Hydrophobic and self-cleaning photocatalytic ceramics and concrete with potential for the superhydrophobicity are promising novel materials for civil engineering applications including buildings, bridges, road pavements, and airport runways. Due to embedded liquid-repellent properties, such materials have low water and salt absorption and, therefore, enhanced durability. However, in applications requiring high traction (e.g., tire and pavement), there is a concern that reduced adhesion may compromise the friction. This paper reports on wetting, dry friction, and roughness properties of TiO 2 coated (hydrophilic) and polymethyl hydrogen siloxane (PMHS) coated (hydrophobic) self-cleaning ceramic tiles. The coefficient of friction values of the tile–rubber interface do not change significantly with the applications of the coatings up to 0.67 for hydrophilic TiO 2 based and up to 0.46 for hydrophobic TiO 2 + PMHS coatings versus 0.45 for uncoated reference. Friction has adhesion and roughness-related components and this response can be attributed to the roughness component of friction due to TiO 2 coating. The challenges related to hydrophobic coatings, including the durability and future research, are also discussed.

The purpose of this study is to investigate the evolution of cavitation bubbles for the high-speed water-lubricated spiral groove thrust bearing. A theoretical model of cavitation bubble evolution considering multiple effects (interface, breakage, and coalescence of bubbles) was established for the bearing. A high-speed experimental setup was developed to measure the distribution of bubbles. The theoretical model is verified by the experimental data. The results show that the Boltzmann-type bubble transport equation can be used to describe the bubble evolution of the bearing under the breakup and coalescence at high-speed conditions; the volume of the bubble group presents a skewed distribution in equilibrium; the number of small-sized bubbles is greater than that of large-sized bubbles at high rotational speed; the bubbles are mainly distributed at the inlets and outlets of spiral grooves; the bubble number density increases with the groove depth and spiral angle; more bubbles are generated near the outer diameter of the bearing. The study provides a theoretical and experimental basis for the bubble evolution of the water-lubricated spiral groove bearing under high speeds.

Electric submersible pumps (ESPs) provide artificial lift within oil wells. ESPs commonly fail from mechanical vibrations that increase as bearing clearances increase from debris, gas, and liquid pumped through the ESP. In order to understand journal bearing wear within an ESP, three stages of a mixed flow electric submersible pump were subjected to hydraulic fracture sand slurry in water. One hundred seventeen hours were conducted with sand and water, followed by 68 h with air added at 15% inlet gas volume fraction. The journal bearings were severely worn by the end of testing, and pump vibrations increased with increased bearing clearances. Bearing vibrations and clearances became significantly larger than the impeller labyrinth seal vibrations and clearances, indicating that the labyrinth seals became the dominant rotor support once the bearings were worn. Adding air increased the wear and rotor vibration orbit variability. Rotor vibration orbits were entirely independent of gas void fraction by the end of testing, indicating that the lubricant composition no longer directly impacted vibrations. Fine axial cracks from heat checking were observed on the journal of the bearings. Results indicate that controlling journal bearing wear is a critical factor for increasing operating lifetimes. Alternative bearing geometry and materials should be investigated to prevent the occurrence of three-body abrasion, limit the resultant wear rate from three-body abrasion, and limit the damage from heat checking.

In this paper, triethanolamine modified graphene oxide (TMGO) has been synthesized by filtering and drying the high-temperature reaction solution of graphene oxide (GO) and triethanolamine. The tribological performance of TMGO and GO in de-ionized water were investigated using a four-ball tribometer. The microscopic morphology of the worn surface was analyzed by optical microscope and scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results showed that the average friction coefficient (AFC) and wear scar diameter (WSD) of 0.1 wt % TMGO decreased by 21.9% and 6.2% compared with the two values of 0.1 wt % GO, and no corrosion occurred on metal surface. The minimum of the AFC and WSD occurred at 0.3 wt % TMGO. This study provides a new reference for the application of graphene oxide in lubrication.

The purpose of this study is to explore the effect of water on the contact and friction properties of a friction lining. The results show that the water absorption capacity and the sensitivity to the water molecules of the friction lining determine the load-carrying capacity. The change of the actual contact area is related to the load-carrying capacity under dripping water condition. The presence of water played a role in lubricating the surface, which resulted in a reduction of the friction coefficient. In addition, water absorbed onto the surface of the lining to produce an absorbent layer, and the load-carrying capacity of the absorbent layer exerted a more intuitive effect on the friction coefficient.

In this work, two polymer materials have been tested in a lubricated reciprocating pin-on-plate contact geometry using water-based hydraulic fluids to simulate sliding conditions of seal materials used in offshore equipment. The effect of load, speed, water content of the lubricant, and soaking of the ultra-high molecular weight polyethylene (UHMWPE) and a polyketone (PK) sliding against a super-duplex stainless steel (SDSS) was studied. The results showed that for UHMWPE, an increase in normal force leads to a decrease in coefficient of friction for all velocities. While under the same sliding conditions, no relevant influence of load on friction coefficient was found for PK. On the other hand, an increase in sliding speed decreased the coefficient of friction for both materials. The effect of the water content of the hydraulic fluid on the tribological performance was also studied. In UHMWPE-SDSS system, increasing water content in the hydraulic fluid resulted in steady growth of the transfer film. One reason for this might be the decreasing lubricant viscosity, which moves the system toward the boundary lubrication regime. In addition, it was found that the incubation of both UHMWPE and PK in water-based lubricants showed a beneficial effect on friction and wear, which was explained by the change in polymer visco-elastic behavior.

A thermohydrodynamic lubrication model of turbulent cavitating flow for high-speed spiral groove thrust bearing was developed considering the effects of cavitation, turbulence, inertia, breakage, and coalescence of bubbles. Comparing with the classical thermohydrodynamic model, this model can predict not only the distributions of pressure and temperature rise but also the distribution of bubble volume and bubble number density. Static characteristics of the water-lubricated spiral groove thrust bearing in the state of turbulent cavitating flow were analyzed, and the influences of multiple effects on the static characteristics of the bearing were researched. The numerical calculation result shows that the bubbles are mainly distributed in inlet and outlet of the spiral groove, the distribution of bubble volume is skewed under the equilibrium state, and small bubbles account for a large proportion of the cavitating flow under high-speed condition. Furthermore, the load carrying capacity and the leakage flow of the bearing decrease due to the effect of cavitation under high-speed. The maximum temperature rise of the bearing decreases due to the effect of cavitation effect.

This study sought to investigate the tribological properties of nitrile rubber (NBR)/ultrahigh molecular weight polyethylene (UHMWPE)/nano-molybdenum disulfide (nano-MoS 2 ) nanocomposites containing various quantities of nano-MoS 2 . The apparatus used for these tests was a marine stern tube bearing testing apparatus SSB-100V that was water-lubricated and was run at low speed under heavy duty conditions. The coefficient of friction coefficient (COF), wear rate, and surface abrasion of the composite were obtained to determine the effect of the addition nano-MoS 2 and to obtain the optimum nano-MoS 2 content. The mechanical and physical properties of the rubber-plastic material met the requirements of the Chinese Ship standard CB/T769-2008 and U.S. military standard MIL-DTL-17901C(SH). The experimental results showed that the nanocomposites that contained 9 phr nano-MoS 2 (parts by weight per hundred parts of rubber materials) exhibited good comprehensive friction and wear properties. It is believed that the experience achieved from this study can form a theoretical foundation for the improving the properties of the subject rubber-plastic material.

The present study includes the investigation on the frictional dynamics of hard and soft solid interface using low velocity linear tribometer. The effects of gelatin concentration, nanoparticles concentration, normal stress, and sliding velocity on the static and dynamic frictional shear stresses acting on the sliding gel block are studied using response surface methodology (RSM). The shear sliding experiments are conducted in steady sliding regime, well above the critical velocity. L 31 orthogonal array consisting of five levels for each factor is selected for the experimentation and second-order quadratic model has been generated for both the responses. The mathematic models are validated with the available trends mentioned in the literature.

With a subscale rolling-sliding apparatus, the objective of this study is to explore the adhesion and rolling contact fatigue characteristics of wheel/rail rollers with sanding under water condition. Sanding improves adhesion coefficient but aggravates the surface damage of wheel and rail materials. With the particle diameter and feed rate increasing, the adhesion coefficient is further improved. However, the surface damage (spalling and pits) becomes severer as well as the surface roughness. Note that pitting is a special damage type when sanding is used to improve the adhesion. Big pits and fatigue cracks appear on subsurface under larger particle diameter and feed rate conditions. Severe cracks initiate from big pits and develop into material to a depth, which results in bulk material breaking.

The cavitation erosion resistance of an X5CrNi18-10 stainless steel, solution treated at temperatures in the range of 1000–1100 °C for 5–50 mins, was investigated using a piezoceramic vibrating system. The variation of the technological parameters led to changes in the degree of the chemical homogeneity and the grain size of the austenite. Heating at 1050 °C for 25 mins, followed by water quenching, led to an increase in the cavitation erosion resistance of about 2.45 times compared to the samples heated for 50 mins. A significant improvement of the cavitation resistance was obtained for the sample maintained at 1050 °C compared to the samples annealed at 1000 and 1100 °C. It was found that the associated cavitation erosion resistance is improved for finer granulation and for higher degree of chemical homogeneity of the austenite.

The ability to design, control, and synthesize a material surface with superhydrophobicity is of great interests in many engineering applications. Here, we report a cost-effective process to fabricate poly(vinylidene fluoride) (PVDF)/zirconium(IV) oxide (ZrO 2 ) composites with superhydrophobicity. This is achieved by combining an antisolvent that induces phase separation, i.e., the precipitation of PVDF from the solution through a spray-on method on various liquids. The material surfaces possess wrinkled micron-sized beads which displayed superhydrophobicity in water without any chemical treatment. The process developed in this research presented a fast and simple approach in making hydrophobic surfaces.

The erosion–corrosion (E–C) wear behaviors of electroless nickel phosphorus (Ni-P) coating, carburizing and untreated low alloy steel AISI 5117 in water–sand slurry and saline–sand slurry were investigated using whirling-arm tester. The E–C wear mass loss was measured to evaluate the effect of mediums and surface modifications. The microstructure of carburizing and Ni-P coating was analyzed using an optical and scanning electron microscope (SEM) and X-ray diffraction (XRD) technique. Results showed that Ni-P coating and carburizing are effective in increasing wear resistance of low alloy steel. However, the Ni-P coating is more effective in increasing the E–C resistance. Also, the results showed that Ni-P coating, carburizing and untreated carbon steel behaved as ductile materials under erosion and E–C tests, and the maximum mass loss occurred at an impact angle of 45 deg. The synergism ratio was the lowest for the Ni-P coating, indicating that Ni-P coating improved an anti-E–C wear resistance.

Ti(C,N)-based cermets offer good high temperature strength, perfect chemical stability, excellent wear resistance, and relatively better machinability. In the present work, the tribological behaviors of Ti(C,N)/SiC sliding pairs lubricated in water and seawater were evaluated using a ball-on-disk tribometer. The experimental results show that a relatively low friction coefficient (about 0.025) can be obtained when lubricated with artificial seawater at the sliding speed of 200 mm/s, while the friction coefficient is about 0.2 in purified water. The wear surface profiles and the lubricants collected after running-in process for the high and low friction conditions were compared. In addition, the effects of salt molar concentration of the lubricant on the Ti(C,N)/SiC friction properties were investigated. It was found that the smooth and flat surface is the premise to gain the low friction. At the same time, the proper concentration of silica colloid, which is affected by the salt ions, is also an essential one. Moreover, the high sliding speed (200 mm/s) is beneficial to achieve low friction.

The formation of a ring area around the cavitation erosion pit on carbon steel is due to the cavitation erosion–corrosion. For the ultrasonic irradiation in water, both the ultrasonic cavitation and the acoustic streaming are generated. Due to the oscillation of the horn, the acoustic streaming flows from the tip of the horn to the bulk water. So far, the acoustic streaming has not been considered in previous studies on the ultrasonic cavitation erosion–corrosion. This study first reveals that the acoustic streaming noticeably affects the evolution of the nascent ring area. The mean velocity of acoustic streaming is inversely proportional to the gap (H) between the tip of the horn and the surface of the specimen. When H is 65 mm and 40 mm, the corresponding ring area is mainly composed of vertical sandwich sheets. In contrast, when H is 17 mm, the corresponding ring area is mainly composed of horizontal thin sheets. This study provides a complete picture to understand the ultrasonic cavitation erosion–corrosion on carbon steel.

In dipped (splash) lubrication, a rotating component, such as a gear, is partly submerged in a reservoir of liquid lubricant and acts to distribute it within the lubricated machine. Dipped lubrication is widely used for low to medium speed applications in the industrial and automotive sectors and there is a significant interest in the associated energy loss (the “churning” loss) because of its influence on efficiency and fuel consumption. In this study, a simple test rig consisting of a spur gear rotating in a cylindrical enclosure, partly filled with a liquid, was used to study the effect of fluid properties on the churning loss. The inertia rundown method was used to determine the power losses. Lubricating oils, water and aqueous glycerol solutions were among the fluids used. Correlations with Froude and Reynolds and Bond numbers are presented. It was found that the churning losses were significantly affected by the fluid disposition within the housing. In turn this was affected by the ratio of inertial forces to gravity (Froude number) and by air pressure. The influence of the pressure of the air within the enclosure was also investigated. When the air was evacuated from the enclosure, the churning losses increased, by a factor of up to 4.5 times. This can be explained by the effect of air (windage and aeration) on the liquid disposition, factors neglected in most previous work.

Even if water has more favorable thermal characteristics than oil, its use in the realm of bearings is still restricted to some rare applications. Moreover, the presence of water in lubricating circuits is seen as not at all desirable. The contamination of oil by water results in dangerous effects on lubrication. In relation to this, the study of thermal enhancement that this contamination can provide is seen to be insignificant. The literature demonstrates the damaging effects of this type of contamination. However, the existing studies are commonly based on an analysis of the results obtained after a bearing failure. The present study evaluates the instantaneous effect of the water-oil mixture on hydrodynamic lubrication for significant levels of water concentration, up to 10% by mass. The aim of the work is to identify the conditions for which the presence of water is detrimental in lubrication. Such conditions could then be avoided and a new generation of lubrication circuits could be designed to be immune against water contamination. Moreover, any positive effects of water contamination on lubrication deserve to be studied, the possibility being that new lubricant concepts might emerge. Thus, the rheological behavior and thermal characteristics of the mixture (density, specific heat, and thermal conductivity) were numerically modeled and simulations of bearings operating with this mixture were performed. The lubrication characteristics were also measured on a tilting pad thrust bearing, similar effects to those obtained numerically being observed. The presence of water has a slight effect on lubrication, which is nevertheless recognized to amount to an improvement in the lubrication characteristics. In fact, it is found that pure oil could be replaced by a water-in-oil emulsion having the same viscosity. In this case, the film thickness and the friction coefficient will be weakly modified, whereas the bearing will run at a lower temperature. From the point of view of safety, this indicates a significant advantage in operating conditions.

The oxidized multiwalled carbon nanotubes (MWCNTs) were modified with stearic acid (SA) molecules. The SA-modified MWCNTs were characterized with scanning electron microscopy, transmission electron microscopy, and Fourier transform-infrared spectroscopy. The tribological properties of the oxidized and SA-modified MWCNTs as additives in water were comparatively investigated with a four-ball tester. The results showed the SA-modified MWCNTs in water have better tribological properties including friction reduction and antiwear than oxidized MWCNTs. The possible mechanism of SA-modified MWCNT as an additive in water was discussed. This research provides the opportunity for the lubricant application of MWCNTs.

This paper deals with the analysis of eroded surfaces obtained from cavitation-erosion experiments on stainless steel in water and oil-in-water (o/w) emulsions using image processing. Two analysis techniques that are very promising in this respect are the wavelet decomposition transform and fractals. These can be used to extract parameters that characterize the cavitation intensity in a similar manner to that of the mean depth of erosion (MDP). The extracted parameters are the wavelet energy and entropy as well as the fractal dimension. Both of the image feature parameters and the MDP decrease with adding oil to water. Also, it was found that the variation of image feature parameters versus concentration of oil-in-water emulsions has a general trend that does not depend on magnification factor. The cavitation erosion behavior and mechanism for water and o/w emulsions were analyzed and it was found that the predominant failure mode was fatigue for water and o/w emulsions. The results show that a corrosive effect appears at 5 and 10 wt% o/w emulsions.

Taking the water pump bearing with one roller row (WR)-type auto water pump bearing as a research sample, an analytical calculation method is developed to improve the accuracy and efficiency of the current calculations for the bearing loads and life in engineering application. Considering the misalignment due to the deflection of the bearing spindle, the bearing internal loads and deformations under the action of the complicated external space loads are obtained. The bearing fatigue life including the lives of the rollers and the balls is also calculated with considering the non-normal load distribution caused by the spindle deflection and the roller tilt. The bearing load and life calculation results are compared with those calculated by the traditional method in which the deflection of the bearing spindle and the roller tilt are ignored. The effects of the bearing spindle deflection on the load distribution and the life of the auto water pump bearing are analyzed and discussed. The life decrease in the auto water pump bearing is significant due to the deflection of the bearing spindle and it is recommended to give more attention to this deflection for the high quality of the bearing design and calculation.