COMPLEX FAILURE DIAGNOSIS OF AVIATION BEVEL GEARS

Failure diagnosis of spiral bevel gears in assembly gearbox of aero engine is performed. With the use of physical methods of testing (scanning electron microscopy, electron-probe X-ray microanalysis) and microhardness testing the fracture origins and fracture kinetics are determined, the microstructure and microhardness of case are analyzed. It is found that the surface hardness in gear teeth root areas for fractured gears essentially less than for fault-free gears with big operating time. Service conditions of the gears on various engine setting are observed. 3D finite element modeling of the gears stress state is carried out. On the basis of the modeling it is shown that in operating range of the gears rotational speed there is the gears resonance under mode of bending vibration with three nodal diameters. With this, the location of maximum stress amplitude coincides with the site of the fatigue fracture origins. Finite element data are proved at the gears stress measurement in the course of engine tests. Thus, as a result of the complex study it is found that the cause of the bevel gears failure is intense gear resonance in the conditions of reduced surface hardness for gear teeth root areas. The measures intended to elimination of the failure causes are developed, approved and introduced.

bevel gear, fatigue, fractography, crack kinetics, stress strain state, finite element modeling, resonance vibration, microhardness

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