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With the development of green tribology in the shipping industry, the application of water lubrication gradually replaces oil lubrication in stern bearings and thrust bearings. In terms of large-scale and high-speed ships, water-lubricated bearings with high performance are more strictly required. However, due to the lubricating medium, water-lubricated bearings have many problems such as friction, wear, vibration, noise, etc. This review focuses on the performance of marine water-lubricated bearings and their failure prevention mechanism. Furthermore, the research of marine water-lubricated bearings is reviewed by discussing its lubrication principle, test technology, friction and wear mechanism, and friction noise generation mechanism. The performance enhancement methods have been overviewed from structure optimization and material modification. Finally, the potential problems and the perspective of water-lubricated bearings are given in detail. [ABSTRACT FROM AUTHOR]

The performance of cylinder liner piston ring (CLPR) that worked under harsh conditions significantly affected the reliability of diesel engines. Nano‐copper lubricant additives have recently been introduced due to their good anti‐wear properties. This study aims to gain insights into the interactions between concentrations of nano‐copper lubricant additives and the tribological performance of CLPR. Tests are performed on a reciprocating sliding test rig under different operating conditions, and the tribological performances are characterized by the friction coefficient, wear mass losses, and morphologies of worn surface. The experimental results indicated that the optimal concentration of nano‐copper additives is 2 wt%. Additionally, deposition of the Cu nanoparticles on the worn surface during the friction process facilitates the formation of the mending layer. These findings would aid to provide a technical reference for the application of nano‐copper additives in diesel engines. [ABSTRACT FROM AUTHOR]

As one of the important friction pairs of a diesel engine, the cylinder-liner piston ring (CL-PR) faces a harsh high-temperature working environment. To explore the mapping relationship between the friction performance of the CL-PR and the change in temperature, the reciprocating-friction and wear-testing machine was used to analyze the friction performance and lubrication performance of four kinds of lubricating oil at different temperatures (room temperature, 60 °C, 90 °C, and 120 °C) from the friction coefficient, contact resistance and surface topography. The results show that the tribological properties of the four lubricating oils show different trends with the increase in temperature. The friction coefficient of the base oil first decreases and then increases with the increase in temperature; this shows that the friction property of the base oil is improved by a certain temperature rise, and the increase in temperature promotes the formation of an oxide film and reduces the friction coefficient. While the friction coefficient of other three lubricating oils with specific application scenarios increases first and then remains stable, the wear of the friction pair is the most severe at 120 °C. The wear forms are abrasive wear and adhesive wear. [ABSTRACT FROM AUTHOR]

The running-in of cylinder liner-piston rings (CLPRs) is the most important process that must be performed before a marine diesel engine can be operated. The quality of running-in directly affects the reliability of a CLPR. The surface texture of a CLPR has been proven to significantly affect its lubrication performance. In this study, the tribological behavior of a CLPR during running-in is investigated. Three types of surface textures are generated on the CLPR via laser processing: dimple texture on piston rings, groove texture on cylinder liners, and co-texture on both sides. Subsequently, a series of tests are performed on a slice tester. A load of 300 N (1.64 MPa) is applied, and two speeds (50 and 100 rpm) are adopted. The CLPR running-in quality is characterized based on three parameters, i.e., the friction coefficient, contact resistance, and wear topography. Experimental results show that, compared with a non-textured surface, the three types of surface textures mentioned above improved the friction performance during running-in. The lubricant supply capacity of the dimple texture on the piston ring, as a mobile oil reservoir, is stronger than that of the groove texture on the cylinder liner serving as a static oil reservoir. By contrast, the wear resistance of the dimple texture, as a movable debris trap on the piston ring, is weaker than that of the groove texture on the cylinder liner, which serves as a static debris trap. It is demonstrated that the co-texture combines the advantages of dimples and groove textures. Compared with non-textured surfaces, the friction coefficient decreased the most at 100 rpm (44.5%), and the contact resistance improved the most at 50 rpm (352.9%). The coupling effect provides the surface with improved running-in quality by optimizing the tribological performance, particularly at the dead center. This study provides guidance for the tribological design and manufacturing of CLPR in marine diesel engines. [ABSTRACT FROM AUTHOR]

The existence of micro‐structures endows the materials with some novel characteristics. In this study, the hot‐spot material thermoplastic polyurethane (TPU) is used as the experimental object, and the water‐lubricating composites are prepared by introducing well‐hydrophilic polyvinyl alcohol (PVA) fibers, which can spontaneously and continuously produce micro‐convex textures in water. By observing and analyzing the internal structures, physical and chemical properties, coefficient of friction, wear surface, wear loss, etc. of the materials, the relationship between the micro‐convex structures on the material surface and its tribological properties is studied. The experimental results show that the existence of micro‐convex structures can make the material show better wear resistance during the friction process, and they will not disappear completely with the process. The most obvious effect is the sample containing 15% PVA fibers and with soaking and polishing treatments, its coefficient of friction is 0.11, which is 74.42% lower than that of the pure sample without any treatments, the main reason is due to the hydrodynamic lubrication effect and cavitation effect of the micro‐convex structures. For the wear mechanism, pure samples are adhesive wear, and modified samples are mainly abrasive wear. This work will provide new design ideas for tribology in the micro‐nano field. [ABSTRACT FROM AUTHOR]

Aboard ship, the use of lubricating oil in mechanical equipment is sometimes difficult to achieve and applied oil can easily leak. The use of self‐lubricating materials can largely solve this problem. In this study, three kinds of solid lubricant‐enhanced 304 stainless steel‐backed ultrahigh molecular weight polyethylene (UHMWPE) fabric composites were fabricated with the addition of graphite, molybdenum (IV) disulfide, or polytetrafluoroethylene (PTFE). They were tested under various rotating speeds and compared with pure steel‐backed UHMWPE fabric composites. The tribological performance of these composites was evaluated by analysis of friction coefficient, wear rate, and worn face morphology. The results showed that PTFE‐enhanced composites exhibited the best friction reduction performance under all test conditions, better antiwear ability at rotating speeds under 200 rpm, and optimized wear surface morphology, thus indicating better synergy between PTFE and UHMWPE fabric. [ABSTRACT FROM AUTHOR]

Lignum vitae is well-known as the construction material of water-lubricated bearings due to its excellent tribological performance. Except for the included component, the effect of vessel structure on tribological performance is lack of analysis. In this study, a novel bionic polymer was manufactured based on the arrangement, size and density of Lignum vitae's vessel. The results of experimental tests showed that the friction coefficient was down 43% and the wear volume is down nearly 38.3% at harsh condition. The tribological performance of Lignum vitae was concluded positively correlates to the size and density of the vessel. The findings reveal a more direct relation between internal structure and tribological properties of Lignum vitae and mechanisms for excellence in water-lubricated conditions. • The internal structure characterization of Lignum vitae's vessel was observed and mathematically analyzed. • A series of novel biomimetic polymers were designed and manufactured based on the recorded parameter of Lignum vitae. • The experimental results on biomimetic polymer analyzed the precise relationship between Lignum vitae's internal structure and its tribological properties, the mechanism analysis provided a novel design to improve the polymer material under harsh working condition. [ABSTRACT FROM AUTHOR]

ABSTRACT: Polyurethane (PU) has been studied as alternative bearing material for marine water‐lubricated stern tube due to its excellent wear resistance, remarkable mechanical properties and so on. In this study, nine types of PU samples which are composed of different additives were prepared and tested in order to investigate their tribological properties under various working conditions. A pin‐on‐disc tribo‐tester was used to conduct tests. Then comparison analyses were conducted from three aspects, including the friction coefficient, wear mass loss, and the wear surface topography. The analysis results showed that: (1) the different additives as well as the mass fraction of these additives lead to significant difference in terms of tribological properties of PU; (2) the lubricating grease, as one of additives, improved the wear resistance and friction performance effectively; (3) modified PU is eligible to work as matrix because of satisfied mechanical properties and specific internal morphology. It is believed that understandings in this study are beneficial to the improvement of the tribological properties of PU and also provide the real practical basis for the studies of polymer materials which applied on water‐lubricated marine stern tube bearing. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46305. [ABSTRACT FROM AUTHOR]

As one important supporting component in ship propulsion systems, the water-lubricated stern tube bearing has great effects on shipping navigation safety. However, it is difficult to ensure the good lubrication for water-lubricated stern tube bearings under low speed working conditions. The lignum vitae have the significant self-lubricated performance on stern tube bearings. In this study, the present situation of the biomimetic application was introduced. The components of lignum vitae were analyzed to investigate the corresponding mechanism of self-lubricated. The biomimetic materials (0%, 0.5%, 1%, 3% guaiacum and high-density polyethylene (HDPE)) are designed and prepared based on the properties of lignum vitae. A series of experimental tests were then conducted in a specially designed tester to investigate the tribological characteristics of the biomimetic materials. The comparison analyses of the friction coefficients, wear mass losses and the worn surfaces were conducted under different concentration of biomimetic materials and running conditions. The analysis results show that there were significant differences in the tribological properties of the rubbing pairs in different concentration of guaiacum. The wear performance of the biomimetic material with 0.5% concentration of guaiacum was superior to that of other concentrations. In addition, the biomimetic material with 0.5% concentration of guaiacum was the most effective to improve the wear properties at the low sliding velocity of 0.11 m/s. It is believed that the knowledge gained in this study will provide a novel approach for wear reduction and lubrication performance improvement of water-lubricated stern tube bearing in ships. [ABSTRACT FROM AUTHOR]

• Corrosion, thermal damage, and wear issues in gaseous-fueled engines were summarized. • Compatibility of engine materials with hydrogen, ammonia, and natural gas was evaluated. • Tribology was introduced for improving the durability of crucial engine components. • Hydrogen appears to be a promising but challenging fuel for engines. Stringent requirements in emissions and the depletion of conventional fossil fuels drive the development of Gaseous Alternative Fuels (GAF). As a commonly used power source, compatibility issues of the internal combustion engines under the harsh conditions created by the fuels become a technical barrier to improving the safety, reliability, and power performance of real-world engines' applications. This paper systematically reviewed the material performance affected by GAF from the perspective of crucial engine components. Issues related to the compatibility of crucial components with GAF were firstly summarized in corrosion, thermal damage, and wear. Experimental study progresses concerning these compatibility issues and the assessment criteria for the material performances were discussed. Feasible critical technologies for improving material performances were discussed from tribology. Finally, this review briefly discussed the characteristics and plausible future trends for these compatibility issues. This study provides technical assistance for the safe application of GAF on internal combustion engines. [ABSTRACT FROM AUTHOR]

A marine diesel engine, where the cylinder liner-piston ring (CLPR) pair is one of the most important rubbing pairs, is the heart of a marine system. Studying the lubrication characteristics of the CLPR will provide a guide for rational design of the CLPR to reduce wear and prolong its service life. The surface texture features have a significant impact on the lubricating performance of the CLPR. In this study, the tribological system of the CLPR was investigated. Different surface textures (such as different sizes of surface concaves and grooves, etc.) were designed and produced on the cylinder liners using surface treatment. A series of experimental tests were then carried out in a specially designed diesel engine tester to investigate the tribological characteristics of the treated CLPR pairs. The comparison analyses of the worn surface texture features, element content of the lubrication oil, and abrasive particle characteristics were conducted under different wear surface texture features and cylinder liner speeds. The analysis results showed that there were significant differences in the tribological and lubrication properties of the rubbing pairs in different wear surface texture features. The wear performance of the CLPR pair with a regular concave texture was superior to that of the concave and groove, and regular groove textures. In addition, the regular concave with a depth-diameter ratio of 0.1 was the most effective surface texture to improve the lubrication and wear properties of the CLPR pairs. It is believed that the knowledge obtained in this study provides the real practical basis for tribological design and manufacturing of CLPR pair in marine diesel engines. [ABSTRACT FROM AUTHOR]

Severe abrasive wear of water-lubricated bearings usually occurs during low-speed and heavy-duty working conditions. To improve the mechanical properties of composites and reduce friction, functionalized carbon nanotubes (CNTs) were added to promote tribological property and reduce the wear rate during rotation against a copper bushing. Ultra High molecular weight polyethylene (UHMWPE) was used as a matrix material, and carboxylic groups (–COOH), amide groups (–CONH 2), and phenyl groups (–C 6 H 5) were used to functionalize single-walled nanotubes (SWNTs). The functionalized CNTs were blended with UHMWPE to form composites. Molecular mechanics simulations (MM) and molecular dynamics (MD) simulations are used to investigate interfacial bonding between the functionalized CNTs and matrix materials. Interfacial bonding of functionalized CNTs and tribological property of the composites were investigated using pull-out and confined shear simulations, respectively. The simulation results show that the appropriate functionalization of CNTs could strengthen interfacial bonding between the functionalized CNTs and matrix material. Therefore, the simulative mechanical property of composites has been enhanced and simulated wear rate has been reduced. This study provides a simulative basis for the forward verification test and structural design. • The mechanical and tribological properties of CNTs/UHMWPE composites were investigated by molecular dynamic simulation. • Functionalized groups raise the interfacial bonding between CNTs and polymeric matrix, and reduced simulative adhesive rate. • The CNTs composites with phenyl groups showed best interfacial bonding energy and anti-wear properties. [ABSTRACT FROM AUTHOR]

Water-lubricated bearings usually suffer severe abrasion under low-speed working conditions. Use of microencapsulated lubricants to modify the materials seems to be useful for reducing friction and wear in a bearing. In this reported study, palmityl palmitate microcapsules coated with a shell of urea-formaldehyde resin were prepared by in-situ polymerization and were then added to ultra-high molecular weight polyethylene (UHMWPE). Friction tests were performed using the microcapsule/UHMWPE composites by abrading them against tin-bronze discs under normal or heavy loads at low speeds. The experimental results showed that the addition of the microcapsules to the UHMWPE decreased its friction coefficient, reduced wear loss and optimized the wear surface morphology of the composites, consequently improving their tribological properties. • The palmityl palmitate microcapsules were synthesized by in-situ polymerization. • Composites with different concentrations of microcapsules were designed. • Series of tests were carried out to study the tribological properties of the composites. • The composite containing 15% microcapsules showed superior tribological performance. [ABSTRACT FROM AUTHOR]

The cylinder liner-piston ring (CLPR) is one of the most critical frictional pair for energy conversion in diesel engines. In this study, two forms of surface texture were respectively prepared on the liner surface by laser processing, with the modified copper nanoparticles (CNP) applied as the lubricant additives. The reciprocating tribometer and accompanying tribological testing technologies were then used to explore the synergetic effects of surface textures and additives on the tribological properties of CLPR. The results show that the composite lubrication system exhibits good friction-reduction and wear-resistance as the appropriate texture was adopted. Additionally, the synergetic effects among the storage capability of textures and the self-repairing ability of CNP additives can explain the improvement mechanism of CLPR's tribological properties. • CNP additives combined with variety forms of surface texture were used to improve tribological performance of CLPR. • The synergetic effects of suitable texture forms and CNP additives will enhance the and wear resistance of CLPR. • The storage and release mechanisms of different texture forms determine the performance of CNP additives at various loads. [ABSTRACT FROM AUTHOR]

The oriented growth causes obvious anisotropy of lignum vitae wood, and results in different mechanical properties under different cell fiber directions, which lead to different wear behaviors. Investigating the influences of lignum vitae's anisotropy on its tribology properties is useful for exhibiting the best tribological performances of the wood or bionic wood composites to extend their service life. In this study, the wear processes obviously presented two stages due to the anisotropy of lignum vitae cell fiber. The cell fibers were first subjected to the separation process, then the impact and bending processes when the friction forces were perpendicular to the cell fiber direction. Owing to the low mechanical property of lignum vitae under the vertical fiber direction, the fibers and vessel cells were easy to be destroyed and broken, and resulted in severe wear process, larger coefficients of friction (COF) and wear rates. The cell fibers experienced tensile stress caused along the cell fiber direction and were difficult to be broken because of good tensile strength, and the surface damages on the lignum vitae wear surface were at a low level. In particular, the COF was stable around 0.05, and presented excellent self-lubricating properties and wear resistance. This study will provide a powerful guide for the tribological design or application of wood materials and bionic wood frictional composites. [ABSTRACT FROM AUTHOR]