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Static electricity
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Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.mech.c0047935
EISBN: 978-1-62708-225-9
... 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...
Abstract
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.
Image
in Pitting Failure of Ball Bearings in an Electric Motor by Static Electrical Discharges
> ASM Failure Analysis Case Histories: Mechanical and Machine Components
Published: 01 June 2019
Fig. 1 Weld spots on contact surfaces of a type 440C stainless steel ball bearing. The spots are caused by static electrical discharges resulting from use of an electrically nonconductive grease. (a) and (b) Photographs of inner-raceway surface. 10 and 100×, respectively. (c) and (d) SEM
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Image
in Failures of Rolling-Element Bearings and Their Prevention
> Analysis and Prevention of Component and Equipment Failures
Published: 30 August 2021
Fig. 33 Weld spots on contact surfaces of a type 440C (X90CrMoV18 or WN 1.4112) stainless steel ball bearing. The spots are caused by static electrical discharges resulting from the use of an electrically nonconductive grease. (a, b) Photographs of inner-raceway surface. Original magnification
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Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001076
EISBN: 978-1-62708-214-3
... system at appropriate locations were recommended. Electrostatic fields Gas pipelines Static electricity Thrust bearings Turbogenerators Silver (Other, miscellaneous, or unspecified) failure Background The silver layer on a thrust bearing face in a power turbine experienced...
Abstract
The silver layer on a thrust bearing face experienced electrostatic discharge attack (the bombardment of an in-line series of individual sparks onto the soft bearing face), which destroyed the integrity of the bearing surface. The electrical attack appeared as scratches to the naked eye. Macrophotography showed that the attack was more severe at one edge of each pad, resulting in deeper grooving and a buildup of deposits, mostly silver sulfides. Microstructural analysis of a cross section indicated that the interface between the silver overlay and the substrate (beryllium copper) was sound and free of voids and foreign material. Corrosion products contained a large quantity of sulfur. The probable cause of the attack was the presence of electrical current within the system, with sulfides a possible contributing factor. Elimination of residual magnetism and grounding of the rotating system at appropriate locations were recommended.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.usage.c9001499
EISBN: 978-1-62708-236-5
... of the gears were found to be pitted, one low on profile and the adjacent tooth high on profile. The mating gear had a similar characteristic, two adjacent teeth with evidence of pitting and the same difference in profile. It was correctly deduced that the pitting occurred because the gears were in a static...
Abstract
Three spur gears made from 8622 Ni-Cr-Mo alloy steel formed a straight-line train in a speed reducer on a rail-mounted overslung lumber carrier. The gears were submitted for nondestructive examination and evaluation, with no accompanying information or report. Two teeth on one of the gears were found to be pitted, one low on profile and the adjacent tooth high on profile. The mating gear had a similar characteristic, two adjacent teeth with evidence of pitting and the same difference in profile. It was correctly deduced that the pitting occurred because the gears were in a static position under a reverberating load for an extended period of time.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c0046146
EISBN: 978-1-62708-217-4
.... A fracture on the opposite side of the lug (Secondary fracture, Detail A, Fig. 1 ) appeared to be typical for a static overload failure. A section was taken normal to the fracture surface and in the region contacted by the bushing flange, and was prepared for metallographic examination. Results showed...
Abstract
The torque-arm assembly (aluminum alloy 7075-T73) for an aircraft nose landing gear failed after 22,779 simulated flights. The part, made from an aluminum alloy 7075-T73 forging, had an expected life of 100,000 simulated flights. Initial study of the fracture surfaces indicated that the primary fracture initiated from multiple origins on both sides of a lubrication hole that extended from the outer surface to the bore of a lug in two cadmium-plated flanged bushings made of copper alloy C63000 (aluminum bronze) that were press-fitted into each bored hole in the lug. Sectioning and 2x metallographic analysis showed small fatigue-type cracks in the hole adjacent to the origin of primary fracture. Hardness and electrical conductivity were typical for aluminum alloy 7075. This evidence supported the conclusion that the arm failed in fatigue cracking that initiated on each side of the lubrication hole since no material defects were found at the failure origin. Recommendations included redesign of the lubrication hole, shot peeing of the faces of the lug for added resistance to fatigue failure, and changing of the forging material to aluminum alloy 7175-T736 for its higher mechanical properties.
Series: ASM Handbook
Volume: 11A
Publisher: ASM International
Published: 30 August 2021
DOI: 10.31399/asm.hb.v11A.a0006834
EISBN: 978-1-62708-329-4
... depth. (b) Induction hardening. SHD, surface-hardness depth. Source: Ref 1 , 2 For materials that would not reach those hardness levels after heat treatment, the following correction factors for the static ( C 0 ) and dynamic ( C ) load-carrying capacities may be used ( Fig. 5 ). Fig. 5...
Abstract
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.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.homegoods.c0090448
EISBN: 978-1-62708-222-8
... conversion. Parts produced from the previous material, a nylon 6/6 resin, had consistently passed the testing regimen. The housing assembly included a spring clip, which applied a static force on a molded-in boss extending from the main body of the housing. Grease was applied liberally within the housing...
Abstract
Housings (being tested as part of a material conversion) from an electrical appliance failed during an engineering evaluation. They had been injection molded from a commercial polycarbonate/PET blend. Parts produced from the previous material, a nylon 6/6 resin, had consistently passed the testing regimen. Grease was applied liberally within the housing assembly during production. Investigation included visual inspection, 24x SEM images, micro-FTIR in the ATR mode, and analysis using DSC. No signs of material contamination were found, but the thermograms showed a crystallization of the PET resin. The grease present within the housing assembly, analyzed using micro-FTIR, was composed of a hydrocarbon-based oil, a phthalate-based oil, lithium stearate, and an amide-based additive. The conclusion was that the appliance housings failed through environmental stress cracking caused by a phthalate-based oil that was not compatible with the PC portion of the resin blend. Thus, the resin conversion was the root cause of the failures. Additionally, during the injection molding process the molded parts had been undercrystallized, reducing their mechanical strength. More importantly, the resin had been degraded, producing a reduction in the molecular weight and reducing both the mechanical integrity and chemical-resistance properties of the parts.
Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001815
EISBN: 978-1-62708-241-9
... throughout the structure, which was not the case. Standard bend tests for evaluation of HE in coppers, per ASTM B 577, were conducted on samples machined from service-failed pins, and all samples passed. A static load test was also performed on a sample machined from a service-failed pin, similar to ASTM F...
Abstract
Copper electrical feedthrough pins used in a bolting application in a refrigeration compressor had functioned without failure for years of production and thousands of units. When some of the pins began to fail, an investigation was conducted to determine the cause. Visual examination revealed that the observed fractures were mixed brittle intergranular with ductile microvoid dimples. An extensive analysis of failed samples combined with a process of elimination indicated that the fractures were due to stress-corrosion cracking caused by an unidentified chemical species within the sealed compressor chamber. A unique combination of applied stress, residual stress, stress riser, and grain size helped isolate the failure mechanism to a single production lot of material.
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0001810
EISBN: 978-1-62708-180-1
... example, use of an electrically non-conductive grease prevented proper grounding. Example 1: Pitting Failure of Ball Bearings in an Electric Motor by Static Electrical Discharges The electric motor in an office machine was producing intermittent noise. Ball bearings were suspected as the source...
Abstract
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.
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0001820
EISBN: 978-1-62708-180-1
... length. The fatigue cracks had been produced during rail shipment of the pipe as a result of the combination of static stresses produced in the lower layers of stacked pipe by the static weight of the pipe above and cyclic stresses produced by the vertical acceleration of the rail car. When...
Abstract
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.
Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001778
EISBN: 978-1-62708-241-9
... from a 53 mm locked coil track rope. Optical microscopy of failed round wires in the 53 mm diameter rope clearly revealed fully decarburized layers at the surface and a few grain-boundary cracks. From the location of the failure, it was clear that apart from static tensile loads, the wire ropes had...
Abstract
A locked coil track rope (LCTR) is essentially composed of wires (round and rail-shaped) laid helically in different layers. These wire ropes are sometimes used in conveyors carrying empty and loaded buckets in mining areas. During service, such wire ropes may fail prematurely due to disintegration/failure of individual groups of wires. To understand the genesis of LCTR wire failures, a detailed metallurgical investigation of failed rope wires was made and included visual examination, optical microscopy, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). Two types of failed wires were investigated; one is from a 40 mm diameter locked coil track rope and the other from a 53 mm locked coil track rope. Optical microscopy of failed round wires in the 53 mm diameter rope clearly revealed fully decarburized layers at the surface and a few grain-boundary cracks. From the location of the failure, it was clear that apart from static tensile loads, the wire ropes had been subjected to bending and unbending loads near the saddle, as fully loaded or empty buckets traveled access the conveyor. The SEM studies confirmed that the fracture had been caused by initiation of fatigue cracks in the decarburized zone under conditions of repeated bending and unbending stresses superimposed on the static tensile load.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.petrol.c9001603
EISBN: 978-1-62708-228-0
... 10 (PA 370) specification and tested on a 10 ton static universal testing machine (Instron-1195 model, Instron Ltd., High Wycombe Bucks, UK) at a strain rate of 6.6 × 10 −4 /s. Standard Charpy V-notch samples were prepared and tested at 0 °C for Charpy impact energy (CIE). The temperature rise during...
Abstract
The genesis of failure of 6.1 mm thick electric resistance welded API 5L X-46 pipes during pretesting at a pressure equivalent to 90% of specified minimum yield strength was investigated. Cracks were found to initiate on the outer surface of the pipes in the fusion zone and propagate along the through-thickness direction. The presence of extensive decarburization and formation of a soft ferrite band within the fusion zone may have contributed to the nucleation of the cracks. Crack propagation was aided by the presence of exogenous inclusions entrapped within the fusion zone. Analysis of these inclusions confirmed the presence of Fe, Si, Ca, and O, indicating slag entrapment to be the most probable culprit.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.usage.c9001430
EISBN: 978-1-62708-236-5
... opportunity. An alternative method of reclamation, and in many cases a preferable one, employs the technique of metal spraying and although a sprayed metal layer contributes little to the static strength of a built-up shaft, it does not result in severe deterioration in fatigue properties as does the method...
Abstract
An intermediate shaft (3 in. diam), part of a camshaft drive on a large diesel engine, broke after two weeks of service. Failure occurred at the end of the taper portion adjacent to the screwed thread. The irregular saw-tooth form of fracture was characteristic of failure from torsional fatigue. A second shaft carried as spare gear was fitted and failure took place in a similar manner in about the same period of time. Examination revealed that the tapered portion of the Fe-0.6C carbon steel shaft had been built up by welding prior to final machining. A detailed check by the engine-builder established that the manufacture of these two shafts had been subcontracted. It was ascertained that the taper portions had been machined to an incorrect angle and then subsequently built-up and remachined to the correct taper. The reduction in fatigue endurance following welding was due to heat-affected zone cracking, residual stresses, the lower fatigue strength of the weld deposited metal, and weld defects.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c9001459
EISBN: 978-1-62708-234-1
... that the total number of stress cycles imposed in the course of the working life was comparatively small. The early engineers were concerned primarily with “static” stresses and interested themselves particularly in the 99 static” mechanical properties of materials, of which the tensile test came to be regarded...
Abstract
Fundamentals of fatigue failure are outlined. Addressed are fatigue crack characteristics, basic crack types, unidirectional bending, alternate bending, rotary bending, torsion, direct stress, and combined stress. Stress cycle, endurance limits, under and overstressing, stress concentration, and surface condition are discussed. Sections are devoted to fatigue crack assessment, corrosion relation to fatigue failure, and the micro-mechanisms of fatigue failure. Materials considered include steels. Photographs of service failures are used to illustrate features alluded to in the text.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001676
EISBN: 978-1-62708-229-7
... (contained in a Zircaloy-2 guide tube). There are two types of fully encapsulated assemblies: (i) sealed but having a He feed - the system can be permanently flushed with He or periodically purged leaving a static He atmosphere between purges; or, (ii) permanently sealed at the time of manufacture...
Abstract
The self-powered flux detectors used in some nuclear reactors are Pt or V-cored co-axial cables with MgO as an insulator and Inconel 600 as the outer sheath material. The detectors are designed to operate in a He atmosphere; to maximize the conduction of heat (generated from the interaction with gamma radiation) and to prevent corrosion. A number of failures have occurred over the years because of a loss of the He cover gas in the assembly. This has resulted in either acid attack on the Inconel 600 sheath in a wet environment or gaseous corrosion in a dry environment. In the latter case, nitriding and embrittlement occurred at temperatures as low as 300 to 400 deg C (determined from an examination of the oxidation of the Zircaloy-2 carrier rod on which the detectors were mounted). Recent results are described and discussed in terms of the oxidation and nitriding kinetics of Zircaloy-2 and Inconel 600, respectively.
Book Chapter
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0003562
EISBN: 978-1-62708-180-1
... is termed fretting fatigue , or contact fatigue . Fatigue cracks also may initiate where the contacting surfaces are under a very heavy normal load or where there is a static tensile stress in one of the surfaces. There are cases where the movement is not simply tangential but is complicated by the normal...
Abstract
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.
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0001812
EISBN: 978-1-62708-180-1
... of these requirements is necessary before a satisfactory fastener can be selected. The selection of the correct fastener or fastener system may simply involve satisfying a requirement for strength (static or fatigue) or for corrosion resistance. On the other hand, selection may be dictated by a complex system...
Abstract
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.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.mech.c9001721
EISBN: 978-1-62708-225-9
... is static and tensile in nature. The propagation of a SCC crack can be either transgranular or intergranular. In transgranular SCC, the cracks propagate across the grains usually in a specific or preferred crystal plane of low indices (i.e. {100}, {110}, etc.). 1 SCC occurring in a transgranular type mode...
Abstract
Diagnosis of environmentally induced failures is greatly facilitated by metallographic analysis. As an example, a failure analysis of ASTM A574 material grade bolts is presented. The bolts served as bonnet screws in underground valves and failed due to stress-corrosion cracking. Metallographic methods were used to diagnose and provide solutions for the service failure. Included are photos showing crack propagation morphology and fracture surface appearance.
Series: ASM Handbook
Volume: 11A
Publisher: ASM International
Published: 30 August 2021
DOI: 10.31399/asm.hb.v11A.a0006805
EISBN: 978-1-62708-329-4
... system may simply involve satisfying a requirement for strength (static or fatigue) or for corrosion resistance. On the other hand, selection may be dictated by a complex system of specification and qualification controls. The extent and complexity of the system needed is usually dictated by the probable...
Abstract
This article first provides an overview of the types of mechanical fasteners. This is followed by sections providing information on fastener quality and counterfeit fasteners, as well as fastener loads. Then, the article discusses common causes of fastener failures, namely environmental effects, manufacturing discrepancies, improper use, or incorrect installation. Next, it describes fastener failure origins and fretting. Types of corrosion in threaded fasteners and their preventive measures are then covered. The performance of fasteners at elevated temperatures is addressed. Further, the article discusses the types of rivet, blind fastener, and pin fastener failures. Finally, it provides information on the mechanism of fastener failures in composites.
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