This article presents the mechanisms of polymer wear and quantifies wear in terms of wear rate (rate of removal of the material). Interfacial and bulk wear are discussed as well as a discussion on the wear study of "elastomers," "thermosets," "glassy thermoplastics," and "semicrystalline thermoplastics." The article also discusses the effects of environment and lubricant on the wear failures of polymers. It presents a case study on considering nylon as a tribological material and failure examples, explaining wear resistance of polyurethane elastomeric coatings and failure of an acetal gear wheel.

Reinforced polymers (RPs) are widely used in structural, industrial, automotive, and engineering applications due to their ecofriendly nature and the potential to manipulate their properties. This article addresses the technical synthesis of RPs, referring to their tribological behavior, to provide insights into the contribution and interaction of influential parameters on the wear behavior of polymers. It provides a brief discussion on the effects of significant parameters on RP tribology. The article describes abrasive and adhesive wear and provides a theoretical synthesis of the literature regarding the wear mechanisms of RPs. It also describes the synthesis of abrasive wear failure of different types of RPs and highlights the contribution of these influential parameters. The article addresses the synthesis of adhesive wear failure of different types of RPs.

This article first provides an overview of the types of mechanical fasteners. This is followed by sections providing information on fastener quality and counterfeit fasteners, as well as fastener loads. Then, the article discusses common causes of fastener failures, namely environmental effects, manufacturing discrepancies, improper use, or incorrect installation. Next, it describes fastener failure origins and fretting. Types of corrosion in threaded fasteners and their preventive measures are then covered. The performance of fasteners at elevated temperatures is addressed. Further, the article discusses the types of rivet, blind fastener, and pin fastener failures. Finally, it provides information on the mechanism of fastener failures in composites.

A mechanical part, which supports the moving part, is termed a mechanical bearing and can be classified into rolling (ball or roller) bearings and sliding bearings. This article discusses the failures of sliding bearings. It first describes the geometry of sliding bearings, next provides an overview of bearing materials, and then presents the various lubrication mechanisms: hydrostatic, hydrodynamic, boundary lubrication, elastohydrodynamic, and squeeze-film lubrication. The article describes the effect of debris and contaminant particles in bearings. The steps involved in failure analysis of sliding bearings are also covered. Finally, the article discusses wear-damage mechanisms from the standpoint of bearing design.

Bearing in mind the three-legged stool approach of device design/manufacturing, patient factors, and surgical technique, this article aims to inform the failure analyst of the metallurgical and materials engineering aspects of a medical device failure investigation. It focuses on the device "failures" that include fracture, wear, and corrosion. The article first discusses failure modes of long-term orthopedic and cardiovascular implants. The article then focuses on short-term implants, typically bone screws and plates. Lastly, failure modes of surgical tools are discussed. The conclusion of this article presents several case studies illustrating the various failure modes discussed throughout.

This article considers the main characteristics of wear mechanisms and how they can be identified. Some identification examples are reported, with the warning that this task can be difficult because of the presence of disturbing factors such as contaminants or possible additional damage of the worn products after the tribological process. Then, the article describes some examples of wear processes, considering possible transitions and/or interactions of the mechanism of fretting wear, rolling-sliding wear, abrasive wear, and solid-particle erosion wear. The role of tribological parameters on the material response is presented using the wear map concept, which is very useful and informative in several respects. The article concludes with guidelines for the selection of suitable surface treatments to avoid wear failures.

Engineered components fail predominantly in four major ways: fracture, corrosion, wear, and undesirable deformation (i.e., distortion). Typical fracture mechanisms feature rapid crack growth by ductile or brittle cracking; more progressive (subcritical) forms involve crack growth by fatigue, creep, or environmentally-assisted cracking. Corrosion and wear are another form of progressive material alteration or removal that can lead to failure or obsolescence. This article primarily covers the topic of abrasive wear failures, covering the general classification of wear. It also discusses methods that may apply to any form of wear mechanism, because it is important to identify all mechanisms or combinations of wear mechanisms during failure analysis. The article concludes by presenting several examples of abrasive wear.

Fretting is a wear phenomenon that occurs between two mating surfaces; initially, it is adhesive in nature, and vibration or small-amplitude oscillation is an essential causative factor. Fretting generates wear debris, which oxidizes, leading to a corrosion-like morphology. This article focuses on fretting wear related to debris formation and ejection. It reviews the general characteristics of fretting wear, with an emphasis on steel. The review covers fretting wear in mechanical components, various parameters that affect fretting; quantification of wear induced by fretting; and the experimental results, map approach, measurement, mechanism, and prevention of fretting wear. This review is followed by several examples of failures related to fretting wear.

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.

Impact or percussive wear is defined as the wear of a solid surface that is due to percussion, which is a repetitive exposure to dynamic contact by another body. Impact wear, however, has many analogies to the field of erosive wear. The main difference is that, in impact wear situations, the bodies tend to be large and contact in a well-defined location in a controlled way, unlike erosion where the eroding particles are small and interact randomly with the target surface. This article describes some generic features and modes of impact wear of metals, ceramics, and polymers. It discusses the processes involved in testing and modeling of impact wear, and includes two case studies.

Corrosive wear is defined as surface damage caused by wear in a corrosive environment, involving combined attacks from wear and corrosion. This article begins with a discussion on several typical forms of corrosive wear encountered in industry, followed by a discussion on mechanisms for corrosive wear. Next, the article explains testing methods and characterization of corrosive wear. Various factors that influence corrosive wear are then covered. The article concludes with general guidelines for material selection against corrosive wear.

Erosion is the progressive loss of original material from a solid surface due to mechanical interaction between that surface and a fluid, a multicomponent fluid, an impinging liquid, or impinging solid particles. The detrimental effects of erosion have caused problems in a number of industries. This article describes the processes involved in erosion of ductile materials, brittle materials, and elastomers. Some examples of erosive wear failures are given on abrasive erosion, liquid impingement erosion, cavitation, and erosion-corrosion. In addition, the article provides information on the selection of materials for applications in which erosive wear failures can occur.

Erosion of a solid surface can be brought about by liquid droplet impingement (LDI), which is defined as "progressive loss of original material from a solid surface due to continued exposure to erosion by liquid droplets." In this article, the emphasis is placed on the damage mechanism of LDI erosion under the influence of a liquid film and surface roughness and on the prediction of LDI erosion. The fundamentals of LDI and processes involved in initiation of erosion are also discussed.

This article briefly introduces the concepts of failure analysis, including root-cause analysis (RCA), and the role of failure analysis as a general engineering tool for enhancing product quality and failure prevention. It initially provides definitions of failure on several different levels, followed by a discussion on the role of failure analysis and the appreciation of quality assurance and user expectations. Systematic analysis of equipment failures reveals physical root causes that fall into one of four fundamental categories: design, manufacturing/installation, service, and material, which are discussed in the following sections along with examples. The tools available for failure analysis are then covered. Further, the article describes the categories of mode of failure: distortion or undesired deformation, fracture, corrosion, and wear. It provides information on the processes involved in RCA and the charting methods that may be useful in RCA and ends with a description of various factors associated with failure prevention.

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.

An air blower in an electric power plant failed unexpectedly when a roller bearing in the drive motor fractured along its outer ring. Both rings, as well as the 18 rolling elements, were made from GCr15 bearing steel. The bearing also included a machined brass (MA/C3) cage and was packed with molybdenum disulfide (MoS 2 ) lithium grease. Metallurgical structures and chemical compositions of the bearing’s matrix materials were inspected using a microscope and photoelectric direct reading spectrometer. SEM/EDS was used to examine the local morphology and composition of fracture and contact surfaces. Chemical and thermal properties of the bearing grease were also examined. The investigation revealed that the failure was caused by wear due to dry friction and impact, both of which worsened as a result of high-temperature degradation of the bearing grease. Fatigue cracks initiated in the corners of the outer ring and grew large enough for a fracture to occur.

The case study presented in this article details the failure investigation of an M50 alloy steel bearing used in a jet engine gearbox drive assembly. It discusses the investigative steps and analytic tools used to determine the root cause, highlighting the importance of continuous, thorough questioning by the investigating activity. The combined analyses demonstrated that the bearing failed by a single event overload as evidenced by bulk deformation and traces of foreign material on the rolling elements. The anomalous transferred metal found on the rolling elements subsequently led to the discovery of overlooked debris in an engine chip detector, and thus resulted in a review of several maintenance practices.

An aero engine failed due to the misalignment of the ball bearing fitted on the main shaft of the engine. The aero engine incorporates two independent compressors: a six-stage axial flow LP compressor and a nine-stage axial flow HP compressor. The bearing under consideration is a HP location bearing and is fitted at the rear of the nine-stage compressor. It was supposed to operate for at least 5000 h, but failed catastrophically after 1300 h, rendering the engine unserviceable. Unusually high stresses caused by misalignment and uneven axial loading resulted in the generation of fatigue crack(s) in the inner race. When the crack reached the critical size, the collar of the race fractured, causing subsequent damage. The cage also failed due to excessive stresses in the axial direction, and its material was smeared on the steel balls and the outer race.

Material samples collected from failed booster pumps were analyzed to determine the cause of failure and assess the adequacy of the materials used in the design. The pumps had been in service at a power plant, transporting feedwater from a deaerator to a main turbine boiler. Samples from critical areas of the pump were examined using optical and scanning electron microscopy, electrochemical analysis, and tensile testing. Based on microstructure and morphology, estimated corrosion rates, and particle concentrations in the feedwater, it was concluded that cavitation and erosion were the dominant failure mechanisms and that the materials and processes used to make the pumps were largely unsuited for the application.

A ball bearing in a military jet engine sustained heavy damage and was analyzed to determine the cause. Almost all of the balls and a portion of the outer race were found to be flaking, but there were no signs of damage on the inner race and cage. Tests (chemistry, hardness, and microstructure) indicated that the bearing materials met the specification requirements. However, closer inspection revealed areas of discoloration, or nonuniform contact marks, on the ID surface of the inner ring. The unusual wear pattern suggested that the bearing was not properly mounted, thus subjecting it to uneven or eccentric loading. This explains the preferential nature of the flaking on the outer race and points to an assembly error as the root cause of failure.