The film stiffness of dry gas seal must be sufficient to keep gas film stable at high and low speed. A generalized geometric model based on triangles is proposed to characterize spiral grooves. A mathematical model is established and solved using the finite-difference method to obtain steady performance. The optimum spiral grooves for maximum opening force and film stiffness are obtained at low speed, and their steady performance is compared with conventional spiral grooves numerically and experimentally. The pressure and flow field of optimum spiral grooves and conventional spiral grooves are simulated to reveal the mechanism of the performance difference. Results show that through-combined spiral grooves outperform the other derived spiral grooves. Their film stiffness is up to 15% larger than that of conventional spiral grooves at low speed.

In the present work, three kinds of halogen-free ionic liquids (ILs) incorporating long-chain quaternary phosphonium as cations and dioctylsulfosuccinate (DOSS) as the anion were synthesized and characterized and the tribological properties of phosphonium ionic liquids were investigated as neat lubricants for steel ball–steel disc friction pairs at room temperature (RT) and elevated temperature (100 °C). The ILs were found to be noncorrosive and highly thermally stable and showed better antiwear and friction reduction performance than commercially available synthetic lube base oil poly-α-olefin (PAO10) and conventionally used IL 1-methyl-3-hexylimidazolium hexafluorophosphate (L-P106). Scanning electron microscopy (SEM) and energy-dispersive spectroscopic (EDS) analysis of the worn-out surfaces of the steel discs was performed and the results revealed that physical adsorption and tribochemical reactions occurred and formed a protective boundary film on the worn steel surface to prevent direct steel–steel contact between rubbing surfaces.

The friction and wear behavior of 1-octyl-3-methylimidazolium lactate ionic liquid (L-L108) between steel surfaces was investigated in ball-on-disc sliding friction tests. At an applied load of 5 N and rotating speed of 200 rpm, the friction coefficient of L-L108 was measured as 0.023, which is about one third and one fifth the values of ionic liquid L-P108 (0.068) and SAE 10W-40 engine oil (0.107), respectively. Studies on wear surfaces show that the wear morphology improved when lubricated with L-L108. In addition, the anticorrosion property of L-L108 is better than that of L-P108. Possible mechanisms behind these encouraging performances of L-L108 are discussed and it was found that the interactions between L-L108 and steel surfaces are possible reasons for the reduction in friction coefficient and the improved wear morphology.

As a 3D printing technology, selective laser melting has remarkable advantages such as high processing flexibility, high material utilization, and short production cycle. The applications of selective laser melting technology in industry have become quite extensive. There are many tribological studies on selective laser melting materials, but few based on water lubrication (Zhu, et al., Journal of Zhejiang University-Science A, 19(2), pp 95–110). In this article, the tribological properties of 316L stainless steel processed by selective laser melting and traditional methods have been studied under water lubrication. Polyether ether ketone (PEEK) filled with carbon fiber (CF)/polytetrafluoroethylene (PTFE)/graphite was selected as the counterpart. 316L stainless steel and PEEK are a tribopair commonly used in water hydraulics. This study is of great significance to the application of selective laser melting material of tribopairs in water hydraulics. Friction and wear tests were carried out on a pin-on-disc contact test apparatus under different operating conditions. The friction coefficient, specific wear coefficient, scanning electron microscopy (SEM) of the worn surface, and energy-dispersive spectroscopy (EDS) of the surface adhesions of the three tribopairs were measured and compared. The results revealed that the friction coefficient of the selective laser melting (SLM) 316L stainless steel was significantly higher than that of traditionally processed (TP) 316L stainless steel, which might be caused by the pores on the surface of SLM 316L stainless steel. Adhesion and cutting on the surface of SLM 316L stainless steel were also more serious, resulting in a higher specific wear coefficient of its counterpart PEEK composite compared to PEEK composite against TP 316L stainless steel.

Two-body abrasive wear tests of Fe-B alloys with various matrix microstructures were performed using a pin-on-disc tribometer at a normal load of 3 N. The wear behavior was analyzed using scanning electron microscopy (SEM) and color 3D laser scanning microscopy. The results show that the Fe–2 wt% B alloy is mainly composed of a metallic matrix, M2B and M23(C, B)6. A pure pearlitic matrix occurs at a cooling rate of 0.05 °C/s, and a pure martensitic matrix forms at a cooling rate above 0.3 °C/s. Compared to the pearlitic matrix, the martensitic matrix can better support the M2B against fracture and provides higher abrasion resistance for the Fe–2 wt% B alloy. Moreover, with an increase in sliding distance, the abrasion resistance of Fe–2 wt% B alloy decreases slightly at first and then decreases rapidly. To be exact, the M2B is steadily scraped off until the critical sliding distance of 6.06 m is reached, after which the neighboring M2B fractures, leading to high material removal.

Solid-lubricated rolling bearings are widely known in many technical systems where conventional lubrication, such as oil or grease, fails due to critical conditions like vacuum or high temperatures. Polymeric cages (e.g., polyimide) endowed with molybdenum disulfide (MoS2) particles and silver (Ag) coating on the bearing components have proven themselves as dry lubricants that could significantly increase the service life of solid-lubricated rolling bearings. It has been demonstrated that during the bearing operation, material particles of the cage are transferred onto the raceways and lubricate the bearing. Thereby, the energy dissipates due to the momentary sliding at the ball–cage pocket interface. As a result of this behavior, the cage experiences wear apart from serving as a lubrication reservoir. In order to describe the lubrication transfer amount or the wear volume at the cage pocket, it is essential to estimate the material-specific wear rate. This contribution introduces an approach to determine and analyze the wear rates at the ball–cage pocket interface. In this article, only one example of lubrication coatings with specific operating conditions are shown, but the approach applies to other cases as well. This analysis has been achieved by performing bearing experiments under high vacuum conditions together with the combination of computational modeling. As an outcome, there are two aspects considered. The present contribution provides insight into the procedure to estimate material-specific wear rates. Additionally, it shows how wear rate data distribution can be analyzed. The future scope of this work is the input for the development of the model to predict and optimize the service life of such bearings to some extent.

A lubrication model of the piston ring–cylinder liner tribosystem taking account of the honing texture was established in this study. The impact of honing texture parameter, which was characterized by its crossing angle α, groove depth dp, and groove density de, was investigated experimentally and numerically to evaluate the lubrication performance of this tribosystem. The experiment was performed on a reciprocating workbench involving piston ring and cylinder liner segments to verify this model, and the calculated average friction coefficient was in good agreement with the measured data. The numerical analysis of the instantaneous friction coefficient (IFC), minimum oil film thickness (MOFT), and load-carrying capacity of oil (LCCO) were applied to analyze the effect of different honing texture parameters using single-factor analysis. Furthermore, the friction force at the dead center was optimized by multiple-factor analysis and reached the minimum value when α = 40°, dp = 3 μm, and de = 1.5 mm−1. Finally, analysis of parameter sensitivity showed that honing density has the most significant influence on lubrication performance.

Nickel and titanium are common elements in coatings. When Ni and Ti are combined they offer promising characteristics; specifically, the NiTi intermetallic phase. NiTi is a shape memory alloy possessing a stress-induced reversible martensitic transformation. NiTi alloys are used in a variety of industrial applications and are prevalent in the automotive, aerospace, and medical sectors. The problem with using NiTi is its poor machinability and formability. Applying NiTi as a surface coating will provide an alternate manufacturing method that will require limited machining. The objective of this study is to produce a superelastic NiTi surface coating that still possesses excellent wear and dent resistance while reducing forming and machining processes. A full and comprehensive understanding of the formation of the superelastic NiTi phase during coating development is nonexistent. Fabrication of this intermetallic phase is formed through the annealing of sputter-deposited Ti and Ni layers in a coating. Crystalline phases and residual stresses of the coating were established through X-ray diffraction (XRD). The behavior of the coatings was studied through scratch and Hertzian-type indentation testing. XRD and residual stress analysis suggest that intermetallic Ni and Ti phases precipitated at elevated temperatures, which resulted in excellent dent and scratch resistance compared to as-deposited Ni/Ti nanolaminate coating. This indicates that superelastic NiTi can form while annealing nanolaminates, further suggesting that dent- and wear-resistant coatings have the potential to be produced through annealing layers of Ni and Ti to form superelastic NiTi.

The stretching, shearing, deformation, peeling, and temperature rise phenomena at the micro–nano contact interface have a great influence on its tribological properties and significantly affect the service life of key moving parts made of polymers. The physical properties of the three typical polymer materials used for ship bearing polymer materials (ultra-high-molecular-weight polyethylene, synthetic rubber, and polypropylene) were examined to investigate their effects on the wear behaviors. The results showed that synthetic rubber has good wear resistance because of its excellent shear strength, tensile strength, and high initial thermoplastic deformation temperature. Low initial thermoplastic deformation temperature resulted in great wear to the polypropylene material under dry friction, whereas its good wettability resulted in good wear resistance under water-lubricated condition. The ultra-high-molecular-weight polyethylene had the poorest wear resistance under water-lubricated condition because it had the poorest shear strength and tensile strength. The knowledge gained herein provides a better understanding of the relationships between the physical behaviors of polymer materials and their friction and wear mechanisms, along with guidance for selecting and designing polymer friction pairs for ship bearings.

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.

A tolerancing method highlighting trade-offs against key design variables of mechanical systems is proposed and applied to herringbone-grooved gas journal bearings. Gas bearings typically suffer from a subsynchronous instability, demanding a very tight tolerance on the bearing clearance and groove depth. Classical optimization techniques look for the most stable design, which does not necessarily lead to most robust design against manufacturing deviations. The proposed method uses a normalized multidimensional lookup table of stability score (critical mass), covering a large design space of gas bearings. It then dimensionalizes the table for a specific rotor–bearing system, highlighting regions of the hyperspace where the system is stable. The hyperspace is sliced into 2D maps and a Monte Carlo method creates windows within the stable domain along the two most critical design variables regarding manufacturing: the bearing clearance and the groove depth. Width and length of the windows represent the manufacturing tolerance allowed for the two parameters to remain stable. A Pareto front of optimum windows in the entire hyperspace is then compiled. It displays the trade-off between the tolerance against deviation in clearance and groove depth, allowing the designer to select a nominal geometry tailored to the available manufacturing methods. A test rotor is analyzed with this method and the effects of pressure, speed, viscosity, radius, mass, and centrifugal growth on manufacturing tolerances are investigated, highlighting that the radius and viscosity have the greatest impact on the robustness.

Polyamide (PA) is used in industrial applications such as automotive, gears, bearings, and pipeline spacers. As a bearing material, PA can support high contact pressures under low sliding speeds. To achieve high-performing and durable contacts, it is necessary to have low friction, low vibration, and low wear between PA and steel contacts at different operating temperatures. This study proposes the use of an advanced polymer coating, namely, aromatic thermosetting copolyester (ATSP), on the steel surface and investigates the friction and wear properties between PA–ATSP coating and PA–steel at environmental temperatures of 25, 50, and 80 °C. The experiments were carried out using a pin-on-disc configuration under unlubricated sliding conditions. The results showed excellent performance of the coating on reducing the coefficient of friction (COF) by 80% and PA wear by 95% compared to bare steel. The ATSP coating worked as a predeposited transfer layer and showed nonmeasurable wear under moderate to high contact pressure conditions at all temperatures. The worn surfaces and the formation of transfer layers were further examined using scanning electron microscopy and energy-dispersive X-ray spectroscopy.

Due to new pollutant emissions standards, internal combustion engines need several emission control strategies (and related procedures) such as exhaust gas recirculation, diesel/gasoline particulate filters, and selective catalyst reduction that allow them to comply with complete requirements defined on those standards. These strategies result in faster degradation of engine oil, one of the most relevant consequences of which is an increase in soot contamination level. All of these strategies facilitate soot generation. Consequently, soot is one of the most important contaminants present in engine oil. The main technique to measure the content of soot in oil is thermogravimetric analysis (TGA), but this technique has certain limitations. TGA requires a long and specific procedure and has limitations in measuring small concentrations of soot in oil. Therefore, the design of an alternative technique to quantify soot in oil is relevant. One alternative is Fourier transform infrared (FTIR) spectroscopy, but it also has limitations related to low concentrations of soot in oil. This work presents an alternative technique based on ultraviolet-visible (UV-Vis) spectroscopy that allows quantification of small soot contents in used engine oil samples and avoids potential interference from other typical contaminants or those related to measurement processes, such as sample cuvette material.

Different Cu-based brake pads applied in high-speed railway trains were fabricated by the co-addition of Cr and CrFe particles, and the influence of the Cr/CrFe ratio on the tribological behavior of the powder metallurgy brake pads were studied by a reduced scale testing apparatus with the pad-on-disc configuration under various braking speeds. The results indicated that the Cu-based brake pad containing 6 wt% Cr and 4 wt% CrFe exhibited the highest and the most stable friction coefficient as well as the lowest wear loss when the braking speed was higher than 300 km/h. Moreover, a new reasonable explanation is provided for the effect of Cr and CrFe particles during the braking process. The excellent braking properties are attributed to the synergistic effect of Cr and CrFe on promoting the formation and stabilization of a tribofilm. Cr particles, which have high reactivity with Fe and O, act as a steady source of fine oxides in the tribofilm, and CrFe particles bear the load and strengthen the subsurface in the position near the friction surface. It is clear that the application of an appropriate ratio between Cr and CrFe can develop Cu-based brake pads suitable for more serious braking conditions.

Based on the structural features of a double-row tapered roller bearing (DTRB), a test rig for multipoint temperature measurement was built to investigate the temperature filed characteristics of DTRB under different operating conditions. Firstly, the composition of the test rig and the measuring instruments are described and the loading method is introduced. Secondly, a multipoint temperature measurement method for inner and outer rings of DTRBs is introduced, including the arrangement of the sensors and the signal transmission. Finally, the influence of rotational speed and external load on the circumferential, axial, and radial temperature rise and temperature distribution in a DTRB is studied. Results show that for the stationary bearing outer ring, the temperature rise in the load zone is significantly higher than that in the non-load zone. Under combined load, there are obvious temperature differences in the axial, circumferential, and radial directions of a DTRB.

In recent years, extensive use of smart lubricants has been made in order to control the tribological performance of fluid film bearings. The grooved surfaces of the journal bearing greatly influence the performance of bearings. In the present work, various geometric shapes of herringbone grooves (rectangular, triangular, and parabolic) with groove angles (30° and 60°) have been considered to numerically simulate the performance of slot-entry bearings. The work reported in this article deals with the numerical simulation of magnetorheological (MR) fluid–lubricated slot-entry herringbone-grooved hybrid journal bearings. Dave equation, a constitutive relation of the Bingham model, was employed to simulate the flow behavior of MR fluid. Using the finite element method (FEM), the governing Reynolds equation for a hybrid slot-entry bearing model was solved. The result shows that the use of a herringbone-grooved surface and application of MR fluid in a slot-entry bearing offers better stability and higher fluid film stiffness and minimizes frictional torque.

In an effort to improve the surface properties of electrical contact materials in terms of high friction coefficient and wear rate, diamond-like carbon (DLC) films containing different metal elements were prepared on stainless steel substrates using an unbalanced magnetron sputtering system. In the present study, the effect of current-carrying on DLC film, Cu-doped DLC film (Cu/DLC), and Ti-doped DLC film (Ti/DLC) is reported. The structure and mechanical properties of the films were characterized systematically by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Raman spectra; these methods were also used to analyze the initial surface of the films. Moreover, the tribological behaviors of the films sliding against AISI 52100 steel with and without an electric current (1 A) applied were investigated using a tribometer with ball-on-disc configuration in an atmospheric environment. The results demonstrated that the friction coefficients of DLC and Cu/DLC under current-carrying condition were decreased, whereas Ti/DLC showed opposite experimental results. The wear rate of the films with a current was higher than that without a current. Therefore, this study is meaningful to understand the tribological behaviors of microelectromechanical systems.

Based on experimental life data on silicon nitride balls, the stress-life exponent and life constant in the generalized ball life equation, developed earlier, are modified to better simulate the fatigue life of silicon nitride balls in hybrid ball bearings. The modified ball life equation is then integrated with generalized life equations for the outer and inner races to model the life of a complete hybrid ball bearing. It is found that in view of the relatively high stress-life exponent for silicon nitride balls, computation of hybrid bearing life with infinite ball life may not be unreasonable. Model predictions are in good agreement with limited available experimental life data on hybrid ball bearings.

In this study, a novel analytical model considering practical oil pressure and a cantilever plate bending calculation method is proposed to calculate the deformation of a vertical hydrostatic guideway. Based on the governing equations of rectangular thin plates, the finite integral transformation theory and the series-by-item differential transformation theory are used to solve the bending deformation of the target guideway to avoid the errors caused by an artificially selected deflection function and Kirchhoff’s hypothesis. The deformation values obtained from finite element simulation and experiments are compared with those calculated from the model. The comparison results show that the proposed model is capable of providing deformation values that are in better agreement with the experimental values than simulation values and its computation time is much less than that of the finite element method. The quantitative relationship between the actual oil film thickness and the performance of the hydrostatic guideways considering the size effect of the oil film thickness is studied.

The influence of diamond-like carbon (DLC) coating positions—coated flat, coated cylinder, and self-mated coated surface tribopairs—on the fretting behaviors of Ti-6Al-4V were investigated using a fretting wear test rig with a cylinder-on-flat contact. The results indicated that, for tests without coating (Ti-6Al-4V–Ti-6Al-4V contact), the friction (Qmax/P) was high (0.8–1.2), wear volumes were large (0.08–0.1 mm3) under a large displacement amplitude of ±40 µm and small (close to 0) under a small displacement amplitude of ±20 µm, and the wear debris was composed of Ti-6Al-4V flakes and oxidized particles. For tests with the DLC coating, under low load conditions, the DLC coating was not removed or was only partially removed, Qmax/P was low (≤0.2), and the wear volumes were small. Under high load conditions, the coating was entirely removed, Qmax/P was high (0.6–0.8), and the wear volumes were similar to those in tests without coating. The wear debris was composed of DLC particles, Ti-6Al-4V flakes, and oxidized particles. The DLC coating was damaged more severely when deposited on a flat surface than when deposited on a cylindrical surface. The DLC coating was damaged more severely when sliding against a DLC-coated countersurface than when sliding against the Ti-6Al-4V alloy.