During routine quality control testing, small circuit breakers exhibited high contact resistance and, in some cases, insulation of the contacts by a surface film. The contacts were made of silver-refractory (tungsten or molybdenum) alloys. Infrared analysis revealed the film to be a corrosion layer that resulted from exposure to ammonia in a humid atmosphere. Simulation tests confirmed that ammonia was the corrodent. The ammonia originated from the phenolic molding area of the plant. It was recommended that fumes from molding areas be vented outside the plant and that assembly, storage, and calibration areas be isolated from molding areas.

Electrical contact-finger retainers blanked and formed from annealed copper alloy C65500 (high-silicon bronze A) failed prematurely by cracking while in service in switchgear aboard seagoing vessels. In this service they were sheltered from the weather but subject to indirect exposure to the sea air. About 50% of the contact-finger retainers failed after five to eight months of service aboard ship. Investigation (visual inspection, 250x images etched with equal parts NH4OH and H2O2, emission spectrographic analysis, and stereoscopic views) supported the conclusion that the cracking was produced by stress corrosion as the combined result of: residual forming and service stresses; the concentration of tensile stress at outer square corners of the pierced slots; and preferential corrosive attack along the grain boundaries as a result of high humidity and occasional condensation of moisture containing a fairly high concentration of chlorides (seawater typically contains about 19,000 ppm of dissolved chlorides) and traces of ammonia. Recommendations included redesign of the slots, shot-blasting the formed retainers, and changing the material to a different type of silicon bronze-copper alloy C64700.

An open electrical circuit was found between plated through-holes in a six-layer printed circuit board after thermal cycling. The copper plating was very thin in the failure area but did make an electrical contact during initial testing. During thermal cycling, differential z-expansion between the epoxy board and copper caused the thin plating to crack. During electrical testing of a four-layer circuit board, an open electrical circuit was found between the plated through-holes. Plating discontinuity was caused by poor drilling using a dull drill with improper speed (rpm) and/or feed rate as was observed by nonuniform plating and nodule formation in the plated layer. In a third example, an open electrical circuit was found in a six-layer board between two adjacent plated through-holes. A plating void was on one side of the conductor joining the two holes. Continuity was found when tested from one side of the board but lost when tested from the other. In a fourth case, an open circuit found between a plated through-hole and contact pad on a six-layer printed circuit board was caused by an etching defect.

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.

Three instances involving the failure of aluminum wiring at the service entrance to single-family homes are discussed. Arcing led to a fire which severely damaged a home in one case. In a second, the failure sequence was initiated by water intrusion into the service entrance electrical box during construction of the home. In the third, failure was caused by a marginal installation. Strict adherence to all applicable electrical codes and standards is critical in the case of aluminum wiring. Electrical components not specifically designed for aluminum must never be used with this type of wiring. All doors, panels and similar portions of electrical boxes should be secured to prevent damage to surroundings in the event of an electrical fault. If symptoms of arcing are observed, professional service should be sought. The latest designs of connectors for use with aluminum wiring are less susceptible to deviations in installation practice.

This article reviews the general characteristics of fretting wear in mechanical components with an emphasis on steel. It focuses on the effects of physical variables and the environment on fretting wear. The variables include the amplitude of slip, normal load, frequency of vibration, type of contact and vibration, impact fretting, surface finish, and residual stresses. The form, composition, and role of the debris are briefly discussed. The article also describes the measurement, mechanism, and prevention of fretting wear. It concludes with several examples of failures related to fretting wear.

Rough operation of the roller bearing mounted in an electric motor/gearbox assembly was observed. The bearing components made of low-alloy steel (4620 or 8620) and the cup, cone and rollers were carburized, hardened and tempered. The contact surfaces of these components (cup, cone and roller) were revealed to be uniformly electrolytically etched by visual examination. The action similar to anodic etching was believed to have occurred as a result of stray currents in the electric motor (not properly grounded) and the presence of an electrolyte (moisture) between the cup and roller surfaces of the bearing. As a remedial action, the bearing was insulated for protection from stray currents by grounding of the motor and the moisture was kept out by sealing both bearings in the assembly.

Problems with materials compatibility were encountered in pyrotechnically driven devices used in a number of ordnance applications requiring rapid mechanical actuation. A fine bridgewire is located in contact with the chemical pyrotechnic, and the charge is ignited by electrical heating of the bridgewire. Evidence of severe corrosion was revealed on examination of the nickel-chromium-iron alloy bridgewire and the nickel-iron alloy pins. Metallic elements in the pin or bridgewire and substantial amounts of chlorine were detected from the x-ray spectra. Morphological changes indicative of decomposition and dissolution were revealed to have occurred in regions of the pyrotechnic that had been in contact with the bridgewire and pin surfaces by examination of the titanium-potassium perchlorate (Ti-K-Cl-O4) pyrotechnic. Substantial amounts of water were revealed to be associated with the surfaces of the titanium particles in the pyrotechnic by nuclear magnetic resonance. It was proposed that the chlorine-containing residue combined with the water from the pyrotechnic to form a thin aqueous film corroding the bridgewire and pins. A new cleaning procedure was implemented for the glass headers to eliminate the chloride contamination and a vacuum drying procedure was instituted for the pyrotechnic.

A housing used in conjunction with an electrical switch failed shortly after being placed into service. A relatively high failure rate had been encountered, corresponding to a recent production lot of the housings, and the failed part was representative of the problem. The housing had been injection molded from a commercially available, medium-viscosity grade of PC, formulated with an ultraviolet stabilizer. In addition to the PC housing, the design of the switch included an external protective zinc component installed with a snap-fit and two retained copper press-fit contact inserts. Investigation supported the conclusion that the switch housings failed via brittle fracture, likely through a creep mechanism. The failure was caused by severe embrittlement of the housing resin associated with massive molecular degradation produced during the molding process. A potential contributing factor was the design of the part, which produced significant interference stresses between the contact and a mating retaining tab.

The operator of an electric transit system purchased a large number of tin-plated copper connectors, putting some in service and others in reserve. Later, when some of the reserve connectors were inspected, the metal surfaces were covered with spots consisting of an ash-like powder and the plating material had separated from the substrate in many areas. Several connectors, including some that had been in service, were examined to determine what caused the change. The order stated that the connectors were to be coated with a layer of tin-bismuth (2% Bi) to guard against tin pest, a type of degradation that occurs at low temperatures. Based on the results of the investigation, which included SEM/EDS analysis, inductively coupled plasma spectroscopy, and x-ray diffraction, the metal surfaces contained less than 0.1% Bi and thus were not adequately protected against tin pest, which was confirmed as the failure mechanism in the investigation.

A tri-lobe cylindrical roller bearing was submitted for investigation to determine the cause of uniformly spaced axial fluting damages on its rollers and outer raceway surfaces. The rollers and raceways were made from premium-melted M50 and M50NiL, aircraft quality steels often used in bearings to minimize the effects of orbital slippage and rolling-contact fatigue. The damaged areas were examined under a scanning electron microscope, which revealed a high density of microcraters, characteristic of local melting and material removal associated with bearing currents. Investigators also examined the effect of electrical discharge on crater dimensions and density and the role that thermoelectric voltage potentials may have played.

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.

Wire ropes, pulleys, counterweights, and connecting systems are used for auto tensioning of contact wires of electric railways. A wire rope in one such auto tensioning system suffered premature failure. Failure investigation revealed fatigue cracks initiating at nonmetallic inclusions near the surface of individual wire strands in the rope. The inclusions were identified as Al-Ca-Ti silicates in a large number of stringers, and some oxide and nitride inclusions were also found. The wire used in the rope did not conform to the composition specified for AISI 316 grade steel, nor did it satisfy the minimum tensile strength requirements. Failure of the wire rope was found to be due to fatigue; however, the ultimate fracture of the rope was the result of overload that occurred after fatigue failure had reduced the number of wire strands supporting the load.

Rolling-element bearings use rolling elements interposed between two raceways, and relative motion is permitted by the rotation of these elements. This article presents an overview of bearing materials, bearing-load ratings, and an examination of failed bearings. Rolling-element bearings are designed on the principle of rolling contact rather than sliding contact; frictional effects, although low, are not negligible, and lubrication is essential. The article lists the typical characteristics and causes of several types of failures. It describes failure by wear, failure by fretting, failure by corrosion, failure by plastic flow, failure by rolling-contact fatigue, and failure by damage. The article discusses the effects of fabrication practices, heat treatment and hardness of bearing components, and lubrication of rolling-element bearings with a few examples.

A cadmium-plated music-wire return spring that operated in a pneumatic cylinder designed for infinite life at a maximum stress level of 620 MPa failed after 240,000 cycles. An extremely hard and small kernel, which looked like a weld deposit, was observed at the center of the fractured surface. The kernel was assumed to have resulted from extreme localized overheating. These springs were reported to have been barrel electroplated after fabrication. The intermittent contact with the dangler (suspended cathode contact) as the barrel rotated allowed high local currents when the last contact was broken was revealed to have resulted in an arc that caused local melting of the metal being plated. The molten metal was interpreted to have been quenched instantly by the plating solution and by the mass of the cold metal of the spring. The hard spot caused by arcing during plating was concluded to be the reason of the fatigue failure. Rack plating or barrels with fixed button contacts at many points instead of dangler-type contacts were recommended to avoid hard spots.

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.

Ball bearings made of type 440C stainless steel hardened to 60 HRC and suspected as the source of intermittent noise in an office machine were examined. A number of spots on the inner-ring raceway were revealed by scanning electron microscopy. The metal in the area around the spot was evidenced to have been melted and welded to the inner-ring raceway. It was revealed by randomly spaced welded areas on the raceways that the welding was the result of short electrical discharges between the bearing raceways and the balls. The use of an electrically nonconductive lubricant in the bearings was suspected to have caused the electric discharge by accumulation and discharge of static charge. The electrical resistance between the rotor and the motor frame lubricated with electrically conductive grease and the grease used in the current case was measured and compared to confirm the fact the currently used grease was nonconductive. It was concluded that the pits were formed by momentary welding between the ball and ring surfaces. The lubricant was replaced by electrically conductive grease as a corrective measure.

This article is dedicated to the fields of mechanical engineering and machine design. It also intends to give a nonexhaustive view of the preventive side of the failure analysis of rolling-element bearings (REBs) and of some of the developments in terms of materials and surface engineering. The article presents the nomenclature, numbering systems, and worldwide market of REBs as well as provides description of REBs as high-tech machine components. It discusses heat treatments, performance, and properties of bearing materials. The processes involved in the examination of failed bearings are also explained. Finally, the article discusses in detail the characteristics and prevention of the various types of failures of REBs: wear, fretting, corrosion, plastic flow, rolling-contact fatigue, and damage. The article includes an Appendix, which lists REB-related abbreviations, association websites, and ISO standards.

At a power plant, C-276 nickel alloy welds (N10276) on a C-276 duct floor completely disappeared in less than half a year. A continuous supply of flue gas came in contact with the closed bypass duct. The unscrubbed combustion products condensed on the cold duct, then the closed damper conducted heat from the chimney and reheated the condensate. Investigation (visual inspection and welded coupon testing) supported the conclusion that the corrosion was caused by “Green Death,” a corrosive medium used to test for pitting resistance (11.9% H2SO4 + 1.3% HCl + 1% FeCl3 + 1% CuCl2) at 103 deg C (217 deg F). Such conditions exist at power plants. Recommendations included repairing the C-276 plates with a 686CPT weld alloy, and if that did not correct the situation, replacing the plates with 686 plate (N06686) welded with 686 CPT.