A heavy duty facing lathe failed when the tool post caught one of the jaws on the rotating chuck, causing the spline shaft that drives the main spindle to fracture. A detailed analysis of the fracture surfaces (including fractography, metallography, and analytical stress calculations) revealed areas of damage due to rubbing with evidence of cleavage fracture on the unaffected surfaces. The results of stress analysis indicated that repeated reversals of the spindle produced stresses exceeding the fatigue limit of the shaft material. These stresses led to the formation of microcracks in a retaining ring groove that were accelerated to sudden failure when the tool post and chuck collided.

Two vertical coal-pulverizer shafts at a coal-fired generation station failed after four to five years in service. One shaft was completely broken, and the other was unbroken but cracked at both ends. shaft material was AISI type 4340 Ni-Cr- Mo alloy steel, with a uniform hardness of approximately HRC 27. Metallographic examination of transverse sections through the surface-damaged areas adjacent to the cracks also showed additional small cracks growing at an angle of approximately 60 deg to the surface. The crack propagation mode appeared to be wholly transgranular. SEM examination revealed finely spaced striations on the crack surfaces, supporting a diagnosis of fatigue cracking. Crack initiation in the pulverizer shafts started as a result of fretting fatigue. Greater attention to lubrication was suggested, combined with asking the manufacturer to consider nitriding the splined shaft. It was suggested that the surfaces be securely clamped together and that an in-service maintenance program be initiated to ensure that the tightness of the clamping bolts was verified regularly.

This paper presents a failure analysis of a reverse shaft in the transmission system of an all-terrain vehicle (ATV). The reverse shaft with splines fractured into two pieces during operation. Visual examination of the fractured surface clearly showed cracks initiated from the roots of spline teeth. To find out the cause of fracture of the shaft, a finite element analysis was carried out to predict the stress state of the shaft under steady loading and shock loading, respectively. The steady loading was produced under normal operation, while the shock loading could be generated by an abrupt change of operation such as start-up or sudden braking during working. Results of stress analysis reveal that the highest stressed area coincided with the fractured regions of the failed shaft. The maximum stress predicted under shock loading exceeded the yield strength and was believed to be the stimulant for crack initiation and propagation at this weak region. The failure analysis thus showed that the premature fatigue fracture of the shaft was caused by abnormal operation. Finally, some suggestions to enhance service durability of the transmission system of ATV are discussed.

The failure of an ATAR engine accessory angle drive gear assembly caused an engine flame-out in a Mirage III aircraft of the Royal Australian Air Force (RAAF) during a landing. Stripping of the engine revealed that the bevel gear locating splines (16 NCD 13) had failed. Visual and low-power microscope examination of the spline of the shaft showed evidence of fretting wear debris; similar wear was observed on the splines of the mating bevel gear. It was concluded that the splines had failed by severe fretting wear. Fretting damage was also observed on the shaft face adjacent to the splines and on the bevel gear abutment shoulder. Additional tests included a metrological inspection of the shaft, bevel gear and support ring; metallographic examination of a section from the shaft; chemical analysis of the shaft material (16 NCD 13); and hardness testing of a sample of the yoke material. The wear had been caused by incorrect machining of the shaft splines, which prevented the bevel gear nut from locating correctly against the gear.

High failure rates in the drive shafts of 40 newly acquired articulated buses was investigated. The drive shafts were fabricated from a low-carbon (0.45%) steel similar to AISI 5046. Investigators examined all 40 buses, discovering six different drive shaft designs across the fleet. All of the failures, a total of 14, were of the same type of design, which according to finite-element analysis, produces a significantly higher level of stress. SEM examination of the fracture surface of one of the failed drive shafts revealed fatigue striations near the OD and ductile dimpling near the ID, evidence of high-cycle fatigue. Based on the failure rate and fatigue life predictions, it was recommended to discontinue the use of drive shafts with the inferior design.

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.

Distortion often is observed in the analysis of other types of failures, and consideration of the distortion can be an important part of the analysis. This article first considers that true distortion occurs when it was unexpected and in which the distortion is associated with a functional failure. Then, a more general consideration of distortion in failure analysis is introduced. Several common aspects of failure by distortion are discussed and suitable examples of distortion failures are presented for illustration. The article provides information on methods to compute load limits, errors in the specification of the material, and faulty process and their corrective measures to meet specifications. It discusses the general process of material failure analysis and special types of distortion and deformation failure.

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.