Wear of metals occurs by plastic displacement of surface and near-surface material, and by detachment of particles that form wear debris. This article presents a table that contains the classification of wear. It describes the testing and evaluation of wear and talks about the abrasive wear, lubrication and lubricated wear, and selection of steels for wear resistance. The article discusses the effect of alloying elements, composition, and mechanical properties of carbon and low-alloy steels at elevated temperatures. It talks about the fatigue resistance characteristics of steels, and describes the forms of embrittlement associated with carbon and low-alloy steels. The article provides information on the effect of composition, manufacturing practices, and microstructure on notch toughness of steels. Finally, it explains the effects of alloy elements, inclusion content, microstructure and heat treatment on fracture toughness of steels.

Friction and wear are important when considering the operation and efficiency of components and mechanical systems. Among the different types and mechanisms of wear, adhesive wear is very serious. Adhesion results in a high coefficient of friction as well as in serious damage to the contacting surfaces. In extreme cases, it may lead to complete prevention of sliding; as such, adhesive wear represents one of the fundamental causes of failure for most metal sliding contacts, accounting for approximately 70% of typical component failures. This article discusses the mechanism and failure modes of adhesive wear including scoring, scuffing, seizure, and galling, and describes the processes involved in classic laboratory-type and standardized tests for the evaluation of adhesive wear. It includes information on standardized galling tests, twist compression, slider-on-flat-surface, load-scanning, and scratch tests. After a discussion on gear scuffing, information on the material-dependent adhesive wear and factors preventing adhesive wear is provided.

This article examines the deformation processes in metal-forming operations and considers the effects introduced by scale factors when microforming. It discusses the process parameters and variables affecting surface interactions, including temperature, speed, reduction, stiffness, and dynamic response of equipment. The article reviews the determination of friction coefficient using laboratory monitoring methods, indirect measurements, and the inverse method. It considers the determination of the interface heat-transfer coefficient by using the ring test and computer simulations. The article describes the behavior of oxide scale on the surface of hot metal undergoing thermomechanical processing. It concludes with information on the effects of process and material parameters on interfacial phenomena.

Analysis of the failure of a metal structure or part usually requires identification of the type of failure. Failure can occur by one or more of several mechanisms, including surface damage (such as corrosion or wear), elastic or plastic distortion, and fracture. This leads to a wide range of failures, including fatigue failure, distortion failure, wear failure, corrosion failure, stress-corrosion cracking, liquid-metal embrittlement, hydrogen-damage failure, corrosion-fatigue failure, and elevated-temperature failure. This article describes the classification of fractures on a macroscopic scale as ductile fractures, brittle fractures, fatigue fractures, and fractures resulting from the combined effects of stress and environment.

Total joint replacement in orthopedic surgery can be achieved by excision, interposition, and replacement arthroplasty. This article details the most common materials used in total replacement synovial joints, such as metals, ceramics, and ultrahigh molecular weight polyethylene (UHMWPE). The principal physical properties and tribological characteristics of these materials are summarized. The article discusses the pin-on-disk experiments and pin-on-plate experiments for determining friction and wear characteristics. It details the use of various types of joint simulators, such as hip joint simulators and knee joint simulators, to evaluate the performance of engineering tribological components in machine simulators. The article describes in vivo assessment of total joint replacement performance.

Fatigue failures may occur in components subjected to fluctuating (time-dependent) loading as a result of progressive localized permanent damage described by the stages of crack initiation, cyclic crack propagation, and subsequent final fracture after a given number of load fluctuations. This article begins with an overview of fatigue properties and design life. This is followed by a description of the two approaches to fatigue, namely infinite-life criterion and finite-life criterion, along with information on damage tolerance criterion. The article then discusses the characteristics of fatigue fractures followed by a discussion on the effects of loading and stress distribution, and material condition on the microstructure of the material. In addition, general prevention and characteristics of corrosion fatigue, contact fatigue, and thermal fatigue are also presented.