An AISI 4320 H transfer gear shaft that was part of a transmission sustained severe surface damage after 12 h of dynamometer testing at various gearing and torque loads. The damage was characterized by generalized wear and spalling. Examination of a cross section of the shaft that intersected undamaged, burnished, and surface-spalled zones revealed no anomalies in the chemistry, microstructure, or hardness that could have caused the damage. The physical evidence suggested that the operable mechanism was contact fatigue caused by misalignment of the shaft in the assembly.

A high-speed pinion gear shaft, part of a system that compresses natural gas, was analyzed to determine why it failed. An abnormal wear pattern was observed on the shaft surface beneath the inner race of the support bearings. Material from the shaft had transferred to the bearing races, creating an imbalance (enough to cause noise and fumes) that operators noted two days before the failure. Macrofeatures of the fracture surface resembled those of fatigue, but electron microscopy revealed brittle, mostly intergranular fracture. Classic fatigue features such as striations were not found. To resolve the discrepancy, investigators created and tested uniaxial fatigue samples, and the microfeatures were nearly identical to those found on the failed shaft. The root cause of failure was determined to be fatigue, and it was concluded that cracks on the pinion shaft beneath the bearings led to the transfer of material.

A shaft, which carried both a worm wheel and hoist barrel, fractured at a reduction in diameter adjacent to a mating gearbox. The appearance of the fracture was characteristic of a fatigue failure of a rotating shaft resulting from excessive bending stresses. Cracks of the fatigue type broke out all around the circumference at the change of section and progressed inwards. Microscopic examination of the material showed it to be an alloy steel in the hardened and tempered condition, with no abnormal features. It was considered that the bending stresses due to the deflection of the shaft arising from misalignment were responsible for the fatigue failure, which occurred in a region of stress concentration where insignificant fillet radius had been provided.

The specified elongation of 10% could not be achieved in several hollow pinion gear shafts made of cast Cr-Mo steel GS 35 Cr-Mo 5 3 that were heat treated to a strength of 90 kp/sq mm. The steel was melted in a basic 3 ton arc furnace and deoxidized in the furnace and in the pan with a total of 7 kg aluminum. Fracture of a tensile specimen occurred with low elongation and, apparently, also with low reduction of area. In some places it was coarse grained conchoidal. It was found that the exceptionally low elongation of the cast specimens was due to excessive deoxidation by aluminum.

Two shafts that transmit power from the engine to the propeller of a container ship failed after a short time in service. The shafts usually have a 25 year lifetime, but the two in question failed after only a few years. One of the shafts, which carries power from a gearbox to the propeller, is made of low alloy steel. The other shaft, part of a clutch mechanism that regulates the transmission of power from the engine to the gears, is made of carbon steel. Fracture surface examination of the gear shaft revealed circumferential ratchet marks with the presence of inward progressive beach marks, suggesting rotary-bending fatigue. The fracture surfaces on the clutch shaft exhibited a star-shaped pattern, suggesting that the failure was due to torsional overload which may have initiated at corrosion pits discovered during the examination. Based on the observations, it was concluded that rotational bending stresses caused the gear shaft to fail due to insufficient fatigue strength. This led to the torsional failure of the corroded clutch shaft, which was subjected to a sudden, high level load when the shaft connecting the gearbox to the propeller failed.

The types of metal components used in lifting equipment include gears, shafts, drums and sheaves, brakes, brake wheels, couplings, bearings, wheels, electrical switchgear, chains, wire rope, and hooks. This article primarily deals with many of these metal components of lifting equipment in three categories: cranes and bridges, attachments used for direct lifting, and built-in members of lifting equipment. It first reviews the mechanisms, origins, and investigation of failures. Then the article describes the materials used for lifting equipment, followed by a section explaining the failure analysis of wire ropes and the failure of wire ropes due to corrosion, a common cause of wire-rope failure. Further, it reviews the characteristics of shock loading, abrasive wear, and stress-corrosion cracking of a wire rope. Then, the article provides information on the failure analysis of chains, hooks, shafts, and cranes and related members.

A cylindrical spiral gear, part of a locomotive axle assembly, cracked ten days after it had been press-fit onto a shaft, after which it sat in place as other repairs were made. Workers at the locomotive shop reported hearing a sound, and upon inspecting the gear, found a crack extending radially from the bore to the surface of one of the tooth flanks. The crack runs the entire width of the bore, passing through an oil hole in the hub, across the spoke plate and out to the tip of one of the teeth. Design requirements call for the gear teeth to be carburized, while the remaining surfaces, protected by an anti-carburizing coating, stay unchanged. Based on extensive testing, including metallographic examination, microstructural analysis, microhardness testing, and spectroscopy, the oil hole was not protected as required, evidenced by the presence of a case layer. This oversight combined with the observation of intergranular fracture surfaces and the presence of secondary microcracks in the case layer point to hydrogen embrittlement as the primary cause of failure. It is likely that hydrogen absorption occurred during the gas carburizing process.

An oil scavenge pump was found to have failed when a protective shear neck fractured during the start of a jet engine. Visual inspection revealed that the driven gear in one of the bearing compartments was frozen as was the corresponding drive gear. Spacer wear and thermal discoloration (particularly on the driven gear) were also observed. The gears were made from 32Cr-Mo-V13 steel, hardened and nitrided to 750 to 950 HV. Micrographic inspection of the gear teeth revealed microstructural changes that, in context, appear to be the result of friction heating. The spacers consist of Cu alloy (AMS4845) bushings force fit into AA2024-T3 Al alloy spacing elements. It was found that uncontrolled fit interference between the two components had led to Cu alloy overstress. Thermal cycling under operating conditions yielded the material. The dilation was directed inward to the shaft, however, because the bushing had only a few microns of clearance. The effect caused the oil to squeeze out, resulting in metal-to-metal contact, and ultimately failure.

High-horsepower electric motors were utilized to drive large compressors (made of 4340 steel shafts and gear-type couplings) required in a manufacturing process. The load was transmitted by two keys 180 deg apart. Six of the eight compressor shafts were found cracked in a keyway and one of them fractured after a few months of operation. Visual examination of fractured shaft revealed that the cracks originated from one of the keyways and propagated circumferentially around the shaft. The shaft and coupling slippage was indicated by the upset keys and this type of fracture. The shaft surface both near and in the keyways indicated fretting which greatly reduced the fatigue limit of the shaft metal and initiated fatigue cracks. Fatigue marks were observed on the fractured key. Repetitive impact loading was responsible for propagation of the cracks. The high cyclic bending stresses were caused by misalignment between the electric motor and compressor and were transmitted to the shaft through the geared coupling. Flexible-disk couplings capable of transmitting the required horsepower were installed on the shafts as a corrective measure.

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.

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.

Gears can fail in many different ways, and except for an increase in noise level and vibration, there is often no indication of difficulty until total failure occurs. This article reviews the major types of gears and the basic principles of gear-tooth contact. It discusses the loading conditions and stresses that effect gear strength and durability. The article provides information on different gear materials, the common types and causes of gear failures, and the procedures employed to analyze them. Finally, it presents a chosen few examples to illustrate a systematic approach to the failure examination.