EDAX showed that the slivers recovered from the grease had the same composition (Fe-Cr-Ni alloy) as that of the bearing race-way material or the bearing ball material. The spherical particles sticking to the craters had the same composition as that of the parent metal.
Fig. CH55.1 Failed bearing
Fig. CH55.2 The bearing in the dismantled condition showing the inner and outer ring raceways, the split cage, and the bearing balls
DOI:10.1361/faes2005p197 www.asminternational.org
Discussion
The presence of burned craters on the inner ring raceway and the ball surfaces is typical of electrical arcing with local melting of the metal. Due to the heat of the arc, the metal melts and is pulled apart by the force of rotation of the balls and the inner raceway. This can lead to bruising of the raceway with continued operation. Electrical pitting is produced by the passage of current between two surfaces. In applications such as electric motor, there is a possibility of the current passing through the bearings. When the current is broken at the contact surfaces between raceways and rolling elements, arcing or sparking occurs, producing high tem-peratures and localized damage.
It is known that electrical discharges result from the use of an electrically nonconductive lubricant in the bearings, which permits a static charge to be accumulated and discharged. In this case, the lubricant grease used was tested by measuring the resistance across two copper plates with the grease as the separator, and it was found that the grease was a poor conductor of electricity.
Conclusion
The bearing failed because of electrical pitting of the inner race-way and the ball bearing due to static discharge and consequent melting and detachment of metal particles. The detached metal particles would have caused further damage leading to seizure of the bearing. Use of a nonconductive lubricant is a probable cause for the electrical discharge.
Recommendation
Replacement of the lubricant by an electrically conductive grease would permit proper grounding of the rotor and eliminate welding between the balls and the raceways.
Fig. CH55.3 Craters and metal bruising seen on the inner ring raceway
Fig. CH55.4 Craters seen on one of the bearing balls
5
Fig. CH55.5 Spherical metal particles sticking to the craters Fig. CH55.6 Detached metal particles having worked into the inner ring raceway
Index
Kanishka, VT-EFO, 3, 45, 49, 57 Kasmir Princess, 45
Aircraft
accident mitigation, wing blisters, 54 accidents
Air India
Kanishka, VT-EFO, 3, 45, 49, 57 Kashmir Princess, 45
Aloha Airlines, 35
Indian Airlines, VT-ECR, 45, 48
aileron control cable failure, 90–91, 152–153 assembly errors, 13(F), 14–15
center support bearing failure, 95–96 compressor blade failure
compressor disk fracture, 57, 59 compressor rotor failure, 115–117 cylinder cooling fin, 172
dowel bolt failure, 102–106, 102–106(F), 104(T) electronic pod adapter failure, 76–77
elevator hinge pin failure, 113–114 exfoliation corrosion, 17
explosive sabotage, 45–51, 55 explosives, placing on, 60 filter components, 165–167 fuel nozzle failure, 126–127 fuel pump failure, 74–75, 92–94 gear system failure, 177–179 nose bullet, 160, 161(F)
quill shaft failure, 122–123, 148, 149(F) retraction jack support beam, 180–181 security and sensors, 60
shutter bolt failure, 130–132 stabilizer link rod, 78–79 throttle end fitting failure, 65–66 tie-rod failure, 80–81
torque sensor bearing failure, 97–99 turbine blades
aircraft engine, 87–89
foreign object damage, 16 (F), 17 high-pressure, 138, 139–140(F)
low-pressure turbine rotor (LPTR), 67–69, 67–69(F) second-stage, 135–136
turbine disk, 168–171
undercarraige strut failure, 120–121 universal joint failure, 101–102
wheel bearing housing flange failure, 72–73, 72–73(F) wheel hub failure, 84–86, 84–86(F)
wing control cable, 158–159, 158–159(F) wing root fitting, 146–147
Aloha Airlines
explosive decompression, 3 FRASTA analysis of, 35
Aluminum Alloy. See also Materials extrusion, blisters in, 13(F), 15 American Petroleum Institute (API)
Standard 650
Ashland oil tank collapse, 60 Standard 653
Tank Inspection and Repair, 60 Antiques, 56
API. See American Petroleum Institute Arrhenius Relation, 37
Bath Tub Curve, 3, 4(F) Beach Marks
compressor blade case 36, 151, 151(F) compressor disk, 173
connecting rod bolts, 185, 186(F) crack propagation and, 25, 26(F), 121 dowel bolts of aircraft engine, 102, 105 fatigue failure of aircraft hub, 72, 72(F) fatigue failure of helicopter rotor blade, 154–155 first-stage aircraft compressor blade, 118, 128, 129(F) fretting fatigue of aircraft fuel pump
93–94, 94(F)
gear system, 177, 178(F)
low-pressure turbine rotor blade, 68, 143, 144(F) piston failure in marine engine, 12(F), 14 turbine blade of aircraft engine, 88, 88(F) turbine vane, 189, 189(F)
202 / Failure Analysis of Engineering Structures
Brake System Failure, 13–14(F), 15–16, 59 Brinelling, 97, 98(F)
Brittle Failures
Ashland oil tank collapse, 3, 60 cooling fin, 172
elevator hinge pins of aircraft, 113, 114(F) second-stage compressor blade, 133
elevator hinge pins of aircraft, 113–114 hydrogen embrittlement and, 71, 113–114 rocket lug, 11–12
quill shafts in gear box, 148–149 retraction jack support beam, 180–181 shutter bolts, 130–132
stabilizer link rod, 78–79 throttle end fitting, 65–66 tie-rod of towing tractor, 80–81 torque sensor bearing, 97–99
wheel bearing housing flange, 72–73 wheel hub, 84–86
wing control cable, 158–159 wing root fitting, 146–147 connecting rod bolts, 185–188
fertilizer plant turbine rotor blade, 182–184 fuel-injection pumps, 196
helicopter
case 18 tail rotor blade, 107–109 case 9 tail rotor blade, 82–83 main rotor blade skin, 154–155 mixing unit attachment, 110–111 tail boom attachment, 162–164 tail rotor blade, 156–157
hydraulic pump plungers, 175–176 low-pressure turbine rotor (LPTR) blade case 2, 67–69 Ceramic Tensile Spalling Strain, 32 Charpy Impact Test, 32
Chatter, 97, 99(F)
Chemical Analysis. See also Electron-dispersive X-ray analysis dowel bolt, 104(T) crack propagation and, 25, 26(F) dovetail mounting failure, 115–117 undercarraige strut failure, 121 Clam Shell Marks. See Beach Marks Combined-Cycle Power Plant, 191–195
aircraft engine 4th stage, 173–174 fracture, 57, 59
Compressor Rotor, 115–116(F), 115–117 Computed Tomography (CT)
airline baggage check technique, 60 NDE technique, 21
age, estimated via oxide analysis, 37 bulk vs crack-tip environment, 35 component life, 3
fatigue, via, 66
SLM use via conjugate fracture surfaces, 34 Crack Opening Displacement, (d), 35 Craters, 47, 47(F)
Creep Rupture, 20
Critical Strain Energy Density, 32 Cross-Sectional Plots (XSP)
fracture toughness determined by, 35
fractured-area-projection plots and, 34–35, 35(F)
Index / 203
Crude Oil Release, 3
CT. See Computed Tomography Curled and Curved Fragments
explosive force, resulting in, 46, 46(F) stantion damage on aircraft, 50 Cut Set, 39 defined, by various sources, 5 design
chemical plant, 7–8 connecting rod system, 185 defined with examples, 6 gas turbine rotor, 194–195 retraction jack support beam, 181 steam turbine, 7
heat treatment, nitrided quill shaft, 10–11 imperfection, versus, 5
origin of, 3 processing failures hip prosthesis, 9
hydrogen embrittlement, 11
machining, titanium alloy compressor blade, 10 material, nimonic alloy turbine blade, 9 residual stress relief, I-beam, 12–13 Defective Manufacture, 6
Defence Research and Development Organisation (DRDO) Laboratories, 57
Diesel Fuel Release, 3 Dimples
double fractures and, 103, 105(F) shear overload
aircraft
compressor blade, 141, 141(F) LP turbine disc, 170, 171(F) filter components, 165, 166(F) helicopter rotor blade, 154(F), 155 retraction jack support beam, 181, 181(F) stress states and, 28(F)
tensile overload
aircraft wing control cable, 158
helicopter tail boom attachment, 163, 164(F) rod bolts, 185, 187–188(F)
Dowel Bolts, 102–106, 102–106(F), 104(T) Drive Shaft, 168(F), 169(F)
Ductile Overload Failure, 108(F) Ductile Tensile Fracture, 25, 26(F)
E
ECP (Electric Current Perturbation Method), 21 EDAX. See Electron-dispersive X-ray Analysis Eddy Current Inspection, 21
EDS. See Energy-Dispersive X-ray Spectroscopy Elastic Modulus, 32, 35
Electric Current Perturbation Method (ECP), 21 Electric Power Research Institute (EPRI), 21, 32 Electric Resistance Welded (ERW) pipe
Minnesota, 60 wing root fitting, 147, 147(F) ball bearing, 197
cardon shaft failure in aircraft, 123–124 hydraulic pump plungers, 175
LP turbine disk, 170
quill shaft failure in aircraft, 123 shutter bolts, 131
gold smuggling case, using, 56 NDE analysis technique, 55 wing root fitting, 147(F) Environmental Effects, 6
EPRI (Electric Power Research Institute), 21, 32 ERW. See Electric Resistance Welded
Exfoliation Corrosion, 17
passenger aircraft, 45–51, 55, 60
Exponent Failure Analysis Associates, 21, 32
F
Failure
categories of, 5
clearance inadequacies, 194–195 cleavage
aircraft cooling fin, 172, 172(F) aircraft HP turbine blade, 138, 138(F) aircraft wheel hub, 84–85, 86(F)
helicopter tail boom attachments, 162, 163(F) defined, 3
electrical pitting, 197 high-temperature overload, 68 reverse slant, 154–155 tearing
aircraft throttle end fitting, 65, 66(F)
helicopter rotor blade, 82–83, 82–83(F), 154–155 torsional overload
background information required for, 19 examination techniques, 25
Failure Analysis Associates, 31
Failure Modes and Effects Analysis (FMEA) fault tree analysis and, 38
process described, 39–40