The purpose of this investigation was to determine the cause of the ultrasonic signal attenuation noted during an inspection of a composite aircraft component. Although ultrasonics was able to identify the location of the defective areas, destructive analysis had to be utilized to determine the exact nature of the defect. The investigation describes how cross-sectioning, fractography, and chemical analysis were utilized to determine the type of defect responsible for the signal attenuation.

The paper discusses the analysis of a coating defect on a high phosphorus electroless nickel (Ni-11 wt. % P) deposit plated on an aluminum alloy substrate. Preliminary investigations had indicated that the elongated defects were possibly caused by the entrapment of long fibers or particles during the plating. The possible sources of fibers were identified. The SEM/EDS analysis of fibers collected from the air duct filters correlated very well with the defect shape and the EDS profile collected from under the defect site. It appears that the fibers from air duct filters directly above the plating line were blown into the plating tank and getting co-deposited. The paper describes the step-by-step analysis of the defect that led to successful identification of the root cause of the defect.

A component of a water filtration unit failed while being used in service for approximately eight months. The filter system had been installed in a commercial laboratory, where it was stated to have been used exclusively in conjunction with deionized water. The failed part had been injection molded from a 30% glass-fiber and mineral-reinforced nylon 12 resin. Investigation, including visual inspection, 118x SEM images, 9x micrographs, energy-dispersive x-ray spectroscopy, micro-FTIR in the ATR mode, and TGA, supported the conclusion that the filter component failed as a result of molecular degradation caused by the service conditions. Specifically, the part material had undergone severe chemical attack, including oxidation and hydrolysis, through contact with silver chloride. The source of the silver chloride was not established, but one potential source was photographic silver recovery.

A number of plastic sleeves used in an automotive application cracked after assembly but prior to installation into the mating components. The sleeves were specified to be injection molded from a 20% glass-fiber-reinforced polybutylene terephthalate (PBT) resin. After molding, electronic components are inserted into the sleeves, and the assembly is filled with a potting compound. Investigation of the cracked parts and some reference parts available for testing included visual inspection, micro-FTIR in the ATR mode, and analysis using DSC. Subtle spectrum differences suggested degradation of the failed part material, and the thermograms supported this. The conclusion was that the failed sleeves had cracked due to embrittlement associated with severe degradation and the corresponding molecular weight reduction. The reduction in molecular weight significantly reduced the mechanical properties of the sleeves. The cause of the degradation was not evident, but the likely source appears to be the molding operation and exposure to elevated temperature for an extended period of time.

Argonne National Laboratory has conducted analyses of failed components from nuclear power-generating stations since 1974. The considerations involved in working with and analyzing radioactive components are reviewed here, and the decontamination of these components is discussed. Analyses of four failed components from nuclear plants are then described to illustrate the kinds of failures seen in service. The failures discussed are (1) intergranular stress-corrosion cracking of core spray injection piping in a boiling water reactor, (2) failure of canopy seal welds in adapter tube assemblies in the control rod drive head of a pressurized water reactor, (3) thermal fatigue of a recirculation pump shaft in a boiling water reactor, and (4) failure of pump seal wear rings by nickel leaching in a boiling water reactor.

Two silica phenolic nozzle liners cracked during proof testing. The test consisted of pressuring the nozzles to 14.1 MPa (2050 psia) for 5 to 20 s. It was concluded that the failure was due to longitudinal cracking in the convergent exhaust-nozzle insulators, stemming from the use of silica phenolic tape produced from flawed materials that went undetected by the quality control tests, which at the time, assessed tape strength properties in the warp rather than the bias direction. Once the nozzle manufacturer and its suppliers identified the problem, they changed their quality control procedures and resumed production of nozzle liners with more tightly controlled fiber/fabric materials.

Molded plastic couplings used in an industrial application exhibited abnormally brittle properties, as compared to previously produced components. The couplings were specified to be molded from a custom-compounded glass-filled nylon 6/12 resin. An inspection of the molding resin used to produce the discrepant parts revealed that the pellets were of two general types, neither of which matched the pellets from a retained resin lot. Investigation included visual inspection, micro-FTIR in the ATR mode, and analysis using DSC. The thermograms supported the conclusion that the brittle couplings contained a significant level of contamination, polypropylene and nylon 6/6. The source of the polypropylene was likely the purging compound used to clean the compounding extruder. The origin of the nylon 6/6 resin was unknown but may represent a previously compounded resin.

A production lot of mechanical hinges used in an automotive application had failed during incoming quality-control routine actuation testing. A change in part supplier had taken place between the approval of the prototype parts that performed acceptably and the receipt of the first lot of production parts. The mechanical hinges were specified to be injection molded from an impact-modified, 13% glass-fiber-reinforced nylon 6/6 resin. Investigation of samples representing the failed components and the original prototype parts included visual inspection, 118x SEM images, micro-FTIR, DSC analysis, and TGA. It supported the conclusion that the hinge assemblies failed through brittle fracture associated with stress overload during the actuation of the parts. The failed part material was found to be degraded, most likely occurring during the compounding of the resin or during the actual molding of the parts. While resins for both failed and non-failed parts produced results characteristic of a 13% glass-fiber-reinforced, impact-modified nylon 6/6, the failed part material, contained a significantly lower level of rubber, which rendered the parts less impact resistant and subsequently lowered the ductility of the molded hinge assemblies. No recommendations were made.

This article focuses primarily on what an analyst should know about applying X-ray diffraction (XRD) residual stress measurement techniques to failure analysis. Discussions are extended to the description of ways in which XRD can be applied to the characterization of residual stresses in a component or assembly. The article describes the steps required to calibrate instrumentation and to validate stress measurement results. It presents a practical approach to sample selection and specimen preparation, measurement location selection, and measurement depth selection, as well as an outline on measurement validation. The article also provides information on stress-corrosion cracking and corrosion fatigue. The importance of residual stress in fatigue is described with examples. The article explains the effects of heat treatment and manufacturing processes on residual stress. It concludes with a section on the XRD stress measurements in multiphase materials and composites and in locations of stress concentration.

This article commences with a summary of fatigue processes and mechanisms. It focuses on fractography of fatigue. Characteristic fatigue fracture features that can be discerned visually or under low magnification are described. Typical microscopic features observed on structural metals are presented subsequently, followed by a brief discussion of fatigue in nonmetals. The article reviews the various macroscopic and microscopic features to characterize the history and growth rate of fatigue in metals. It concludes with a description of fatigue of polymers and composites.

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 reviews the abrasive and adhesive wear failure of several types of reinforced polymers, including particulate-reinforced polymers, short-fiber reinforced polymers (SFRP), continuous unidirectional fiber reinforced polymers (FRP), particulate-filled composites, mixed composites (SFRP and particulate-filled), unidirectional FRP composites, and fabric reinforced composites. Friction and wear performance of the composites, correlation of performance with various materials properties, and studies on wear-of failure mechanisms by scanning electron microscopy are discussed for each of these types.

This article discusses the effect of using unsuitable alloys, metallurgical discontinuities, fabrication practices, and stress raisers on the failure of a pressure vessel. It provides information on pressure vessels made of composite materials and their welding practices. The article explains the failure of pressure vessels with emphasis on stress-corrosion cracking, hydrogen embrittlement, brittle and ductile fractures, creep and stress rupture, and fatigue with examples.

Chemical analysis is a critical part of any failure investigation. With the right planning and proper analytical equipment, a myriad of information can be obtained from a sample. This article presents a high-level introduction to techniques often used for chemical analysis during failure analysis. It describes the general considerations for bulk and microscale chemical analysis in failure analysis, the most effective techniques to use for organic or inorganic materials, and examples of using these techniques. The article discusses the processes involved in the chemical analysis of nonmetallics. Advances in chemical analysis methods for failure analysis are also covered.

Failure analysis results were employed to identify a better alloy. Chipper knives used in the field to chip logs failed frequently. The knives were made of alloys with a composition of Fe-0.48C-0.30Mn-0.90Si-8.50Cr-1.35Mo-1.20W-0.30V. The development of tougher alloy steel with superior properties was initiated. The nominal composition of Fe-0.50C-0.30Mn-0.40Si-5.00Cr-2.00Mo was developed which achieved the goals of edge retention, resistance to softening under frictional heating, wear resistance, ease of heat treatment, dimensional stability in heat treatment, grindability, and low alloy cost. A chip harvester made from this composition was tested in field with older composition knives. It was found that the new knives outperformed the older knives. The key to the development was interpreted to be careful study of a number of failed knives with different problems used in different types of operations.

An electron probe microanalyzer was applied to the study of service failures (due to severe heating) of aluminum wire connections in residential electrical circuits. Perturbed regions in which the composition underwent a change during the failure were revealed by optical and scanning electron microscopy of the contacts. A sequence of iron-aluminum compositions that shift from the pure aluminum of the wire to the nearly pure iron of the screw was revealed by analyses of two distinct layers formed on the aluminum/iron region. The compositions were found to correspond to specific intermetallic compounds found in the aluminum-iron phase diagram. Similar compositional variations were noted at the aluminum/brass interface. It was concluded that the failure of the electrical junction due to extreme heating was related to the formation of intermetallic compounds at the current carrying interfaces. These intermetallics were established to have a high resistance causing significant resistive heating.

Stainless steel bolts broke after short-term exposure in boiler feed-pump applications. Specifications required that the bolts be made of a 12% Cr high-strength steel with a composition conforming to that of AISI type 410 stainless steel. Several bolts from three different installations were examined. It was found that fracture of the bolts was by intergranular stress corrosion. A metallic copper-containing antiseizure compound on the bolts in a corrosive medium set up an electro-chemical cell that produced trenchlike fissures or pits for fracture initiation. Because the bolts were not subjected to cyclic loading, fatigue or corrosion fatigue was not possible. To prevent reoccurrence, bolts were required to conform to the specified chemical composition. The hardness range for the bolts was changed from 35 to 45 HRC to 18 to 24 HRC. Petroleum jelly was used as an antiseizure lubricant in place of the copper-containing compound. As a result of these changes, bolt life was increased to more than three years.

A cast steel bracket manufactured in accordance with ASTM A 148 grade 135/125 steel failed in railroad maintenance service. Ancillary property requirements included a 285 to 331 HB hardness range and minimum impact energy of 27 J (20 ft·lbf) at -40 deg C (-40 deg F). The conditions at the time of failure were characterized as relatively cold. Investigation (visual inspection, chemical analysis, and unetched 119x and 2% nital etched 119x SEM images) supported the conclusion that the bracket failed through brittle overload fracture due to a number of synergistic factors. The quenched-and-tempered microstructure contained solidification shrinkage, inherently poor ductility, and type II Mn-S inclusions that are known to reduce ductility. The macro and microscale fracture features confirmed that the casting was likely in low-temperature service at the time of failure. The composition and mechanical properties of the casting did not satisfy the design requirements. Recommendations included exerting better composition control, primarily with regard to melting, deoxidation, and nitrogen control. Better deoxidation practice was recommended to generate the more desirable Mn-S inclusion morphology, and reevaluation of the casting design was suggested to minimize shrinkage.

A sledge hammer chipped during use. The chip struck a by stander in the eye, leading to its loss. The hammerhead surface was examined visually, nondestructively (magnetic particle method), and stereo microscopically, and a microstructural analysis of a cross section of the head was conducted using optical microscope. Chemical composition of the hammerhead was determined by emission spectrometry. The chemical compositions of the chip and hammer head were compared using energy-dispersive analysis. Microhardness versus distance from the striking face was also determined. The hammerhead material was UNS G10800 (AISI/SAE grade 1080). Excessive hardnesses were measured in the first 3 mm (0. 12 in.) below the striking surface, indicating that there was lack of control during the final tempering operation.

An air blower in an electric power plant failed unexpectedly when a roller bearing in the drive motor fractured along its outer ring. Both rings, as well as the 18 rolling elements, were made from GCr15 bearing steel. The bearing also included a machined brass (MA/C3) cage and was packed with molybdenum disulfide (MoS 2 ) lithium grease. Metallurgical structures and chemical compositions of the bearing’s matrix materials were inspected using a microscope and photoelectric direct reading spectrometer. SEM/EDS was used to examine the local morphology and composition of fracture and contact surfaces. Chemical and thermal properties of the bearing grease were also examined. The investigation revealed that the failure was caused by wear due to dry friction and impact, both of which worsened as a result of high-temperature degradation of the bearing grease. Fatigue cracks initiated in the corners of the outer ring and grew large enough for a fracture to occur.