Rolling contact fatigue is responsible for a large number of industrial equipment failures. It is also one of the main failure modes of components subjected to rolling contact loading such as bearings, cams, and gears. To better understand such failures, an investigation was conducted to assess the role of friction in subsurface fatigue cracking in rolling-sliding contact applications. Based on the results of stress calculations and x-ray diffraction testing of steel samples, friction contributes to subsurface damage primary through its effect on the distribution of orthogonal shear stress. Although friction influences other stress components, the effect is relatively insignificant by comparison. It is thus more appropriate to select orthogonal shear stress as the critical stress when assessing subsurface rolling contact fatigue in rolling-sliding systems.

Galvanized A36 steel unsleeved shear-type anchor bolts failed during installation. The galvanized steel bolts were approximately 18 mm (0.7 in.) in diameter with a 90 deg bend between the long and short legs. As-fractured, sawcut, and unfractured specimens were examined. Failure analysis revealed dark thumbnail regions at the fracture origins and a very narrow and uniform shear lip. The thumbnail region exhibited zinc deposits with no apparent fracture detail, indicating preexisting cracks that had occurred before galvanizing. The balance of the fracture exhibited a transgranular mode with cleavage and ductile, dimpled shear. Hardness values as high as 35 HRC were measured in the bend area. The as-galvanized bolts fractured in a brittle manner. Failure was attributed to improper bending of the bolts, which provided a severely cold-worked bend area susceptible to strain-age embrittlement.

A 6 x 19 fiber core steel wire rope failed as it was being used to lower a steel television tower. Fracture of the rope occurred at a point under one of two clips used to fashion a spliced loop that was directly connected to the top of the tower. Microscopic examination of the fracture surfaces and the condition of the individual wires revealed that 59% of the wires failed by shear, 39% failed in tension, and 2% had been cut. In addition, 87% of the wires showed some degree of crushing damage, ranging from mild to severe. The failure was attributed to improper installation of the clips.

This article describes the failure characteristics of high-pressure long-distance pipelines. It discusses the causes of pipeline failures and the procedures used to investigate them. The use of fracture mechanics in failure investigations and in developing remedial measures is also reviewed.

A crane hook of 200T rated capacity failed suddenly at an indicated load of 143T, while the crane was undergoing a load test. Fracture took place through the intrados of the hook at the region of maximum stress. The jib and other portions suffered subsequent damage following the sudden release of the load. Fracture was wholly of the brittle cleavage type except for a small crescent shaped lip at the top right-hand side. In this zone, fracture occurred at an angle of 45 deg to the general plane of fracture, indicative of failure in shear. Failure of the hook had taken place where a deposit of weld metal had been made, probably to eliminate a surface defect but apparently, without complete removal of the defect down to sound metal prior to welding. On many occasions it is preferable to blend out surface defects by local dressing. The effect of the resulting loss of strength is insignificant compared with the increased chance of failure associated with a weld repair.

Sheet forming failures divert resources from normal business activities and have significant bottom-line impact. This article focuses on the formation, causes, and limitations of four primary categories of sheet forming failures, namely necks, fractures/splits/cracks, wrinkles/loose metal, and springback/dimensional. It discusses the processes involved in analytical tools that aid in characterizing the state of a formed part. In addition, information on draw panel analysis and troubleshooting of sheet forming failures is also provided.

This article describes the preliminary stages and general procedures, techniques, and precautions employed in the investigation and analysis of metallurgical failures that occur in service. The most common causes of failure characteristics are described for fracture, corrosion, and wear failures. The article provides information on the synthesis and interpretation of results from the investigation. Finally, it presents key guidelines for conducting a failure analysis.

Drive cables from a rubber processing machine were failing in less than 8 h of operation, the expected service life being much greater than 100 h. Comparison cables were tested to failure under known stress conditions, including tensile overload, torsional loading, reversed bending alternating stress, and buckling (compressive) cyclic loading. The mode of failure was found to be reversed bending fatigue caused by drive cables moving over guide pulleys of small radii. Modifications of the machinery and drive cable system were suggested.

A splined shaft on a wood chip-to-fiber refiner failed during equipment start-up. The shaft broke into two pieces at a location close to the end of the splined part of the shaft. The failed component showed the classical fatigue-cracking fracture face. The shaft had a diam of approximately 140 mm (5.5 in.) in the unsplined section and was made of 4340 Ni-Cr-Mo alloy steel heat treated to a uniform hardness of HRC 31. Cracks from at least seven different origins had coalesced to produce the single large crack that resulted in failure. The origins of these cracks were on the flanks of the splines. SEM examination revealed the splined shaft failed by fretting fatigue.

An axle shaft in an open-pit mining truck hauling overburden failed after operating for 27,000 h. Previous failures had resulted from longitudinal shear, but this had not, bringing material quality into question. Chemical analysis verified that the part was SAE4340 Ni-Cr-Mo alloy steel and thus met material specification. The failure was a result of torsional fatigue in the tensile plane, originating from one of several gouges around the splined radius of the shaft. The fatigue crack progressed for a large number of cycles before final fracture. The shaft met metallurgical requirements and should have withstood normal operating conditions. The spacing of the gouge marks coincided with the spacing of the splines, indicative of careless assembly with the mating wheel gear.

JIS SCM435 steel bolts that connected the slewing ring to the base carrier on a truck crane failed during the lifting of steel piles. The bolts were double-ended stud types and had been in operation for 5600 h. Failure occurred in the root of the external thread that was in contact with the first internal thread in the slewing ring. Examination of plastic carbon replicas indicated that failure was the result of fatigue action. Failure was attributed to overloading during service and increased stress concentration on a few bolts due to nonuniform separations around the slewing ring. A design change to achieve equal separation between bolt holes was recommended.

Coiled tubing used in drilling operations failed at the halfway point of its estimated fatigue life. The failure was found to be transverse to the tubing axis. Visual examination revealed a flat fracture surface extending 13 mm with the rest of the fracture showing shear lips indicative of tensile overload. The flat portion of the fracture surface was typical of fatigue cracking. Fatigue striations were revealed by SEM. Corrosion pitting on the tubing ID from which the fatigue crack had propagated were observed on closer examination. The corrosion pitting was speculated to have occurred when the tubing was idle and fluids accumulated at the bottom of the tubing wraps. The coiled tubing was concluded to have failed prematurely due to low-cycle fatigue initiated at corrosion pitting sites. Corrosive attack on the coiled tubing was recommended to be reduced by completely removing fluids or modifying the fluids in the tubing or purging by flowing dry nitrogen to dry it out.

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.

Fatigue failure of engineering components and structures results from progressive fracture caused by cyclic or fluctuating loads. Fatigue is an important potential cause of mechanical failure, because most engineering components or structures are or can be subjected to cyclic loads during their lifetime. This article focuses on fractography of fatigue. It provides an abbreviated summary of fatigue processes and mechanisms: fatigue crack initiation, fatigue crack propagation, and final fracture,. Characteristic fatigue fracture features that can be discerned visually or under low magnification are then described. Typical microscopic features observed on structural metals are presented subsequently, followed by a brief discussion on fatigue in polymers and polymer-matrix composites.

A wire hoisting rope on a drilling rig failed during a lift, after a few cycles of operation, causing extensive damage to support structures. The failure investigation that followed included mechanical property testing and chemical, metallurgical, and finite element analysis. The rope was made from multiple strands of 1095 steel wire. Its chemical composition, ferrite-pearlite structure, and high hardness indicate that the wire is a type of extra improved plow steel (EEIPS grade). The morphologies of the fracture surfaces suggest that the wires were subjected to tensile overloading. This was confirmed by finite element analysis, which also revealed compressive contact stresses between the wires and between the rope and sheave surface. Based on the results, it was concluded that a tensile overload, due to the combined effect of a sudden load and undersized sheave, is what ultimately caused the rope to fail.

Over a period of 2 or 3 years, 40 to 50 premature failures of drawn high-tensile, pearlitic high-carbon (0.8 wt% C) steel wires used as cables for towing targets behind aircraft occurred. Six service failures were examined in detail. Four types of failure characteristics were noted. A close examination of wire that had been flown several times without failure was also made, and dynamic tests were conducted to investigate the fracture characteristics of wire subjected to dynamic loading. It was concluded that dynamic shock loading transmitted by the target during unsteady flight conditions was the major cause of failure. Recommendations emphasized the need for a suitable shock absorber to be fitted at the constant-tensioning device of the winch system.

During a work over of an oil well, the 9% Ni steel production tubing parted three times as it was being pulled from the well. The tubing had performed satisfactorily for more than 30 years in the well A representative failure, a circumferential fracture in a connection, was analyzed. Reported to be a hydril CS connection, the pin end parted near the last threads. The external surface exhibited mechanical damage marks from the fishing operation. No signs of external corrosion or damage were detected. Visual surface examination revealed shear lips at the outside pipe, indicating that the fracture initiated at the inside surface and grew across the wall. Longitudinal cross sections revealed heavy corrosion damage to the inside pipe surface. Metallographic examination indicated that the tubing failed as a result of severe weakening from internal corrosion. Gray-colored corrosion deposits, which penetrated the pipe throughout the grain boundaries of the material and concentrated in the matrix in a layer near the inside surface of the pipe, were observed. The presence of H2S in the produced fluids and the appearance of the gray deposit indicated that the tube suffered H2S corrosion. Chemical analysis of the base metal and corrosion deposits did not detect iron or nickel sulfides, however Replacement of the remaining pipe strings according to a scheduled program was recommended. Because 9% Ni steel was not available, 13% Cr martensitic stainless steel was recommended as a replacement.

Failed ferrous components were analyzed from a crane that operated on an offshore platform. The crane failed during operation and fell into the sea. The brake spring on the boom hoist was found to have fractured in four places. The spring contained a line defect (seam) that was the source of each crack. The fracture of the oil quenched and tempered (HRC 50 ASTM A229) spring was by stress-corrosion cracking after the crane fell into the sea because fatigue cannot account for the fractures observed. The crane failure was caused by an overload created by the operator catching a free-falling load.

During the routine hydraulic pressure test of a boiler following modification, failure by leakage from the drum took place and was traced to a region where extensive multiple cracking had occurred. Catastrophic rupture or fragmentation of the vessel fortunately did not take place. Prior to the test, cracking was present already, extending up to 90% of the wall thickness. Analyses of brownish deposit material did not reveal the presence of any substances likely to cause stress-corrosion cracking of a Ni-Cu-Mo low-alloy steel.

A ‘worn-out’ spiral bevel gear and pinion set was submitted for examination and evaluation. This was a spiral bevel drive set with the gear attached to a differential. The assembled unit was driving a new, large, experimental farm tractor in normal plowing and tilling operations. The primary failure was associated with the 4820H NiMo alloy steel pinion, and thus the gear was not examined. The mode of failure was rolling contact fatigue, and the cause of failure improper engineering design. The pattern of continual overload was restricted to a specific concentrated area situated diagonally across the profile of the loaded side, which was consistent on every tooth.