Lubricants, Volume 10, Issue 11 (November 2022) – 48 articles

Due to the electrification of vehicles, new demands are being imposed on gears, which translates to the tolerances of manufacturing errors. However, not many studies treat the impact of manufacturing error combinations on the lubricant behavior of gear sets. Therefore, a simulation method is developed, including its derivation, discretization, and implementation. The method solves the thermal elasto-hydrodynamic lubrication (TEHL) problem, taking into account the varying temperature, viscosity, density, and cavitation of the lubricant. To account for manufacturing errors, the load distribution from a loaded tooth contact analysis (LTCA), developed by the authors, is used as input to the TEHL method. Comparison is made with a standard load distribution assumption, and a numerical example is used to show some preliminary results. The results show good agreement with results from other studies. It is shown that there is a great effect of manufacturing errors on the TEHL behavior, such as temperature, due to the change in load distribution such errors impose. It can be concluded that manufacturing errors of different tolerances have a great impact and that they should therefore be taken into consideration when analyzing gear set behavior and constructing gear sets for new applications. Full article

Alcohol aqueous solvents were prepared by individually adding n-propanol, isopropanol, 1,2-propanediol, and glycerol to deionized water for use as lubricants for the electrostatic minimum quantity lubrication (EMQL) machining of aluminum alloys. The tribological characteristics of those formulated alcohol solvents under EMQL were assessed using a four-ball configuration with an aluminum–steel contact, and their static chemisorption on the aluminum surfaces was investigated. It was found that the negatively charged alcohol lubricants (with charging voltages of −5 kV) resulted in 31% and 15% reductions in the coefficient of friction (COF) and wear scar diameter (WSD), respectively, in comparison with those generated using neutral alcohol lubricants. During the EMQL, static charges could help dissociate the alcohol molecules, generating more negative ions, which accelerated the chemisorption of those alcohol molecules on the aluminum surfaces and thereby yielded a relatively homogeneous-reacted film consisting of more carbon and oxygen. This lubricating film improved the interfacial lubrication, thus producing a better tribological performance for the aluminum alloys. The results achieved from this study will offer a new way to develop high-performance lubrication technologies for machining aluminum alloys. Full article

Operating parameters affect the wear of abrasive tools during the polishing stage in building stone processing plants. This study investigates the effects of essential operating parameters including polishing head pressure, head rotation speed and water flow rate on the wear of the abrasive tools. For this purpose, a building stone abrasivity test was used to determine the weight loss of the abrasive tools during laboratory polishing of fifteen different types of Iranian granitic building stones. The standard operating parameters of the test were a polishing head pressure of 5 bar, a head rotation speed of 300 revolutions per minute (rpm), and a water flow rate of 4 L/min. The values of the operating parameters were changed to values within the range from ±25% and ±50% of the standard conditions in order to investigate the effect of variations in these parameters on the wear of the abrasive tools during the polishing stage. The results of different tests showed that the wear of the abrasive tools was directly proportional to the pressure up until a critical value of around 6.25 bar, after which it gradually decreased. This nonlinear wear behavior does not conform to Archard’s well-known classical wear law. The FESEM images of the worn surfaces showed that due to excessive load, debonded abrasive particles could not be pulled out from the pin surface and led to an interlocking phenomenon between the pin and stone surface. It was also found that the wear of the abrasive tools increased with increasing head rotation speed, while it decreased with the water flow rate. Moreover, the main wear mechanism of tests was abrasive wear and in some cases with a mixture mode of adhesion and delamination. Full article

The synergistic effect of simultaneous mechanical wear, chemical/electrochemical corrosion (tribocorrosion) and microbial attack poses a serious threat to marine and coastal infrastructure. To address this important problem, we have developed composite coatings consisting of TaC (25–35 at.%) and a corrosion-resistant α-Fe(Cr,Ni,Mo)-based metal matrix, as well as bactericidal elements (Cu, Ag). Coatings 50–75 μm thick were obtained by electrospark deposition in vacuum. The coatings possess high hardness (up to 10 GPa) and resistance to cyclic dynamic loads compared with the stainless steel (SS) substrate. Tribocorrosion experiments showed that the decrease in the corrosion potential associated with the removal of a passivating film from the surface during friction was 2–2.5 times smaller for the Ag-containing coating than for the other tested materials. The material passivation rates were also different: almost instantaneous passivation of the Ag- and Cu-doped coatings, and slow passivation for several minutes of the Ag/Cu-free coating and SS. The Ag-containing coating shows the lowest friction coefficient (0.2–0.25) and a minimal wear rate (1.6 × 10⁻⁶ mm³/Nm) in artificial seawater. The Ag-doped coating also exhibits the most positive value of corrosion potential and the lowest current density. After exposure in seawater for 20 days, only the Ag-doped coating showed no signs of pitting corrosion. All the studied materials have a pronounced bactericidal effect against Bacillus cereus Arc30 bacteria. The resulting coatings can be used to protect steel products from tribocorrosion and fouling in seawater. Full article

The tribo-dynamics performance of the piston–cylinder system is affected by multiple physical fields. The current work presents a novel multiphysics coupling method to model and analyze the lubricated piston skirt–cylinder interface considering the cylinder liner vibration. This method is implemented by coupling multibody dynamics of the crank-connecting rod–piston–cylinder system, the heat transfer of the cylinder and piston, hydrodynamics lubrication on the skirt–cylinder interface, vibration of the cylinder liner, and thermal as well as elastic deformation in the piston–cylinder system together with rheological characteristics of lubricating oil. The proposed method is adopted into a four-stroke gasoline engine to predict its dynamics and tribological characteristics, with the purpose of revealing the influence of cylinder liner vibration on the tribo-dynamics implementation of the piston–cylinder system. The results indicate that increasing the stiffness and damping coefficient of the cylinder is beneficial to suppress the vibration of the system, but it has little effect on the tribological characteristics of the piston skirt–cylinder interface. Full article

This work uses the solvent casting method to fabricate an elastomeric tool with polyurethane as the base material and silicon carbide (SiC) as embedded abrasive particles. The distribution of abrasive particles and the pore structure in the fabricated tools are analyzed. The fabricated tools are porous in nature and have self-replenishing as well as self-lubrication properties. Aluminum 6061 alloy and electroless nickel-phosphorus plating having different initial roughness are selected as workpieces to study the wear mechanisms and loading of the flexible abrasive tool. The rotational speed of the tool, tool compression, and feed rate are fixed input process parameters. Total finishing time, sliding distance, and roughness are varied to obtain output responses. The workpiece material is also taken into account as a variable parameter in this study. These materials are classified as different counter surfaces as their surface roughness and mechanical properties vary. The finishing time and sliding distance for these counter surfaces differ in order to relate their effects on tool wear and loading. The nickel-plated surface shows a higher percentage reduction in surface roughness of 92% as compared to the aluminum surface, with a 62% reduction in surface roughness. The coefficient of friction, wear, and tool condition are analyzed to understand the mechanism of tool wear and tool loading. In this process, both two-body and three-body abrasions occur simultaneously and continuously. Full article

Three different laminated composites are used in this study: carbon fiber, woven glass fiber, and glass-fiber-reinforced epoxy. The composite laminate structures were fabricated using the hand lay-up technique at room temperature. The laminates were reinforced with epoxy resin, carbon fibers (CFRP), woven glass fibers (GFRP-W), and random-orientation glass fibers (GFRP-R) to obtain laminates with eight layers. The wear test was performed using a pin-on-disc tribometer with five different loads of 10, 20, 30, 40, and 50 N at room temperature and a constant speed of 3 m/s. In addition, three different surfaces were lubricated: dry, with grease, and with oil. The effect of lubrication on the weight loss of the laminates was measured. The linear elastic finite element model FEM was derived to simulate the pin on the disc and the failure mode in shear mode for the case of dry lubrication. In addition, the FEM allows the friction force to be measured to determine the friction coefficient numerically. For validation, a simple analytical model based on the shear stress induced by the laminates at the interfaces was extracted to measure the friction coefficients. Tensile strength is a characteristic property that is very important for the purpose of material description from FEM and the analytical model. Therefore, it was determined experimentally with a simple tensile test. The results show that the wear rate is better with GFRP-R composites. Moreover, the wear rate with grease is lower than with oil or dry. The FEM showed that the coefficient of friction decreases with normal force to a minimum value of 0.02 for the case of 50 N normal force and for GFRP-R, while the maximum value of the coefficient of friction was 0.55 for CFRP at 10 N normal load and the FEM results were in good agreement with the analytically determined data. Full article

The research focuses on slurry abrasion and erosion of martensitic steels used in the mining and agricultural industries. A traditionally constructed slurry pot tester with corundum abrasives in slurry form was used for wear characterisation. Wear testing was performed on each specimen for 180 h. Every 20 h, pauses were taken to characterise the specimen size, weight, hardness, and surface roughness. The worn zone’s damage progression was studied using optical microscopy. As the test period rose, the mass loss due to the wear, which was governed by the impact angle of the slurry flow, followed a linear pattern. The impact of specimen orientation on the wear rate was more pronounced than that of abrasive flow velocity. High-speed video recordings highlighted the varied contact conditions that caused the wear mechanism to shift from abrasion to slurry erosion. Slurry abrasion was seen at the bottom of the specimen as a result of pure sliding conditions, while pitting was observed at the top of the specimen as a result of fatigue from particle impact. Studies of 3D surfaces demonstrated a decrease in wear rate while transitioning from the abraded zone, which witnessed polishing and minor hardness, to the pitting zone. The wear performance of the materials was rated, with tempered martensitic steel coming out on top. Full article

Nickel-based super alloys exhibit high strength, oxidation and corrosion resistance; however, the machining of these alloys is a challenge that can be overcome with effective cooling/lubrication techniques. The use of a minimum quantity lubrication (MQL) technique is limited to lower cutting parameters due to the tremendous heat produced during the machining of Inconel 718. Sustainable and eco-friendly machining of Inconel 718 can be attained using MQL and lubricants based on nanofluids because of their improved heat transfer capabilities. For that purpose, the performance of hybrid nanofluid-MQL is examined. In this novel study, graphene and hexagonal boron nitride (hBN) nanoparticles are reinforced with palm oil and delivered to the machining interface using an MQL setup. The machining experiments are performed under the conditions of dry, wet, MQL and MQL with graphene/hBN deposited in palm oil. The machining performance under selected cutting conditions is assessed by analyzing the surface roughness, tool wear, chip morphology and surface quality of the machined workpiece. A comparison of results showcased the effectiveness of hybrid nanofluid-MQL with improvement in surface finish, reduction in tool wear and favorable chip forms concerning all other machining conditions. Full article

To improve the accuracy of the calculation analysis of crank journal bearings in motorcycle engines and accurately understand lubrication conditions, the oil film conditions of actual crankshafts and journal bearings should be measured. This research study focuses on the oil film pressure generated in the main bearing, and by using an original thin-film pressure sensor with improved durability achieved through the use of DLC (Diamond-like Carbon), it was possible to perform experiments at a maximum of 13,000 rpm and full load, which was not possible before. This established a method for measuring the oil film pressure generated in the main bearing of a high-speed motorcycle engine during operation without changing the surrounding environment. The maximum oil film pressure was 140 MPa, and the oil film pressure generated by each main bearing was successfully measured under different experimental conditions. The timing of pressure onset agreed well between the calculation and experiment stages, but the peak oil film pressure values were different. By varying the temperature of the engine in the calculation model, the calculated values approached the measured values. In the future, we plan to investigate ways to improve the accuracy of the current analytical model. Full article

Improving efficiency is a general task in the design process of high-speed journal bearings. A specific fixed-pad bearing geometry featuring reduced pad length and additional design measures with the intention of reducing frictional power loss is investigated, experimentally and theoretically, for a journal diameter of 500 mm up to surface speeds of 94 m/s and unit loads of 5.0 MPa. To model fluid flow in the bearing outside the lubricant gap, an extension to Elrod’s cavitation algorithm based on assuming the inertia of fluid flow is proposed. Validation of the extended thermo-elasto-hydrodynamic lubrication (TEHL) model shows good agreement between measurement and prediction in wide operating ranges, however, with systematic tendencies of the remaining deviations. Furthermore, measured local pressure and film thickness distributions indicate a complex formation of cavitation with an influence of axial flow that is not covered by pure Couette-flow in the cavitation region. Measured as well as predicted data prove increased bearing efficiency for high rotor speeds. To provide understanding on the impact of the applied design measures improving efficiency, their combination is separated into the individual ones. Reduced axial and peripheral pad length both contribute almost equally to the reduction in power loss and improve its value by 37% compared to the standard design. Finally, further steps to deeper identify the behavior of the bearing are comprehensively discussed. Full article

Nanoparticles as lubricant additives demonstrate powerful friction reduction and antiwear properties and are potential alternatives to traditional additives in line with green and environmentally friendly requirements. However, the vast majority of currently available research focuses on the tribological properties of various nanoparticles in base oils at laboratory, which has a large gap with their application in engineering. To cope with the rapid economic and industrial development in China, there is a need to improve the tribological properties of nanoparticles. This paper highlights the current status and development trend of nanoparticles as lubricant additives in China. The factors influencing the tribological properties of nanoparticles, such as their composition, particle size and morphology, as well as the base stocks and their combination with other additives, are summarized. Furthermore, the research progress in the lubrication mechanism of nanoparticles is discussed, and the issues concerning the application of nanoparticles as lubricant additives as well as their future directions are discussed. This review is expected to provide an impetus to guide the design of high-performance, fully formulated lubricant systems containing nanoparticles as the lubricant additive. Full article

For transient mixed Elastohydrodynamic lubrication (EHL) problems, a novel solution is required to predict friction loss and wear in sliding or rolling parts. However, existing solutions have numerous limitations. In general, the lower the oil film thickness is, the more serious the non-linear problem is. This paper presents an efficient solution to tackle the non-linearity of the mixed EHL problem. The elastic deformation in the fluid–solid iteration coupling problem is divided into two parts: One is induced by the hydrodynamic pressure. This part of the deformation is obtained by the unsteady EHL-FBNS (Fischer–Burmeister–Newton–Schur) solver by considering both mass-conserving cavitation and elastic deformation. The other part of the deformation is introduced by the asperity contact pressure. It can be obtained by the Newton–Raphson method. After some limited iterations, the mixed EHL problems can be solved by evaluating the residual total pressure (including hydrodynamic pressure and asperity contact pressure). The proposed methodology was validated against the results from the published literature and applied to characterize the tribological performance of point contact with moving texturing. It appears that the developed method can be effectively used for tracking the tribological behavior of friction pairs. Full article

This research focuses on the study of the simulation capabilities of the lagrangian (LAG) model and Smoothed Particle Hydrodynamics (SPH) model for the orthogonal dry machining of aluminum alloy Al6061-T6. A three-dimensional finite element model was developed and verified using experimental data from the published literature. The numerical models were developed using lagrangian boundary conditions via finite element modeling in ABAQUS/Explicit 6.14. The cutting simulations were carried out at low and medium cutting speeds. Johnson–Cook material constitutive law and Johnson–Cook damage law were used in both models. The numerical methodologies are compared based on cutting forces, chip morphology, shear angle, chip separation criterion, and chip thickness. The findings of the present work show that the LAG model is good for predictions regarding cutting forces and chip morphology, while the SPH model is good for predictions regarding the shear angle and chip thickness. The difference between results generated by both models mainly occurred due to the friction coefficient. The comparative study shown here offers a guidance approach for various numerical models for appropriate parameter analysis. Full article

The use of cutting fluids during machining processes remains one of the main challenges toward greener manufacturing, mainly when applied by flooding. The use of vegetable-based cutting fluids stands out as one of the alternatives toward more sustainability by making the process eco-friendlier without much impact on the economic aspects of the chain. In this paper, the performance of two vegetable-based cutting fluids applied by flooding was compared to one mineral-based during the turning process of the AISI 1050 steel. They were also tested after aging for microbiological contamination to assess the fluids’ sustainability further. The machinability of the cutting fluids was evaluated by considering the tool life and wear mechanisms, workpiece surface roughness, and cutting temperatures. After microbial contamination, all the fluids increased kinematic viscosity and specific weight, except for the emulsion of vegetable-based fluid, where its kinematic viscosity decreased. The vegetable-synthetic fluid obtained the best machining results in cutting temperature and roughness (Ra) and also had the best behavior for microbial growth. However, considering the tool life, the best result was obtained with the emulsion of the vegetable-based fluid. Full article

Compacted graphite iron (CGI) has been considered an excellent option for heavy-duty engine blocks due to its superior mechanical properties, which allow reduction of weight, enhancing engine performance. Abrasion is a recognized wear mechanism in engine blocks, meaning it deserves to be evaluated for CGI. This study analyzed two grades of high-strength CGI (GJV450 and GJV500) submitted to microscale abrasion tests in free ball configuration using two different slurries: diamond and silica. There was more wear to the surfaces tested with silica due to the particle size, which was one order of magnitude larger than the diamond. The data obtained showed that both materials presented similar resistance when tests were performed with the diamond slurry. On the other hand, when silica was used, GJV500 presented 2.5 times greater wear resistance than GJV450, even though its global hardness was only 17% greater. Full article

Supercritical CO₂ foil bearings are promising bearing technology for supercritical CO₂ high-speed turbomachinery. The partial derivative method including complete variable perturbation of the compressible turbulent lubrication Reynolds equation is effective to predict the frequency dependent dynamic stiffness and damping coefficients of supercritical CO₂ bearings. In this research, the structural perturbation of foil dynamic model was introduced into this method and then the dynamic coefficients of supercritical CO₂ foil bearings were calculated. The results of parametric analysis show that the structural loss factor has little influence on the trend of dynamic coefficients changing with the dimensionless support stiffness but mainly affects the value of stiffness coefficients as well as damping coefficients. Due to the turbulence effect, the bearing number is not able to directly determine the characteristics of supercritical CO₂ foil bearings, which is different from air bearings. Compared to the bearing number, the influence of the average Reynolds number on the change of dynamic coefficients with dimensionless support stiffness is more obvious. Full article

One of the most important factors influencing the study of the tribological behaviour of a rolling bearing is the calculation of the loads transmitted by individual rolling elements of the bearing. However, the calculation of the internal load distribution of rolling bearings is quite complicated. It is a nonlinear, statically indeterminate problem, which can only be solved numerically, through a number of iterations. This is often a problem in analysis because it complicates the mathematical model. This paper is presenting a case study with the goal to show the benefits of the application of a new approach for the calculation of the load of the most-loaded rolling element in the rolling bearing with the internal radial clearance. The calculation is based on the so-called load factors. By multiplying the load factors with the value of the external radial load, the load that is transferred by the most-loaded rolling element of the bearing is obtained. The accuracy of the results largely depends on the correct choice of the load factor. The case study aims to define guidelines for the correct choice of load factors. The case study is made for two types of bearings: the ball bearing and the roller bearing. Obtained results were compared with the results obtained based on the calculation using some of the most commonly used methods so far. The analysis showed greater precision of the considered model with the same or much simpler use. For this reason, the proposed model is considered very suitable for practical application. Full article

Two kinds of graphene coatings are obtained by the graphene drop-coating drying method (DCDM) and the coating graphene conductive adhesive (CGCA). The effects of these two kinds of graphene coatings on the friction, wear, and voltage signals of the electrical contact interface are explored. The test results show that the presence of the graphene coating can effectively reduce the friction coefficient and friction force, and the graphene coating prepared by the DCDM possesses the best ability in reducing the friction coefficient. Although the presence of the graphene coating will lead to the increase in interface contact voltage at the initial stage, the voltage signal gradually becomes stable with the progress of friction and wear, suggesting that the graphene coating will not affect the stability of sliding electrical contact. Wear analysis results show that the graphene coating prepared by the DCDM has a good anti-wear effect, and the graphene particles in the abrasion area play the role of solid lubrication. Finite element analysis results show that the graphene coating will generate thermal expansion when electric current is applied, accordingly avoid the direct contact between the metal substrate, and, thus, reduce the interface friction and alleviate the wear degree of interface. However, the normal force fluctuation of the interface may increase. Full article

Nanopeening treatment was applied to the AISI 420 steel to decrease its sensitivity to tribocorrosion damage. The microstructural investigation highlighted that the nanopeening treatment led to high plastic deformation and a nanostructured surface layer with a 110 µm depth. In order to study the combined effect of corrosion and mechanical wear, tribocorrosion tests were performed on non-treated and nanopeened samples in boric acid and lithium hydroxide solutions, considering both continuous and intermittent sliding. It was found that the AISI 420 steel is sensitive to the synergy between mechanical friction and electrochemical corrosion with the dominance of abrasive wear. Adhesive wear was also detected in the wear track. Indeed, the mechanical wear was pronounced under intermittent sliding because of hard wear debris generation from the repassivated layer during rotating time. The nanopeening treatment led to enhanced mechanical performance and corrosion properties. Such improvement could be explained by the high plastic deformation resulting in the nano-structuration of grains and the increasing hardness of AISI 420 steel. Full article

The focus of this study was the combined effects of sliding velocity (SV) and martensite volume fraction (MVF) on the tribological behavior of dual-phase (DP) steel. Dry frictional tests were realized on a ball-on-disk tribometer by unidirectional sliding at 0.1 m/s, 0.6 m/s, and 1 m/s. Considering the increase in SV, both the friction coefficient (COF) and wear rate decrease due to the increase in oxidative wear. At 0.1 m/s, the major wear mechanism is abrasive wear, accompanied by partial material flaking and less oxidation wear; at 0.6 m/s, the wear mechanism is in the transition between abrasive wear and oxidation wear; at 1 m/s, oxidation wear becomes the dominant wear mechanism. For the same SV, specimens with lower MVF exhibited lower wear compared to specimens with higher MVF; this phenomenon is especially evident at low SV. As the SV increases, the effect of MVF on the wear decreases, and the velocity becomes the dominant factor. Full article

Gas bearings have been widely applied to high-speed rotating machines due to their low friction and high rotational speed advantages. Nevertheless, gas lubrication is low viscosity and compressible. It causes the gas bearing-rotor system easy to produce self-excited vibration, which leads to instability of the rotor system and hinders the increase of rotor system speed. It is necessary to study the nonlinear behaviors of the aerostatic bearing-rotor system and the nonlinear vibration of the gas bearing-rotor system, especially considering the distribution mass and flexible and gyroscopic effects of the real rotor. In this paper, the nonlinear behavior of the gas bearing-rotor system is investigated from the viewpoint of nonlinear dynamics. Firstly, the dynamics model of a gas bearing rotor is established by combining the transient Reynolds equation and rotor dynamic equation obtained by finite element method (FEM). The transient Reynolds equation is solved using a hybrid method combining the differential transform method (DTM) and finite difference method (FDM). Then the transient gas force is substituted into the FEM rotor dynamic equation. In the end, based on the bifurcation diagram, the orbit of the rotor center, the frequency spectrum diagram and Poincaré map, the rotor system’s nonlinear behaviors are studied using a solution for the rotor dynamic equation with the Newmark method. Results show that there exists a limited cycle motion in the autonomous rotor system and half-speed whirl in the nonautonomous rotor system. Full article

Sustainable technologies draw attention in the machining industry thanks to their contributions in many aspects such as ecological, economic, and technological. Minimum quantity lubrication (MQL) is one of these techniques that enable to convey of the high pressurized cutting fluid toward the cutting zone as small oil particulates. This study examines the potency of MQL technology versus dry conditions on the machining quality during the milling of structural Strenx 900 steel within the sustainability index. High strength and toughness properties make this steel a hard-to-cut material providing an important opportunity to test the performances of dry and MQL environments. The outcomes of the experimental data demonstrated that MQL is superior in enhancing the quality of significant machining characteristics namely surface roughness (up to 35%), flank wear (up to 94%), wear mechanisms, cutting energy (up to 28%), and cutting temperatures (up to 14%). Furthermore, after analyzing the main headings of the sustainable indicators, MQL provided the same (+5) desirability value with a dry (+5) medium. This experimental work presents a comparative approach for improved machinability of industrially important materials by questioning the impact of sustainable methods. Full article

The present work demonstrates the novel composition of nanoparticles (NPs) of polyaniline (PANI) solo and, in combination with particles of polytetrafluoroethylene (PTFE) ~230 nm, as a powerful additive (antiwear-AWA and extreme-pressure additive EPA) in lubricating oils. The concentration of PANI NPs varied from 1–4 wt.% in a base oil and commercial 5W30 engine oil. The tribo-performance was evaluated on a four-ball tester. The PANI-based oils significantly enhanced the load-bearing ability, and 3 wt.% of PANI NPs led to enhancement in EP properties by 220% in a base oil and 58% in engine oil. Additionally, hybrid combinations of NPs of PTFE with PANI in base oil were prepared by mixing in a ratio of 3:1 and 2:1 and were explored for possible tribo-synergism in EP properties. The hybrid nano-oils led to the highest reported ~ 535% enhancement in the load-carrying capacity of mineral oil. The lubrication mechanisms for enhanced tribo performance were linked with studies on a scanning electron microscope, an energy-dispersive X-ray analyzer, and with the use of Raman spectroscopy. Full article

Magnetic field-assisted magnetic compound fluid (MCF) ultra-precision machining technology is regarded as an effective method to obtain a smooth surface. However, due to the evaporation and splashing of water in the polishing fluid during processing, the service life of the MCF slurry is reduced. This paper presents a material removal model for MCF polishing, and a novel experimental apparatus is proposed to extend the service life by supplying MCF components into the MCF slurry. Firstly, in order to obtain the ideal polishing tool, the appearance morphologies and the formation process of the MCF slurry were observed by an industrial camera. On this basis, the optimum parameters were determined by multi-factor and multi-level orthogonal experiments. Finally, the investigation of the MCF service life was carried out under the optimal processing parameters. The main findings are summarized as follows. (1) Excellent MCF polishing tools are obtained when the eccentric distance r is 4 mm and the MCF slurry supply V is 1 mL. (2) When the eccentric distance increases from 2 mm to 4 mm, the forming time of the MCF tool decreases sharply, but when the eccentricity exceeds 4 mm, the decreasing trend becomes slow. The molding time grows steadily as the supply is increased. (3) When the machining gap Δ, the MCF carrier speed n_c, the eccentricity r, and the revolution speed of magnetic n_m are 1 mm, 500 rpm, 4 mm, and 600 rpm, respectively, the ideal machining effect can be obtained. (4) It could be proven that the polishing device is feasible to extend the service time of the MCF slurry by adding MCF components. Full article

During their service, engine oils suffer from various influencing parameters such as thermo-oxidative stress and nitration, hence, the accumulation of degradation products and the entry of contaminants. Accordingly, ICEs need to be able to operate satisfactorily, especially with a degraded lubricant, making it highly recommendable to use such oils for component testing in ICE development. Thus, a new nitrative thermo-oxidative ageing method is presented for closer-to-reality simulation of engine oil alteration with the intention to provide reproducibly aged oils for subsequent bench testing. With this method, a target used oil from field application was replicated and the comparability of oil condition in the lab vs. field regarding oxidation, nitration, additive depletion, and acidification amongst others was verified by conventional and advanced analyses. Special focus was laid on the identification of nitration products, proving them to be predominantly oxidized aromatic species or organophosphates. The presented method gives valuable benefit for the closer-to-reality ageing of engine oils in reasonable time frames with moderate costs and, hence, for the provision of test oils for ICE bench testing enabling rapid engine component assessment. Full article

This paper presents the formability results of galvanized Zn-Fe-based interstitial-free (IF) “galvanneal” steel sheets with different degrees of alloying. The Fe content of the Zn-Fe coatings was determined by titration method and the phase composition of the coatings was determined by raster electron microscopy with EDX analyzer. A deterioration of the adhesion of the Fe-Zn coating to the substrate was observed in the pre-alloyed coating. The applied modes of annealing and smooth rolling after the surface galvanization resulted in a change in the surface microgeometry parameters Ra and Pc. The suitability of the surface microgeometry of the used Zn-Fe-coated sheets was assessed using control diagrams and the capability indexes C_pk with respect to the defined specifications. The coefficient of friction was determined by dry friction cup test, and using Anticorit lubricant and microtene film as lubricants. With increasing Fe content in the coating, a slight increase in friction coefficient values was observed—a slight deterioration in formability. The results obtained indicate that for car body surface parts, the Fe content of the Zn-Fe coating should range from 7% to 12%. Full article

The dry sliding wear behavior of as-cast pristine and boron-modified Ti-6Al-4V (Ti64) alloys (having 0.3 and 0.55 wt% B) is investigated using pin-on-disc experiments with the pin being Ti64 alloy and the EN31 steel disc. Experiments are performed at sliding speeds (s) of 1, 2, and 4 m/s and temperatures 300 and 573 K. A mixed response in wear behavior is observed. At the lowest sliding speed, all three alloys (except 0.55B alloy at 300 K) exhibit similar wear rates, with abrasive wear being the dominant wear mechanism. At 2 m/s, temperature and s increase, and adhesive wear takes over along with delamination wear. Here, the 0.55B sample shows the highest wear rate due to the debonding of more TiB particles, which increases three body abrasion wear. With further increase in s to 4 m/s, delamination and oxidation wear are observed for all the samples. XRD evaluation shows traces of TiO₂ and Fe₂O₃, which imply the formation of MML in samples tested at s = 4 m/s, which is also validated through subsurface microstructure analysis. It is found that MML having more TiB particles has more stability, because of which 0.3B samples show higher wear rate. Full article

Aerostatic bearings are widely used in ultra-precision manufacturing equipment as a crucial support component. However, turbulent vortices in the recess can induce micro-vibration of the aerostatic bearing, which can severely affect stability. To further suppress the formation of turbulent vortices and reduce the micro-vibration, an aerostatic bearing with a square micro-hole arrayed restrictor (SMAR) was designed and the influences of structural parameters of the SMAR on its static and dynamic performance were investigated using numerical simulations and experiments. The transient flow characteristics of aerostatic bearings with different numbers and spacing of micro-holes were studied using 3D large eddy simulation (LES), and the formation mechanism of turbulent vortices and the law of turbulent interaction between adjacent micro-holes were analyzed. The static performance and micro-vibration of the aerostatic bearing were measured experimentally to verify the effectiveness of the SMAR. The results show that the formation of turbulent vortices and micro-vibrations can be effectively reduced by the optimized design of the SMAR, while the static performance of the bearing is basically unchanged. The micro-vibration decreases rapidly with the number of micro-holes ranging from 1 to 36 and remains steady with the number of micro-holes ranging from 36 to 100. The micro-vibration decreases rapidly with the spacing of micro-holes ranging from 2 d_n to 8 d_n and remains steady with the spacing of micro-holes ranging from 8 d_n to 10 d_n. This study contributes to further understanding the mechanism of turbulent vortex formation in aerostatic bearings with a SMAR. Full article

This paper presents a detailed three-dimensional (3D) thermo-elastic-hydrodynamic (TEHD) multi-physics model of the bump-type gas foil thrust bearing based on computational fluid dynamics (CFD). In this model, the moving mesh technology is applied in the fluid flow domain, and the new boundary condition of fully developed flow is applied at the inlet and outlet boundaries, which is consistent with the continuous property of fluid flow and has better convergence performance in CFD. The groove between pads is set as the symmetry boundary. The contact pairs with Coulomb friction and contact/separation behaviors are considered in the structure deformation and heat transfer. The simulation results indicated that the boundary pressure has a significant influence on the foil deformation. It also revealed the heat flux transfer path and temperature distribution in the gas foil thrust-bearing (GFTB) system. Full article