This paper describes an investigation on the failure of a large leaded bronze bearing that supports a nine-ton roller of a plastic calendering machine. At the end of the normal service life of a good bearing, which lasted for seven years, a new bearing was installed. However the new one failed catastrophically within a few days, generating a huge amount of metallic wear debris and causing pitting on the surface of the cast iron roller. Following the failure, samples were collected from both good and failed bearings. The samples were analyzed chemically and their microstructures examined. Both samples were subjected to accelerated wear tests in a laboratory type pin-on-disk apparatus. During the tests, the bearing materials acted as pins, which were pressed against a rotating cast iron disk. The wear behaviors of both bearing materials were studied using weight loss measurement. The worn surfaces of samples and the wear debris were examined by light optical microscope, SEM, and energy-dispersive x-ray microanalyzer. It was found that the laboratory pin-on-disk wear data correlated well with the plant experience. It is suggested that the higher lead content ~18%) of the good bearing compared with 7% lead of the failed bearing helped to establish a protective transfer layer on the worn surface. This transfer layer reduced metal-to-metal contact between the bearing and the roller and resulted in a lower wear rate. The lower lead content of the failed bearing does not allow the establishment of a well-protected transfer layer and leads to rapid wear.

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.

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 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.

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.

An investigation was conducted to determine what caused a bearing sleeve in a locomotive turbocharger to fail. The sleeve, which is made of nitrided 38CrMoAl steel, fractured at the transition fillet between the cylinder and plate. Visual examination revealed significant wear on the external surface of the cylinder, with multiple origin fatigue fracture appearing to be the dominant fracture mechanism. Metallurgical examination indicated that the nitrided layer was not as deep as it was supposed to be and had worn away on the outer surface of the sleeve, exposing the soft matrix underneath. This led to further wear and an increase in friction between the sleeve and bearing bush. Fatigue crack initiation occurred at the root fillet because of stress concentration and large frictional forces. Insufficient nitriding depth facilitated the propagation of fatigue cracks.

When a roller-bearing assembly was removed from an aircraft for inspection after a short time in service, several areas of apparent galling were noticed around the inside surface of the inner cone of the bearing. These areas were roughly circular spots of built-up metal. The bearing had not seized, and there was no evidence of heat discoloration in the galled areas. The inner cone, made of modified 4720 steel and carburized for wear resistance, rode on an AISI type 630 (17-4 PH) stainless steel spacer. Consequently, it was desirable to determine whether the galled spots contained any stainless steel from the spacer. Other items for investigation were the nature of the bond between the galled spot and the inner cone and any evidence of overtempering or rehardening resulting from localized overheating. Analysis (visual inspection, electron probe x-ray microanalysis, microscopic examination, and hardness testing) supported the conclusions that galling had been caused by a combination of local overload and abnormal vibration of mating parts of the roller-bearing assembly. No recommendations were made.

Two intermediate impeller drive gears (made of AMS 6263 steel, gas carburized, hardened, and tempered) exhibited evidence of pitting and abnormal wear after production tests in test-stand engines. The gears were examined for hardness, case depth, and microstructure of case and core. It was found that gear 1 had a lower hardness than specified while the case hardness of gear 2 was found to be within limits. Both the pitting and the wear pattern were revealed to be more severe on gear 1 than on gear 2. Surface-contact fatigue (pitting) of gear 1 (cause of lower carbon content of the carburized case and hence lower hardness) was found to be the reason for failure. It was recommended that the depth of the carburized case on impeller drive gears be increased from 0.4 to 0.6 mm to 0.6 to 0.9 mm to improve load-carrying potential and wear resistance. A minimum case-hardness requirement was set at 81 HRA.

River water was pumped into a brine plant by a battery of vertical pumps, each operating at 3600 rpm and at a discharge pressure of 827 kPa (120 psi). The pumps were lubricated by means of controlled leakage. The 3.8 cm (1 in.) OD pump sleeves were made of an austenitic stainless steel and were hard faced with a fused nickel-base hardfacing alloy (approximately 58 HRC). Packing for the pumps consisted of a braided PTFE-asbestos material. After several weeks of operation, the pumps began to leak and to spray water over the platforms on which they were mounted at the edge of the river. Analysis supported the conclusions that the leaks were caused by excessive sleeve wear that resulted from the presence of fine, abrasive silt in the river water. The silt, which contained hard particles of silica, could not be filtered out of the inlet water effectively.

An antifriction bearing made from a nylon/ polyethylene blend failed. The bearing came into contact with a steel shaft. Investigation (visual inspection and 417X images) supported the conclusion that movement of the shaft against the bearing caused abrasion due to fine iron oxide particles. No recommendations were made.

A hypoid pinion made from 4820 Ni-Mo alloy steel was the driving member of a power unit operating a rapid transit car. The pinion had been removed from service at the end of the initial test period because it showed undue wear. The mode of failure was severe abrasive wear. The cause of failure was insufficient surface hardness, resulting from improper heat treatment. A service recall for the remaining pinions was immediately initiated.

A high-chromium white cast iron shell liner installed in an ore crusher sustained impact damage in the course of operation. Visual-optical examination revealed horizontal cracks on the surface of the liner along with particles that had fractured off. Metallographic examination indicated a heavily deformed surface layer with chip formation at the wear surface. The chemical composition of the liner was found to be Fe-2.74C-0.75Mn-0.55Si-0.51Ni-19.4Cr-1.15M. This alloy is highly resistant to abrasive wear, yet at the same time, prone to chipping because little plastic displacement will occur at the surface. The liner failed as a result of severe abrasion caused by the impact of taconite rock. This was a material-selection problem in that the wrong alloy was used for a condition not anticipated in the original choice.

The drive-shaft hanger bearings failed after 300 to 400 h in service. The shaft, supported by labyrinth-sealed single row radial ball bearings of ABEC-1 tolerances, was made of aluminum 2024-T3 tubing (2.5 cm diam and 1.2 mm wall thickness). The bearings were lubricated with a paste-type mineral-oil lubricant (containing molybdenum disulfide and polytetrafluoroethylene particles) or grease conforming to MIL-G-81322 (containing thickening agent and synthetic hydrocarbons) and had two-piece spot-welded retainers. On visual examination, the balls were observed to be embedded in the inner-ring raceway which had been softened by the elevated temperatures reached during the failure. Broken retainers and worn and bent out of shape seals were found. Penetration of gritty particles, water and other corrosive agents and leakage of lubricant out of the bearing permitted by the worn seals was observed. It was concluded that overheating was caused by lubricant flow was permitted by wear of the labyrinth seals. Positive rubbing seals and MIL-G-81322 grease lubricant were found to have longer life than those with the labyrinth seals and mineral-oil-paste lubricant on testing under simulated environmental conditions and were installed as a corrective measure. Importance of dirt free supply and drainage of oil was discussed.

In an industrial application, 24 speed-increaser gearboxes were used to transmit 258 kW (346 hp) and increase speed from 55 to 375 rev/min. The gears were parallel shaft, single helical, carburized, and ground. The splash lubrication system used a mineral oil without antiscuff additives with ISO 100 viscosity. After about 250 h of operation, two gearboxes failed by bending fatigue. Investigation showed the primary failure mode was scuffing, and the earlier bending fatigue failures were caused by dynamic loads generated by the worn gear teeth. Testing of a prototype gearbox showed that the failure resulted from several interrelated factors: the lubricant viscosity was too low causing high temperatures; no antiscuff additives were used; a gearbox designed as a speed reducer was used as a speed increaser (the designer selected a long-addendum tooth for the pinion); the gear teeth were not provided with a coating or plating to ease running-in; and the gears were not run-in properly under reduced loads. The case suggests that such gear failures can be avoided if designers and operators recognize that the lubricant is an important component of a gearbox and appreciate that gear design requires the consideration and control of many interrelated factors.

An investigation of wear and failure of babbitt bushes was completed in this study. The results showed that wear at dry sliding of babbitt obtained by plasma spraying was less than that of babbitt in the as-cast state and after a deformation heat treatment. The failure of babbitt bushes was caused by a simultaneous and interrelated exhibition of fatigue and wear processes that depend considerably on cohesion strength between the bush and the bearing base and accumulation of defects on the contact surface between the bush and the shaft.