The locking collar on a machine failed suddenly when the shaft it restrained was inadvertently subjected to an axial load slightly higher than the allowable working load. The locking collar fractured abruptly, producing four large fragments. This allowed the shaft to be propelled forcefully in the direction of the load, causing substantial damage to other machinery components in the vicinity. The failed component, which was 43 cm (17 in.) in diameter, was machined from 4140 plate and heat treated to 34 to 36 HRC. Analysis (visual inspection, composite micrographs, scanning electron microscopy, and mechanical-property analysis) supported the conclusions that the alloy steel plate used in this application contained significant brittle microstructural fibering or banding. This condition produced considerable anisotropy in ductility and toughness as revealed by mechanical testing. Unfortunately, the potential effects of anisotropy were apparently neglected when this component was designed and manufactured from the plate stock, because the loading was applied in a direction that stressed the weakest planes in the material, that is, a direction normal to the fibering. No recommendations were made.

The shaft-and-bearing assembly in a freon compressor was subjected to severe pounding and vibration after six years of service. After about one year of service, the compressor had been shut down to replace a bearing seal. One month before the shaft failed, a second seal failure occurred, requiring the collar, spacer sleeve, seal, roller bearing, and lock washer to be replaced. The shaft was made of 4140 steel, heat treated to a hardness of 20 to 26 HRC. The seal, bearing, and lock washer were commercial components. Investigation (visual inspection, 4.5x images, x-ray diffraction, hardness testing, and microscopic exam) supported the conclusion that shaft failure was initiated by fretting between the bearing race and the bearing surface on the shaft because of improper bearing installation. Once clearance was established between the bearing and the shaft, the shaft began pounding on the inner bearing race, causing final failure of the shaft surface. Recommendations included proper fitting of the shaft and bearing race to preventing movement of the bearing on the shaft. Also, the lock washer and locknut must be installed properly.

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.

This article discusses different types of mechanical fasteners, including threaded fasteners, rivets, blind fasteners, pin fasteners, special-purpose fasteners, and fasteners used with composite materials. It describes the origins and causes of fastener failures and with illustrative examples. Fatigue fracture in threaded fasteners and fretting in bolted machine parts are also discussed. The article provides a description of the different types of corrosion, such as atmospheric corrosion and liquid-immersion corrosion, in threaded fasteners. It also provides information on stress-corrosion cracking, hydrogen embrittlement, and liquid-metal embrittlement of bolts and nuts. The article explains the most commonly used protective metal coatings for ferrous metal fasteners. Zinc, cadmium, and aluminum are commonly used for such coatings. The article also illustrates the performance of the fasteners at elevated temperatures and concludes with a discussion on fastener failures in composites.

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.

On 21 April 1995, the contents of a large blender (6 cu m) reacted and caused an explosion that killed and injured a number of workers at a plant in Lodi, NJ. A mixture of sodium hydrosulfite and aluminum powder was being mixed at the time of the accident. This report focuses on evaluations of the blender to determine if material or mechanical failures were the cause of the accident. The results indicate that the mixing vessel was metallurgically sound and did not contribute to the initiation of the failure. However, the vessel was not designed for mixing chemicals that must be isolated from water and excessive heat. Water leaking into the vessel through a graphite seal may have initiated the reactions that caused the accident.

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.

This article reviews the general characteristics of fretting wear in mechanical components with an emphasis on steel. It focuses on the effects of physical variables and the environment on fretting wear. The variables include the amplitude of slip, normal load, frequency of vibration, type of contact and vibration, impact fretting, surface finish, and residual stresses. The form, composition, and role of the debris are briefly discussed. The article also describes the measurement, mechanism, and prevention of fretting wear. It concludes with several examples of failures related to fretting wear.

This article briefly reviews the general causes of weldment failures, which may arise from rejection after inspection or failure to pass mechanical testing as well as loss of function in service. It focuses on the general discontinuities observed in welds, and shows how some imperfections may be tolerable and how the other may be root-cause defects in service failures. The article explains the effects of joint design on weldment integrity. It outlines the origins of failure associated with the inherent discontinuity of welds and the imperfections that might be introduced from arc welding processes. The article also describes failure origins in other welding processes, such as electroslag welds, electrogas welds, flash welds, upset butt welds, flash welds, electron and laser beam weld, and high-frequency induction welds.

This article is dedicated to the fields of mechanical engineering and machine design. It also intends to give a nonexhaustive view of the preventive side of the failure analysis of rolling-element bearings (REBs) and of some of the developments in terms of materials and surface engineering. The article presents the nomenclature, numbering systems, and worldwide market of REBs as well as provides description of REBs as high-tech machine components. It discusses heat treatments, performance, and properties of bearing materials. The processes involved in the examination of failed bearings are also explained. Finally, the article discusses in detail the characteristics and prevention of the various types of failures of REBs: wear, fretting, corrosion, plastic flow, rolling-contact fatigue, and damage. The article includes an Appendix, which lists REB-related abbreviations, association websites, and ISO standards.