Artificial intelligence and, in particular, machine learning methods have gained notable attention in the tribological community due to their ability to predict tribologically relevant parameters such as, for instance, the coefficient of friction or the oil film thickness. This perspective aims at highlighting some of the recent advances achieved by implementing artificial intelligence, specifically artificial neutral networks, towards tribological research. The presentation and discussion of successful case studies using these approaches in a tribological context clearly demonstrates their ability to accurately and efficiently predict these tribological characteristics. Regarding future research directions and trends, we emphasis on the extended use of artificial intelligence and machine learning concepts in the field of tribology including the characterization of the resulting surface topography and the design of lubricated systems.

Many industrial processes are dependent on the proper application of modern tribological knowledge for the purposes of maintaining equipment integrity and minimizing total energy losses. Consequently, the development of modern lubricants is vital for satisfying growing performance standards and increasingly stringent environmental regulations. Industrial lubricants are regulated based on demanding technical requirements and characteristics, such as high viscosity index, hydraulic stability, corrosion prevention, thermal stability, wide operating temperature ranges, demulsibility, and oxidative stability. Escalating environmental and sustainability concerns have shifted significance towards non-technical criteria for the evaluation of lubricants. Biodegradability and renewability are two influential factors in the discussion regarding the long-term sustainability of future tribological applications. Emphasis is placed on the development of environmentally friendly, non-toxic, and biodegradable lubricants that would minimize industrial pollution associated with oil-related spills and leakages. Bio-based lubricants, manufactured from renewable, organic resources, present themselves as viable alternatives to traditional petroleum-based lubricants. A major section of this review paper will provide a comparative analysis of renewable resource-based lubricants and mineral oil-based lubricants in terms of their chemical properties and respective advantages. Further discussion concerning biolubricants and use of non-edible plant feedstocks will highlight the clear economic and environmental incentives of implementing modern tribological knowledge. This review paper will conclude with the examination of the obstacles that modern day biolubricants must overcome and the future expectations of green tribology.

Electric vehicle sales are growing globally in response to the move towards a greener environment and a reduction in greenhouse gas emissions. As in any machine, grease lubricants will play a significant role in the component life of these new power plants and drivetrains. In this paper, the role of grease lubrication in electric vehicles (EVs) and hybrid vehicles (HVs) will be discussed in terms of performance requirements. Comparisons of grease lubrication in EVs and HVs for performance requirements to current internal combustion engines (ICEs) will be reviewed to contrast the major differences under different operating conditions. The operating conditions for grease lubrication in these EVs and HVs are demanding. Greases formulated and manufactured to meet specific performance specifications in EVs and HVs, which will operate within these specific electrification components, will be reviewed. Specifically, the thermal and electrified effects from the higher operating temperatures and electromagnetic fields on lubricant degradation, rheology, elastomer compatibility, and corrosion protection of the grease need to be evaluated to accurately meet the performance requirements for EVs and HV. The major differences between EVs and conventional ICEVs can be grouped into the following technical areas: energy efficiency, noise, vibration, and harshness (NVH), the presence of electrical current and electromagnetic fields from electric modules, sensors and circuits, and bearing lubrication. Additional considerations include thermal heat transfer, seals, corrosion protection, and materials’ compatibility. The authors will review the future development trends of EVs/HVs on driveline lubrication and thermal management requirements. The future development of electric vehicles will globally influence the selection and development of gear oils, coolants, and greases as they will be in contact with electric modules, sensors, and circuits and will be affected by electrical current and electromagnetic fields. The increasing presence of electrical parts in EVs/HVs will demand the corrosion protection of bearings and other remaining mechanical components. Thus, it is imperative that specialized greases should be explored for specific applications in EVs/HVs to ensure maximum protection from friction, wear, and corrosion to guarantee the longevity of the operating automobile. Low-viscosity lubricants and greases will be used in EVs to achieve improvements in energy efficiency. However, low-viscosity fluids reduce the film thickness in the driveline application. This reduced film thickness increases the operating temperature and reduces the calculated fatigue life of the bearings. Bearing components for EVs/HVs will be even more crucial as original equipment manufacturers (OEMs) specify these low-viscosity fluids. The application of premium bearing components using low-viscosity grease will leverage materials, bearing geometries, and surface topography to combat the impact of low-viscosity lubricants. In addition, EVs and HVs will create their own NVH challenges. Wind and road noise are more prominent, with no masking noise from the ICE. Increasing comfort, quality, and reliability issues will be more complicated with the introduction of new electrified powertrain and E-driveline subsystems. This paper elaborates on the current development trends and industrial test standard for the specified grease used for electrical/hybrid driveline lubrication.

This review summarizes the recent advancements in the mechanical properties of nanocomposites reinforced with surface-modified carbon nanotubes (CNTs). A range of matrices, namely, polymers, metals, and cement, is investigated, which have demonstrated increasing importance in a broad range of industrial sectors, such as 3D printing, automotive, construction, and coatings. The strengthening mechanisms that CNTs impart in composites are reviewed, and synergistic effects with their surface groups or co-additives are analyzed, including wettability, mechanical interlocking, and chemical bonding. Different mechanical and functional properties of the CNT-reinforced nanocomposites are analyzed, such as tensile strength, flexural strength, impact resistance, thermal conductivity, and electrical conductivity. The improvements in these properties for a variety of CNT-based composites are presented, and details on how these improvements were attained are discussed. The review concludes that surface modification of CNTs has proven to be of high importance, enhancing compatibility with various matrices and facilitating improvements in the nanocomposite properties. Suggestions for viable CNT-based composites for use in the studied applications are also provided.

Additive manufacturing (AM) has recently become an increasingly popular form of production due to its advantages over traditional manufacturing methods, such as accessibility, the potential to produce parts with complex geometry, and reduced waste. For the widespread industry adoption of AM components, metal AM has the most potential. The most popular methods of metal AM are powder-based manufacturing techniques. Due to the layer-by-layer nature of AM, the mechanical and tribological properties of an additive manufactured part differs from those of traditionally manufactured components. For the technology to develop and grow further, the tribological properties of AM components must be fully explored and characterized. The choice of material, surface textures, and post-processing methods are shown to have significant impact on friction and wear. Therefore, this paper focuses on reviewing the existing literature with an emphasis on the development of advanced materials for AM applications as well as the optimization of the resulting surface quality via post-processing and presents areas of interest for further examination in this prospective technology.