PSI - Issue 16

Andrzej Gębura et al. / Procedia Structural Integrity 16 (2019) 184 – 191 Andrzej Gębura, Sylwester Kłysz, Tomasz Tokarski / Structural Integrity Procedia 00 (2019) 000 – 000

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 The earliest failure of all examined failures was initiated a fatigue cracking of two subsequent teeth of a gear wheel (the same by which other teeth suffered from being broken or milled). The initiation of fatigue cracks occurred at the teeth’ root at approximately two -thirds (2/3) of its length. The region of fatigue cracking occupies 85 – 90% of the fracture area, which signifies low loads accompanying the development of fatigue cracks.  In the region of the initiation of fatigue cracks, the presence of micro-areas of fracture of temporary character was found, which indicates that the cracks were initiated presumably by short-term exposure to high loads of teeth (load impulse). Duration of this impulse, assuming that it simultaneously initiated the cracking of both teeth, was estimated at approx. 1/3 ms. 8. Summary 1. Resonance phenomena in the mechanical power transmission system are dangerous and lead to the accelerated destruction of bearing nodes and gear wheels. 2. Resonance phenomena in rolling bearings are difficult to detect with the use of traditional methods, e.g. vibroacoustic methods since the increased energy absorbed from the drive unit is closed in the bearing, and reduces the vibration energy emitted from outside. The situation looks different in the case of detecting resonances with the FAM-C method. This method distinguishes them without any difficulty by tracing the dynamics of angular speed. 3. For the power plants, a crucial aspect is to provide parallelism of the rotation axis of shafts, on which gear wheels are mounted. Failure to comply with this parameter may contribute to the mutual skew of the above mentioned shafts and undercutting the root of teeth. 4. The skew of the shaft and increased radial clearances decrease its angular frequency to the first subharmonic. If this angular frequency will equal the frequency of other subassembly, e.g. the upper bearing of the main transmission, then, the spatial resonance of both subassemblies is created. 5. In spatial resonances, the subassemblies with smaller constructional offcuts are the first, which are subject to destruction. 6. Synchronous interaction of rolling bearing during resonance on the pair of gear wheels may end in undercutting of two teeth, production of focal points of fatigue cracks at the root and its breakage. Augustyn, Sł., Gębura, A., 2012. Capabilities of the FAM-C method to diagnose the accessory gearboxes and transmission - train assemblies of the Mi-24 helicopters. Aviation Advances & Maintenance, 30.30: 199÷220. ISSN 1234 -3544. Barszewski, W., 1956. A helicopter in flight. Wyd. MON, Warszawa. (in Polish) Bukowski, L., Kłysz, S., 1993. Fatigue of aircraft structures against the background of a 4 -year experience activity. Biuletyn Wojskowej Akademii Technicznej, XLII, 3(487), Warszawa. (in Polish) Dudziński, A., Dudzińska, A., Flotyńs ka, A., 2011. Report No. 03/36/2011 from damage to the gearbox components of agreements, bearings and components of the helicopter rear shaft Mi-24W No. 410737 and two intermediate shafts with toothed wheels of the accessory gearbox 24-512-00 – type. ITWL, Warszawa. (in Polish) Gębura, A., 1999. Skew of splin connections and frequency modulation. Scientific Problems of Machines Operation and Maintenan ce, 34.4 (120): 763 – 772. (in Polish) Gębura, A., Tokarski, T. 2009. The monitoring of the Bering nodes with excessive radial clearances using the FAM-C and FDM-A methods. Research Works of Air Force Institute of Technology 25, 89 – 127. (in Polish) Gębura, A., Stefaniuk, M., 2017. Monitoring the helicopter transmission using the FAM -C diagnostic method, Diagnostyka 2, 75 – 85. Ghaffari, M.A., Pahl, E., Xiao, S., 2015. Three dimensional fatigue crack initiation and propagation analysis of gear tooth under load conditions and fatigue life extension with boron/epoxy patches. Engineering Facture Mechanics 135, 126 – 146. Jakielaszek, Z., Nowakowski, M., 2014. Selected characteristics of the electric propulsion system of aircraft as found out the ground-based laboratory tests, Journal of KONES Powertrain and Transport 4, 203 – 210. Kłysz, S., Lisiecki, J., 2009. Strength test ing and analysis of fatigue crack growth in selected aircraft materials, in: Niepokólczycki A.: Fatigue of aircraft structures, monographic series, pp. 74 – 83, Institute of Aviation Scientific Publication, Warsaw. Padfield, G.D., 1998. Helicopter Flight Dynamic. The theory and Application of Flying Qualities and Simulation Modelling. WKiŁ, Warszawa. (in Polish) Żurek, J., et al., 2006. Helicopters life. Warszawa. (in Polish), References