Bending Fatigue Failure of a Helical Pinion Bevel Gear
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CASE HISTORY—PEER-REVIEWED
Bending Fatigue Failure of a Helical Pinion Bevel Gear George A. Pantazopoulos
Submitted: 11 February 2015 ASM International 2015
Abstract The analysis of pinion gear damage operated in a tube coiler machine gearbox was investigated. Visual inspection, SEM fractographic analysis, and metallographic evaluation are employed as the principal analytical techniques for the investigation. Fractographic observations indicated the occurrence of bending fatigue started at the maximum load surface of the gear teeth, known as active flank, and propagated to the opposite area resulting in catastrophic tooth fracture. Unbalanced stress conditions led to the consecutive damage and fracture of adjacent teeth resulting in machine interruption and immediate replacement of the gear system. The multiple fatigue crack initiation sites suggest significant stress concentration probably caused likely by gear misalignment. Metallographic evaluation revealed an entirely heat-treated gear microstructure consisted of tempered martensite free from microstructural abnormality that could be associated to the failure. Regular gear inspection and system alignment checks together with the consideration of increasing surface hardness, through selected surface strengthening procedures, are suggested as further corrective actions to minimize similar failures and machine downtime in the future. Keywords Bending fatigue Fractography Pinion gear Failure analysis Introduction and Background Information Cyclic loading takes place under normal operation condition of various machine components, such as torque and power G. A. Pantazopoulos (&) ELKEME Hellenic Research Centre for Metals S.A., 252 Pireaus Str., 17778 Athens, Greece e-mail: [email protected]
transmission elements, causing the action of fatigue failure mechanisms [1, 2]. Synopsis of the main failure mechanisms, embracing mainly wear, plastic deformation, impact, spalling, and fatigue fracture, acted during the operation of gear elements is presented in Refs [3, 4]. Power transmission elements, gears, and shafts are subjected to various cyclic loading modes, attributed mainly to bending and torsional stresses. Contact stresses and relative motion induce friction and wear of mating surfaces and surface contact fatigue that could lead to surface cracking, pitting, and spalling [1, 5, 6]. Spalling is manifested by the formation of extended pits on the surface of gears or rolling elements (rolls and bearing components) as a result of rolling-sliding contact fatigue and surface cracking or cracking at the hardened layer/core interface [6]. Extensive fatigue cracking and tooth breakage could be caused at the spall areas of the gear, as it was observed in helical gear component [7]. Misalignment could induce high stress concentration and may serve as a contributor of fatigue crack initiation at the active gear flank area. Gear teeth fracture, due to bending fatigue, is another common gear failure mechanism which involves crack initiation at the active flank
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