Rolling-contact fatigue (RCF) is a common failure mode in components subjected to rolling or rolling-sliding contact. This article provides a basic understanding of RCF and a broad overview of materials and manufacturing techniques commonly used in industry to improve component life. A brief discussion on coatings to improve surface-initiated fatigue and wear is included, due to the similarity to RCF and the increasing criticality of this failure mode. The article presents a working knowledge of Hertzian contact theory, describes the life prediction of rolling-element bearings, and provides information on physics and testing of rolling-contact fatigue. Processes commonly used to produce bearings for demanding applications are also covered.

This article presents a brief discussion on the main applications for low- and high-viscosity polyalphaolefins (PAOs) and highlights key areas of interest and shows why PAOs are used in these applications. It discusses the physical properties of passenger car motor oils (PCMOs) based on or containing PAOs. The properties include Noack volatility and pour point. The article also discusses the properties and applications of heavy-duty engine oil (HDEO), industrial lubricants, food-grade lubricants, greases, transportation gear oils, compressor oils, hydraulic fluids, and transmission fluids.

This article provides a summary of the concepts discussed in the articles under the Section “Introduction and Basic Theory of Wear” in ASM Handbook, Volume 18, Friction, Lubrication, and Wear Technology .

This article discusses the physical signs of rolling-contact wear (RCW). It lists the major considerations in gear design and describes the mechanisms of RCW. The article provides a guide to rolling-contact fatigue (RCF) testing methods. It explains the steps involved in the processes of RCF and RCW.

This article describes two variations of carbon-base coatings: diamondlike carbon (DLC) coatings and polycrystalline diamond (PCD) coatings. It discusses the basics of a few deposition methods as they apply to industrially relevant coatings. The methods include deposition of tungsten-containing hydrogenated amorphous carbon films, deposition of tetrahedral amorphous carbon films, and deposition of silicon-incorporated hydrogenated amorphous carbon films. The most common deposition technologies for diamond films are also discussed. The article provides information on surface preparation for DLC and diamond deposition. It also provides a discussion on the coating composition and structure, mechanical and tribological properties, and applications of DLC and diamond coatings. The quality control techniques for DLC and diamond coatings are specified to meet customer requirements and ensure repeatable quality.

This article describes friction force as a function of normal force in dry forming. It focuses on metal forming operations usually classified as cold working and hot working based on metallurgical considerations. The article discusses surface flattening and roughening of workpiece asperities in metal forming. It presents advanced tribology models and results for friction in isothermal forging operations in which the tooling is maintained at a temperature close to that of the workpiece. The article provides information on heat transfer models. It discusses the effect of wear in manufacturing processes. The article concludes with information on the main categories of tool and die materials used for a variety of manufacturing application.

Vibroacoustic analysis of mechanical systems has an important role in the engineering discipline. This can be used as a monitoring tool to obtain insights about the condition of a system, identify its probable defects, and determine the time window that the maintenance should happen. This article introduces the basics of signal processing in time, frequency, and time-frequency domains. It focuses on statistical analysis of the time-domain data. Various measures of data distribution and variability are pointed out. Important signal-processing functions in the frequency domain are presented and explained with examples. The article discusses and clarifies the benefits of time-frequency domain based on short-time Fourier transform with some practical applications. The article presents the most frequently used statistical functions. It concludes with information on some real-world applications of vibroacoustic analysis.

Stainless steels are characterized as having relatively poor wear resistance and tribological properties, but they are often required for a particular application because of their corrosion resistance. This article describes the classification of stainless steels and wear. Stainless steels have been classified by microstructure and are categorized as austenitic, martensitic, ferritic, or duplex. The main categories of wear are related to abrasion, erosion, adhesive wear, and surface fatigue. The article presents a list that proposes the alloy family that could be the optimal selection for a particular wear mode. The corrosion modes include dry sliding, tribocorrosion, erosion, erosion-corrosion, cavitation, dry erosion, erosion-oxidation, galling and fretting.

Impact wear can be defined as the wear of a solid surface that is due to percussion, which is a repetitive exposure to dynamic contact by another solid body. This article discusses the volume (or mass) removal of material either at or under engineering contact stress levels and outlines a rational, semi-empirical impact wear theory. It illustrates a linear wear mechanism that occurs in print heads and repetitive impacts that take place in metallic machine contacts. The article concludes with information on plotting a wear curve for an originally plane, massive carbon steel machine platen subjected to repetitive compound impact by a hard, nonwearing spherical-ended steel alloy component.

Seals are mechanical components that prevent the leakage, diffusion, transfer, or mixing of different liquid, gas, solid, and multiphasic substances. This article begins by discussing the classifications of seals: static and dynamic. Static seals involve both self-energizing elastomeric materials such as O-rings, which merely react to a sealed fluid pressure, and passive materials that require clamping forces to achieve sealing, such as gaskets. The types of dynamic seals include rotary seals and reciprocating seals. The article describes the factors affecting seal wear and failure. It provides a list of some common seal wear modes and failures, namely abrasion, cavitation damage, chemical attack, compression set, corrosion, damage during abrupt decompression, dieseling damage, extrusion damage, installation damage, spiral or rolling damage, and vaporization damage. The article concludes with specific recommendations for reducting of seal friction and wear.

This article is concerned with gear tooth failures influenced by friction, lubrication, and wear, and especially those failure modes that occur in wind-turbine components. It provides a detailed discussion on wear (including adhesion, abrasion, polishing, fretting, and electrical discharge), scuffing, and Hertzian fatigue (including macropitting and micropitting). Details for obtaining high lubricant specific film thickness are presented. The article describes the selection criteria for lubricants, such as oil, grease, adhesive open gear lubricant, and solid lubricants. It discusses the applications of oil and gear lubricants and the types of standardized gear tests. The article presents some recommendations for selecting lubricants and lubricant viscosity for enclosed gear. It provides some examples of failure modes that commonly occur on gears and bearings in wind turbine gearboxes.

This article describes the numerous techniques used to measure friction. It provides a brief description of the historical development of friction testing. The article discusses the tests and equipment available for friction testing. It explains the procedural considerations that should be addressed to ensure that valid data are derived from a friction test. The article presents definitions of terms commonly used in tribology such as static friction, kinetic coefficient of friction, stick-slip behavior, and lubricated friction. It provides information on the precautions that must be taken to ensure valid test results. The article also describes how to report data and how to analyze these data.

Strategies for the lubrication of mechanical systems operating in extreme environments must exclude the liquid lubricants and greases and rely on alternative methods of lubrication, such as gases and solids. This article provides a survey of some of the more effective alternative methods of lubrication. It provides a discussion on the solid materials that have been most commonly used as lubricants: carbon-base materials, transition metal dichalcogenides, polymers, and soft metals.

This article provides a brief introduction to abrasive wear-resistant coating materials that contain a large amount of hard phases, such as borides, carbides, or carboborides. It describes some of the commonly used methods of producing thick wear-resistant coatings. The article also provides information on metal-matrix composites and cemented carbides. The three base-alloying concepts, including cobalt-, iron-, and nickel-base alloys used for wear-protection applications, are also described. The article compares the tribomechanical properties of the materials in a qualitative manner, thus allowing a rough materials selection for practitioners. It presents a brief discussion on hot isostatic pressing (HIP) cladding, sinter cladding, and manufacturing of thick wear-resistant coatings by extrusion or ring rolling. The article also discusses the processing sequence of thick wear-resistant coatings, namely, compound casting, deposition welding, and thermal spraying.

This article introduces the structure, tribological properties, advantages, and applications of ionic liquids (ILs) as lubricating media. It discusses the mechanisms of IL lubrication for different contacts. The advances in studies focusing on tribological properties of a wide range of ILs are reviewed. The article concludes with the challenges that limit the applications of ILs in tribology engineering.

This article describes the characteristics of three types of gas bearings, such as aerostatic bearing, precision aerodynamic bearing (PAB), and compliant aerodynamic bearing (CAB). It discusses the applications for aerostatic bearings and advantages in lubricating a bearing with a compressible gas. The article also describes the different types of aerostatic bearings, such as annular thrust bearings and orifice-compensated journal bearings. It presents a discussion on load capacity and stiffness, friction and power loss, and stability and damping of the aerostatic bearings. The article provides a discussion on the types of PAB and CAB. The types include spiral groove annular thrust bearings, cylindrical journal bearings, three-sector journal bearings, tilting-pad journal bearings, and helical-grooved journal bearings. The types of CAB include foil bearings and pressurized-membrane bearings. The article concludes with a description of factors that influence materials selection for gas-lubricated bearings.

Machining tribology poses a significant challenge due to the multiple parameters that must be simultaneously considered to arrive at a cost-minimized solution in production. This article provides information required to make informed decisions about machining parameters. It describes the relationships between machining parameters, workpiece material properties, cutting forces, and the corresponding temperature field in the chip. The article provides information on tool life, with an empirical model, common wear features, and the relationship between tool life and machining cost. The cutting fluids and their effect on tool life are also discussed. The article discusses machining process dynamics and corresponding vibrations. It contains a table that provides a summary of high-pressure coolant research.

This article describes the main advantages of using grease as a lubricant rather than oil. It discusses the formulation, lubricating mechanism, degradation, and characterization of grease. The article describes the parameters that determine lifetime of grease, including low-temperature limit, low-temperature performance limit, high-temperature performance limit, and high-temperature limit. The article concludes with information on the practical use of grease as a lubricant reservoir.

This article first describes surface forces, and the methods of measuring them, followed by a discussion on adhesion. It discusses the instrumental requirements and techniques, including Atomic Force Microscopy (AFM), used for the measurement of surface forces. Measurements of surface roughness, with AFM, can provide a precise picture of surface roughness and can be used as input for contact mechanics computer models. The article also describes microscale adhesion and adhesion measurement methods using microelectromechanical systems technologies. It reviews certain considerations used for the measurement of adhesion, such as fundamental adhesion measurements, history dependence and sample preparation, and practical adhesion measurements. The article describes various arrangements that can be employed in adhesion tests.