specific wear rate of HNT filler loading (0-4wt %) in Glass-Epoxy nanocomposites fabricated by vacuum bagging technique are evaluated experimentally. For this purpose, the specimens are prepared and tests are conducted as per the ASTM G-99 standard for a number of trials with the assistance of a pin-on-disc machine by varying load and speed values, keeping time and track diameter constant. The results obtained from experiments reveals that reduction in specific wear rate and the amount of material loss is quite significant for HNT loaded specimens when compared with neat sample even at higher operating conditions. This indicates that HNT comprises of hard ceramic elements viz. SiO2 and Al2O3 which eventually enhances the antiwear behaviour of prepared nanocomposites. Finally, a study on wear mechanisms and morphologies are carried out by analyzing the worn surfaces through SEM micrographs.

Comparative Experimental Study of Tribo-Mechanical Performance of Low-Temperature PVD Based TiN Coated PRCL Systems for Diesel Engine

Piston ring and cylinder liner (PRCL) interface is a major contributor to the overall frictional and wear losses in an IC engine. Physical vapor deposition (PVD) based ceramic coatings on liners and rings are being investigated to address these issues. High temperature requirements for applications of conventional coating systems compromise the mechanical properties of the substrate materials. In the current study, experimental investigation of tribo-mechanical properties is conducted for various titanium nitride (TiN) coated PRCL interfaces in comparison with a commercial PRCL system. Low-temperature PVD based TiN coating is successfully achieved on the grey cast iron cylinder liner samples. Surface roughness of the grey cast iron cylinder liner substrates and the thickness of TiN coating are varied. A comprehensive comparative analysis of various PRCL interfaces is presented and all the trade-offs between various mechanical and tribological performance parameters are summarized. Coating thickness between 5 and 6 micrometres reports best tribo-mechanical behaviour. Adhesion and hardness are found to be superior for the TiN coatings deposited on cylinder liner samples with higher roughness, i.e., ~ 5-micron Ra. Maximum 62 % savings on the COF is reported for a particular PRCL system. Maximum 97% saving in cylinder liner wear rate is reported for another PRCL system.

Tribological Failure Analysis and Suitability of Grease Lubrication for Sugarcane Crushing Mill Journal Bearings

Influence of tribological performance parameters like speed, eccentricity ratio, load and frictional torque on the performance of sugarcane mill heavily loaded slow-speed journal bearing was examined. Reasons for tribological failure of sugarcane crushing mill journal bearings were identified. It was observed that an increase in pressure of lubricant with the increase in eccentricity ratio increases load carrying capacity of heavily loaded journal bearing. The total load supported by bearing was evaluated. This load carrying capacity was compared with actual operating load of heavily loaded journal bearing. Theoretical load carrying capacity of heavily loaded journal bearing evaluated was much smaller than actual load carrying capacity. Regime of lubrication for sugarcane mill journal bearings was evaluated as mixed lubrication. For the experimental analysis, actual conditions of sugarcane mill journal bearing were maintained at the laboratory on journal bearing test rig. Frictional torque, coefficient of friction and temperature profiles were obtained by operating journal bearing on test rig for the duration of 8 h. Suitability of grease lubrication over oil lubrication was checked experimentally. Grease lubrication showed less wear as compared to oil lubrication.

Tribological characteristics comparison of formulated palm trimethylolpropane ester and polyalphaolefin for cam/tappet interface of direct acting valve train system

PurposeThere is a continuous drive in automotive sector to shift from conventional lubricants to environmental friendly ones without adversely affecting critical tribological performance parameters. Because of their favorable tribological properties, chemically modified vegetable oils such as palm trimethylolpropane ester (TMP) are one of the potential candidates for the said role. To prove the suitability of TMP for applications involving boundary-lubrication regime such as cam/tappet interface of direct acting valve train system, a logical step forward is to investigate their compatibility with conventional lubricant additives.Design/methodology/approachIn this study, extreme pressure and tribological characteristics of TMP, formulated with glycerol mono-oleate (GMO), molybdenum dithiocarbamate (MoDTC) and zinc dialkyldithiophosphate (ZDDP), has been investigated using four-ball wear tester and valve train test rig. For comparison, additive-free and formulated versions of polyalphaolefin (PAO) were used as reference. Moreover, various surface characterization techniques were deployed to investigate mechanisms responsible for a particular tribological behavior.FindingsIn additive-free form, TMP demonstrated better extreme pressure characteristics compared to PAO and lubricant additives which are actually optimized for conventional base-oils such as PAO, are also proved to be compatible with TMP to some extent, especially ZDDP. During cylinder head tests, additive-free TMP proved to be more effective compared to PAO in reducing friction of cam/tappet interface, but opposite behavior was seen when formulated lubricants were used. Therefore, there is a need to synthesize specialized friction modifiers, anti-wear and extreme pressure additives for TMP before using it as engine lubricant base-oil.Originality/valueIn this study, additive-free and formulated versions of bio-lubricant are tested for cam/tappet interface of direct acting valve train system of commercial passenger car diesel engine for the very test time. Another important aspect of this research was comparison of important tribological performance parameters (friction torque, wear, rotational speed of tappet) of TMP-based lubricants with conventional lubricant base oil, that is, PAO and its formulated version.

Transient lubrication of piston compression ring during cold start-up of SI engine

Cold start-up conditions differ from the normal operating conditions for an engine, and this discrepancy adversely affects the tribological performance of interfaces. The majority of health-hazardous engine exhaust emissions occur during the cold start-up of an engine; consequently this condition generates a major environmental concern. This study numerically investigates the transient hydrodynamic lubrication of the first compression ring during initial start-up of a cold engine by combining lubrication theory with the realistic oil rheology of multigrade oils. Specifically, in this study transient speed, variation in cylinder pressure, and high lubricant viscosity during start-up are considered to determine developing pattern of the lubricating film and of other tribological performance parameters. The cycle-by-cycle developments of lubricating film, friction force, power loss, and oil transport are analyzed as well. The start-ups of a cold and a warm engine are also compared in terms of frictional losses and oil transport. Different monograde and multigrade engine oils are used to evaluate oil-dependent performance. Results show that in all cases, performance during cold start-up is of greater significance than that of a warm engine. Low lubricant temperature and stated start-up conditions substantially increase amount of energy loss and net oil transport. Temperature-dependent variations in performance are also more significant in high viscosity-grade oils.

Optimization of Tribological Performance of Al-6061T6-15% SiCp-15% Al<sub>2</sub>O<sub>3</sub> Hybrid Metal Matrix Composites Using Taguchi Method & Grey Relational Analysis

In this investigation, optimization of tribological performance parameters of Al-6061T6 alloy reinforced with SiC (15% by weight) and Al2O3 (15% by weight) particulates having particle size of 37 μm each has been presented. The wear and frictional properties of the hybrid metal matrix composites have been studied by performing dry sliding wear test using pin-on-disc wear tester. A L27 orthogonal array is selected for the analysis of the data. From the test results it is observed that sliding distance has the significant contribution in controlling the friction and wear behaviour of hybrid composites. A confirmation test is also carried out to verify the accuracy of the results obtained through the optimization. In addition an optical micrograph test is also performed on the wear tracks to study the wear mechanism.

Study on variation of tribo‐performance of commercial engine oils

PurposeThe purpose of this paper is to study the performance variability of the commercially available engine oils based on physico‐chemical and tribological performance parameters.Design/methodology/approachThe study does this by evaluation of physico‐chemical parameters of flash point, pour point, TAN, sulphated ash, viscosities @ 40 and 100°C and VI; and the tribological performance in terms of friction, wear, weld load and the load bearing capacity of the lubricant film under the point and line contact geometries.FindingsCorrelation between some of the physico‐chemical properties and tribological performance parameters could be made and the variation in performance of the lubricants assessed.Originality/valueThe findings will be important to the engine oil producers and the users.