Failure analysis is an investigative process that uses visual observations of features present on a failed component fracture surface combined with component and environmental conditions to determine the root cause of a failure. The primary means of recording the conditions and features observed during a failure analysis investigation is photography. Failure analysis photographic imaging is a combination of both science and art; experience and proper imaging techniques are required to produce an accurate and meaningful fracture surface photograph. This article reviews photographic principles and techniques as applied to failure analysis, both in the field and in the laboratory. The discussion covers the processes involved in field and laboratory photographic documentations, provides a description of professional digital cameras, and gives information on photographic lighting and microscopic photography. Special techniques can be employed to deal with highly reflective conditions and are also described in this article.

Several pressurized air containers (i.e., diving tanks) made of non-heat-treatable Al-5Mg aluminum alloy failed catastrophically. Catastrophic failure occurred when a subcritical stress corrosion crack reached a critical size. Critical crack size for unstable propagation was reached prior to wall penetration, which could have led to subsequent loss of pressure, resulting in explosion of the cylinder. It was recommended that more stress corrosion resistant alloys be used for sea diving applications. Furthermore, cylinders should have a reduced wall thickness that can be determined employing the “leak-before-break” design philosophy, developed using fracture mechanics, to eliminate the possibility of catastrophic ruptures.

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.

A 1984 Chevrolet Blazer was being pushed by three youths after it ran out of gas when it was hit from behind by a 1979 Mercury Cougar. One of the youths was crushed between the two vehicles and killed. Optical microscopy was used to examine the tungsten filaments from the headlamps of the Cougar and from the four signal/emergency/parking lights of the Blazer to determine whether the vehicles lights were in use at the time of the accident. Based on degree of distension and brittle fragmentation, it was determined that the low-beam headlights of the Cougar and the parking lights of the Blazer were on at the time of the collision.

A steam turbine developed excessive noise and vibration during routine operation. It was found that the nut that locked the turbine disk In place had worked its way out from the threads and the disk had come of the shaft. Examination of the locking mechanism indicated that its design was responsible for the loosening of the nut. It was recommended that the locking mechanism be redesigned and changed in all existing turbines.

A stainless steel flexible connector failed after a short period of service. Visual examination of the failed part revealed that a fracture had occurred in the thin-walled stainless steel bellows brazed into the flanges at each end. Surface examination by SEM fractography showed that failure of the bellows occurred via fatigue. The crack in the bellows had widened considerably after the fracture, and the bellows had been severely compressed on the fracture side prior to failure. Based on these observations, it was concluded that bellows had been damaged prior to installation. The damage resulted in high mean tensile stresses upon which were superimposed cyclic stresses, with fatigue failure the final result.

An ASTM A193-83a grade B7 (AISI 4140) steel turbine impeller shaft fractured after 2 months of service. Failure had initiated at three separate points around the periphery of the shaft, each associated with one of three keyways. SEM fractography, metallography, and chemical analysis indicated that the mechanism of fracture initiation was torsional fatigue. Intermittent deceleration and acceleration resulting from power surges during operation of the turbine caused torsional vibration and was considered the most probable source of the required cyclic stress. Final failure took place by torsional shear.

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.

An ASTM A 504 carbon steel railway car wheel that was used on a train in a metropolitan railway system failed during service, causing derailment. The wheel was completely fractured from rim to hub. Macrofractography of the fracture surface showed road grime, indicating that the crack had existed for a considerable time prior to derailment and initiated in the flange. Failure propagated from the flange across the rim and down the plate to the bore of the hub. Two zones that exhibited definite signs of heating were observed. The fracture initiation site was typical of fatigue fracture. No defects were found that could have contributed to failure. The wheel conformed to the chemical, microstructural, and hardness requirements for class A wheels. Failure was attributed to repeated severe heating and cooling of the rim and flange due to brake locking or misapplication of the hand brake. It was recommended that the brake system on the car be examined and replaced if necessary.

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.

Two hot water reheat coil valves from a heating/ventilating/air-conditioning system failed in service. The values, a 353 copper alloy 19 mm (3/4 in.) valve and a 360 copper alloy 13 mm (1/2 in.) valve, had been failing at an increasing rate. The failures were confined to the stems and seats. Visual examination revealed severe localized metal loss in the form of deep grooves with smooth and wavy surfaces. Metallographic analysis of the grooved areas revealed uniform metal loss. No evidence of intergranular or selective attack indicating erosion-corrosion was observed, Recommendations included use of a higher-copper brass, cupronickel, or Monel for the valve seats and stems and operation of the valves in either the fully opened or closed position.

An AISI 9260 steel railroad spike maul failed after a relatively short period of service. The maul head fractured in two pieces when struck against a rail. Visual, fractographic, metallographic, and chemical analyses were conducted on sections taken from the maul head, which was found to have fractured across both sides of the eye. Failure occurred in at least three separate events: formation of two cracks immediately adjacent to the eye, extension of one of the original cracks over a portion of one of the eye sides, and abrupt extension of the original crack across the eye sides, resulting in separation into two halves.

A trunnion bolt that was part of a coupling in a metropolitan railway system failed in service, causing cars to separate. The bolt had been in service for more than ten years prior to failure. Visual examination showed that the failure resulted from complete fracture at the grease port and surface groove located at midspan. Drillings machined from the bolt underwent chemical analysis, which confirmed that the material was AISI 1045 carbon steel, in accordance with specifications. Two sections cut from the bolt were subjected to metallographic examination and hardness testing. The fracture origin was typical of fatigue. The ultimate tensile strength of the bolt was in excess of requirements. Wear patterns indicated that the bolt had been frozen in position for a protracted period and subjected to repeated bending stresses, which resulted in fatigue cracking and final complete fracture. It was recommended that proper lubrication procedures be maintained to allow free rotation of the bolts while in service.

A type 316L stainless steel “Jewett nail” hip implant failed after 2 months of service. Fracture occurred through the first of five screw holes in the plate section. Microscopic examination of mating fracture surfaces showed that failure had initiated at the outside (convex) surface of the plate and proceeded through its thickness. The fracture morphology was characteristic of fatigue. A beveled area on the inside surface of the plate indicated that the implant had been fractured for some time prior to removal. Metallographic examination of samples cut from the plate section revealed a series of hidden repair welds on the inside surface of the plate in the vicinity of the fracture. Comparison of the microstructure in the area of the fracture with that in an area away from the weld indicated that the repair welding had resulted in the creation of an annealed, softened zone. Manufacturers should never attempt to salvage this type of critical device by welding or any other procedure that might compromise its integrity.

A cast stainless steel femoral head replacement prosthesis fractured midway down the stem within 13 months of implantation. Visual examination showed severe “orange peel” around the fracture on the concave side. This effect was not observed on the convex side, which suggested fatigue fracture. Metallographic examination of samples revealed an extremely large grain size and corroborated fatigue fracture. Chemical analysis indicated that the material conformed to the requirements for type 316L stainless steel. Substandard-size tensile bars machined from another prosthesis from the same manufacturer showing identical grain sizes were used for mechanical testing. Tensile tests indicated that the material did not meet the manufacturer's stated strength criteria in the portion of the stem that fractured. The failure was attributed to low strength, which resulted in fatigue. The extremely coarse grain size was considered a major factor in strength reduction.

A carbon steel ball-peen hammer ejected a chip that struck the user's eye. Failure occurred when two hammers were struck together during an attempt to free a universal joint from an automotive drive shaft. Two samples were cut from the face of the hammer one through the chipped area on the chamfer and the other from the undamaged area on the chamfer. The shape and texture of the fracture surfaces were typical of spalling. The fracture was conchoidal and exhibited a complete lack of plastic deformation. White etching bands that intersected the face and chamfer were revealed during metallographic examination. Fracture occurred through a white band. Failure was attributed to formation of envelopes of untempered martensite under the chamfer that ruptured explosively during service.

A high-pressure steam pipe specified to be P22 low-alloy steel failed after 25 years of service. Located at the end of the steam line, the pipe reportedly received no steam flow during normal service. Visual examination of the failed pipe section revealed a window fracture that appeared brittle in nature. Specimens from the fracture area and from an area well away from the fracture were examined metallographically and chemically analyzed. Results indicated that the pipe had failed by hydrogen damage that resulted in brittle fracture. Chemical analysis indicated that the pipe material was 1020 carbon steel, not P22. The misapplication of pipe material was considered to be a contributing factor. Position of the pipe within the system caused the localized damage.

A brass (CDA alloy 230) pipe nipple that was part of a domestic cold water bath system failed two weeks after installation. Macrofractography, SEM examination, metallography, and chemical analyses were performed on specimens cut through the main fracture surface. The physical and background evidence obtained indicated failure due to cracking initiated by stamped markings on the pipe wall and extended by high circumferential residual stresses. It was recommended that annealed pipe be used.

Several type 316L stainless steel wires in an electrostatic precipitator at a paper plant fractured in an unexpectedly short time. Failed wires were examined using optical and scanning electron microscope, and hardness tests were conducted. Fractography clearly established that fracture was caused by fatigue originating at corrosion pits on the surface of the wire. It was recommended that higher-molybdenum steel in the annealed condition be used to combat pitting corrosion.

Creep crack growth and fracture toughness tests were performed using test material machined from a seam welded ASTM A-155-66 class 1 (2.25Cr-1Mo) steel steam pipe that had been in service for 15 years. The fracture morphology was examined using SEM fractography. Dimpled fracture was found to be characteristic of fracture toughness specimens. Creep crack growth generally followed the fusion line region and was characterized as dimpled fracture mixed with cavities. These fracture morphologies were similar to those of an actual steam pipe. It was concluded that creep crack growth behavior was the prime failure mechanism of seam-welded steam pipes.